Early Patellofemoral Cartilage and Bone Degeneration in a Rat Model of Noninvasive Anterior Cruciate Ligament Rupture

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Background Anterior cruciate ligament rupture (ACLR) is a well-known risk factor for the development of post-traumatic osteoarthritis (PTOA). While clinical and pre-clinical studies have characterized the onset and progression of PTOA in the tibiofemoral joint compartment, very little is known about degenerative changes in the patellofemoral compartment after ACL injury.

Hypothesis/Purpose To evaluate the extent to which ACL rupture induces acute patellofemoral joint degeneration by quantifying articular cartilage morphology and remodeling of subchondral and trabecular bone microarchitecture in the patellofemoral compartment.

Study Design Descriptive laboratory study.

Methods Adult female Lewis rats were randomized to undergo either a non-surgical ACL rupture or a Sham procedure (n = 6 per group). Ex vivo contrast-enhanced micro-computed tomography (µCT) and histological evaluation of the patellofemoral compartment were performed at 2-weeks post-injury, representing a timepoint of documented early PTOA in the tibiofemoral compartment in this model.

Results ACL rupture causes osteophyte formation in the patella and mild degeneration in the superficial zone of articular cartilage (AC), including surface fibrillation, fissures, increased cellularity, and abnormal chondrocyte clustering at two weeks post-injury. Contrast-enhanced µCT analysis demonstrates significant increases in AC thickness of patellar and trochlear cartilage. Loss of subchondral bone thickness, bone volume fraction, and tissue mineral density, as well as changes to trabecular microarchitecture in both the patella and trochlea, were indicative of catabolic bone remodeling.

Conclusion These results demonstrate that the patellofemoral joint develops mild but evident degenerative changes in the acute time period following ACL rupture, extending the utility of this rat model to the study of degenerative patellofemoral changes following joint trauma.

Clinical Relevance ACL rupture causes mild degeneration and swelling of articular cartilage, coupled with catabolic bone remodeling in the patellofemoral compartment. Characterizing the pathophysiology of patellofemoral PTOA in its early stages may provide a better understanding of disease progression and provide opportunities for preventative therapeutic intervention.