Biomechanical Comparison of Internal Rotational Effectiveness following Medialized Glenoid and Lateralized Humerus Reverse Shoulder Arthroplasty with Tendon Transfers: Isolated latissimus dorsi, Combined Latissimus dorsi/teres major, and Pectoralis major tendon transfers

Background: The restriction of active internal rotation (IR) after reverse shoulder arthroplasty (RSA) poses a challenging problem for reconstructive shoulder surgeons, particularly in patients suffering from massive rotator cuff tears (mRCT) with subscapularis (SSC) deficiency. This study aims to evaluate the biomechanical effectiveness of different tendon transfer techniques following medialized glenoid and lateralized humerus RSA in improving internal rotation (IR) strength.

Methods: Eight cadaveric shoulder specimens were evaluated using a custom shoulder testing system designed to simulate loading conditions typical of mRCT with SSC insufficiency. The study examined four different conditions: 1) RSA alone, 2) RSA with pectoralis major (PM) tendon transfer, 3) RSA with latissimus dorsi (LD) transfer, and 4) RSA with combined LD and teres major (LDTM) transfer. Testing was conducted at abduction angles of 0º, 20º, and 40º under three distinct muscle loading conditions. IR torque was quantitatively assessed using a torque wrench at 60º IR. Additionally, the anterior dislocation force was measured at 20º abduction and 10° IR.

Result: PM and LDTM transfers following RSA significantly increased IR strength at all abduction angles and loading conditions, (p < .001 for PM; p < .006 for LDTM) except at 0° under normal load. LD transfer only showed a significant increase in IR strength at 20° with triple load (p = .022). PM and LDTM transfers significantly increased IR strength across all positions and loading conditions compared to LD transfer, with PM transfers demonstrating notably higher strength improvements at 0° and 20° abduction under increased loads compared to LDTM transfer (p's < .026). Anterior dislocation forces were highest for PM, followed by LDTM and LD, with no significant differences compared to RSA alone or among the transfers (p > .864).

Conclusion: PM and LDTM transfers significantly improved IR strength in medialized glenoid and lateralized humerus RSA for mRCT with SSC deficiency, unlike isolated LD transfer. No difference in anterior dislocation force was noted among the transfers. However, further research is warranted to determine the effects of tendon transfers on IR strength across various RSA prosthesis designs.