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Tendon and pulleys at the metacarpophalangeal joint of a finger
PW Brand, KC Cranor and JC Ellis
J Bone Joint Surg Am. 1975;57:779-784.

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Publisher Information          The Journal of Bone and Joint Surgery
                               20 Pickering Street, Needham, MA 02492-3157
 Tendon                                 and                Pulleys                          at the                    Metacarpophalangeal                                                 Joint                      of          a Finger*t
                             BY        PAUL           W.       BRAND,               F.R.C.S4,         CARVILLE,              KENNETH              C.     CRANOR,                M.D.,            BATON                     ROUGE,              AND

                                                                                  JOHN          C.    ELLIS,          B.S.E.E.t,        CARVILLE,                 LOUISIANA

             ABSTRACT:                 In     fresh          frozen               traumatically                    amputat-           published              of     the     relationships                 between                   tendons            and        joints.
ed      forearms                  with          a constant                  tension              of one          kilogram             Iton was our purpose                      to show   that much can be learned       from
the          flexor          profundus                       tendon                and          the     interphahangeal               a few measurements                           made  through    the limited   exposures
joints      fixed      in full    extension        by a Kirschner             wire,                                                   one has at surgery.
                                                                                                                                        the                                     These studies    on amputated   hands were
excursion           of the      tendon       at the       metacarpophalangeal          therefore                                                         made             through            standard            surgical               incisions             without
joint      and      the   force      at the      finger     tip were        correlated extensive                                                           dissection     and denudation      of the skeleton.
with      different       angles       of flexion       of the joint,         first   with    At                                                        operation      it is often   possible   to expose      a tendon
the finger                  intact            and then     after    varying                              amounts           proximal
                                                                                                                        of ad-                             to a joint,      and to measure       the distance      that it
vancement                      of           the   metacarpophalangeal                                 joint      pulley    moves                       in association        with  a measured      amount     of move-
system.                Pulley               advancement                         increased               the tendon      ment
                                                                                                                        ex-                      of      a joint.    These   two measurements         become   mean-
cursion               required                to flex this                  joint      and          thus    the mechan- ingful                         when       we apply     the geometric     rule    that when   a
ical         advantage                  at this            joint,           but      only         when     the joint    radius
                                                                                                                       was                             of a circle     moves     through   an angle    of one radian
partly     flexed.                          The            extra            excursion                  required                at     (57.29
                                                                                                                                        the         degrees)              any        point      on       that          radius           will         have         moved
metacarpophalangeal                                        joint             would               be       expected                    through
                                                                                                                                     to                 an arc equal                  in length            to the             distance               between             that
weaken                the          interphalangeal                           joints             at     full       flexion.           point
                                                                                                                                     Ad-         and         the     center          of the          circle.           Thus,           if a finger                with       its
vancement                    also            permitted                 ulnar-radial         displacement                               interphalangeal
                                                                                                                                         of                                 joints            held         in          extension                 flexes             at      the
the   tendon                    at           the     level             of the       metacarpophalangeal                                metacarpophalangeal                            joint      through                   one       radian,          then        the tip
joint            and   hence                 could           accentuate    ulnar                         or       radial           drift. the finger
                                                                                                                                       of                will                 have       moved            a distance                  equal          to the length
 Pulley            advancement                             is not recommended.                                                     of the    finger                    measured     from      the axis   of the metacar-
                                                                                                                                   pophalangeal                      joint.   A point    halfway    down   the finger will
             The         flexor-tendon                          pulley                mechanism                        at      the have moved                       half as far, and a point        near the axis (out of
metacarpophalangeal                                   joint  of a finger   may be adversely      af-
                                                                                                  the sight and reach      of                                                                the surgeon,                     in the palm)                   will   also
fected    by disease,                                trauma,     or poorly     planned    surgery.have moved    a distance                                                                    equivalent                    to that point’s                  distance
Flatt        2   demonstrated                     that       some           of the serious                    deformities             in
                                                                                                                                      from        the joint   axis.                    The       tendon     that moves   the joint                                          be-
rheumatoid                 arthritis     are due                         in part to loss of restraint                                    of
                                                                                                                                      haves         as though       it                 were        attached     near the base      of                                       the
the flexor              tendons      at this joint                        resulting in bow-stringing                                    in
                                                                                                                                      finger,           and         the       distance           that           it         moves          while             the      finger
both     the anteroposterior         and the lateral       plane.   Following moves                                                                    one         radian        is equivalent                        to     the       perpendicular                     dis-
flexor-tendon       grafting      when     the slings    or pulleys            in-
                                                                          are tance                                                               between              the tendon    and                             the     joint         axis,        a distance
adequate      or poorly      placed,    such bow-stringing        may be as-  known                                                                 as the            moment    arm.
 sociated      with    loss of ability                                      to     move    As shownthe interphalangeal
                                                                                                          in Figure     1-A,      if the intact       finger    moves
joints    effectively.      Capsulodesis,                                          done
                                                                                  the radian,
                                                                                   one            for paralysis
                                                                                                    then the tendon of     excursion                 m
                                                                                                                                           will equal , which
intrinsic        muscles      of the hand,       is often     supplemented         isbythe   moment     arm. If the pulley          system    is advanced,       how-
pulley        advancement          at the      metacarpophalangeal           joint.ever,    as shown     in Figure    1-B, the moment             (m1)
                                                                                                                                                  arm will be
Most       descriptions       of this operation       are vague     with   respect greater     and so will    the tendon      excursion.        Thus,     for any p0-
to how far the pulley             should     be advanced       and do not men-     sition    of a finger    it is possible      to derive       the exact     moment
tion      possible      harmful     effects,    but Leddy       and co-workers arm of any tendon              with respect      to any axis of movement               of
suggested      that a pulley         may be advanced            to the level of the joint
                                                                                    any          of that finger   if the tendon       can be exposed                                                                                                              proxi-
finger    webs,      and sometimes            further.                              mally   and its excursion        measured       as the finger       is                                                                                                        moved
       In the       study      reported         here     we     demonstrated        the
                                                                                    around    only   one axis of one joint       and the movement                                                                                                                   of the
mechanical        effects     of various          degrees     of advancement          of
                                                                                    finger  at this joint   is measured.      If either    the location                                                                                                             of the
the flexor      pulley     at the metacarpophalangeal                  joint and axis or the length
                                                                                    ne-                     of the moment         arm changes        during                                                                                                            that
duced     them to terms          that would         be useful     to the practicing movement,       then the measured        tendon      excursion       will                                                                                                         rep-
surgeon.      We       did    not     attempt        to repeat       the many       fine
                                                                                    resent   the average     moment      arm for that movement.                                                                                                                      Since
mathematical                           and        engineering                      analyses             that        have            been
                                                                                                                                      the    tendon’s                moment              arm     can           be determined                         from          its ex-
                                                                                                                                      cursion,           it is possible                   to calculate                       the force            relationships
         *    Read     at the          Annual         Meeting          of    the    American            Society       for    Surgery
                                                                                                                                      around           the joint.    In                 any system                     of      pulleys           or levers,                 the
of      Hand,
       the       Dallas,     Texas,      January     16, 1974.
         t            in part by Social          and Rehabilitation           Service     Grant   mechanical
                                                                                                  RC                                                           advantage      is equivalent        to the ratio    between
75 MPO.
                                                                                                  the distance                                                 moved     by the force and the distance          moved      by
    1: U. S. Public Health Service Hospital,               Carville,        Louisiana      70721.
    § 3955 Government            Street,     Baton    Rouge,        Louisiana       70806.        the object.                                                 Therefore,    in a given      finger    the mechanical      ad-

