Analyzing anterior knee laxity with an arthrometer for assisting diagnosis of anterior cruciate ligament rupture

The anterior knee laxity was frequently evaluated with an arthrometer test. The displacement and compliance index at certain loading were used as diagnosis criteria of anterior cruciate ligament (ACL) injury with excellent specificity but only moderate sensitivity. The force-displacement diagram from the test demonstrated three regions of stiffness changes, which have not been discussed separately. The purpose of this study was to analyze the characteristics of anterior knee laxity, and compare between healthy controls and patients with ACL rupture in order to explore proper diagnosis criteria. Forty patients with unilateral ACL rupture and 40 healthy controls were enrolled and tested their anterior knee laxity with KT-2000 arthrometer. The displacement (D1, D2, D3) and stiffness (k1, k2, k3) for each of the three regions in the force-displacement diagram were extracted and compared between groups. The results showed the laxity behavior was mostly affected in the second and third regions. The ROC curve suggested D2 larger than 3.7 mm, and k3 smaller than 5 lb/mm can be good indicators of ACL rupture with higher diagnostic accuracy than other previous criteria. The analysis in this study could provide diagnosing criteria for ACL rupture, which have both sensitivity and specificity at high level.