Restoration of shoulder biomechanics according to degree of repair completion in a cadaveric model of massive rotator cuff tear: importance of margin convergence and posterior cuff fixation.

BACKGROUND: Complete repair in massive rotator cuff tear may not be possible, allowing for only partial repair. However, the effect of partial repair on glenohumeral biomechanics has not been evaluated. Therefore, the purpose of this study was to compare the rotational range of motion (ROM), glenohumeral kinematics, and gap formation at the repaired tendon edge following massive cuff tear and repair according to the degree of repair completion.

HYPOTHESIS: Posterior fixation will restore the altered biomechanics of massive rotator cuff tear.

STUDY DESIGN: Controlled laboratory study.

METHODS: Eight cadaveric shoulders were tested at 0°, 30°, and 60° of abduction in the scapular plane. Muscle loading was applied based on physiological muscle cross-sectional area ratios. Maximum internal (MaxIR) and external rotations (MaxER) were measured. Humeral head apex (HHA) position and gap formation at the repaired tendon edge were measured using a MicroScribe from MaxIR to MaxER in 30° increments. Testing was performed for intact, massive cuff tear, complete repair, and 4 types of partial repair. A repeated-measures analysis of variance was used to determine significant differences.

RESULTS: Massive tear significantly increased ROM and shifted HHA superiorly in MaxIR at all abduction angles (P < .05). The complete repair restored ROM to intact (P < .05), while all partial repairs did not. Abnormal HHA elevation due to massive tear was restored by all repairs (P < .05). Release of the anterior single row alone and release of the marginal convergence significantly increased gap formation at the anterior tendon edge (P < .05).

CONCLUSION: This study emphasizes the importance of anterior fixation in massive cuff tear to restore rotational range of motion and decrease gap formation at the repaired tendon edge and of posterior fixation to restore abnormal glenohumeral kinematics due to massive cuff tear.

CLINICAL RELEVANCE: If complete repair of massive cuff tear is not possible, posterior cuff (infraspinatus) repair is necessary to restore abnormal glenohumeral kinematics, and margin convergence anteriorly is recommended to decrease gap formation of the repaired tendon edge, which may provide a better biomechanical environment for healing.