Background: Anterior cruciate ligament reconstruction (ACLR) has been shown to alter kinematics, which may influence dynamic tibiofemoral joint congruency (a measure of how well the bone surfaces fit together). This may lead to abnormal loading of cartilage and joint degeneration. However, joint congruency after ACLR has never been investigated.
Hypotheses: The ACLR knee will be more congruent than the contralateral uninjured knee, and dynamic congruency will increase over time after ACLR. Side-to-side differences (SSD) in dynamic congruency will be related to cartilage contact location/area and subchondral bone curvatures.
Study design: Descriptive laboratory study.
Methods: The authors examined 43 patients who underwent unilateral ACLR. At 6 months and 24 months after ACLR, patients performed downhill running on a treadmill while synchronized biplane radiographs were acquired at 150 images per second. Dynamic tibiofemoral kinematic values were determined by use of a validated volumetric model-based tracking process that matched patient-specific bone models, obtained from computed tomography, to biplane radiographs. Patient-specific cartilage models, obtained from magnetic resonance imaging, were registered to tracked bone models and used to calculate dynamic cartilage contact regions. Principle curvatures of the subchondral bone surfaces under each cartilage contact area were calculated to determine joint congruency. Repeated-measures analysis of variance was used to test the differences. Multiple linear regression was used to identify associations between SSD in congruency index, cartilage contact area, contact location, and global curvatures of femoral or tibial subchondral bone.
Results: Lateral compartment congruency in the ACLR knee was greater than in the contralateral knee ( P < .001 at 6 months and P = .010 at 24 months). From 6 to 24 months after surgery, dynamic congruency decreased in the medial compartment ( P = .002) and increased in the lateral compartment ( P = .007) in the ACLR knee. In the lateral compartment, SSD in joint congruency was related to contact location and femur global curvature, and in the medial compartment, SSD in joint congruency was related to contact area.
Conclusion: ACLR appears to affect dynamic joint congruency. SSD in joint congruency was associated with changes in contact location, contact area, and femoral bony curvature.
Clinical relevance: Alterations in tibiofemoral contact location, contact area, and bone shape affect dynamic joint congruency, potentially contributing to long-term degeneration after ACLR.
Keywords: ACL; anterior cruciate ligament reconstruction; congruency; dynamic stereo x-ray system; subchondral bone; tibiofemoral.