Pathological anatomy and dynamic by ldd0229

VIEWS: 54 PAGES: 11

									Ann R Coll Surg Engl 1997; 79: 58-68




Pathological anatomy and dynamic effect of
the displaced plantar plate and the
importance of the integrity of the plantar
plate-deep transverse metatarsal ligament
tie-bar
            G D Stainsby      FRCS
            Consultant Orthopaedic Surgeon
            Royal Victoria Infirmary and Freeman Hospital Trusts*, and Nuffield Hospital, Newcastle upon Tyne




Key words: Foot deformities; Hallux valgus; Toes; Metatarsophalangeal joint




Normal and deformed forefeet have been investigated                SECTION ONE
by cadaver anatomical dissections and experiments,
by radiographs, CT and MRI scanning, and by clinical               The multisegmental tie-bar system and the
studies.                                                           normal foot
  Evidence is presented to show that the skeleton of
the foot rests on and is controlled by a multi-                    The transverse tie-bar
segmental ligamentous and fascial tie-bar system.                  Anatomical studies
Transversely across the plantar aspect of the forefoot,
the plantar plates and the deep transverse metatarsal              A sagittal section through the metatarsophalangeaI joint
ligaments form a strong ligamentous structure which                of a lesser toe of a normal cadaver foot shows that below
prevents undue splaying of the forefoot. Longitudin-               the metatarsal head the capsule is thickened to form the
ally, the five digital processes of the deeper layer of the        'plantar plate'. It is firmly attached to the base of the
plantar fascia are inserted into the plantar plates and            proximal phalanx. Below and anterior to this is the
control the longitudinal arch of the foot.
  It is suggested that many forefoot deformities result            thickened subcutaneous tissue adapted for weight-bearing
from the failure of parts of the tie-bar system and the            which is the plantar pad (Fig. la).
dynamic effect of displacement of the plantar plates.                The plantar plates of the metatarsophalangeal joints
Understanding this allows a more logical approach to               and the intervening deep transverse metatarsal ligaments
their treatment.                                                   form a continuous band of strong ligamentous tissue
                                                                   across the forefoot (Fig. lb), and on transverse section each
                                                                   plantar plate is seen to be anchored to its metatarsal head
                                                                   by the collateral ligaments (Fig. lc).
*Retired from National Health Service appointnents on 1 July
1993                                                               Radiological studies
Based on a Hunterian Lecture given at the Meeting of the British   Radiological studies on normal living feet demonstrated
Orthopaedic Association in Nottingham on 16 September 1994         that weight-bearing increases the width across the
Correspondence to: Mr G D Stainsby, 9 Meadow Court, Darras         forefoot. Measurements were made from the medial
Hall, Ponteland, Newcastle upon Tyne NE20 9RB                      border of the first metatarsal to the outer border of the
                                                                                            Displaced plantar plate       59
                                                               more medially, and the fourth and fifth metatarsals more
                                                               laterally away from the second and third metatarsals.
                                                                  It was seen that the plantar plates and the deep
                                                               transverse metatarsal ligaments form a segmental 'tie-
                                                               bar' across the forefoot which controls the splay between
                                                               neighbouring metatarsals as well as between the first and
                                                               the fifth.

                                                               The longitudinal tie-bar mechanism
                                                               Hicks (1,2) described the mechanisms supporting the
                              (a)                              longitudinal arch of the foot; the 'beam' mechanism which
                                                               operates when the ends of the arch are not fixed, and the
                                                               'truss (or tie-bar)' mechanism (Fig. 2). Everyone
                                                               remembers his explanation of the windlass mechanism
                                                               controlling the plantar fascia, and that the longitudinal
                                                               arch of the foot rises as a result of dorsiflexion of the big
                                                               toe (Fig. 3a), but Hicks also pointed out that this
                                                               mechanism is present in all the toes, and that the
                                                               windlass works in reverse when the flat foot is submitted
                                                               to a weight-bearing strain (Fig. 3b).

