A novel test for assessment of anterolateral rotatory instability of the knee: the tibial internal rotation test (TIR test)

Abstract

Background: Rotational instability of the knee may persist after anterior cruciate ligament (ACL) reconstruction, which may be due to insufficiency of anterolateral stabilizing structures. However, no reliable diagnostic tool or physical examination test is available for identifying patients with anterolateral rotatory instability (ALRI). As shown in cadaveric studies, static internal rotation of the knee is increased in higher flexion angles of the knee after severing the anterolateral structures. This might also be the case in patients with an ACL-deficient knee and concomitant damage to the anterolateral structures. The objective of this study is to assess anterolateral rotatory instability of the knee during physical examination with a tibial internal rotation test. Methods: ACL-injured knees of 52 patients were examined by two examiners and side-to-side differences were compared. Both lower legs were internally rotated by applying manual internal rotation torque to both feet in prone position with the knees in 30°, 60° and 90° of flexion. For quantification of the amount of rotation in degrees, a torque adapter on a booth was used. Intra-rater, inter-rater and rater-device agreement were determined by calculating kappa (κ) for the tibial internal rotation test. Results: Tibial internal rotation is increased in 19.2% of the patients with ACL injury according to the tibial internal rotation test. Good intra-rater agreement was found for the tibial internal rotation test, κC = 0.63 (95%CI -0.02-1.28), p = 0.015. Fair inter-rater agreement was found, κF = 0.29 (95%CI 0.02–0.57), p = 0.038. Good rater-device agreement was found, κC = 0.62 (95%CI 0.15–1.10), p = 0.001. Conclusion: The tibial internal rotation test shows increased tibial internal rotation in a small amount of patients with ACL injury. Even though no gold standard for assessment of increased tibial internal rotation of the knee is available yet, the test can be of additional value. It can be used for assessment of internal rotatory laxity of the knee as part of ALRI in addition to the pivot shift test. No clinical implications should yet be based on this test alone.