VOL.         57-A,     NO.        6.   SEPTEMBER                1975                                                                                                                                                                                          779
780                                                                  P.    W.     BRAND,             K.      C.     CRANOR,          AND          J.        C.      ELLIS

                                            FIG.     1-A                                                                                               FIG. 2
     When     the interphalangeal           joints     are held      immobile       in extension        with Apparatus        used to measure          tendon   excursion      during      movement      of the
the pulley        mechanism         intact      the tension        (T)   of the profundus                 metacarpophalangeal
                                                                                                     tendon                            joint.       Measurement          is by     means      of     a marker
will    be in equilibrium           with      a force      (F) at the finger         tip = M/m
                                                                                          if T/F          affixed    to the suture       connecting        the tendon      and a one-kilogram           weight.
where M is the length             of the finger         and is the perpendicular
                                                          m                                 distance      As joint       movement       occurs      the marker      moves      along     the top scale.       The
                                                                                                          lower    scale    is the read-out       for the spatular      force   transducer       that was held
from     the joint    axis (A) to the tendon                 as it crosses     the joint.       If the joint
moves      through     one radian        the finger       tip will     move    through      an arc equal  against     the finger    tip as the finger         was allowed        to flex or was extended
to M and the tendon            will     move       a distance      equal m. to                            (see text).

