Collateral Ligament Injuries of the Stifle in Horses

Rupture or sprain of the medial or lateral collateral ligament of the stifle in horses is usually the result of an acute traumatic episode in which the distal limb is forced medially or laterally, thereby stressing the ligament. Rupture or sprain is more common in the medial collateral ligament than in the lateral collateral ligament.

In some horses, fibers from the cranial aspect of the medial collateral ligament are attached to the abaxial medial meniscus. Concurrent injury of the menisci or cruciate ligaments is common, particularly in severe injuries. Lameness depends on the severity of the injury but is usually quite severe initially. Localized edema and joint effusion is evident, particularly in the acute stages.

Flexion tests of the stifle usually exacerbate lameness that is due to collateral ligament injury. Clinical signs usually improve within a few days, unless there is notable joint instability. Intra-articular anesthesia of the femorotibial joint does not always alleviate lameness.

If ligament rupture is complete, stressed caudocranial radiographs of the stifle can demonstrate joint widening on the affected side. Enthesiophyte formation at the origin or insertion of the ligament might be evident radiographically in chronic cases. Diagnosis is usually confirmed by ultrasonographic examination.

Horses with mild collateral ligament sprains can be treated conservatively with stable rest and anti-inflammatory medication for 6–8 weeks, followed by a controlled, ascending exercise rehabilitation program for an additional 6–8 weeks.

Horses with mild sprains and no joint instability have a fair prognosis for return to athletic use. The prognosis for horses with severe injury is poor.