Anatomy of the knee extensor mechanism: correlation with patellofemoral arthrosis

The patellofemoral articulation is a common and significant source of disability and discomfort in the aging population. This study examined the anatomy of the knee extensor mechanism in patients having primary total knee arthroplasties, characterized the anatomic variations of the extensor mechanism, and correlated these findings with the location and extent of osteoarthritic change of the patellar undersurface. Sixty-two knees (57 patients) were evaluated prospectively. Specific characteristics that were analyzed included the mean Outerbridge grade for rating patellar cartilage degeneration and anatomic patterns of the extensor mechanism. Knees with a quadriceps tendon width at 2 and 5 cm above the patella that differed by less than 1 cm had more statistically significant patellar degeneration in all patellar locations than knees with tendon width differences greater than 1 cm. Anatomic variations, such as tendons with minimal increments in width in the proximal-distal direction, may be associated with an increasing amount of patellar arthrosis at the lateral facet, central ridge, and, most significantly, medial facet.