                                                                                                                             The interphalangeal        joints     were     stabilized        in exten-
                                                                                                                      sion    by a Kirschner         wire      which      passed        longitudinally
                                                                                                                      through     the phalanges    and projected         beyond        the end of the
                                                                                                                      finger   serving   as a marker      for measurement             of the range of
                                                                                                                      motion.      The finger    was moved          passively        at the metacar-
                                                                                                                      pophalangeal                joint    by                     means           of         the      force        spatula           held
                                                                                                                      against    the          finger    pulp.
                                                                                                                                 Readings              taken              on a finger              in which             the      whole         flexor
                                                                                                                      mechanism               was                intact          are     given          in     Figure           3-A,     with          the
                                                                                                                      angular         changes      at the metacarpophalangeal                                                joint         plotted
                                                                                                                      against         the excursion       of the    profundus                                            tendon             in the
                                                                                                                      forearm,          the   readings      being   closely                                          grouped             along     a
                                                                                                                      straight        line.            In        this       finger         the        entire        90-degree            range           of
                                                FIG.    1-B
                                                                                                                      motion          was accomplished                                    with          eighteen              millimeters                of
   When         the flexor sheath is partly excised                 m
                                                         the distance will    increase     to
m1,the         force    (F1) that can be resisted   by the tendon        tension      (T) will                        tendon
                                                                                                                        be           excursion.
proportionally            greater    and the tendon will   move    a greater      distance     (m,)                        In the largest    of the five                                     fingers    tested,      the excursion
for the same           finger     movement.
                                                                                                                      for 90 degrees    of flexion  was                                     twenty-four         millimeters.        The
vantage           may     be the            ratio      between            the     distance           moved            moment
                                                                                                                       by        arm in these fingers                                        ranged     from     about       twelve    to
the      tendon         and     the        distance       moved            by     the      finger          tip.
                                                                                                        sixteen     millimeters.
         Our       experimental                      models         were           two         fresh
                                                                                                  frozen       Since the tracing                                            for        an intact          finger        is a straight            line,
hands       obtained               after     proximal        traumatic                amputation.     The
                                                                                                        the moment          arm of                                        the     tendon   at the joint   could                          not         have
radius      and ulna               were      bolted       to a stand              with   the dorsum      of
                                                                                                        changed       significantly                                             as the joint    angle   changed.                                In     the
the    hand    resting   on                    a block            (Fig.           2).  A one-kilogram                 specimen              shown,    when    the joint                                  was nearly                straight two
weight      was attached                       to the          flexor           tendon   of choice                     by
                                                                                                                      millimeters             of tendon    excursion                                   resulted in               10 degrees   of
means   of a long                  suture       which   was passed    over two                              pulleys movement,     and when    the joint was                                                    flexed    80 degrees,                     10
with  a graduated                    scale      between    them,  from    which                              the ex-degrees   more flexion (to 90 degrees)                                                     still required   two                  mil-
cursion  could    be determined                   as a marker
                                                         directly    on the su-  himeters      of excursion.        When     the finger    was moved       to full
tune moved     along   the scale                finger    motion.
                                                         during                  lateral    and full medial        deviation     with the tendon     sheath     in-
       Force  was measured       with a transducer        fashioned         from tact,    no longitudinal         movement        of the profundus        tendon
a flexible   spatula    with  a strain    gauge    attached       proximally. resulted,          indicating     that the sheath        mechanism     holds     the
As the spatula       was pressed     against    the finger      tip the force    tendon      exactly      over the axis of deviation         and that contrac-
could      be     read        on      the     scale     just      below           the      one       for      excur- tion     of the flexor   profundus        would  not produce    a vector  for
sion.                                                                                                                  either    radial  or ulnar    deviation.
         One       television               camera        was        directed             at     these            scales      The force recorded        at the finger    tip, as the finger   was
and a second    was                    focused   on the specimen                           itself.          Using allowed
                                                                                                                        a     to flex very     slowly    due to the one-kilogram                                                                      ten-
split-image  format,                      all of the data were                          recorded             on vid- sion on the tendon,     was plotted    against the joint    angle.                                                                 As
eotape simultaneously.                              This  set-up permitted                      rapid        testing shown  in Figure    3-B, the force did not remain        constant                                                                but
of each specimen                       while          it was in optimum                        condition              decreased
                                                                                                                     and                 sharply                  beyond               80 degrees of
                                                                                                                                                                                                   flexion.                      When         the
analysis          of    the     data        later      at our       leisure.                                          procedure             was         reversed                  and     the flexed               finger,       still   with         one

                                                                                                                                                                    THE         JOURNAL          OF     BONE AND        JOINT       SURGERY
                                                       TENDON                               AND            PULLEYS                        AT        THE                 METACARPOPHALANGEAL                        JOINT         OF       A     FINGER                                         781

        35-                                                                                                                                                                   as the         sheath         was      advanced                 beyond       the     rim     of the              articular
                                                                                                                                                                              surface     at the base of the proximal          phalanx.
        30-                                                                                                                                                                          In their    recent   analysis   Doyle    and Blythe     referred   to
                                                                                                                                                                              the part of the sheath        proximal    to the metacarpophalangeal
                                                                                                                                                                              joint    as annulus     I and to the part arising      from  the proximal

