A Prospective, Quantitative MRI-Based Assessment on the Progression of Fatty Infiltration after Rotator Cuff Repair

OBJECTIVES: Fatty infiltration is a negative prognostic factor for outcomes after rotator cuff repair. Efforts on evaluating fatty infiltration have been limited by the reproducibility of the Goutallier classification. The objective of this study is to evaluate the progression of fatty infiltration before and after surgical treatment using IDEAL MRI, which accurately measures intra-muscular fat content. We hypothesized that patients with isolated supraspinatus tears would show less progression of fatty infiltration than patients with tears involving multiple tendons. We also hypothesized that patients with eventual repair failure would have higher baseline levels of intramuscular fat. METHODS: A total of 35 patients with full-thickness rotator cuff tears (61.5 ± 10.5 years, 17 female) underwent a baseline MRI prior to repair and a repeat scan 6 months after rotator cuff repair. Imaging sequences included standard clinical sequences and sagittal six-point IDEAL. The supraspinatus (SS), infraspinatus (IS), subscapularis, and teres minor muscles were segmented on four consecutive sagittal slices, centered at the scapular-Y. The intramuscular fat fraction was calculated from the IDEAL map. Pre-operative tear size and post-operative repair integrity were recorded. Fat fractions before and after rotator cuff repair were compared with t-tests. To investigate the effect of tear size, patients were divided into two groups based on intra-operative findings: isolated supraspinatus tears and multi-tendon tears. Fat fractions were compared between groups based on repair integrity. Statistical significance was defined as p < 0.05. RESULTS: There were 19 patients with an isolated supraspinatus tear, 15 patients with a multi-tendon tear, and 1 patient with an isolated subscapuarlis tear. Intact repairs were present for 26 patients at 6 months, while a failed repair was present in 9 patients. The follow-up fat fractions were significantly higher than baseline fat fractions for the SS (9.8 ± 7.0% vs. 8.3 ± 5.7%, p = 0.025) and IS (7.4 ± 6.1% vs. 5.7 ± 4.4%, p = 0.027) muscles. There was no significant difference for the fat fractions for the subscapularis (8.2 ± 4.5% vs. 8.9 ± 6.5%, p = 0.48) or teres minor (9.9 ± 15.3% vs. 9.4 ± 13.9%, p = 0.50) muscles. Patients with isolated SS tears showed a significant progression in the SS fat fraction from baseline to follow-up (6.8 ± 4.9% to 8.6 ± 6.8%, p = 0.0083). The IS fat fraction also increased though did not reach the level of statistical significance (5.3 ± 4.6% to 6.6 ± 6.6%, p = 0.074). The baseline SS fat fractions were significantly higher in patients with eventual failed repairs as compared to those with intact repairs (11.7 ± 6.8% vs. 7.1 ± 4.8%, p = 0.037). CONCLUSION: Intramuscular fat content increases significantly following rotator cuff repair. In isolated supraspinatus tears, fatty infiltration advanced over the 6 months following surgical repair. Eventual repair failure was associated with higher baseline SS fat fractions. This finding suggests that even lower levels of fatty infiltration than previously reported may impact post-surgical outcomes.