Early Postoperative Evolution of Fatty Infiltration and Muscle Atrophy in Posterosuperior Rotator Cuff Tears: An MRI Study

Background Fatty infiltration and muscle atrophy are common findings in posterosuperior rotator cuff tears and are associated with poorer clinical and structural outcomes. Their early postoperative evolution after rotator cuff repair remains incompletely understood. The purpose of this study was to evaluate early postoperative changes in fatty infiltration and muscle atrophy after rotator cuff repair and to identify factors associated with structural MRI outcomes. Methods This imaging-based retrospective case series included patients who underwent rotator cuff repair and had both preoperative MRI and postoperative MRI obtained between 6 and 12 months after surgery. Fatty infiltration and muscle atrophy were assessed by a blinded musculoskeletal radiologist using the Goutallier and Thomazeau classifications, respectively. Demographic, imaging, and surgical variables included age, sex, tear size according to Cofield, tendon retraction according to Patte, surgical technique, and postoperative tendon integrity according to the Sugaya classification. Results Seventy-five patients were included (mean age, 55.4 ± 8.4 years). The mean imaging follow-up was 7.6 ± 2.1 months (median 7.0 months; range 6–12 months). No significant overall differences were observed in fatty infiltration or muscle atrophy between the preoperative and postoperative periods (supraspinatus fatty infiltration, P=.423; infraspinatus fatty infiltration, P=.660; supraspinatus muscle atrophy, P=.655). Age correlated positively with supraspinatus fatty infiltration (ρ = 0.385, P < .001), and male sex was associated with higher baseline fatty infiltration (P = .027). Larger tear size and greater tendon retraction were associated with increased fatty infiltration (P < .001 and P=.001, respectively). Preserved tendon integrity (Sugaya I–III) was associated with lower postoperative fatty infiltration (P = .010), whereas muscle atrophy did not differ significantly (P = .370). Patient-level transitions showed that most patients remained unchanged (supraspinatus fatty infiltration, 74.7%; infraspinatus fatty infiltration, 81.3%; supraspinatus muscle atrophy, 93.3%), whereas improvement (12.0%, 8.0%, and 2.7%, respectively) and worsening (13.3%, 10.7%, and 4.0%, respectively) were less frequent. Conclusion Fatty infiltration and muscle atrophy showed limited overall change during early postoperative follow-up after arthroscopic rotator cuff repair, rather than reversal of established muscle degeneration. Preserved tendon integrity was associated with lower postoperative fatty infiltration, whereas postoperative muscle atrophy did not differ significantly according to tendon integrity. Level of Evidence Level IV, Case Series, Prognosis Study