Incidence and Risk Factors for Arthrogenic Muscle Inhibition in the Early Postoperative Period After ACL Reconstruction. A Cohort Study From the SANTI Study Group

Background: Arthrogenic muscle inhibition (AMI) is a process in which neural inhibition after injury or surgery to the knee results in quadriceps activation failure and knee extension deficit. A recent study showed that AMI occurs in over half of patients with acute ACL injuries. Purposes: To (1) determine the incidence of AMI within the 6 weeks after an anterior cruciate ligament reconstruction (ACLR) and (2) identify the risk factors associated with AMI after an ACLR. Study Design: Case-control study; Level of evidence, 3. Methods: Consecutive patients who sustained a primary ACLR between January and October 2023 were considered for study inclusion. Eligible patients underwent a standardized physical examination at 3 and 6 weeks postoperatively. This included an assessment of quadriceps inhibition, identification of any extension deficits, and grading of AMI and its clinical reversibility according to the Sonnery-Cottet classification. Results: A total of 210 consecutive patients with a primary ACLR were prospectively enrolled in the study. Respectively, 48.6% of patients had AMI at 3 weeks and 24.3% at 6 weeks postoperatively. Among them, 79.4% and 72.5% demonstrated reversible types (grade 1A or 2A), respectively. Multivariate analysis revealed that patients who had a preoperative AMI (odds ratio [OR], 8.27 [95% CI, 4.177-17.138]; P < .001), experienced immediate postoperative pain exceeding 7 out of 10 on the visual analog scale (VAS) (OR, 4.689 [95% CI, 2.144-10.814]; P = .0002), or did not have preoperative physical therapy (OR, 2.303 [95% CI, 1.186- 4.530]; P = .0149) were associated with a significantly greater risk of AMI at 3 weeks postoperatively. No risk factors were found at 6 weeks postoperatively. Conclusion: AMI occurs in 48.5% of patients at 3 weeks, and 24.2% at 6 weeks after an ACLR. Important risk factors identified for the presence of AMI at 3 weeks postoperatively included the presence of preoperative AMI, immediate postoperative VAS pain score of >7, and absence of preoperative physical therapy.