                                                                                                                                                                              phalanx          as annulus               II.     In the         hands       we used,              the      annulus            II
                                                                                                                                                                              portion          of      the        digital         flexor          sheath          extended                distally               to
  E      15-                                                                                                                                                                  about      the          middle          of the proximal   phalanx,                                   five          to eight
 z                                                                                                                                                                            millimeters              distal        to the webs of the fingers.                                  When            the last
 In      10-                                                                                                                                                                   segment       of the phahangeal            part of the sheath         was removed
                                                                                                                                  l                       -
                                                                                                                                                                               only    a distal    five-millimeter            band of annulus          II remained,
                                                                                                                                                                               located      about     one millimeter            distal     to the finger       webs,     a
                                                                                                                                                                               level      sometimes           advised        in     surgical     operations.         The
                         I                I             I                   I                 I            I             I                I          I
               0     10                       20                30                   40               50                60            70                      $0            90 excursion-angle          curve       for this level         of advancement         (Fig.
                                                            ANGLE                    (deg.)                                                                                    4-A)    was exponential             rather    than straight.       Thus,      when    the
                                                                     FIG.             3-A
                                                                                                                                                                              metacanpophahangeal                             joint             was          nearly                   straight              a
     In the situation      in which       the flexor     pulley     mechanism           was intact      and
                                                                                                        10-degree                                                                                     change           of      angle           was       accomplished                     by      a two-
there     was a constant       tension      of one kilogram          on the profundus            tendon,
the plot of the excursion            of the tendon       in millimeters         against    the angle millimeter
                                                                                                          of                                                                                          excursion    ofthe tendon,     whereas      when the joint
flexion       of the index    finger      metacarpophalangeal             joint    shows     a straight-
                                                                                                       was flexed                                                                                      almost   to 90 degrees,     four    millimeters     of ten-
line    relationship,      “0    degrees”        being    full   extension        of the finger        ( 180
degrees        to the palm).                                                                           don excursion                                                                                        was required   to make      10 degrees     of change
                                                                                                                                                                              in the joint             angle.
kilogram            of tension                    flexor
                                                       on the  tendon,        was extended            (by
                                                                                                                Therefore,           the mechanical                advantage             of the tendon
pressing           the spatula                      the finger
                                                       against         tip) from 90 degrees
                                                                                                       doubled            when        the joint          was       in flexion,              and      an extra
of flexion          to full        extension         the readings             were higher.            The
                                                                                                       centimeter            of excursion             was required                 to move          the joint
sharp       drop       in force          as full          flexion       was approached                   oc-
                                                                                                       through          90 degrees           (Fig.     4-B).
curred when              tissue        turgor        and tightness               of the capsule
                                                                                                                Five fingers           in two hands were studied                        and the pattern
finally       increased          sufficiently           to equal       the force           exerted       by
                                                                                                       was        similar       in all of them.                 The        data       points       were      nor-
the tendon.
                                                                                                       malized           by the method               described            in Appendix               I so that
        In      the     arc        where       joint          movement             was       free,       the
                                                                                                       they could            be represented              by a smooth                 curve      that would
curve       is nearly          straight       and approximately                     level,      demon-
                                                                                                       average          out all the readings                for ease of interpretation.
strating        again      that with an intact                 sheath     the mechanical              ad-
                                                                                                                Since      pulley        advancement            is sometimes               performed          to
vantage         of the system               is constant.
                                                                                                       compensate             for intrinsic          paralysis,          it should          be noted        that
        Segments             of the flexor                pulleys        and digital            vaginal
                                                                                                       advancement                does        not     increase           mechanical               advantage
sheath       were then excised,                  five millimeters               at a time         begin-
                                                                                                       when         the metacarpophalangeal                     joint       is in full extension               or
ning      proximally              in the palm.               After     each        five-millimeter
                                                                                                       hyperextension,                 yet      it   is      in     this         position          that      the
segment          was excised,             the change              in angle        and the tendon
                                                                                                        intrinsic-minus              hand        needs       help.       Conversely,               when       the
excursion           were      measured.            Little       change        in the curve           was
                                                                                                       hand          is closing           in grasp         and        the      patient        needs        inter-
noted      after the first annular                   and cruciate            portions        were ex-
                                                                                                       phalangeal           flexion,        the bow-stringing                   of the tendon           at the
cised,      but the shape of the curves                          began      to change          as soon
                                                                                                       metacarpophalangeal                     joint     weakens             intenphalangeal             joint
       300-                                                                                                         Experimental                    -.#
                                                                                                                                                                              flexion.          This         loss       of      flexion          force       at the         interphalangeal
                                                                                                                    Theoretical                 -                             joints          could   not            be demonstrated      in                      our experiment                           be-
       250-                                                                                                                                                                    cause         the tendon              tension was constant                          at one kilogram                          in
                                                                                                                                                                              all positions      and the amplitude      of excursion     of the tendon
  .    200-                                                                                                                                                                   was not limited.       In real life the pnofundus      muscle    is able to
                                                                                                                                                                              maintain      optimum      tension    for only   pant of its excursion
       150-                           -                                ----                                                                                                   and this      is not enough        to flex completely       all the joints
 0                                                                                                                                                                            crossed          by      the      tendon.
                                                                                                                                                                                        If    pulley            advancement                     increases           the          excursion                 re-
                                                                                                                                                                              quired          at      the       metacarpophalangeal                           joint,             it     must         result
                                                                                                                                                                              in inadequate                  tendon           excursion                at other        joints.
                             I                I             I                    I                I                 I                 I                       I    r                 There     is great loss of the strength                                      of grasp as the pro-
               0         10                       20             30                       40                   50            60                70                      80     fundus
                                                                                                                                                                                 90      contracts     fully and approaches                                      the end of its excur-
                                                                                      ANGLE(deg.)                                                                             sion.   This             loss can             be demonstrated                    easily    by               measuring
                                                                     FIG.            3-B                                                                                      the strength              ofgnasp             while the wrist                 is progressively                   flexed
    For the same situation       the plot ofthe    force   (F) on the finger                 by external
                                                                                   tip against                                                                                                           force.     In most    cases                        the ability     to flex    the
the angle     of flexion    of the metacarpophalangeal            joint    shows    a constant
force   throughout       the greater    part  of finger    motion       with    an abrupt
                                                                                                      fully                                                                                              at all joints  is decreased                          at 20 degrees    of wrist
crease    in force    at about   80 degrees     of flexion    (see text).                    flexion   and                                                                                             is lost before     the wrist                        is flexed    to 40 degrees.