                                                               Anatomical studies
                                                               Dissections of cadaver feet have confirmed the findings of
                                                               Poirier (3) and Bojsen-M0ller and Flagstad (4) that in the
                              (b)                              distal part of the sole of the foot, at about the level of the
                                                               necks of the metatarsals, the plantar fascia divides into
                                                               superficial and deep layers. The deeper layer of the
                                                               plantar fascia is thick and strong and divides into five
                                                               processes. Each process goes towards its corresponding
                                                               toe, and close to the metatarsal head divides into two
                                                               strong slips, between which the flexor tendons emerge to
                                                               come to lie on the plantar aspect of the plantar plate.
                                                                  These two slips pass dorsally around the flexor tendons
                                                               and are inserted into the medial and lateral sides of the
                                                               plantar plates of the metatarsophalangeal joints (and the
                                                               sesamoids under the first metatarsal head). Fibres from
                              (c)
                                                               these plantar fascial slips were found to sweep medially
                                                               and laterally into the proximal edges and substance of the
Figure 1. (a) Sagittal section through lesser MTP joint of a   intervening deep transverse metatarsal ligaments, and in
normal foot showing the thickened plantar capsule (plate)      doing this fibres from neighbouring medial and lateral
beneath the metatarsal head. (b) The transverse tie-bar        slips interdigitated (Fig. 4).
(altemate plantar plates and deep transverse metatarsal           The effect of tightening the deeper part of the plantar
ligaments). (c) Transverse section through normal fore-        fascia in a normal cadaveric foot with intact metatarso-
foot at metatarsal head level showing the plantar plates
and the collateral ligaments.                                  phalangeal joints was studied. When the plantar fascia was
                                                               relaxed the toes could be dorsiflexed at the metatarso-
                                                               phalangeal joints. When weight-bearing was simulated
                                                               with pressure under the metatarsal heads, the longitudinal
fifth, the average increase in 20 female feet was 3 mm, and    arch flattened, the plantar fascia tightened, the toes flexed
5   mm   in the feet of 10 males.                              down, and it was then found that the proximal phalanges
                                                               of the toes could not be dorsiflexed from this position.
Cadaver studies with division of the deep transverse
metatarsal ligaments                                           Clinical investigation
Lateral traction was applied to the metatarsals of three       The reversed windlass mechanism can be observed in the
dissected cadaver forefeet before and after division of the    normal living foot when standing with the toes over the
deep transverse metatarsal ligaments. It was found that        edge of a footstool or table. When weight-bearing on the
after division of the ligaments the first metatarsal moved     metatarsal heads the toes flex down and the proximal
60      G D Stainsby




                    Figure 2. The 'beam' and the 'truss (or tie-bar)' mechanisms as described by Hicks.

phalanges resist being pushed up into dorsiflexion. The            The windlass effect is greatest in the big toe and is seen
interphalangeal joints remain mobile, indicating that the        in gradually lessening degrees in the second, third, and
long flexor and extensor tendons are not responsible, and        fourth rays and is almost absent in the fifth. This can be
that the flexion of the proximal phalanges is due to the         related to the size of the metatarsal head, which is the
tight plantar fascia tethering the plantar plates.               pulley, and the length of the lever, which is the toe (or its
   This has been called the 'footstool edge weight-bearing       proximal phalanx).
test'. Normally all the toes (or to be more correct the
proximal phalanges) come down to the same level and are          Discussion
in slight plantarflexion (Fig. 3c,d). This test can be used to
assess the integrity and performance of the windlass             The transverse tie-bar (plantar plates and deep transverse
mechanism of the plantar fascial process to each toe.            metatarsal ligaments) controls the splay of the forefoot.




                 Figure 3. (a) Dorsiflexion of the big toe and the windlass effect of the plantar fascia as
                 described by Hicks. (b) The 'reversed' windlass mechanism (with weight-bearing the
                 longitudinal arch flattens, the foot lengthens, the plantar fascia tightens, the proximal
                 phalanx becomes plantarflexed and the mechanism comes to a stop when the proximal
                 phalanx presses against the ground). (c) and (d) The 'footstool edge weight-bearing test'.
                                                                                         Displaced plantar plate        61
                                                             The five longitudinal processes of the deeper layer of the
                                                             plantar fascia form a longitudinal tie-bar system. They are
                                                             inserted into the whole of the transverse tie-bar and they
                                                             are very strong.
                                                               The longitudinal tie-bar system (the deeper layer of the
                                                             plantar fascia) controls the longitudinal arch of the foot
                                                             when the normal foot is weight-bearing. Both tie-bars are
                                                             centred on the plantar plates and are activated by weight-
                                                             bearing pressure on the metatarsal heads. If two or more
          lnterdigitatng fibres                     l
                                                             metatarsal heads are submitted to upward pressure from
                                                             weight-bearing they will tend to splay apart and the
                                                             corresponding metatarsal rays will flatten. For example,
                                                             when weight-bearing on only the medial three metatarsal
                                   .........   --
                  |J   ... .....




