Quantifying anterior tibial translation and rotation in chronic ACL-deficient knees: a prospective, observational study using weight-bearing CT.

Abstract

To evaluate the ability of weight-bearing computed tomography (WBCT) to detect and quantify differences in anterior tibial translation (ATT) and tibiofemoral rotation (TFR) between anterior cruciate ligament (ACL)-injured and uninjured knees in patients with chronic ACL tears. This prospective, observational study included 20 patients (40 knees) with chronic unilateral ACL injuries confirmed by clinical exam and MRI. Knee WBCT was performed in four standardized positions: full extension and 30° flexion (bipodal), and internal and external rotation (unipodal). ATT was measured in medial and lateral compartments. TFR was assessed using two angular parameters: femorotibial rotation angle (TFR 1) and trochlear groove-patellar tendon angle (TFR 2). Intra- and inter-observer reliability was evaluated using intraclass correlation coefficients (ICCs). WBCT detected significant differences in ATT and TFR between injured and uninjured knees during bipodal loading. At 30° flexion, lateral ATT was greater in injured knees (7.9 ± 3.8 mm vs. 4.7 ± 2.0 mm, p = 0.001), as was medial ATT (2.9 ± 2.9 mm vs. 0.8 ± 1.4 mm, p = 0.007). TFR 1 was increased (10.9° ± 6.3° vs. 7.6° ± 4.6°, p < 0.001), while TFR 2 was decreased (12.3° ± 7.2° vs. 17.3° ± 6.1°, p = 0.004). Similar trends were seen in full extension. Under unipodal loading, only lateral ATT remained significantly elevated. All measures showed good to excellent reliability (ICC > 0.7). WBCT enables objective quantification of ATT and TFR differences in chronic ACL injury and may support biomechanical assessment in clinical practice.