The effect of anterior cruciate ligament deficiency and reconstruction on the patellofemoral joint

Abstract

Background: Little is known about the effect of anterior cruciate ligament deficiency and reconstruction on the patellofemoral joint.

Hypothesis: Anterior cruciate ligament deficiency changes the patellofemoral joint biomechanics. Reconstruction of the ligament does not restore the altered patellofemoral joint function.

Study design: Controlled laboratory study.

Methods: Eight patients with an acute anterior cruciate ligament injury in 1 knee and the contralateral side intact were included in the study. Magnetic resonance and dual-orthogonal fluoroscopic imaging techniques were used to compare the patellofemoral joint function during a single-leg lunge between the intact, the anterior cruciate ligament-injured, and the anterior cruciate ligament-reconstructed knee. Data on the patellar tendon apparent elongation and orientation, patellar tracking, and patellofemoral cartilage contact location were collected preoperatively and at 6 months after reconstruction.

Results: Anterior cruciate ligament deficiency caused a significant apparent elongation and change in orientation of the patellar tendon. It decreased the flexion and increased the valgus rotation and tilt of the patella. Anterior cruciate ligament injury caused a proximal and lateral shift in patellofemoral cartilage contact location. Anterior cruciate ligament reconstruction reduced the abnormal apparent elongation but not the orientation of the patellar tendon, and it restored the patellar flexion and proximal shift in contact. The abnormal patellar rotation, tilt, and lateral shift in cartilage contact persisted after reconstruction.

Conclusion: The altered function of the patellar tendon in anterior cruciate ligament deficiency resulted in an altered patellar tracking and patellofemoral cartilage contact. Persistent changes in patellofemoral joint function after anterior cruciate ligament reconstruction imply that reconstruction of the anterior cruciate ligament does not restore the normal function of the patellofemoral joint.

Clinical relevance: The abnormal kinematics of the patellofemoral joint might predispose the patellofemoral cartilage to degenerative changes associated with anterior cruciate ligament deficiency, even if the ligament is reconstructed in a way that restores anteroposterior knee laxity.

Figure 1

The knee models for a typical subject at 0°, 15°, 30°, 60°, and 90° of flexion.

Figure 2

The sagittal plane angle (A), measured in the sagittal plane between the patellar tendon (PT) and the long axis of the tibia; the coronal plane angle (B), measured in the coronal plane between the PT and the long axis of the tibia; and twist (C), measured in the transversal plane between the patellar and tibial attachment sites of the PT.

Figure 3

Coordinate systems used to quantify the patella tracking. The femoral coordinate system consisted of the transepicondylar axis (TEA) and the long axis intersecting at the center of the knee joint (midpoint of TEA). A cuboid was enclosed around the patella to determine the patellar center. The patellar coordinate system consisted of the proximodistal, anteroposterior, and mediolateral axes. Patellar flexion, lateral shift, lateral tilt, and valgus rotation rotation are considered positive as shown in the figure.

Figure 4

A, the centroid (a) of the intersection of the patellar (b) and femoral (c) cartilage was used to determine the patellofemoral contact locations. B, the coordinate system on the patellar cartilage surface for patellofemoral cartilage contact analysis. The proximal (P)–distal (D) axis was called the centerline. The medial (M)–lateral (L) axis was called the midline. Contact proximal to the midline and medial to the centerline was positive. A, anterior.

Figure 5

The biomechanical function of the patellar tendon. A, apparent elongation; B, sagittal plane angle; C, coronal plane angle; and D, twist of the patellar tendon as a function of knee flexion angle. Central, central portion of the patellar tendon; Deficient, ACL-deficient knee; Intact, intact knee; Lateral, lateral portion of the patellar tendon; Medial, medial portion of the patellar tendon; Postop, postoperative ACL-reconstructed knee. Mean ± SD; *P < .05.

Figure 6

Patellar tracking. A, flexion; B, shift; C, rotation; and D, tilt of the patella as a function of knee flexion angle. Deficient, ACL-deficient knee; Intact, intact knee; Postop, postoperative ACL-reconstructed knee. Mean ± SD; *P < .05.

Figure 7

Patellofemoral cartilage contact points. Cartilage contact in the (A) proximodistal and (B) mediolateral direction as a function of knee flexion angle. Deficient, ACL-deficient knee; Intact, intact knee; Postop, postoperative ACL-reconstructed knee. Mean ± SD; *P < .05.