  Figr4. Digamai ilutrto of th pate of                  ........::

 ineto of th plna        fasc*ials prcse int
                                          thels              heads the medial part of the tie-bar system will be active
  trnves Xtie|-bar. _ _|                                     and tighten. The proximal phalanges of the medial three
                                                             toes are then held down in flexion but the lateral two toes
                                                             remain mobile.
                                                                The foot skeleton therefore rests on and is controlled by
                                                             a multisegmental ligamentous transverse and longitudinal
                                                             tie-bar system. This system is capable of automatically
                                                             responding to the weight-bearing surface and adjusting the
                                                             posture of the foot skeleton, and of altering the alignment
                                                             of the mid-foot and hind-foot when the forefoot only is
                                                             weight-bearing and the toes are dorsiflexed during 'heel
                                                             elevation'. Differing tensions in the medial and lateral parts
                                                             ofthe longitudinal system can be adjusted by movement of
                                                             the os calcis as occurs with inversion and eversion of the
                                                             heel (Fig. 5).




                                                             SECTION TWO
                                                             Deformities of the foot and defects in the
                                                             multisegmental tie-bar system
                                                             Further studies have shown that defects in the tie-bar
                                                             system can explain why common forefoot deformities
                                                             develop.

                                                             Hallux valgus
                                                             In the normal first metatarsophalangeal joint, the
                                                             sesamoid bones articulate with grooves on either side of
                                                             a longitudinal ridge (the crista) on the plantar aspect of
                                                             the metatarsal head. A V-shaped pulley is therefore
                                                             formed (Fig. 6a).
                                                               Anatomical and CAT scan studies have been carried
                                                             out on eight cadaver feet with hallux valgus and these
                                                             confirm Haines and McDougall's (5) findings that as
                                                             hallux valgus develops the crista is gradually eroded away
                                                             by the medial sesamoid (Fig. 6b), and that the metatarsal
                                                             head then drifts medial to the sesamoid bones as the
                                                             medial capsule becomes stretched. In severe hallux valgus
                                                             the lateral sesamoid groove of the metatarsal head comes
                                                             to articulate with the medial sesamoid and the lateral
Figure 5. Diagrammatic illustration of the multisegmental    sesamoid migrates to the lateral side of the metatarsal
fascial and ligamentous tie-bar system of the foot.          (Fig. 6c).
62   G D Stainsby




                    (a)




                     (b)




