Objective.
Anterior cruciate ligament (ACL) injuries cause rotational instability of the knee joint. The pivot shift test (PS) is widely used to assess rotational instability. However, PS under consciousness often does not accurately identify rotational instability due to the influence of muscle tension. Recently, anterior tibial subluxation (ATS) on MRI has been reported to be associated with rotational instability. We hypothesized that ATS measured perpendicular to the tibial bone axis (bone axis method) would better reflect rotational instability than conventional ATS measured parallel to the tibial plateau (plateau method). This study aimed to investigate the relationship between PS under anesthesia and ATS on preoperative MRI measured with the bone axis method and plateau method.
Methods.
A total of 156 patients with preoperative MRI and IKDC grade assessment of PS data both under anesthesia and consciousness, enrolled in the ACL multicenter study by April 2024 were included. Cases with revision ACL reconstruction, concomitant posterior cruciate ligament or collateral ligament injury were excluded. Furthermore, we excluded cases with conscious PS grades C and D. Thus, 122 cases (mean age: 28.2 years) with conscious PS grades A and B, potentially affected by muscle tension, were analyzed. Medial and lateral ATS on preoperative MRI were measured with the bone axis method and with the plateau method, respectively. The difference between the lateral and medial ATS (dATS) was calculated. Patients with IKDC grades A and B under anesthesia were classified as the Low (L) group, and those with IKDC grades C and D as the High (H) group. The medial ATS, lateral ATS and dATS measured with the bone axis method and with the plateau method were compared between the L and H groups using the t-test. Statistical significance was set at P < 0.01. ROC analysis was performed with group H as positive for each measurement method.
Results.
There were no differences between the two groups (i.e., H vs L) in the medial ATS both of the bone axis method and the plateau method (p=0.044, 0.089) and in the lateral ATS as well (p=0.275, 0.495). dATS did not differ between the groups with the plateau method (p=0.033). However, dATS was greater with the bone axis method in the H group than in the L group. (p=0.004). Of all the measurement methods, the ROC-AUC for dATS with the bone axis method was the highest at 0.648.
Discussion.
The plateau method may not accurately assess the positional relationship between the femur and tibia due to the influence of the posterior tibial slope. These results suggest that ATS with the bone axis method is more valuable than the plateau method as an indicator of rotational instability.
Conclusion.
The difference between the lateral and medial ATS measured by the bone axis method on preoperative MRI was associated with PS under anesthesia.