VOL.     57-A,     NO.           6.   SEPTEMBER                                 1975
782                                                                                        P.   W.        BRAND,                   K.       C.     CRANOR,            AND           J.      C.         ELLIS

         35-                                                                                                                                          the finger              was        30 degrees                     and         resulted                in a longitudinal                            ex-
                                                                                                                                                      cursion  of              two to three      millimeters        of the profundus        ten-
                                                                                                                                                      don. Since                the finger   deviated       through    half a radian     while
                                                                                                                                                      the tendon                  moved    two      millimeters,        an uhnar-deviating
                                                                                                                                                     moment        arm of about        four millimeters            in length      could    be
         20-                                                                                                                                         produced.        In a patient     with    intrinsic     paralysis     this moment
                                                                                                                                                     could     be a serious       defonming          factor.
  I      15-                                                                                                                                               We also tested to determine                  the optimum       location      of a
                                                                                                                                                     new     pulley      to replace         the proximal           part   of the flexor
 In      10-                                                                                                                                          sheath.         A       pulley              at the               base         of        the     proximal                        phalanx            was
                                                                                                                                                      found      to             restore                      the            most                   nearly                normal                   flexion
                                                                                                                                                              In     view            of          the         serious                mechanical                         consequences                           of
                          I         I              I               I          I        I              I              I         I
                0             10        20               30     40                     60
                                                                                       50            70             80                 90             flexor     pulley     advancement     in these                                                 amputated     hands,                               it is
                                                       ANGLE (deg.)                                                                                   surprising        that more complications                                                      of this procedure                                 have
                                                             FIG.       4-A
                                                                                                                                                      not    been           reported.                   It     seems                probable                   that          a sling             of      scar
     In the situations in which              the digital       vaginal      sheath    was     intact     and
                                                                                                           tissue                                                  restores          part         of what has been deliberately                                                     removed.
then was removed              distally    to a pointjust         distal   to the finger     webs     leaving
five    millimeters        of the distal         part of the sheath           intact.   the plots       of Forthe                                            our     own            part,         we gained  so much respect                                                     for the essen-
excursions          of the profundus          tendon     against      the degrees     of flexion       of the
                                                                                                           tial                                             role     of    the    systems                                      of    restraint    at the      metacar-
index      finger     metacarpophalangeal             joint    show      exponential      curves.
                                                                                                                                                     pophalangeal        joint     that we                                    would      rarely  remove      them;     if
         35-                                                                                                                                         this became        necessary,      we                                    would     then favor    replacement
                                                                                                                                                     or reconstruction         of a broad                                     pulley     at the base of the prox-
                                                                                                                                                     imal   phalanx.                   Having   done    so, we                                            would   check                        the effi-
                                                                                                                                                     ciency   of the                 new pulley    at operation                                            by measuring                          the ex-
         25-                                                                                                                       I 3.9             cursion    of             the tendon                      associated                   with   the first                             30 degrees
                                                                                                                                                     of flexion                from   full                   extension                    compared     with                              the last 30
                                                                                                                                                     degrees           of       flexion                 to      a night                  angle.             If     the            excursions                       in
     I                                                                                                                             I 2.2
     I   15                                                                                                                                          these two maneuvers       were                                         about             the     same             the            pulley          could
                                                                                                                                                     be accepted  as satisfactory.
 ;       10-                                                                                                                                                  As        a      result              of          these            studies                   we           believe                 that       any
 S                                                                                                           Nrusal                -
                                                                                                          Iss.ct.d                                    surgeon    who changes     the pathway         of a tendon                                                                       on transfers
                                                                                                                                                      it to a new   location  would     benefit    by measuring                                                                          the tendon
                                                                                                                                                      excursion    and the joint    motion      associated    with                                                                      it at opera-
                          I             I                I                I            II             I         I              I
                0             10            20           30              40            60
                                                                                       50            70             $0                 90             tion,   and could                     use these measurements                                             to estimate                       the ef-
                                                       ANGLE           (dsg.)                                                                         fective    moment                      arm created  at each                                         affected     joint.
                                                             FIG.       4-B
    The same curves                   with   the              data points              not       shown    but              the coordinates                                                                   Appendix                         I
for the 10 degrees                  of motion                 between     80           and       90 degrees                 of flexion    mdi-
                                                                                                                                                      Reduction                of        Hand            Surgery                    Data