                           Figure 6. Transverse CT scans of
                           forefeet. (a) The normal first MTP
                           joint with the sesamoid bones
                           straddled over the crista. (b) Moder-
                           ate hallux valgus with erosion of the
                           crista by the medial sesamoid. (c)
                           Medial displacement of the first MT
                           head and medial sesamoid articulat-
                           ing with the lateral groove under the
                           metatarsal head.
                    (C)
                                                                                            Displaced plantar plate      63
  When the big toe is normal and unconstrained, and the           When the big toe windlass mechanism fails, then
foot is weight-bearing, the equal tension in the two            control and support of the longitudinal arch of the foot
plantar fascial slips to the sesamoids, straddled over the      will depend increasingly on the tie-bar mechanism of the
prominence of the crista, will keep the toe straight (Fig.      plantar fascial processes to the lateral four toes,
7a). However, if the toe is pushed laterally into valgus by     particularly the second and third.
the tightness or shape of a shoe, the plantar fascia will
tend to bow-string across the lateral side of the               Digitus minimus varus
metatarsophalangeal joint. The medial sesamoid must
then impinge with increased pressure against the medial         Haines and McDougall (5) suggested that this deformity
side of the crista of the metatarsal head. If the crista        can be regarded as a 'mirror-image' to hallux valgus.
becomes eroded the stability of the sesamoid articulation       Cadaver dissections, and CAT and MRI scans have
and its ability to resist lateral displacement is lost (Fig.    confirmed this and demonstrated that the lateral capsule
7b,c). Once the first metatarsal head moves medially, the       of the fifth metatarsophalangeal joint stretches allowing
bow-string effect of the plantar fascia, which is tight         the metatarsal head to drift laterally away from the plantar
throughout the weight-bearing period, will be established       plate and the proximal phalanx. The plantar fascial
and will inevitably cause progressive valgus angulation of      process to the little toe then becomes a deforming force
the big toe. It is therefore suggested that the wearing of      as it bow-strings across the medial side of the metatarso-
narrow and pointed-toed shoes is a potent cause of hallux       phalangeal joint.
valgus.
   Patients with hallux valgus have been assessed by the        Claw toes
'footstool edge weight-bearing test' and it was found that
the ability of the plantar fascia to keep the proximal          Cadaver dissections and MRI scan studies have shown
phalanx of the big toe plantarflexed became progressively       that as clawing of a lesser toe develops, and the metatarso-
less as the valgus deformity increased. Indeed, when the        phalangeal joint becomes dorsiflexed when the foot is
deformity was severe the test failed to produce any             weight-bearing, the plantar plate and the plantar pad are
response and the toe remained dorsiflexed and rotated.          pulled distally and follow the proximal phalanx around
This can be explained by the realisation that, as the valgus    the metatarsal head (Fig. 8a). When the claw deformity
deformity develops, the plantar plate and sesamoid bones        becomes severe and the metatarsophalangeal joint
fall off their pulley (the metatarsal head), so the             dislocated, the plantar plate is then displaced on to the
effectiveness of the windlass mechanism of the plantar          dorsal aspect of the metatarsal head. The head is then
fascia of the big toe gets less and less as the metatarsal      invariably prominent on the plantar aspect of the forefoot
head moves medially. The resulting slackening of the            with very little tissue cover (Fig. 8b).
longitudinal fascial tie-bar on the medial side of the foot       When a lesser toe is clawed the proximal phalanx is no
explains the loss of height of the medial longitudinal arch     longer held down into flexion by its plantar fascial process
of the foot which is usually seen in feet with hallux valgus.   when the foot is weight-bearing and so the flexor and
   Hicks showed that the excursion of the sesamoids             extensor tendons can cause the typical deformity. For this
around the first metatarsal head of the normal foot when        to happen the windlass mechanism of the plantar fascia to
the big toe is dorsiflexed is only about 1 cm (2). Our          the toe must be defective.
studies have confirmed this. Therefore, only a slight              The middle of the plantar plate of lesser toes is thinner
defect in its plantar fascial windlass mechanism will have a    where it is grooved for the flexor tendons. Dissections of
profound weakening effect.                                      cadaver feet with clawed toes have shown that as the
                                                                metatarsophalangeal joint of a lesser toe becomes dorsally
                                                                subluxed the proximal part of the plantar plate stretches
                                                                and even ruptures in the grooved area. This confirms the
                                                                previous reports of Fitton and Swinburne (6) and
                                                                Johnston et al. (7). This defect allows the distal part of
                                                                the plantar plate to move to the dorsal aspect of the
                                                                metatarsal head with the base of the proximal phalanx and
                                                                the plantar fascial slips to slide dorsally around the sides
                                                                of the metatarsal head (Fig. 9a,b). They are therefore no
                                                                longer around the circumference of the metatarsal head
                                                                and become ineffective. Indeed, when the slips have
                                                                moved dorsal to the axis of rotation of the metatarso-
                                                                phalangeal joints, they will depress the metatarsal head as
                                                                they tighten.
Figure 7. (a) Normal alignment of the plantar fascial              It has been shown experimentally that when the plantar
process to the big toe. (b) With the big toe pushed into        plate is displaced dorsally it is tethered by the deep
valgus the medial sesamoid impinges against the crista. (c)     transverse metatarsal ligaments and this causes depression
The bow-string effect of the plantar fascia when the crista     of the metatarsal head by a 'plunger' effect (Fig. 9a). It is
is eroded.                                                      considered that this 'plunger' mechanism and the
64     G D Stainsby
                                                               Hammer toe
                                                               Hammer toe deformity is seen frequently in second toes
                                                               which are longer than the big toe. Typically, when the
                                                               foot is weight-bearing the metatarsophalangeal joint is
                                                               dorsiflexed, the proximal interphalangeal joint flexed and
                                                               the distal interphalangeal joint extended. For the
                                                               metatarsophalangeal joint to be dorsiflexed when
                                                               weight-bearing (and when the footstool edge weight-
                                                               bearing test is performed) the longitudinal tie-bar to that
                                                               toe must be defective, and the central part of the plantar
                                                               plate stretched, allowing the plantar fascial slips to slide
                                                               off the greatest diameter of the metatarsal head. A possible
                                                               explanation is the wearing of shoes that are too short so
                            (a)                                causing the long toe to 'buckle'.

