Knee rotation influences the femoral tunnel angle measurement after anterior cruciate ligament reconstruction: a 3-dimensional computed tomography model study

Abstract

Purpose Femoral tunnel angle (FTA) has been proposed as a metric for evaluating whether ACL reconstruction was performed anatomically. In clinic, radiographic images are typically acquired with an uncertain amount of internal/external knee rotation. The extent to which knee rotation will influence FTA measurement is unclear. Furthermore, differences in FTA measurement between the two common positions (0° and 45° knee flexion) have not been established. The purpose of this study was to investigate the influence of knee rotation on FTA measurement after ACL reconstruction. Methods Knee CT data from 16 subjects were segmented to produce 3D bone models. Central axes of tunnels were identified. The 0° and 45° flexion angles were simulated. Knee internal/external rotations were simulated in a range of ±20°. FTA was defined as the angle between the tunnel axis and femoral shaft axis, orthogonally projected into the coronal plane. Results Femoral tunnel angle was positively/negatively correlated with knee rotation angle at 0°/45° knee flexion. At 0° knee flexion, FTA for anterio-medial (AM) tunnels was significantly decreased at 20° of external knee rotation. At 45° knee flexion, more than 16° external or 19° internal rotation significantly altered FTA measurements for single-bundle tunnels; smaller rotations (±9° for AM, ±5° for PL) created significant errors in FTA measurements after double-bundle reconstruction. Conclusion Femoral tunnel angle measurements were correlated with knee rotation. Relatively small imaging malalignment introduced significant errors with knee flexed 45°. This study supports using the 0° flexion position for knee radiographs to reduce errors in FTA measurement due to knee internal/external rotation. Level of evidence Case–control study, Level III.

Does radiographic location ensure precise anatomic location of the femoral fixation site in medial patellofemoral ligament surgery?

“…3D CT has previously been used to evaluate in vivo the femoral insertion site in anterior cruciate ligament reconstruction [4, 13]. Moreover, it has also been used to analyse the femoral insertion site in MPFL reconstruction [6, 15].…”

Influence of axial limb rotation on radiographic lower limb alignment: a systematic review

“…In osteotomies in varus knees, malrotation resulted in an undercorrection in 20° IR and overcorrection in 20° ER [56]. Errors during surgery can occur due to wrong knee rotation, leading to different ACL bone tunnel orientation [57] or over-or undercorrection during osteotomies [28]. Kawahara et al [26] analyzed the effect of limb malrotation between 10° ER and 10° IR on preoperative planning of open-wedge HTO.…”