Forty  degrees    of                         wrist    flexion    used up about   ten millime-       In                                                                evaluating    the   results                                              of our   study,    statistical
ters of profundus                             excursion       in our cadaver   hands.         methods                                                                  were applied     to fit the                                            data to an equation       which
     Thus,      the loss of power        in the interphalangeal                                                                                  joints provided            a consistent                       means                for           graphic              representation                         of
from   pulley      advancement      at the metacarpophahangeal                                                                                    joint the data.
is about      equivalent      to the loss of power        produced                                                                                by 40 This                equation,                    which                is      not           based              on        the       geometry
degrees    of wrist   flexion.     After                                           pulley advancement,                              there-
                                                                                                                                         of the joint     but is a simple                                                            flexible               equation                     selected              so
fore,   a patient   might      need to                                            hold the wrist   in 40                          degreesthat   it conforms     easily     to                                                   either               straight                    or      curved-line
more donsiflexion                            than            he did               before        in order                  to grasp with  graphs    of data points,     is:
the same strength.
                                                                                                                                                             (1)                                                   E    =     aO’
          If        the       bow-stringing                              occurred                    in     only               one          finger.
as after    a flexor                             tendon                graft,  the               profundus                             tendon     Itof is a power                        equation                  withE representing                                  tendon              excur-
the affected     finger                            might               not provide                  the extra                    excursion sion and 0 representing                                                 joint      angle.    Zero     excursion       and
even    with    the wrist                              extended     because    the                                       cross-linkages angle are at the extended                                                     position      of the joint    with   positive
between      the profundus                                tendons   might   limit    its movement. values   for excursion   and angle     signifying                                                                                                                              joint  flexion.
      When       we tested                              lateral   movements        at the metacar- The values a and b are used to fit this equation                                                                                                                              to a particu-
pophalangeal                       joint    with                       the          finger   fully       extended,                                     lar set of data points.
                                                                                                                                                        we                       The                                            actual               curves                 in        Figures           3-A,
found    that             after       the sheath                       was         advanced,       leaving     only                                    4-A,
                                                                                                                                                    five      and 4-B were derived                                             by a computer                              programmed                        to
millimeters                   of   annulus                   II,       the        maximum                  ulnar           deviation                   select the best smooth
                                                                                                                                                        of                     curve                                            to fit the data                          points   using                   the

                                                                                                                                                                                                   THE         JOURNAL                   OF        BONE          AND        JOINT          SURGERY
                                                   TENDON                       AND          PULLEYS              AT       THE             METACARPOPHALANGEAL                                         JOINT             OF     A     FINGER                                         783

        175-                                                                                                                                             curved             line,   on the contrary,      has a non-constant        slope and
                                                                                                                                                         therefore             b does not equal      1 .0. The values      obtained     afor
       ;so-                                                                                                                                              and b as well                        as the                theoretical              values          for     the      tendon        ex-
                                                                                                                                          1.84           cursion    at 90 degrees    and the                                            slope         of    the      curve          at 90 de-
                                                                                                                                                         grees are shown       in Table  I.
                                                                                                                                                                The data for each finger                                                before             and      after      increasing
                                                                                                                                          1.18           advancement                          of         the           pulley         (resection                 levels)       were         nor-
            75-                                                                                                                                          malized              using               the      following                  equation:
 “I                                                                                                                                                              (2)        E(%)      =                             tendon       excursion                          < 100
                                                                                                                    Normal            -                                                       normal           total     excursion        (for    90 degrees)

         25-                                                                                                      Resected                               The           values  for tendon    excursion     at 10-degree     increments
                                                                                                                                                         from           0 to 90 degrees   of flexion   of the metacarpophalangeal
                         S               I           I                           S           I           I             I              S
                                                                                                                                                         joint  of each finger    were the ones obtained       using equation
                         10              20              30       40       50 60                             70            80               90            1 and the a and b values      shown  in Table   I.
                                                              ANGLE (dig.)
                                                                                                                                                               These   normalized     values, obtained   using     equation   2,
                                                              FIG.          5
                                                                                                                                                         were   subsequently                               averaged.       These   average                                values  were
      Thecurves   for the average      or‘composite’
                                        ‘                                                ‘       finger based on the nor-
malized     data of the fingers   tested     from    two                                         hands            under         the       same           then fitted
                                                                                                                                                     condi-            to the                           power     equation (E = a9’) and                               the values
tions   as for Figure    4-B.                                                                                                                            so obtained     were                            as follows:
method              of        least             squares.                The            derivative dE/do,                          or         the                                                                                                                    DE(90#{176})
slope   of the curve      at any point,     may  also be evaluated.                                                                                                                                a                            b           E(90#{176})                dO
This   derivative   is simply    an expression      of the amount     of                                                                                                     (per         cent         E/degrees)                       (per cent) (per              cent/degrees)

tendon    excursion   required  for 1 degree    ofjoint    flexion  Sheath
                                                                   at a                                                                                                 normal                     0.817                      1.067          100.0                    I.180
                                                                                                                                                         Sheath         resected                  0.971                       1.118            148.3                  I .841
particular            angle.                   In the case of a straight                                                   line        this          value
remains             constant                    for all angles  b
                                                               and is equal                                                  to       1 .0.          A Figure            5 shows                   the      curves              plotted           from        these         data.

