Patella
The patella is the largest sesamoid bone in the horse and is located at the front of the stifle joint. It is embedded in the quadriceps tendon and glides in the trochlear groove of the femur. Three patellar ligaments (medial, middle, and lateral) attach it to the tibia. In the normal standing horse the medial patellar ligament can hook over the medial trochlear ridge, locking the stifle in extension as part of the stay apparatus.
Upward fixation of the patella (locking stifle) occurs when the medial patellar ligament remains hooked over the medial trochlear ridge, locking the limb in extension. It is more common in young, unfit, or poorly muscled horses and those with straight hindlimb conformation. Mild cases show delayed release with a jerky gait; severe cases leave the limb locked behind. Management often begins with conditioning to improve quadriceps tone; surgical options exist for refractory cases.
## Overview Upward fixation of the patella occurs when the medial patellar ligament catches over the medial trochlear ridge and cannot release, locking the hind limb in extension. The leg drags behin
## Overview Patellar fractures are uncommon breaks of the kneecap, usually from direct trauma. They cause acute stifle lameness, effusion, and pain. Displaced fractures may require surgical repair. N
## Overview Osteochondrosis of the femoral trochlea is abnormal cartilage development on the trochlear ridges of the femur within the stifle. It leads to flaps, fragments, or subchondral defects. Cli
A hind limb that locks straight and then releases with a snap, or a delayed release when starting forward, should be evaluated. Improving fitness and hindquarter strength often helps mild cases.
## Overview Upward fixation of the patella occurs when the medial patellar ligament catches over the medial trochlear ridge and cannot release, locking the hind limb in extension. The leg drags behind until it suddenly releases with a jerk or click. It is common in young, unfit horses and those with straight hind-limb conformation. Mild cases are intermittent and worse at the walk or when starting out. Severe cases may remain locked for hours. ## Causes Poor quadriceps tone, straight conformation, or sudden reduction in fitness. ## Diagnosis Observation of intermittent or persistent locking. ## Treatment Conditioning and hill work for mild cases. Medial patellar ligament splitting or desmotomy for persistent cases. ## Recovery and Prognosis Excellent with appropriate management. ## Prevention Maintain fitness, especially in predisposed horses. Signs include: hind limb locked in extension; leg drags behind; sudden release with a jerk or click; intermittent in mild cases; worse at walk
## Overview Patellar fractures are uncommon breaks of the kneecap, usually from direct trauma. They cause acute stifle lameness, effusion, and pain. Displaced fractures may require surgical repair. Non-displaced fractures can sometimes be managed with rest. ## Causes Direct trauma to the stifle. ## Diagnosis Radiographs of the stifle. ## Treatment Internal fixation for displaced fractures. Conservative management for stable non-displaced ones. ## Recovery and Prognosis Fair to good depending on displacement and articular involvement. ## Prevention Trauma avoidance. Signs include: acute stifle lameness; effusion; pain on palpation of the patella; radiographic fracture
## Overview Osteochondrosis of the femoral trochlea is abnormal cartilage development on the trochlear ridges of the femur within the stifle. It leads to flaps, fragments, or subchondral defects. Clinical signs in young horses include effusion and variable lameness. Treatment is arthroscopic. ## Causes Developmental disturbance of ossification. ## Diagnosis Stifle radiographs. ## Treatment Arthroscopic removal of abnormal tissue. ## Recovery and Prognosis Good. ## Prevention Growth management. Signs include: stifle swelling; hind-limb lameness in a young horse; radiographic trochlear lesions
Upward fixation of the patella (locking stifle) occurs when the medial patellar ligament remains hooked over the medial trochlear ridge, locking the limb in extension. It is more common in young, unfit, or poorly muscled horses and those with straight hindlimb conformation. Mild cases show delayed release with a jerky gait; severe cases leave the limb locked behind. Management often begins with conditioning to improve quadriceps tone; surgical options exist for refractory cases.
A hind limb that locks straight and then releases with a snap, or a delayed release when starting forward, should be evaluated. Improving fitness and hindquarter strength often helps mild cases.
See the Patella (Left) on our interactive 3D horse model. Open 3D Model