Corticospinal and spinal neuromuscular function in physically active adults after unilateral primary anterior cruciate ligament reconstruction: A systematic review and meta-analysis.

Abstract

Objectives: To (1) characterise prevalence of technical methods and neuromuscular variables assessed with transcranial magnetic stimulation (TMS) following anterior cruciate ligament reconstruction (ACLR); (2) quantify differences between ACLR leg, contralateral non-ACLR, and healthy control legs using TMS and peripheral nerve stimulation (PNS); (3) determine changes in neuromuscular variables across post-operative time. Design: Systematic review and meta-analysis. Setting: Systematic searches were conducted across PubMed, Web of Science, CINAHL, and Google Scholar from database inception until September 2025. Participants: Thirty-six studies with physically active adults (18–45 years) with ACLR were included. Outcome measures: Neuromuscular outcomes assessed using TMS and PNS including active motor threshold (AMT), motor evoked potential, short-interval intracortical inhibition, H-reflex, quadriceps voluntary activation (CAR), and quadriceps strength. Results: Most studies (72.2%) assessed quadriceps isometric actions at 90° knee flexion. AMT was higher in the ACLR leg versus contralateral (SMD=0.16) and healthy legs (SMD=0.47); other TMS variables were unchanged. Quadriceps strength (SMD=−0.60 to −0.78) and CAR (SMD=−0.18 to −0.49) were reduced in the ACLR leg. Meta-regression showed no temporal changes in quadriceps neuromuscular function. Conclusion: Methodological variability highlights the need for standardized TMS and PNS protocols. Ongoing corticospinal deficits and quadriceps weakness emphasize targeted rehabilitation of quadriceps neuromuscular pathways.