Clinical SANTI classification of arthrogenic muscle inhibition has an excellent inter-rater and intra-rater reliability in preoperative and post-operative anterior cruciate ligament rupture.

Purpose: Arthrogenic muscle inhibition (AMI) is a reflexive shutdown of the quadriceps muscles following a knee injury or surgery that presents with or without hamstring contracture. This complication can be classified according to the SANTI classification, but the reproducibility of this clinical classification has not yet been demonstrated.

Methods: This single-centre longitudinal observational study included 140 patients who were within 6 weeks of an ACL rupture. The presence of AMI was assessed separately and blindly during the preoperative consultation and at 3 weeks post-operative by an Orthopaedic Surgeon, an Orthopaedic Resident, a Sports Medicine Physician and a Physiotherapist. AMI was also assessed a second time by the physiotherapist, 10 days after the first assessment, before and after reconstruction surgery, in order to measure intra-rater reliability. The inter-rater and intra-rater reliability of the AMI classification was determined by calculating the intraclass correlation coefficient (ICC).

Results: Agreement for the AMI classification between different examiners was excellent pre-operatively (ICC = 0.99 [95% confidence interval, CI: 0.99-0.99]) and post-operatively (ICC = 0.98 [95% CI: 0.98-0.99]). Agreement in the AMI classification, when determined repeatedly by the same assessor (physiotherapist), was excellent pre-operatively (ICC = 0.92 [95% CI: 0.89-0.94]) and post-operatively (ICC = 0.98 [95% CI: 0.97-0.99]).

Conclusion: Excellent intra-rater and inter-rater reliability of the AMI classification system was found in patients with recent ACL rupture and post-operatively.

Level Of Evidence: Level II, diagnostic study prospective cohort study.