Anterior tibial displacement on preoperative stress radiography of ACL-injured knee depending on knee flexion angle

Purpose: To compare side-to-side difference (SSD) of anterior tibial translation in instrumented stress radiography for each series of anterior cruciate ligament (ACL)-injured subjects according to knee flexion angle. Methods: Forty subjects who were suspected of having significant ACL injury by manual Lachman test and MRI were recruited for this prospective study. These subjects took stress radiographs for both knees with corresponding knee flexion of 10° (series M1) and 30° (series M2) using Telos stress device. Mean SSDs of M1 and M2 were compared. Sensitivities of M1 and M2 were assessed using the SSD ≥ 3 mm or ≥ 5 mm as a cutoff value. Results: Mean SSDs in series M1 and M2 were 4.22 ± 3.72 mm and 3.25 ± 3.30 mm, respectively (p < 0.001). When 3 mm of SSD was used as a cutoff value, sensitivities of series M1 and M2 were 47.5% (19/40) and 32.5% (13/40), respectively (p = 0.171). When 5 mm of SSD was used as a cutoff value, sensitivities of series M1 and M2 were 45.0% (18/40) and 22.5% (9/40), respectively (p = 0.033). Conclusions: Anterior tibial translation on stress radiographs using a Telos device is more prominent when knee flexion angle is 10° compared to that when knee flexion angle is 30°. However, stress radiography using Telos device, either at 10° or 30° of knee flexion, might not be suitable to make decision on surgical treatment due to relatively low sensitivities.