Osteochondrosis is one of the most important and prevalent developmental orthopedic diseases of horses. Osteochondritis is the resulting inflammatory response, and the term "osteochondritis dissecans" (OCD) refers to a lesion with an area of cartilaginous or osteochondral separation.
Osteochondrosis arises from a focal disturbance in endochondral ossification, with subsequent trauma or physiological loading that results in lesions. The etiology is multifactorial and includes rapid growth, high-carbohydrate diet, mineral imbalance, and biomechanical injury (ie, trauma to cartilage). Genetics has been implicated, and some breeds are predisposed (eg, Standardbred and Swedish Warmblood).
Osteochondrosis in horses can manifest as cartilage flaps, osteochondral fragments, or subchondral cystic lesions. Lesions can also occur in the vertebral articular facets and can be associated with stenosis of the vertebral canal, ataxia, and proprioceptive deficits.
Nonpainful effusion (distention of the joint, observed most commonly in the tarsocrural and femoropatellar joints) is a common clinical sign of osteochondrosis. The presence of lameness depends on the lesion severity and the joint affected.
Detection of intra-articular osteochondral fragments on radiographic evaluation is diagnostic for osteochondrosis in most instances. Patients are often bilaterally affected. Arthroscopic removal (with some exceptions) of osteochondral fragments, along with postoperative exercise restriction, is the preferred treatment in most cases.
Pearls & Pitfalls
|
Clinical Findings of Osteochondrosis in Horses
The most common clinical sign of osteochondrosis in horses is nonpainful joint effusion. For osteochondrosis in joints in which swelling is difficult to detect (eg, shoulder, medial femorotibial joint), lameness is more often the first clinical sign.
Clinical signs of osteochondrosis in horses can be divided broadly into two categories: those in foals < 6 months old, and those in older animals. Often the first sign noted in foals is a tendency to spend more time lying down. This decrease in activity is accompanied frequently by joint swelling, stiffness, and difficulty keeping up with other animals in the paddock. An accompanying sign can be the development of upright conformation of the limbs.
However, many cases of osteochondrosis have no detectable clinical signs and are identified only on prepurchase/sales repository radiographs.
Lameness is often absent or mild in cases of osteochondrosis in horses, except for in the shoulder, where moderate to severe lameness, muscle atrophy, and pain on joint flexion are typical. In the stifle, many horses with subchondral bone cysts in the medial femoral condyle will present with lameness.
More severe clinical signs of osteochondrosis are also observed when osteochondral fragments come loose within the joint. Such fragment loosening often occurs in yearlings or older horses that show clinical signs of stiffness, pain on flexion, and varying degrees of lameness, often associated with the onset of training.
Diagnosis of Osteochondrosis in Horses
Radiography
Ultrasonography
Arthroscopy
Diagnosis of osteochondrosis is commonly based on radiographic examination of the affected joint after joint effusion has been detected on clinical examination (see image). Ultrasonography can sometimes also be helpful to delineate articular damage and determine whether osteochondral fragments are intra- or extra-articular. When the lesion is restricted to the cartilage, arthroscopic evaluation is required to identify a lesion that might not be apparent radiographically.
Pearls & Pitfalls
|
Courtesy of Dr. Chris Whitton.
Treatment and Management of Osteochondrosis in Horses
Arthroscopic removal of fragments, debridement, and lavage
Exercise restriction and dietary modification
Management of osteochondrosis in horses depends on the site and severity of clinical signs. Mild cases can heal, and a conservative approach might be appropriate in young horses (< 12 months old). The conservative approach involves restriction of exercise for some weeks, combined with a decrease in feed intake to slow the growth rate. Particular care should be taken to ensure appropriate mineral supplementation (eg, in cases of suspected copper deficiency).
Whether correcting the diet actually helps resolve osteochondrosis is controversial; however, it might help limit or prevent new cases on stud farms. Intra-articular medication can be beneficial, but injection of corticosteroids is not recommended in growing horses.
Most cases of osteochondrosis in horses are treated arthroscopically. Damaged cartilage, osteochondral fragments, and compromised subchondral bone are removed, and the joint is flushed extensively with sterile fluids.
The prognosis after removal of discrete osteochondral fragments is good. In cases with more extensive osteochondral damage, the prognosis depends on how much of the joint surface must be removed. The prognosis is poor in cases involving substantial joint surface loss or advanced secondary osteoarthritis (degenerative joint disease), and in certain anatomical locations (eg, the shoulder).
Key Points
Osteochondrosis is among the most common developmental orthopedic diseases in horses.
The tarsocrural and femoropatellar joints are the most commonly affected joints.
After radiographic diagnosis, arthroscopic removal of osteochondral fragments is the treatment of choice.
For More Information
Osteochondrosis dissecans. In: Auer JA, Stick J, Kümmerle JM, Prange T, eds. Equine Surgery. 5th ed. Elsevier; 2019:1509–1527.
McIlwraith CW. Diagnostic and Surgical Arthroscopy in the Horse. 3rd ed. Elsevier Limited; 2005.
Also see pet owner content regarding osteochondrosis in horses.
