Quantitative Magnetic Resonance Imaging measurement of muscle atrophy and fatty degeneration after arthroscopic rotator cuff repair.

Background: It is unclear whether muscle atrophy (MA) and fatty degeneration (FD) have improved after arthroscopic rotator cuff repair (ARCR). Therefore, the objective of this study was to perform quantitative magnetic resonance imaging (MRI) measurement to evaluate MA and FD before and after surgery. Correlations of clinical outcome with changes in MA and FD were also analyzed.

Materials and methods: From March 2013 to March 2017, 40 patients who had no re-tear up to 1 year after ARCR were enrolled. MA and FD of supraspinatus muscle before surgery, at 3 days after surgery, and at 1 year after surgery were measured quantitatively in conventional Y-view and supraspinatus origin-view (SOV). Measurement items were muscle area (mm²), occupation ratio (%), fatty infiltration (FI, %), and fatty degenerative area (mm²). Postoperative clinical outcomes were measured at 1 year after ARCR. Correlation between measure values and outcome scores were analyzed.

Results: Inter-measurement reliability was high (ICC = 0.933, Cronbach-α = 0.963). There was no significant change in MA in conventional Y-view at 1 year after surgery (Occupation ratio, p = 0.2770; MA, p = 0.3049) or in SOV (MA, p = 0.5953). FI and fat area measured with the conventional method on Y-view and showed significant differences (p = 0.0001). However, FI and fat area measured with the modified method on Y-view and SOV showed no significant difference (all p > 0.05). Postoperative clinical outcomes showed significant improvement compared to preoperative ones (p = 0.0001). However, there was no significant correlation between FD and FA (p = 0.653).

Conclusion: Quantitative MRI measurement was shown to be a reliable and valid method. MA and FD do not improve after ARCR considering postoperative anatomical changes of supraspinatus at 1-year follow-up. FD of the supraspinatus in conventional Y-view, but not in SOV, showed a significant change at 1 year postoperatively. MA showed no significant improvement. There was no correlation between improvement in clinical scores and changes in FD and MA.