Rotator Cuff Fixation

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					Rotator Cuff Fixation

  Shannon M. Wolfe, M.D.
                 Deadman Angle:
     Burkhart S. AJARS 1995: 11(1); 119-123.

•   Deadman angle is the angle formed by the suture attached to the
    anchor and a line parallel to the bone axis: optimal angle is less or
    equal to 45 (add figure 4)
•   TcosTheta is a constant and therefore T decreases as Theta
    descreases, and T(x) increases as Theta decreases
•   For rotator cuff tear with anchors, we should lateral place our
    anchors and place the suture obliquely to minimize Theta (figure
    5)
•   Pull out strength of suture anchor increases as Theta decreases,
    with 41% more resistance to pull out at 45 as compared with 90
•   Clinically we can decrease the Theta by placing the anchor
    obliquely: Theta 1 (pull out angle for the anchor) = angle the
    suture makes with the perpendicular to the anchor and Theta 2
    (the tension-reduction angle) = angle the suture makes with the
    pull of the rotator cuff both which are ideal to be less than 45
Sward et al. JBJS(B) 1992: 74-B(4); 585-
                  588.
• 26 fresh cadavers, created 5mm defect in supraspinatus and
  divided into 3 groups: 1
     Burkhart et al. AJARS 1993: 9(6); 611-616

•   Idea of the rotator cuff comprised of cable and crescent, the cable
    is thicker and acts as stuts and the crescent is lateral and thin
    figure
•   Cable extends anteriorly from the bicep to as far back posteriorly
    as the infraspinatus
•   Most rotator cuff tears identified arthroscopically are identified in
    the rotator cuff crescent and therefore when tore, the tear acts
    much like and suspension bridge
•   Mechanical testing has shown that under massive loads, the tears
    will not propagate through the cable and in intact cuffs, the
    crescent is stress shielded
•   Seems that younger patients, the crescent is not stress shielded
•   ??? Are rotator cuff tears in the crescent tissue inconsuential
    since this tissue is stress shielded
    Burkhart et al. AJARS 1993: 9(6); 611-616

• Therefore tears in the cable system are more important in a
  patient with cable dominant shoulders
  Burkhart S. AJARS 1997: 13(6); 720-724

• 16 cadavers (average age of 41, 50% < 45 yrs. And 50% > 45
  yrs.) had a 1x2 cm defect created in supraapinatus and repaired
  by RC suture anchors time 3 with Ethibond #2 suture utilizing
  simple through
• Physiologic rates and loads were then applied at 33mm/s and
  180N were performed in the direction of the longitudinal pull of
  the supraspinatus (failure in single load to failure is usually
  tendon whereas failure in cylic loading is usually bone)
• Failure = 50% at 5mm gap and 100% failure at 1cm
• 100% failed on average of 285 cycles, 15 failed through tendon
• Significant failure rate b/n those > 45 and those < 45 with 10 mm
  failure cycle at 91 cycles and 478 cycles respectively
• Compared to previous study with transosseous tunnels, bone
  anchors were significantly stronger
  Burkhart S. AJARS 1997: 13(6); 720-724

• Cylcic loading is more physiologic 33mm/s seen in ADL and 180
  N is 2/3 of maximal contraction
• Every specimen had central failure first
• Failure is transferred from bone to tendon now that suture
  anchors are better designed with stronger pull out strength
• Need to design tendon grasping stitch that can be used with
  application of suture anchors
  Burkhart S. AJARS 1997: 13(2); 172-176

• 16 cadaver 1x2 cm rotator cuff repairs were tested in cyclic
  fashion to failure
• Repairs were made through 3 bony tunnels, with 3 simple
  throughs, and with 8 specimens using #2 cottony Dacron and 8
  using #2 Ethibond
• Specimens were loaded to 180 N at 33 mm/s
• All showed 100% failure with cottony failing on average of 195.88
  cycles and ethibond failing at 169.63 (not statistically significant)
• 50% failed at 5mm with only 25 cylcles
• 1 suture failure, 6 tendon failure, 6 bone failure, and 3 both
• When distal bone hole was in cortical bone, 6 of 7 had primary
  cuff failure, as opposed to suture in metaphyseal bone in which 6
  of 9 had primary bone failure
  Burkhart S. AJARS 1996: 12(6); 704-708

• 17 cadavers used to test rotator cuff repairs with 2 simple knot
  repairs through bone tunnel versus 1 mattress knot repair through
  2 bone tunnels
• The tendons used were the supra and infraspinatus as a unit and
  the subscapularis; these tendons were randomized to site of
  repair being either greater or lesser tuberosity
• Each was preloaded at 8.9 N and displaced at 31mm/s until
  failure
• Average ultimate load for simple repair was 189.62N compared
  mattress at 135.71 N, a 39.72% decrease: statistically significant
  (suture failure in simples averaged 193N and in mattress at
  147.74N)
• 22 failures were suture with all but two breaking at the knot, bone
  failure occurred 7 times 6 in the mattress group, tendon failure
  occurred 5 times 4 in the simple group
  Burkhart S. AJARS 1996: 12(6); 704-708

• Mechanically the simple throw have an advantage because there
  is twice the amount of suture limbs bypassing the defect and
  twice the number of knots, therefore suture failure would occur at
  higher loads
• Simple thowes also have large amount of bone bridge than
  mattress and would expect the mattress group to have more bony
  failure *mattress stitch is a better gathering stitch which may have
  transferred the stress to the bone therefore see more bony
  failures
    Gerber et al. JBJS 1994: 74(B),3; 371-380

