Incidence and risk factors for arthrogenic muscle inhibition after ACL reconstruction

Background: Arthrogenic muscle inhibition (AMI) is a common clinical complication following anterior cruciate ligament (ACL) injury and reconstruction, characterized by quadriceps activation deficits and potential knee extension loss. While the pathophysiology involving spinal reflex dysfunction and supraspinal alterations is increasingly understood, the specific postoperative incidence and associated risk factors remain inadequately defined in current orthopedic literature.

Objective: This study aimed to determine the incidence of AMI during the first six weeks following ACL reconstruction and to identify clinical variables associated with its occurrence.

Key Points: A prospective analysis of 210 patients undergoing primary or revision ACL reconstruction was conducted. The incidence of AMI was 48.6% at three weeks postoperatively, decreasing to 24.3% at six weeks. Multivariate analysis identified three significant risk factors for AMI at the three-week interval: preoperative presence of AMI (OR 8.2), immediate postoperative pain scores exceeding 7/10 on a numerical rating scale (OR 4.6), and the absence of preoperative physiotherapy (OR 2.6). Most identified cases were classified as Grade A (clinically reversible). No significant correlations between the studied risk factors and AMI were observed at the six-week mark.

Conclusion: AMI affects nearly half of patients in the early recovery phase following ACL reconstruction. Identification of high-risk patients—specifically those with preoperative deficits, high acute pain levels, or lack of prehabilitation—is essential. Implementation of targeted neuromuscular exercises and early pain management may mitigate these deficits and prevent long-term sequelae such as quadriceps atrophy, gait abnormalities, and secondary joint degeneration.