                                                                                                                                                 TABLE       I

                                                                                                 PARA METERS                 FOR          EXPONENTIAL            C   URVE      FIT:       E   =    aOb

                              Hand           No/Finger,               Sheath          Length (mm)                                                a                             b                               E(90#{176})                  dE(90#{176})/dO
                                               Resection             Level (mm)                                                 (mm/degreesb)                                                                   (mm)                      (mm/degrees)

                              Hand            I/Ring,         18

                                Normal                                                                                                    0.3183                            0.8432                             14.146                            0.1325
                                 3                                                                                                        0.0722                            1.2196                             17.455                            0.2365
                                 8                                                                                                        0.2763                            0.8973                             15.667                            0.1562
                                13                                                                                                        0.2802                            0.9309                             18.483                            0.1912
                                18                                                                                                        0.0745                            1.2122                             17.416                            0.2346

                              Hand            1/Long,         34
                                Normal                                                                                                    0.1463                            1.1238                             22.981                            0.2870
                                  5                                                                                                       0.0996                            1.2279                             24.996                            0.3410
                                14                                                                                                        0.0996                            1.2438                             26.841                            0.3709
                                19                                                                                                        0.1351                            1.1996                             29.855                            0.3979
                                24                                                                                                        0.0351                            1.0470                             33.922                            0.3946
                                29                                                                                                        0.3083                            1.0661                             37.355                            0.4425

                              Hand            1/Index,        26
                                Normal                                                                                                    0.1132                            1.1221                             17.644                            0.2200
                                 5                                                                                                        0.1555                            1.0452                             17.154                            0.1992
                                    10                                                                                                    0.0394                            1.4017                             21.642                            0.3371
                                15                                                                                                        0.1500                            1.1163                             22.789                            0.2821
                                21                                                                                                        0.0798                            1.2881                             26.272                            0.3760

                              Hand           2/Little,         26
                                Normal                                                                                                    0.0908                             1.1750                            17.960                            0.2345
                                 6                                                                                                        0.2255                            0.9903                             19.433                            0.2138
                                11                                                                                                        0.5978                            0.7797                             19.962                            0.1729
                                 16                                                                                                       0.3330                            0.9927                             21.646                            0.2231
                                21                                                                                                        0.2168                            1.0474                             24.152                            0.2811
                              Hand           2/Ring,          31
                                Normal                                                                                                    0.1070                            1.1524                             19.713                            0.2539
                                 6                                                                                                        0.3114                            0.9525                             22.667                            0.2400
                                11                                                                                                        0.0192                            1.1989                             24.047                            0.3203
                                16                                                                                                        0.1375                            1.1805                             27.883                            0.3657
                                21                                                                                                        0.3471                            0.9570                             25.744                            0.2737
                                26                                                                                                        0.0751                            1.3713                             35.907                            0.5471

VOL.        57-A,    NO.       6,     SEPTEMBER                      1975
784                                                                                            P.        W.     BRAND,               K.         C.    CRANOR,              AND        J.      C.    ELLIS

I   .   DoYLE.    J. R. . and BLYIHE.            WIlLIAM:         Macroscopic             and Functional          Anatomy          of the Flexor         Tendon        Sheath.Proceedings
                                                                                                                                                                          in                    of the American
    Society        for Surgery        of the Hand.           J. Bone        and Joint        .Surg.
                                                                                               56-A:       1094,   July      1974.
 2. FIATI.       A. F.: The Pathomechanics                    of Ulnar         Drift.     A Biomechanical           and Clinical         Study.                Social
                                                                                                                                                    Final - Report         and Rehabilitation         Service,      Grant
    No.      RD 2226           M. University          of Iowa,        1971.
3. FlAIl       . A.   E. . and FIsroER.         G. W.: Restraints               ofthe      Metacarpophalangeal              Joints:     A Force      Analysis.        Read at Fundamental           Surgical       Forums    of the
    American           Collegc     of Surgeons.           Atlantic       City.        New    Jersey,      October      1968.
4.   Lioo.        J P.: STARK.        H. H.: ASHWORFH.               C. R.: and BOYES.               J. H.: Capsulodesis             and Pulley        Advancement            for the Correction          of Claw-Finger
    E)efornittv.       J. Bone and Joint Surg.. 54-A:                   1465-1470.            Oct.     1972.
5. SOI ONIN.          K. A. . and HovIR.          PAIl     : Positioning            of the Pulley        Mechanism         when      Reconstructing          Deep      Flexor     Tendons     of Fingers.         Acta Orthop.
    Scandtnavtca,            38: 321-328.           1967.
6. ZANoI1I.            E. A.: Claw-Hand               Caused       by Paralysis           of the Intrinsic        Muscles.         A Simple        Surgical     Procedure         for its Correction.          J. Bone    and Joint
    Surg . 39-A:           1076-1080.       Oct.      1957.

