Abstract
Introduction
Supraspinatus and infraspinatus tears (Massive Rotator Cuff Tear- MRCT) cause compensatory activation of the teres minor (TM) and subscapularis (SubS) to maintain humeral head alignment. This study measures force changes in TM and SubS using a dynamic shoulder testing setup. We hypothesize that combining superior capsule reconstruction (SCR) and lower trapezius tendon (LTT) transfer will correct rotator cuff forces.
Methods
Eight fresh-frozen human shoulder specimens from donors aged 55-75 (mean = 63.75 years), balanced for gender, averaging 219.5 lbs, were used. Rotator cuff and deltoid tendons were connected to force sensors through a pulley system, with the deltoid linked to a servohydraulic motor for dynamic force measurement. The system allowed unrestricted humeral abduction from 0 to 90 degrees.
Results
Teres Minor (TM):
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Control: 7.43 N (SD = 1.66)
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SS tear: 5.46 N (SD = 1.45)
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MRCT: 3.94 N (SD = 1.43)
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LTT post-MRCT: 5.85 N (SD = 1.13)
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SCR post-MRCT: 4.68 N (SD = 0.71)
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Combined LTT+SCR: 6.43 N (SD = 1.24)
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TM force reduction: 26.51% post-SS tear, 46.97% from intact to MRCT, 63.20% increase with LTT+SCR.
Subscapularis (SubS):
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Control: -0.73 N (SD = 0.43)
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SS tear: -0.46 N (SD = 0.36), 36.99% increase
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MRCT: 0.96 N (SD = 0.47), 31.51% increase
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LTT post-MRCT: -0.32 N (SD = 0.47), 66.67% reduction
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SCR post-MRCT: -0.28 N (SD = 0.16), 70.83% reduction
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Combined LTT+SCR: -0.66 N (SD = 0.32), 31.25% reduction
Non-parametric Friedman's ANOVA showed overall statistical significance for TM (P = 1.083×10-6) and SubS (P = 4.77×10-4).
Conclusion
The cadaveric model assesses rotator cuff compensations, showing significant TM force reductions following rotator cuff tears and improvements with LTT and SCR, particularly when combined. SubS exhibited negative force during normal abduction but compensated during MRCT, returning to normal values post-LTT and SCR.
