The loss of extension test (LOE test): A new clinical sign for the anterior cruciate ligament insufficient knee

Background: This prospective study was created to evaluate the reliability of a new clinical test, which we termed the ''loss of extension test'' (LOE test). The LOE test investigates the loss of normal maximum passive extension (MPE) of the knee due to an anterior cruciate ligament tear in comparison to the normal MPE of the healthy knee. Materials and methods: The study was divided into two consecutive parts. Part 1 was designed to assess the side-toside difference in normal MPE in a healthy population. In part 1, 100 healthy adults were enrolled. Part 2 was designed to evaluate the LOE test reliability in injured knees. In part 2, we included 196 selected patients. Results: In part 1, the average side-to-side difference in MPE in the healthy population was not statistically significant. In part 2, the overall average side-to-side difference in MPE of the injured group was 10.1 mm ± 14.1 (min -20; max 60), which was not statistically significant (p = 0.52). An anterior cruciate ligament (ACL) tear was found in 121 knees among 196 patients. The average sideto- side difference in MPE in the ACL-insufficient group was 16.9 mm ± 13.4 (min -20; max 60), which was statistically significant (p<0.0001). The accuracy of the loss of extension test was 83.7 %, its specificity was 93.3 %, its sensitivity was 77.7 %, its positive predictive value was 95 %, and its negative predictive value was 72.2 %. Conclusions: The reliability of the LOE test is comparable to those reported in the literature for the Lachman test and dynamic tests, so the LOE test could represent a useful tool for the diagnosis of the anterior cruciate ligament insufficient knee.