                                                               Discussion
                                                               It is therefore concluded that defects in the ligamentous
                                                               tie-bar systems of the foot allow deformities of the
                                                               forefoot to develop. Failure of the medial capsular
                                                               ligaments of the first metatarsophalangeal joint (after
                                                               erosion of the crista of the metatarsal head) results in
                                                               hallux valgus; stretching of the lateral capsular ligaments
                                                               of the fifth metatarsophalangeal joint is present in digitus
                                                               minimus varus.
                                                                  Clawing of the lesser toes is often seen to develop in feet
                                                               with hallux valgus. It is suggested that in feet with a
                                                               significant deformity of the big toe the powerful windlass
                                                               mechanism of its plantar fascial process is defective and
                            (b)                                that the longitudinal tie-bar function of the plantar fascia,
Figure 8. Sagittal sections through lesser MTP joints of       controlling the medial arch of the foot (particularly for the
cadaver feet. (a) Moderate clawing with distal movement        'push-off' phase of the walking cycle), will fall upon the
of the plantar plate and pad. (b) Severe clawing. Plantar      fascial processes to the lateral four toes. They are not as
plate now on dorsal aspect of the MT head, and very little     strong as the fascial process to the big toe, their
tissue remains under its plantar surface as the plantar pad    mechanical advantage is not as good as they are more
has also moved distally and dorsally.                          closely placed to the axis of movement of the subtalar joint
                                                               complex, and their windlass mechanisms are not as
malalignment of the plantar fascial slips are the causes of    powerful, as the diameters of the metatarsal heads and
metatarsal head depression seen in the severely clawed         the proximal phalanges of the lesser toes are smaller than
lesser toe. The 'plunger' effect has been clearly observed     those of the big toe. Perhaps, therefore, it is not surprising
many times at operation, and corrected by replacing the        that the plantar plates of the central lesser toes then give
plantar plate under the metatarsal head.                       way where they are stretched over the metatarsal heads.




