Factors Affecting Outcomes After Free Functional Gracilis Muscle Transfer for Elbow Flexion in Brachial Plexus Injury: A Systematic Review and Meta-Analysis

Purpose Free functional gracilis transfer (FFGT) is a useful option for reconstruction of elbow flexion following brachial plexus injury presenting late or with poor outcomes from previous nerve surgery. In this systematic review and meta-analysis, we aimed to investigate variables associated with superior outcomes. The efficacy of single versus double FFGT, where the first FFGT is performed to restore elbow flexion, and the choice of donor nerve for neurotization were evaluated. Methods A meta-analysis was conducted, including studies that provided postoperative Medical Research Council (MRC) grade for elbow flexion, Disabilities of the Arm, Shoulder, and Hand and visual analog scale scores, quantitative elbow flexion strength, and range of motion. A random effects meta-regression analysis was performed to identify factors associated with improved outcomes. Results Thirty-seven studies, with 1,607 patients, were analyzed. Single FFGT was reported in 34 studies (n = 1,398), and double FFGT was reported in 10 studies (n = 209). The mean follow-up duration was 37.3 +/- 21.1 months. Following single FFGT, 75.4% and 48.9% achieved MRC grades >= 3 and >= 4, respectively. Following double FFGT, 100% achieved an MRC grade >= 3 and 62.7% >= 4. The likelihood of achieving M3 and M4 was significantly greater for double FFGT. Overall, FFGT innervated by the spinal accessory nerve had significantly better recovery of MRC grade >= 3. When comparing only single and double FFGT innervated by spinal accessory nerve, there was no significant difference in recovery of elbow flexion. The meta-regression analysis showed a significant negative correlation between the patient's age and the probability of achieving an MRC grade of >= 3 and 4. Conclusions In the overall analysis encompassing all innervating nerves, double FFGT was superior to single FFGT. Subgroup analysis of single and double FFGT innervated by the spinal accessory nerve showed no significant difference. Increasing age was a significant risk factor for poorer outcomes.