Overview
The patella is the largest sesamoid bone of the body. It lies in the insertion tendon of the quadriceps femoris and glides over the femoral trochlea, redirecting the muscle's pull to extend the stifle. In cattle it is large and robust, with the base proximal and the apex distal.
Key features
- Articular surface (facies articularis): caudal, fits the femoral trochlea.
- Parapatellar fibrocartilage (fibrocartilago parapatellaris): extends the patella medially and wraps over the medial ridge of the trochlea.
- Patellar ligaments: cattle have three, as in the horse: lateral, intermediate and medial (ligamentum patellae laterale, intermedium et mediale). All three run from the patella to the tibial tuberosity.
- Medial and lateral femoropatellar ligaments: stabilise the patella on each side of the trochlea.
Clinical relevance
- Upward fixation of the patella: the medial patellar ligament and the parapatellar fibrocartilage become hooked over the medial ridge of the trochlea. The limb locks in extension, with the stifle and hock rigid, and the animal drags the toe of the claw; it may be intermittent. It is treated by medial patellar desmotomy.
- Lateral luxation of the patella in calves: congenital or associated with femoral nerve injury and atrophy of the quadriceps, sometimes after forced extraction at calving.