Intra-Tester and Inter-Tester Reliability of the Lachmeter When Measuring Knee Joint Laxity

Knee injuries are common among all age groups, and clinical knee examination is essential for the prognosis, follow-up, and rehabilitation process. The Lachmeter is a newly developed digitized modification of the Rolimeter, making it easier and faster for the test personnel to read the test result. In the present study, we aimed to evaluate the intra-tester and inter-tester reliability of the Lachmeter when testing healthy and traumatic knees. 24 healthy participants and a smaller sample of six ACL patients were examined with the Lachmeter by two intermediate testers and re-examined on a second visit within 21 days. All measurements were performed using two different grip techniques: a Lachman grip and an anterior drawer grip. Intra- and inter-tester reliability was evaluated using intra-class correlation coefficient (ICC), standard error of measurement (SEM), smallest detectable change (SDC), Student's paired t-test, and Bland-Altman plots. The results showed in healthy subjects poor to good intra-tester reliability (ICC range: -0.28-0.87, SEM range: 0.33-1.14 mm, and SDC range: 0.91-3.17 mm) and inter-tester reliability (ICC range: 0.41-0.87, SEM range: 0.27-0.67 mm, and SDC range: 0.75-1.87 mm). In ACL patients, intra-tester reliability was moderate to excellent (ICC range: 0.53-0.94, SEM range: 0.14-0.88 mm, and SDC range: 0.38-2.44 mm), with the exception of one measurement (ICC: 0.26 95% CI [-3.43; 0.89]), whereas inter-tester reliability was overall good (ICC range: 0.61-0.89, SEM range: 0.29-0.71 mm, and SDC range: 0.79-1.97 mm). Reliability measures between grip techniques indicated that the Lachman grip was more reliable than the anterior drawer grip. In conclusion, the Lachmeter showed variation between reliability measures, ranging from poor to good in healthy subjects and moderate to excellent in ACL patients. Future studies are needed to validate the Lachmeter against a gold-standard knee laxity assessment.