Description
Introduction
Arthrogenic Muscle Inhibition (AMI) is a centrally driven process following knee injury or surgery that results in quadriceps inhibition and a reflex hamstring contracture, resulting in the appearance of a “locked” knee.
AMI is not well recognised and is therefore underdiagnosed.
Aim
Primary: to evaluate incidence of AMI in acute knee injuries
Secondary: to correlate AMI to underlying acute knee pathology
Methods
Patients presenting to our Acute Knee Service between 01.01.2023 and 30.04.2023 were prospectively screened for inclusion in the study.
These were examined at the index appointment by a fellowship trained soft tissue knee surgeon and AMI classified according to Sonnery-Cottet et al. 2022’s classification prior to MRI imaging1.
This utilises response to physical exercises as part of the diagnostic process 2.
Patients with MRI proven mechanical block to extension were excluded.
Results
97 patients were reviewed by the acute knee service in the time period, 12 were excluded.
27/85 eligible patients (31%) had AMI.
52% of patients with AMI responded to simple exercises at the index clinic appointment.
AMI had the greatest association with patellofemoral dislocation (6.3 times more likely; p=0.013)
3.45 greater risk of AMI in those with ACL injury
Discussion
This is the first study to describe the epidemiology of AMI in a range of acute knee injuries. The majority of the previous literature reported on this subject is focussed around ACL injuries .
In our study, > 50% of patients with AMI responded to simple exercises in clinic. This enables early return to function.
AMI had the greatest association with patellofemoral dislocation (6.3 times more likely; p=0.013) which has not been previously reported in the literature.
The 3.45 times greater risk of AMI in those with ACL injury adds further weight to the existing literature.
Conclusion
q AMI is common in all patients with acute knee injuries. This is the first study to investigate this in all acute knee pathology. It is most common with patients with patella dislocation which is a novel finding In our study
