Articulatio genus
The stifle joint is the largest and most complex joint in the horse, equivalent to the human knee. It contains the femorotibial joint (medial and lateral compartments), the femoropatellar joint, and the menisci. The patella has a unique locking mechanism in which the medial patellar ligament hooks over the medial trochlear ridge of the femur, locking the stifle in extension. This allows the horse to sleep standing with minimal muscular effort as part of the stay apparatus. The joint allows flexion and extension of the hindlimb.
Origin: N/A (bone)
Insertion: N/A (bone)
Action: Flexion and extension of the hindlimb; the locking mechanism allows the horse to stand with minimal muscular effort (stay apparatus)
Upward fixation of the patella (locking stifle) is a common condition, especially in young or unfit horses. Meniscal injury, cruciate ligament damage, and osteoarthritis are other important causes of stifle lameness. Diagnosis uses clinical examination, flexion tests, and imaging (radiographs, ultrasound, or MRI).
## Overview Osteochondritis dissecans (OCD) of the stifle is a developmental orthopedic disease in which cartilage fails to convert properly to bone, most often on the lateral trochlear ridge of the
## Overview Meniscal injury is tearing of the medial or lateral meniscus in the stifle. The medial meniscus is more commonly affected. It causes moderate to severe hind-limb lameness, stifle effusion
## Overview Cruciate ligament injury in the horse involves the cranial or caudal cruciate ligaments of the stifle. Complete rupture is uncommon but produces marked instability and severe lameness. Pa
## 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 in extension and releases with a snap, or chronic stifle swelling and lameness, should be evaluated. Improving fitness often helps mild cases of upward fixation.
## Overview Osteochondritis dissecans (OCD) of the stifle is a developmental orthopedic disease in which cartilage fails to convert properly to bone, most often on the lateral trochlear ridge of the femur. Young horses develop stifle effusion and intermittent lameness. Radiographs confirm the lesion, and arthroscopic removal has a good prognosis. ## Causes Disturbance of endochondral ossification. Genetics, rapid growth, and nutrition may contribute. ## Diagnosis Radiographs of the stifle in a young horse with effusion or lameness. ## Treatment Arthroscopic removal of the abnormal cartilage and bone. Conservative management for very small lesions in some cases. ## Recovery and Prognosis Good to excellent for most lateral trochlear ridge lesions after surgery. ## Prevention Balanced nutrition and controlled growth in young horses. Signs include: stifle effusion in a young horse; intermittent hind-limb lameness; radiographic lesion on the lateral trochlear ridge
## Overview Meniscal injury is tearing of the medial or lateral meniscus in the stifle. The medial meniscus is more commonly affected. It causes moderate to severe hind-limb lameness, stifle effusion, and pain on flexion. Clicking may be heard. Diagnosis relies on ultrasound, and magnetic resonance imaging provides additional detail. ## Causes Trauma or degenerative tearing, analogous to human knee meniscal injuries. ## Diagnosis Lameness examination, intra-articular analgesia, ultrasound, and sometimes magnetic resonance imaging or arthroscopy. ## Treatment Rest and anti-inflammatories for mild lesions. Arthroscopic debridement for tears that do not respond. Prognosis depends on the extent of the tear and concurrent osteoarthritis. ## Recovery and Prognosis Guarded to fair. Severe tears extending under the femoral condyle have a poorer outlook. ## Prevention None specific. Signs include: moderate to severe hind-limb lameness; stifle effusion; pain on flexion; possible clicking; medial meniscus more often affected
## Overview Cruciate ligament injury in the horse involves the cranial or caudal cruciate ligaments of the stifle. Complete rupture is uncommon but produces marked instability and severe lameness. Partial tears or strains cause more subtle, chronic stifle lameness and are often associated with other stifle soft-tissue damage. ## Causes Trauma from slipping, sudden turns, or falls. Degenerative weakening may predispose. ## Diagnosis Stifle effusion, pain on manipulation, and positive cruciate tests when instability is present. Ultrasound and radiographs evaluate associated structures; arthroscopy or advanced imaging confirms the diagnosis. ## Treatment Partial injuries are managed with prolonged rest and rehabilitation. Complete ruptures have a poor prognosis for athletic use; surgical options are limited in horses. ## Recovery and Prognosis Guarded for partial tears; poor for complete rupture regarding return to performance. ## Prevention Minimizing traumatic incidents and maintaining good conditioning. Signs include: stifle lameness; joint effusion; pain on stifle flexion or manipulation; instability in complete rupture
## 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) is a common condition, especially in young or unfit horses. Meniscal injury, cruciate ligament damage, and osteoarthritis are other important causes of stifle lameness. Diagnosis uses clinical examination, flexion tests, and imaging (radiographs, ultrasound, or MRI).
A hind limb that locks in extension and releases with a snap, or chronic stifle swelling and lameness, should be evaluated. Improving fitness often helps mild cases of upward fixation.
See the Stifle Joint on our interactive 3D horse model. Open 3D Model