3D Muscle Volume and 3D Fat Fraction After Successful and Failed Arthroscopic Rotator Cuff Repair at 5-Year Follow-up.

Background: The results of rotator cuff (RC) repair surgery can be influenced by the presence of muscle atrophy and fatty infiltration. Three-dimensional (3D) quantitative data regarding those degenerative muscle changes after successful or failed RC repair are rare in the current literature.

Hypothesis/purpose: The purpose of this study was to analyze muscle volume and fatty infiltration of the supraspinatus muscle after successful and failed arthroscopic RC tendon repair, with a minimum follow-up of 5 years. It was hypothesized that RC muscle volume and fatty infiltration would improve after successful repair and only to a limited extent after failed repair.

Study design: Cohort study; Level of evidence 2.

Methods: A total of 115 patients (mean age, 59 ± 8 years; 33% women) with RC repair for full-thickness supraspinatus tendon tear were prospectively followed at 3 and 12 months. Of them, 18 patients with unsuccessful RC repairs were matched to 21 patients with successful repairs and reevaluated at a minimum follow-up of 60 months. All patients underwent quantitative 2-point Dixon magnetic resonance imaging at all time points to evaluate full 3D muscle volume and 3D fatty infiltration. The clinical examination included the full Constant-Murley score (CS) and subjective shoulder value.

Results: The relative changes in supraspinatus muscle volume were statistically significant between the 2 groups over time (P < .01). Successful repairs showed a mean volume increase of 18% (P < .001) and 23% (P < .001) from preoperatively and the 3-month follow-up, respectively, and failed repairs were remodeled by 3% (P = .586) and 12% (P = .001), respectively. However, a direct comparison of the volumes revealed comparable results at the latest follow-up with 43 cm³ (95% CI, 38-47 cm³) and 40 cm³ (95% CI, 33-46 cm³) for successful and failed repairs (P = .494), respectively. The supraspinatus 3D fatty infiltration also showed lower fat content for the successful repair preoperatively (6.9% [95% CI, 4.7%-9.2%] vs 9.1% [95% CI, 7.2%-11.1%]; P < .01), at 3 months (7.9% [95% CI, 5.5%-10.4%] vs 12.8% [95% CI, 9.1%-16.5%]; P < .01), at 12 months (7.5% [95% CI, 4.8%-10.1%] vs 11.6% [95% CI, 9.4%-13.8%]; P < .01), and at 60 months (7.4% [95% CI, 4.7%-10.2%] vs 15.5% [95% CI, 11%-20%]; P < .01) postoperatively. Fatty infiltration remained unchanged between preoperatively and from 3-month follow-up in the successful group. However, it increased by 70% (P < .01) from preoperative and by 21% (P = .065) from 3-months follow-up in the failed group. The clinical outcome was similar for successful and failed repairs with an absolute CS of 81 ± 6 versus 72 ± 15 (P = .069) and a relative CS of 94% ± 7% versus 85% ± 17% (P = .078).

Conclusion: Successful RC repair was associated with relevant improvement of supraspinatus muscle mass and an unchanged fatty infiltration at a midterm follow-up of 5 years. However, failed repairs achieved only mild improvement of supraspinatus muscle volume and showed deterioration of fatty infiltration.