Effects of different electrical stimulation protocols for rehabilitation of patients after anterior cruciate ligament reconstruction surgery

Abstract

This study compared the effectiveness of three neuromuscular electrical stimulation (NMES) programs, namely high intensity/short duration, low intensity/long duration and placebo stimulation, in the rehabilitation of patients after anterior cruciate ligament (ACL) reconstruction surgery. Thirty-two subjects (20 males; 12 females) who underwent ACL reconstruction with either patellar tendon or semitendinosus autograft at a teaching hospital in Hong Kong were tested. According to age, gender, leg dominance, graft type and side of injury, subjects were systematically stratified into the following groups: Group 1: high intensity/short duration; Group 2: low intensity/long duration and Group 3: placebo stimulation. Measurements were performed on each subject pre-operatively and at six weeks after surgery for active knee flexion/extension range, postero-anterior laxity at 68 N (15 lbs) and 136 N (30 lbs) of anterior drawing force with the KT-2000 Knee Arthrometer, isometric and isokinetic (60o and 180o/s) peak torque of the quadriceps/hamstrings muscles with the Cybex 6000 Dynamometer, and knee extension pain on a visual analogue scale. Starting in the first week after surgery, all subjects received a standard daily exercise program lasting about one hour. Besides that, subjects in Group 1 received maximal tolerable NMES to their quadriceps and hamstrings for 30 minutes (10s on/50s off); subjects in Group 2 received 1/3 of the maximal tolerable current for 30 minutes (10s on/10s off) and subjects in Group 3 received placebo stimulation for 30 minutes. Each subject received the NMES treatment three times per week for five weeks. The change in each measured variable expressed as ratio or difference scores based on the pre-operative values. One-way MANOVA was used to analyze the isokinetic peak torque data, while the other data were analyzed with repeated measures ANOVA and one-way ANOVA. A sign test was performed to compare the means between Group 1 and Group 2 subjects. No significant difference was found in the ANOVA and MANOVA tests. However, the mean values revealed Group 1 had slightly better improvements than Group 2 in 9 out of 11 tests (sign test: p=0.033), except in joint laxity at 136 N drawing force and knee flexion range. However, results of Group 3 subjects were comparable to that of Groups 1 and 2 in the means, and no trend could be identified if Groups 1 or 2 were different from Group 3. This result may be indicative of the importance of a well-controlled exercise program, which was instituted in all groups, rendering comparable improvements in all groups. The additional effect of a NMES program may be too small to be detected in this study.