Overview
The patella is a sesamoid bone in the tendon of insertion of the quadriceps femoris. It glides in the femoral trochlea and increases the lever arm of the quadriceps when the stifle extends. Distally it continues as the patellar ligament, which inserts on the tibial tuberosity.
Key features
- Base: the proximal edge, where the quadriceps tendon inserts.
- Apex: the distal end, from which the patellar ligament arises.
- Articular surface: smooth, in contact with the femoral trochlea.
- Parapatellar fibrocartilages: widen the gliding surface on each side of the patella.
- Medial and lateral retinacula: fascial bands that keep it centred in the trochlea.
Clinical relevance
- Patellar luxation: in the cat it is almost always medial and often bilateral. The Devon Rex and Abyssinian are predisposed, and it frequently coexists with hip dysplasia. Many cats tolerate it with few signs; severe cases cause lameness or a crouched gait and are corrected surgically.
- Spontaneous patellar fractures: transverse fatigue fractures without previous trauma in young adult cats; they may be bilateral and associated with retained deciduous teeth (patellar fracture and dental anomaly syndrome).
- Extensor mechanism: rupture of the patellar ligament prevents extension of the stifle.