                 Figure 9. (a) When a lesser toe is severely clawed the plantar plate becomes dorsally
                 displaced; tethered by the deep transverse metatarsal ligaments it causes MT head
                 depression by the 'plunger' effect. (b) The plantar fascial slips slide around the MT
                 head as the central part of the plate stretches. If they now tighten the MT head will be
                 depressed.
                                                                                               Displaced plantar plate       65
   Stretching of the central part of the plantar plate of a       preserved, the medial capsule should be tightened and the
lesser toe allows displacement of the slips of the plantar        first metatarsal head replaced over the sesamoid bones.
fascia from off the greatest circumference of the metatarsal      The effectiveness of the windlass mechanism of the
head, making the windlass mechanism of the plantar fascia         plantar fascia will only be fully restored if the first
ineffective. Dorsiflexion deformity can then develop at the       metatarsal head is correctly positioned above the sesamoid
metatarsophalangeal joint when the foot is weight-                bones. Should an osteotomy of the first metatarsal be
bearing, and this can progress to dorsal dislocation of           required (if there is restricted movement at, or malalign-
the joint and dorsal displacement of the plantar plate. The       ment of, the first tarsometatarsal joint) then shortening of
'plunger' effect of the displaced plantar plate, and              the first metatarsal needs to be avoided as this will weaken
malalignment of the plantar fascial slips, then cause             the windlass mechanism. If a lateral release procedure is
depression of the metatarsal head and metatarsalgia.              carried out to the first metatarsophalangeal joint, then
                                                                  division of the deep transverse metatarsal ligament
                                                                  between the first and second metatarsals should be
                                                                  avoided, and the integrity of the lateral slip of the
                                                                  plantar fascia and its lateral sesamoid attachment needs
                                                                  to be preserved as otherwise a varus deformity of the big
SECTION THREE                                                     toe may result from the unbalanced pull of the medial
                                                                  plantar fascial slip.
The multisegmental tie-bar ligamentous                               When the first metatarsophalangeal joint is degenerate
system of the foot and the principles of                          and cannot be retained, then, if an excisional arthroplasty
surgical treatment of forefoot deformities                        is carried out, it is suggested that the medial capsule
                                                                  should still be tightened to restore the integrity of the
When it is realised that the skeleton of the foot is to a great   transverse tie-bar, and so prevent splaying of the first
extent controlled by a ligamentous tie-bar system, and            metatarsal postoperatively.
that defects in this system result in deformities of the fore-
foot and toes, it is surely logical to try to repair these
defects when the deformities are corrected surgically.            Digitus minimus varus
                                                                  It has been demonstrated that in this deformity the lateral
Hallux valgus                                                     capsule of the fifth metatarsophalangeal joint becomes
Many surgical procedures have been described for the              stretched. It would seem logical, therefore, that when this is
correction of hallux valgus-soft tissue operations,               corrected the surgical procedure should include tightening
osteotomies of the first metatarsal and the proximal              of the lateral capsule so that the fifth metatarsal head is
phalanx of the big toe, and arthroplasties of the                 moved medially and replaced over its plantar plate.
metatarsophalangeal joint of the excision and replace-
ment type. The results of these operations have usually
been assessed with regard to patient satisfaction, cosmetic       Claw toes
appearance and alignment of the big toe, and the                  For the early deformity, where the metatarsophalangeal
reduction in the angle between the first and second               joint is still stable and the capsular ligaments intact,
metatarsals has been measured on radiographs. The                 procedures such as fusion of the proximal interphalangeal
postoperative position of the first metatarsal head relative      joint and flexor-extensor transfer have produced satisfac-
to the sesamoid bones has rarely been recorded, and the           tory results. Both these procedures aid plantarflexion
function of the big toe with regard to the restoration of its     control of the proximal phalanx and may be sufficient to
plantar fascial windlass mechanism does not appear to             prevent progression of the dorsiflexion at the metatarso-
have been assessed.                                               phalangeal joint.
  Our studies indicate that one of the most important                Treatment of the severe claw deformity is notoriously
functions of the big toe during the weight-bearing phase          difficult. Metatarsalgia has often persisted after excision of
of walking is to activate the windlass mechanism of the           the base of the proximal phalanx, and the previously
most medial process of the plantar fascia. It is the              reported good results from various types of metatarsal
strongest part of the longitudinal tie-bar system which           osteotomy (8-10) have recently been questioned.
elevates the arch of the foot, and realigns the bones of the         The investigations and studies reported here show
foot skeleton so that the direct weight-bearing thrust from       that in severe claw deformity of a lesser toe the plantar
the ankle is transferred down the medial side of the foot         plate becomes displaced onto the dorsal aspect of the
when the heel is elevated. To restore this function, if it is     metatarsal head. This results in depression of the
possible, must surely be one of the main aims of surgery          metatarsal head owing to the 'plunger effect'. To correct
for hallux valgus. The stretched medial capsule of the first      this, and relieve the metatarsalgia, it is therefore
metatarsophalangeal joint also requires tightening so that        necessary to replace the plantar plate to its normal
the medial splay of the first metatarsal is controlled.           position beneath the metatarsal head and to preserve the
   It is suggested that if, when surgery for hallux valgus is     length of the metatarsal. Shortening of the metatarsal
carried out, the first metatarsophalangeal joint can be           will cause slackening of the plantar fascia and loss of
66     G D Stainsby
                                                              bearing. The added power of the short flexor tendon, now
                                                              acting to plantarflex the proximal phalanx, assists the
                                                              weakened windlass mechanism of the plantar fascia and
                                                              helps to prevent dorsiflexion at the metatarsophalangeal
                                                              joint when the foot is weight-bearing.

