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Patella instability

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The patella is a sesamoid bone found within the powerful extensor mechanism of the leg. The quadriceps tendon connects the quadriceps muscle complex to the patella, and the extensor mechanism continues from the patella to the tibial tubercle as the patellar tendon. Proper patella tracking and mechanics is essential to correct function of the extensor mechanism.

Image Removed Image Added The patella articulates with the trochlear groove of the femur throughout flexion and extension of the knee. The undersurface of the patella contains a medial and lateral articular facet covered with articular cartilage. In full extension, the patella sits superior to the trochlear groove. As motion is initiated in early knee flexion, the distal aspect of the patellar articular surface begins to enter the superior aspect of the trochlear groove. Variations in the bony anatomy of the trochlea and tibial tubercle may have an effect on how the patella enters and tracks within the trochlea.