The Effects of Interferential Stimulation on Pain and Motion after Shoulder Surgery: A Prospective Randomized Study

Purpose: The purpose of this study is to determine the effects of interferential stimulation on pain and motion after shoulder surgery. Study Design: Randomized Controlled Trial. Methods: 102 patients undergoing arthroscopic rotator cuff repair or labral repair were prospectively randomized to receive either an interferential stimulation unit immediately after surgery (STIM) or not to receive the unit (NO-STIM). Each patient was measured for the range of motion (ROM) in forward flexion (FF), abduction (ABD), internal rotation (IR) and external rotation (ER). These measurements were taken prior to surgery and at the 6 weeks post-operative time point. Visual Analogue Scale (VAS) scores (0 10) and the amount of narcotic taken (standardized to 10 mg equivalents of hydrocodone) were measured and compared between the two groups at 2 days and 4 weeks post-operatively. 51 patients were excluded due to failure to document VAS scores and medication usage, lack of follow-up at the 6 weeks post-operative time point or hospitalization after surgery. This left 27 patients in the STIM group and 24 patients in the NO-STIM group. Results: No difference was found in the amount of narcotic taken after 2 days (STIM 14.37 ± 1.02, NO-STIM 15.88 ± 1.22, p = 0.34) or after 4 weeks (STIM 45.32 ± 4.36, NO-STIM 48.96 ± 5.50, p = 0.60). No difference in mean VAS scores were found at 2 days (STIM 5.56 ± 0.53, NO-STIM 4.63 ± 0.57, p = 0.24) or 4 weeks (STIM 1.68 ± 0.39, NO-STIM 1.38 ± 0.34, p = 0.57). At 6 weeks post-operatively, a difference was found in ER (STIM 62.5 ± 4.09, NO-STIM 50.4 ± 4.09, p = 0.04), and no differences found in FF (STIM 134.2 ± 5.29, NO-STIM 133.3 ± 4.85, p = 0.60), ABD (STIM 124.8 ± 6.22, NO-STIM 119.6 ± 5.42, p = 0.53) or IR (STIM 60.0 ± 3.69, NO-STIM 55.9 ± 3.03, p = 0.39). A post-hoc power analysis performed using an á = 0.05 revealed the study to be 90% powered to identify a difference of one narcotic equivalent between groups and 90% powered to identify a 0.3 difference in VAS scores. Conclusions: The use of an interferential stimulator in the immediate post-operative period had no effect on pain or narcotic usage following arthroscopic rotator cuff repair or labral repair. External rotation was significantly greater in the interferential stimulator group while no differences were found in other motion parameters.