Changes of fatty infiltration according to the immediate postoperative time point in magnetic resonance imaging after arthroscopic rotator cuff repair

Fatty infiltration (FI) is known to be an irreversible change which continues degeneration after rotator cuff repair. Previous studies evaluated postoperative changes in FI using a preoperative baseline. This study aimed to investigate the changes in FI using an immediate postoperative baseline. We hypothesized that FI was progressed more when measured relative to an immediate postoperative baseline than to a preoperative baseline. From 2008 to 2010, 77 patients who met the following criteria were included in this study: arthroscopic rotator cuff repair of a full-thickness rotator cuff tear and presence of preoperative (approximately 1 month before surgery), immediate postoperative (approximately 3 days after surgery), and 1-year postoperative (at least 9 months to 1 year after surgery) magnetic resonance imaging (MRI) undertaken. The exclusion criteria were: absence of any of the three MRIs, isolated subscapularis repair, and rotator cuff repair with margin convergence only. The MRIs were examined to assess the Goutallier grade of the rotator cuff muscles for the assessment of FI. Structural integrity was evaluated using the Sugaya classification. Measurements 1 year after surgery were compared with those at the preoperative and immediate postoperative time points according to the integrity. In the total and retear group, FI in the supraspinatus and infraspinatus 1 year after surgery did not change significantly relative to the preoperative baseline (all n.s.), but progressed compared to the immediate postoperative baseline (all p < 0.001). In the retear group, FI in the supraspinatus and infraspinatus reduced for seven and two of 20 patients, respectively, compared with the preoperative baseline; however, no patients showed a reduced FI compared with the immediate postoperative baseline. The results of the study showed that the changes in FI reduced, remained or progressed in accordance with the baseline and structural integrity. FI progressed when compared with the immediate postoperative baseline than with the preoperative baseline. The immediate postoperative time point would be considered as the baseline to monitor the true changes of FI after repair. Retrospective comparative study, Level III.