The incidence of arthrogenic muscle inhibition in acute knee injuries: a prospective cohort study in a tertiary acute knee unit

Background: Arthrogenic Muscle Inhibition (AMI) is not well recognised and is therefore underdiagnosed. Improved understanding of AMI would allow improved patient treatment pathways and rehabilitation after acute knee injuries. The primary aim of this study was to evaluate the incidence of AMI in acute knee injuries. The secondary aim was to evaluate correlation between AMI and type of underlying knee injury.
Methods: This was a prospective cohort study. All patients reviewed by the acute knee service in a tertiary referral centre between January 01, 2023 and April 30, 2023 were included (n = 97). The patients were diagnosed with AMI by a fellowship trained orthopaedic consultant knee surgeon. The incidence was evaluated with descriptive statistics and logistic regression analysis performed to ascertain association of AMI with the underlying acute knee injury diagnosis.
Results: Of the 97 patients reviewed, 12 were excluded due to a mechanical block to extension on MRI imaging. Twenty-seven (31.8 %) of the 85 eligible patients were diagnosed with AMI. Nine of the twenty-seven patients (52 %) presenting with AMI had resolution of symptoms at the index clinic appointment with directed physical therapy. Patients with AMI were 6 times (OR 6.3, 95 % CI 1.48) more likely to have a diagnosis of patellofemoral (PFJ) dislocation (p = 0.013) than those with bone bruising or minor sprain. Other associations of AMI which did not reach statistical significance were meniscal tear (OR 4.2, 95 % CI 0.4) and ACL rupture (OR 3.5, 95 % CI 0.72).
Conclusions: AMI is common in acute knee injuries, affecting nearly a third of all patients reviewed. Patients with AMI were more likely to have an underlying diagnosis of PFJ dislocation than any other acute knee injury diagnosis, and was the only statistically significant association. Correct diagnosis and instituting immediate treatment can resolve >50 % cases at the index clinic appointment. Treatment workflows incorporating early review and management could result in improved patient outcome and expedited recovery from AMI.