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

Objective: 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.

Materials And Methods: 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).

Results: 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).

Conclusion: WBCT enables objective quantification of ATT and TFR differences in chronic ACL injury and may support biomechanical assessment in clinical practice.