Cyclic Loading of Transosseous Rotator Cuff Repairs" Tension Overload as a Possible Cause of Failure

Summary: Previous experimental studies of failure of rotator cuff repair have involved a single pull to ultimate load. Such an experimental design does not represent the cyclic loading conditions experienced in vivo. We created 1 cm X 2 cm rotator cuff defects in 16 cadaver shoulders, repaired each defect with transos-seous imple sutures, and cyclically loaded the repairs by a servohydraulic materials test system actuator at physiologic rates and loads (rate of 33 mm/sec to a load of 180 N.). A progressive gap was noted in each specimen, for a 100 % rate of failure of the repairs. A 5 mm gap developed at an average of 25 cycles, and a 10 mm gap developed at an average of 188 cycles. The central suture always failed first and by the largest magnitude. This study suggests that rotator cuff tears that are repaired with a "tension overload " of a portion of the muscle-tendon units will undergo gradual failure with physiologic yclic loading until the normal resting lengths of the muscle-tendon units are restored. This "controlled failure" of the repairs may explain residual defects that have been demonstrated byultraso-nography and by arthrography in patients with "successful " rotator cuff repairs