• First test of different suture material tested to meaure elongation
  under load and ultimate tensile strength (rate of 6mm/min)
• Tests were performed on five dry and five wet of each suture
  type, compared to each other and then to whole group. Suture
  was knotted using 6 simple square knots
• Results: all threads failed at the knot, the braided polyesters
  (Ethibond, Mersilene, Tevdek) showed high tensile strength as
  well as high stiffness, the braidable absorbable(Bondek, Dexon,
  and Vicryl) faired well with stiffness and tensile strength, the
  monofilament had decreased stiffness and variable ultimate
  strengths
• For same suture, one size larger increase ultimate tensile
  strenght by an average of 35% from 0 to 1 and 30% from 1 to 2
   Gerber et al. JBJS 1994: 74(B),3; 371-380

• From test 1, the most favorable suture (Ethibond 1,3 and
  Tevdek 1) were tested under 8 different knots
• Maxon 1 was used in comparison
• Recorded slippage or failure of knots in relation to the load
• 1=1=1=1 and 2=1=1 demonstrated good knot security and more
  knots didn’t change elongation of ultimate tensile strength
• 2=1 and 1=1 knots slipped badly
• Slippage caused damage to the suture and therefore lowered
  the ultimate tensile strength 10% for ethibond and 21% for
  Tevdek
• Monofilament Maxon 1 had stable knots at 2=1=1 and 1=1=1
  however 30% decrease in ultimate strength was seen with
  simple knots compared to surgeon’s knot
    Gerber et al. JBJS 1994: 74(B),3; 371-380

• Then measure formation of a gap caused elongation of suture
  under tensile load they compared the average length of suture
  used to repair a supraspinatus tear with mattress suture, then
  took that length of that suture (7cm) and tied it around two bars,
  tested it to elongation and recorded the load
• Braided polyester did much better at a load of 200N (Ethibond 3
  2.2mm, 1 at 3.5mm, Tevdek 1 at 2.8) in contrast to PDS II #1 at
  10.2 mm
   Gerber et al. JBJS 1994: 74(B),3; 371-380

• 4 common suture grasping techniques and five alternatives
  were then tested of 159 infraspinatus tendons
• Recorded the ultimate strength and the gap between the bottom
  of the bony trough and the end of the tendon stump under
  tensile load
• Most had two sutures placed in end of tendon, the simple stitch
  was tested at 2, 4, and 6 stitches
• The tendon was preloaded under 30N and #3 Ethibond was
  used for all
• Tissue was secure with 6 simple square knots
• Most successful technique was redone with augmentation by
  1.4mm thick, Poly(L-/D-lactide) membrane and re-tested
• Five tendon structures were retested using cyclical loading to
  maximum of about 70% ultimate tensile failure load
    Gerber et al. JBJS 1994: 74(B),3; 371-380

• Results: the ultimate tensile strength, separation at 200 N and
  mode of failure was recorded
• Modified Mason-Allen showed no slippage and all failure
  occurred suture rupture at average of 359N
• The simple stitch, augmented first modification of the Kessler
  stitch and the mattress werer significantly less strong
• Modified mason-allen allowed the least gap formation
• Augmentation on the tendon side did not improve strength and
  did not allow the suture to grasp the fibre bundles of the tendon
• Most techniques caused deformation of the tendon except the
  simple and modified Mason-Allen which gave the best suture to
  tendon grasp
    Gerber et al. JBJS 1994: 74(B),3; 371-380

• Results: cyclic testing to 250N at 40c/min\
• The best result was seen in Modified Mason-Allen stitch which is
  the only stitch to withstand 1000 cycles and had 4.9mm
  diastasis at 0N and 6.6mm at 250 N
    Gerber et al. JBJS 1994: 74(B),3; 371-380

• Tested different techniques for the fixation of tendon to bone: 1.
  4 hole 2.7 DC Plate compressed tendon to cortex, 2.metallick
  brush used to squeeze the tondon to bone, 3. Double
  transosseous suture, 4. Single transosseous suture, 5.GII
  anchor, 6.double transosseous tied over 2.0 mm thick poly(L-/D-
  lactide) augmentation
• These were test on verified osteoporotic bone and compared
  young proximal humeri
• Pull out tests were performed at extension rate of 1mm/min with
  recording ultimate tensile strength and modes of failure
   Gerber et al. JBJS 1994: 74(B),3; 371-380

• Results:
• The GII pulled out in osteoportic bone at 142N, single and
  double transosseous cut through osteoportic bone at 139 N and
  146N respectively
• Only double transosseous augmented with poly gave strength
  that was limited by the #3 Ethibond
    Gerber et al. JBJS 1994: 74(B),3; 371-380

• Overall Results:
• Tendon to bone suturing gave the best results and in optimal
  bone and optimal tissue the weak link obviously become the
  suture, because even Ethibond #3 will have 2.2mm elongation
  at 200N and many consider a 3mm elongation a failure
• Take caution if braided absorbable suture results as eventhough
  the good findings are true, there is generally a 50% reduction if
  ultimate strength by 2 weeks
• Monofilament will lose 50% by 4-5 weeks which gives enough
  time for rotator cuff to heal, however the elongation of this
  material is too great

				
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