In vivo motion of femoral condyles during weight-bearing flexion after anterior cruciate ligament rupture using biplane radiography

Abstract

The purpose of this study was to investigate in vivo three- dimensional tibiofemoral kinematics and femoral condylar motion in knees with anterior cruciate ligament (ACL) deficiency during a knee bend activity. Ten patients with unilateral ACL rupture were enrolled. Both the injured and contralateral normal knees were imaged using biplane radiography at extension and at 15°, 30°, 60°, 90°, and 120° of flexion. Bilateral knees were next scanned by computed tomography, from which bilateral three-dimensional knee models were created. The in vivo tibiofemoral motion at each flexion position was reproduced through image registration using the knee models and biplane radiographs. A joint coordinate system containing the geometric center axis of the femur was used to measure the tibiofemoral motion. In ACL deficiency, the lateral femoral condyle was located significantly more posteriorly at extension and at 15° (p < 0.05), whereas the medial condylar position was changed only slightly. This constituted greater posterior translation and external rotation of the femur relative to the tibia at extension and at 15° (p < 0.05). Furthermore, ACL deficiency led to a significantly reduced extent of posterior movement of the lateral condyle during flexion from 15° to 60° (p < 0.05). Coupled with an insignificant change in the motion of the medial condyle, the femur moved less posteriorly with reduced extent of external rotation during flexion from 15° to 60° in ACL deficiency (p < 0.05). The medial- lateral and proximal-distal translations of the medial and lateral condyles and the femoral adduction-abduction rotation were insignificantly changed after ACL deficiency. The results demonstrated that ACL deficiency primarily changed the anterior-posterior motion of the lateral condyle, producing not only posterior subluxation at low flexion positions but also reduced extent of posterior movement during flexion from 15° to 60°. Key PointsThree-dimensional tibiofemoral kinematics and femoral condylar motion in ACL-deficient knees during upright weight-bearing flexion were measured using biplane radiography with the geometric center axis.ACL deficiency caused posterior subluxation of the lateral condyle with excess external femoral rotation at early flexion positions.On flexion from 15° to 60°, the lateral condyle moved slightly posteriorly in ACL deficiency leading to reduced extent of external femoral rotation.

Keywords: anterior cruciate ligament; femoral condyle; injury; kinematics; radiography; tibiofemoral.

Figure 1.

The knee was imaged by two X-ray machines from orthogonal directions during flexion from extension to 15°, 30°, 60°, 90°, and 120°.

Figure 2.

The 3D tibiofemoral model was simultaneously matched to its corresponding two 2D images on biplane radiographs at extension, 15°, 30°, 60°, 90°, and 120°. The spherical marker was indicated in white

Figure 3.

A joint coordinate system was used to measure the tibiofemoral kinematics and condylar motion. The geometric center axis (GCA) of the femur passed the centers of the medial (M) and lateral (L) posterior condyles. AP: anterior-posterior, ML: medial-lateral, PD: proximal-distal, FC: femoral center, TC: tibial center.

Figure 4.

Anterior-posterior (AP) translations of the femoral condyles relative to the tibia (* p < 0.05). A Medial condylar (MC) translations. B Lateral condylar (LC) translations. Posterior translation is positive and anterior translation is negative. Ex: extension