Importance of Initial Peak Torque of the Supraspinatus Muscle during Shoulder Flexion

BACKGROUND: Most previous studies have evaluated flexion strength to assess recovery after arthroscopic rotator cuff (RC) repair. However, limited data are available regarding peak torque at the initial angle (iPT) because most studies have measured flexion strength for peak torque (PT), particularly in small- and medium-sized supraspinatus tears. The purpose of this study was to compare conventional PT and iPT to evaluate supraspinatus muscle strength after arthroscopic RC repair in patients with small- and medium-sized supraspinatus tears. METHODS: Isokinetic muscle performance testing was performed in 42 patients with small tears and in 47 patients with medium-sized tears. PT and iPT were evaluated before and 1 year after surgery and were recorded at an angular velocity of 60°/sec and 180°/sec with an isokinetic test. RESULTS: PT and iPT were significantly lower in the involved-side shoulders than in the uninvolved-side shoulders (PT: small tear, p < 0.001; medium tear, p < 0.001; iPT: small tear, p < 0.001; medium tear, p < 0.001) in both groups, preoperatively. However, postoperatively, in the involved-side shoulders, PTs were not different in both small- and medium-sized tears (all p > 0.05), but iPTs were significantly lower in the involved-side shoulders (small tear, p < 0.001; medium tear, p < 0.001). iPT was significantly lower in the involved side shoulders in the medium-sized tear group than in the small-sized tear group before and after surgery (p < 0.05). In the small- and medium-sized tear groups, tear size was significantly correlated with preoperative iPT in the involved-side shoulders (small tear: r = −0.304, p = 0.046; medium tear: r = −0.323, p = 0.027). However, pain visual analog scale was significantly correlated with preoperative (small tear: r = −0.455, p = 0.002; medium tear: r = −0.286, p = 0.044) and postoperative (small tear: r = −0.430, p = 0.005; medium tear: r = −0.354, p = 0.021) iPT in the involved-side shoulders. Furthermore, fatty infiltration grade of the supraspinatus muscle and global fatty degeneration index were not associated with preoperative and postoperative PT and iPT in each group (all p > 0.05). CONCLUSIONS: iPT is as important as conventional PT in isokinetic testing to assess supraspinatus muscle strength before and after RC repair.