Lower Trapezius Tendon Transfer Restores Deltoid Function and Shoulder Stability More Effectively Than Superior Capsular Reconstruction in Massive Rotator Cuff Tears.

PURPOSE

To compare the biomechanical effectiveness of superior capsular reconstruction (SCR) and lower trapezius tendon transfer (LTT) to restore the native shoulder kinematics in managing massive rotator cuff tears (MRCTs) using a dynamic shoulder testing system in a cadaver model.

METHODS

Eight fresh-frozen cadaveric hemithoraces were tested using a custom-made dynamic shoulder testing system. The conditions tested are intact, supraspinatus tear, MRCT (supraspinatus and infraspinatus tear), LTT with Achilles allograft, SCR combined with LTT, and SCR alone. Measurements included cumulative deltoid force, humeral head translation (HHT), and subacromial peak pressure during humeral abduction at various angles.

RESULTS

Significant reductions in cumulative deltoid force were observed from intact to MRCT conditions ( = .023). LTT alone significantly improved deltoid force compared to its combination with SCR ( = .017) and outperformed SCR alone ( = .023). The intact condition showed increasing subacromial peak pressure with higher abduction angles, peaking at 541 kPa at 90°. MRCT exhibited the highest HHT and peak pressure, indicating significant instability. LTT reduced HHT and peak pressure compared to MRCT, indicating partial restoration of stability. The combined LTT + SCR condition demonstrated HHT values close to the intact condition and lower peak pressures, indicating substantial restoration of glenohumeral stability.

CONCLUSIONS

Simulated active unconstrained humeral abduction in the scapular plane using an entire hemithorax model suggests that LTT can restore dynamic stability and deltoid function in MRCTs, while SCR offers static stability without restoring deltoid function. Combining LTT and SCR may result in lower subacromial peak pressures on the undersurface of the acromion than either procedure alone.

CLINICAL RELEVANCE

This study will contribute to understanding shoulder kinetics concerning current surgical techniques and suggest a dynamic concept of shoulder biomechanics testing.