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 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 This is the same developmental condition as osteochondrosis of the femoral trochlea: defective ossification of cartilage on the femoral trochlear ridges in the stifle of young horses. It
## Overview Medial patellar ligament desmotomy is a surgical procedure in which the medial patellar ligament is cut to treat persistent upward fixation of the patella. It prevents the patella from lo
## 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
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 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 This is the same developmental condition as osteochondrosis of the femoral trochlea: defective ossification of cartilage on the femoral trochlear ridges in the stifle of young horses. It produces effusion and lameness and is treated by arthroscopic debridement with a generally favorable outlook. ## Causes Disturbance in endochondral ossification. ## Diagnosis Radiographs of the stifle. ## Treatment Arthroscopy. ## Recovery and Prognosis Good. ## Prevention Controlled growth. Signs include: stifle effusion; lameness; radiographic evidence of trochlear osteochondrosis
## Overview Medial patellar ligament desmotomy is a surgical procedure in which the medial patellar ligament is cut to treat persistent upward fixation of the patella. It prevents the patella from locking over the medial trochlear ridge. The procedure is performed standing or under general anesthesia and has a high success rate for resolving locking. ## Causes Performed to correct upward fixation that has not responded to conditioning. ## Diagnosis Clinical confirmation of upward fixation of the patella. ## Treatment Surgical transection of the medial patellar ligament. Post-operative exercise is encouraged to prevent adhesions. ## Recovery and Prognosis Excellent for resolution of locking. Occasional fragment formation at the cut end has been reported but is uncommon with modern technique. ## Prevention Not applicable (it is a treatment). Signs include: performed for intermittent locking of the hind limb that does not respond to conditioning
## 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
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 (Right) on our interactive 3D horse model. Open 3D Model