                                                              The rheumatoid forefoot
                                                              Severe deformity of the toes can occur in patients with
                                                              rheumatoid arthritis. Gross hallux valgus and marked
                                                              clawing of the lesser toes with prominence of the
                                                              metatarsal heads in the sole of the foot is commonly seen.
                                                                 In 1912, HofEman (12) recommended excision of the
                                                              metatarsal heads for the severely deformed rheumatoid
                                                              forefoot. A number of modifications to this procedure
                                                              have been described (13-15). So, for over 80 years,
                                                              excision arthroplasty with removal of the metatarsal heads
                                                              has been the usual procedure for this condition. Although
                                                              some good results have been reported it is accepted that
                                                              the foot is inevitably shortened, that there can be
                                                              subsequent problems with exostoses developing on the
                                                              stumps of the metatarsals, that plantar callosities recur
                                                              (16), and that postoperatively many patients need surgical
                                                              shoes (17).
Figure 10. Diagrammatic illustration of the 'modified           When it is accepted that the metatarsal heads control
Keller's procedure' for severely clawed lesser toes. (a) V-   the multisegmental tie-bar system of the foot, it follows
shaped incision to avoid longitudinal skin contracture. (b)   that excision of the metatarsal heads must completely
Extensor tendon divided at the level of the MT neck and       destroy the ligamentous tie-bar support to the foot.
reflected distally. (c) Proximal phalanx sectioned through       Since 1976 the author has carried out a forefoot
the neck and the shaft and base removed preserving the
plantar plate. (d) and (e) Plantar plate replaced beneath     reconstruction procedure preserving the metatarsal heads
the MT head using a periosteal elevator which is taken        (Fig. 11). In this operation the valgus deformity of the big
under the MT neck. (t) Stabilise toe in correct alignment     toe is corrected by a Keller's procedure with division of
with an intramedullary wire, suture the extensor tendon       both long and short extensor tendons and tightening of
to the flexor tendons without tension, and excise any         the medial capsule. The severe clawing of lesser toes is
excess extensor tendon. Close wound with small sutures.       corrected by the procedure previously described for the
                                                              treatment of the single severely clawed toe. The
                                                              metatarsal heads are preserved and an attempt is made
the windlass mechanism, and the weight-bearing struc-         to reconstruct the ligamentous tie-bar system as far as is
tures (the plantar plates and pads) are left distal to        possible. The plantar plates are replaced to their correct
the metatarsal head. Osteotomy of the distal shaft of         position and the transverse tie-bar tightened. The plantar
the metatarsal without replacement of the plantar plate       pad also returns to its weight-bearing position beneath the
can result in uncontrolled displacement of the head           metatarsal heads and any plantar skin callosities move
fragment by the 'plunger mechanism'.                          proximally and subsequently separate spontaneously.
   Since 1976, the author has corrected severe clawing of        The results of this forefoot reconstruction on 42 feet
lesser toes by a procedure which preserves the metatarsal     were reviewed independently (11). The mean follow-up
head and replaces the plantar plate. The principal steps of   was 5 years (range 2 years to 11 years 7 months). At
the procedure are shown in Fig 10.                            review, 34 feet (81%) were considered excellent and 5
   The results of this operation in 74 feet with a single     (12%) good (example shown at Fig. 12). Many patients
severely clawed toe were reviewed independently in 1990       were able to dispense with surgical shoes, the length of the
(11). The average length of follow-up was 3.5 years. In       feet was preserved, 39 (93%) had no pain, only three had
85% the results were considered to be excellent or good       plantar callosities and 14 patients were able to walk
with satisfactory cosmetic appearance, and relief of pain     comfortably on the forefoot alone.
and metatarsalgia.

Hammer toe                                                    Conclusion
Provided the metatarsophalangeal joint is not subluxed or     The foot skeleton is supported and controlled by a multi-
dislocated, fusion of the proximal interphalangeal joint      segmental ligamentous and fascial tie-bar system centred
usually corrects the deformity and the proximal phalanx       on the plantar plates of the metatarsophalangeal joints.
comes down against the ground when the foot is weight-          The integrity and correct positioning of the compo-
                                                                                               Displaced plantar plate        67




                   Figure 11. (a) Incisions for forefoot reconstruction. (b) Diagrammatic illustration of
                   correction of displaced plantar plates and repair of the medial and lateral ends of the
                   transverse tie-bar.




                                                                 nents  of the multisegmental longitudinal and transverse
                                                                 tie-bars are necessary for the normal function of the foot.
                                                                   The longitudinal tie-bar system (the deeper layer of the
                                                                 plantar fascia) is controlled by the windlass mechanism as
                                                                 described by John Hicks.
                                                                   The function of the longitudinal tie-bar system can be
                                                                 assessed by the 'footstool edge weight-bearing test'.
                                                                   Defects in the ligamentous tie-bar system and
                                                                 malalignment of the plantar plates allow and cause
                                                                 deformities of the forefoot and toes to develop.
                                                                   When deformities of the forefoot and toes are corrected
                                                                 surgically, an attempt should be made to reconstruct the
                                                                 tie-bar system, and so restore normal foot anatomy and
                                                                 function as far as is possible.
                                                                   When there is severe clawing of a lesser toe the
             (a)                            (b)                  'plunger' effect of the dorsally displaced plantar plate
                                                                 causes depression of the metatarsal head. When treated
                                                                 surgically it is important to replace the dorsally displaced
                                                                 plantar plate to its correct position under the metatarsal
                                                                 head.
                                                                   When the severely deformed rheumatoid forefoot is
                                                                 treated surgically, it is recommended that the metatarsal
                                                                 heads be preserved as they are an essential part of the
                                                                 weight-bearing structure of the forefoot and they control
                                                                 the tie-bar systems.

