Effects of Neuromuscular Electrical Stimulation on Quadriceps Femoris Muscle Strength and Knee Joint Function in Patients After ACL Surgery: A Systematic Review and Meta-analysis of Randomized Controlled Trials

Background: Quadriceps weakness is a common barrier to effective rehabilitation after anterior cruciate ligament (ACL) surgery. Neuromuscular electrical stimulation (NMES)-the application of electrical currents to induce muscle contraction-has been used as part of the postoperative rehabilitation regimen.

Purpose: To investigate the effects of NMES on the recovery of quadriceps strength and knee function after ACL surgery.

Study design: Systematic review; Level of evidence, 1.

Methods: A search was conducted in the Web of Science, Embase, Cochrane Library, and PubMed databases between inception and August 2023 according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Included were randomized controlled trials of patients undergoing NMES as postoperative rehabilitation after ACL reconstruction or repair, with standard physical therapy as the control intervention. The quality of the included studies was assessed according to the Cochrane Collaboration risk-of-bias tool. Lower limb function was assessed qualitatively, and standardized mean differences (SMDs) in muscle strength and Lysholm scores were analyzed quantitatively and pooled using a random-effects model.

Results: Eleven studies (N = 202 patients) met our inclusion criteria. The meta-analysis of muscle strength values, which included 9 studies, showed that patients who underwent physical rehabilitation with adjunctive NMES had better recovery and improvement in quadriceps muscle strength compared with standard physical therapy at both short- and long-term follow-ups (≤6 weeks: SMD, 0.53 [95% CI, 0.27-0.79] vs >6 weeks: SMD, 0.59 [95% CI, 0.18-0.99]; p < 0.001). Moreover, subgroup analyses showed that earlier physical rehabilitation with the assistance of NMES resulted in better muscle strength recovery (≤1 week: SMD, 1.48 [95% CI, 0.80-2.17] vs >1 week: SMD, 0.44 [95% CI, 0.21-0.67]; p < 0.001). The meta-analysis of Lysholm scores, which included 3 studies, did not indicate any significant differences between the assisted NMES and control groups.

Conclusion: Our study demonstrated that in both short- and long-term follow-up studies, postoperative rehabilitation with NMES after ACL surgery significantly increased quadriceps muscle strength compared with standard rehabilitation alone.