Surgical repair of the supraspinatus: architectural changes in the muscle pre- and postoperatively.

INTRODUCTION Shortening of the tendon and muscle is recognised as a strong predictor for surgical failure of supraspinatus tendon tears. Changes in muscle architecture following repair have not been thoroughly investigated. We aimed to compare the architecture of the supraspinatus pre- and postoperatively. METHODS We recruited eight participants with full-thickness supraspinatus tears. Images of the supraspinatus were captured preoperatively (pre-op) and postoperatively at one (post-op1), three (post-op2) and six (post-op3) months in relaxed and contracted states (0° and 60° glenohumeral abduction). Fibre bundle length (FBL), pennation angle (PA) and muscle thickness (MT) were quantified. Self-reported function, and maximal isometric abduction and external rotation strengths were assessed. RESULTS Mean FBL increased from pre-op to post-op1 (p = 0.001) in the relaxed state and from pre-op to post-op2 (p = 0.002) in the contracted state. Decrease in FBL was observed from post-op2 to post-op3 in the relaxed state. Mean PA decreased from pre-op to post-op1 (p < 0.001) in the relaxed state, but increased from post-op2 to post-op3 in both relaxed (p = 0.006) and contracted (p = 0.004) states. At post-op3, external rotation (p = 0.009) and abduction (p = 0.005) strengths were greater than at post-op2. Overall function increased by 47.67% from pre-op to post-op3. CONCLUSION Lengthening of the supraspinatus occurs with surgery, altering the length-tension relationship of the muscle, which can compromise muscle function and lead to inferior surgical outcomes. These findings may guide clinicians to optimise loads, velocities and shoulder ranges for effective postoperative rehabilitation.