                                                                 The anatomical studies would not have been possible without the
                                                                 help and guidance of Professor Simon Miller, and I am
                                                                 particularly grateful to Mrs Christine Harkness who kindly
                                                                 carried out the cadaver dissections in the School of Anatomy of
                                                                 the University of Newcastle upon Tyne.
                                                                   The co-operation, generosity and enthusiasm of the staff ofthe
             (C)                           (d)                   X-ray Department and the Alliance Medical MRI Unit at the
Figure 12. (a) and (b) Severely deformed rheumatoid              Nuffield Hospital, Newcastle upon Tyne, and the Radiology
forefoot before surgery. (c) and (d) One year after forefoot     Department and CT Unit at the Royal Victoria Infirmary, are
reconstruction.                                                  gratefully acknowledged.
68      G D Stainsby
  The author also wishes to thank Mr John Bulmer, Mr Peter             8 Giannestras NJ. Plantar keratosis, treatment by metatarsal
Briggs, Professor Garth Johnson and, in particular, Professor            shortening. J Bone joint Surg 1966; 48A: 72-6.
Leslie Klenerman, for their help, advice, and encouragement.           9 Helal B, Greiss M. Telescoping osteotomy for pressure
                                                                         metatarsalgia. J Bone joint Surg 1984; 66B: 213-17.
                                                                      10 Mann RA, Coughlin MJ. Keratotic disorders of the plantar
                                                                         skin. In: Mann RA, Coughlin MJ, eds. Surgery of the Foot
                                                                         and Ankle, 6th Edition. St Louis: CV Mosby 1993: 427.
References                                                            11 Stainsby GD, Briggs PB. Modified Keller's procedure for the
                                                                         lateral four toes. J Bone joint Surg 1990; 72B: 530.
 1 Hicks JH. The foot as a support. Acta Anat 1955; 25: 34-45.        12 Hoffman P. An operation for severe grades of contracted or
 2 Hicks JH. The mechanics of the foot. II. The plantar                  clawed toes. Am J Orthop Surg 1912; 9: 441-8.
   aponeurosis and the arch. J Anat 1954; 88: 25-30.                  13 Fowler AW. A method of forefoot reconstruction. J Bone
 3 Poirier P. Traite d'Anatomie Humaine. Vol 2, Paris: L                 joint Surg 1959; 41B: 507-13.
   Battaille et Cie, 1892: 296.                                       14 Clayton ML. Surgery of the forefoot in rheumatoid arthritis.
 4 Bojsen-Moller F, Flagstad KE. Plantar aponeurosis and                 Clin Orthop Rel Res 1960; 16: 136-40.
   internal architecture of the ball of the foot. J Anat 1976; 121:   15 Kates A, Kessel L, Kay A. Arthroplasty of the forefoot. J
   599-611.                                                              Bone joint Surg 1967; 49B: 552-7.
 S Haines RW, McDougall A. The anatomy of hallux valgus. J            16 Barton NJ. Arthroplasty of the forefoot in rheumatoid
   Bone joint Surg 1954; 36B: 272-93.                                    arthritis. J Bone joint Surg 1973; 55B: 126-33.
 6 Fitton JM, Swinburne L. Degenerative lesions of the                17 Craxford AD, Stevens J, Park C. Management of the
   accessory plantar ligaments. Int Orthop 1981; 4: 295-8.               deformed forefoot: a comparison of conservative and
 7 Johnston RB, Smith J, Daniels T. The plantar plate of the             surgical methods. Clin Orthop Rel Res 1982; 166: 121-6.
   lesser toes: an anatomical study in human cadavers. Foot
   Ankle Int 1994; 15: 276-82.                                        Received 29 July 1996

								
To top