                                                                           The                       Fascia                            of             the           Distal                         Phalanx
                                       BY      MARVIN                   SHREWSBURY,                             PH.D.*,              AND             R.    K.     JOHNSON,       M.D.t,              SAN       JOSE,         CALIFORNIA

             ABSTRACT:               The           anatomy       of                            the distal                    phalanx                     which
                                                                                                                                                        of               are     in line           with      the two             lateral        tubercles           at the    base
the          human               finger            was   studied                               in preserved                      and                    ofthe
                                                                                                                                                     fresh               phalanx.             From         each        ofthese         two        lateral         tuberches     an
specimens                        and the     fascia                                was            related                   to        associated inverted                       V-ridge     extends    proximally                              for      the insertion            of
structures                      as a mechanism                                     for          prehension.                          Particular the long                       flexor   tendon.     At the base                            of the      phalanx     (Fig.         1,
attention                      was       directed              to the                     lateral      interosseous                                    liga- there
                                                                                                                                                          B)                is an insertion                   ridge  for the extensor                         aponeurosis.
ments               of         the       distal             phalanx                       and     their      possible                                 func- profile
                                                                                                                                                          In                  the straight                 dorsal   edge of the shaft                        abruptly      rises
tion          during                 gripping                   with         the           digital                 pulp.                                  proximally        at the base of the phalanx.                                        The shaft of the dis-
                                                                                                                                                          tally    narrowing      phalanx  is convex                                        from   the radial  to the
             Only          a few            detailed   studies  of the fascial  anatomy    ulnar
                                                                                           of       border.                                                                                The dorsal                crescent    of the                  ungual         process
the distal                 phalanx              have been presented     This paper    is a represents.     the                                                                             attachment              of the distal    half                of the        nail bed.
report   of               a more              complete    study  of the fascia             No consistency
                                                                               of the distal                                                                                                   in size        of       the    ulnar         spines          was     noted,     ex-
phalanx              as a mechanism                                 for          its      prehensile                      functions.                      cept     that they were   more   marked                                      in the         thumb         than in all
                                                                                                                                                          other     digits  and more pronounced                                       on the          ulnan       than the ra-
                                       Materials                       and             Methods                             dial side of the thumb’s       ungual     tuberosity.       The distal    un-
             Thiry     preserved                        human                    digits         were disarticulated        gual tuberosity
                                                                                                                            at                 covers   a smaller     portion     of the dorsum        of
the          metacanpophalangeal                            joint                   and        the terminal       segments the phalanx     than does the volar        ungual     portion.   Distal     to
were examined      with                               a dissecting                         microscope (X 10). Nine         the volan flat surface     for attachment         of the flexor     tendon,
fresh   specimens      of                             the terminal                                  phalanx    were                         also    the
                                                                                                                                                    ex- shaft    slopes dorsodistally,                                             creating           an ungual   fossa,
amined.     A composite                                  illustration                           was       made  for                       all       and it then ends abruptly
                                                                                                                                                speci-                                 at the                                      proximal           edge of the volar
mens.                                                                                                                                               surface   of the ungual     tuberosity.
             Not         all     features             described                        were              equally           developed                      in
                                                                                                                                                          Ligaments      and                  Tendons
every           digit.    although                       all of              the terminal     segments      of                                            the
digits          contained       the                   features               to be described.     Inconsistent                                                   A confluence                       of      five       fibrous         elements              is attached        to
or anomalous                         osteofibrous                      structures                         are not          mentioned                      each
                                                                                                                                                          in        of     the      lateral         tubencles            of the        distal         phalanx         (Fig.    2).
this study.                                                                                                                                                      Strands      of tendinous       fibers    of the long    flexor tendon
                                                                                                                                                          insert into the lateral        tubencles.      The tendon    also has a more
                                                                                                                                                          distal    insertion    into the volar        peniosteum   of the shaft along
Osu’ologv                                                                                                                                      the proximal       edge of the                                          ungual      fossa,  and laterally      into
             A volar             view         (Fig.         ,   A ) ofthe
                                                                I                         distal               phalanx           shows      an the volar    plate of the distal                                         interphalangeal       joint.   Its insen-
expanded                   base        with        a progressive                               distal waisting’
                                                                                                         ‘ ‘                     ‘   of the    tions   into    the thickened                                           surface       of the volar       plate    are
shall,             ending              with        a crescent-shaped                                           rough         cap            of        somewhat
                                                                                                                                                    bone                         looser.
epiphysis,     the ungual        tuberosity      (process).     At the                                       collateral     ligament       has distal
                                                                                                                                                base of    volan
                                                                                                                                                           The       at-       oblique
the phalanx.        proximal        to the beginning            of the sloping    tachments       into     the     lateral    tubercles.      It wraps        forward
shaft,   are the two lateral         tubercles.      Projecting     proximally    around      the    sides     of      the joint      from     its origin        on    the
from     the ungual      tuberosity         are two    lateral   ungual           lateral
                                                                             spines         pit of the head of the middle                   phalanx.      The volar
                                                                                                                                                          plate firmly    attaches   distally        to the shelf                                     of bone at the be-
         *    San    Jose        State        University.                  San         Jose.        California             951       14.
                                                                                                                                                          ginning    of the peniosteal       insertion     of the                                    flexor  tendon, but
    1- 25            North            Fourteenth                 Street,           Suite            960,           San      Jose,           California
951 12.                                                                                                                                                   not     to the         lateral           tubercles.

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