Osteochondritis dissecans (OCD) is a joint disorder that can significantly impact the health and performance of horses. Understanding why it happens and how to manage it is crucial for horse owners.
What is osteochondritis dissecans?
OCD is a developmental orthopedic disease. There are three terms that are commonly used in association with the disease:
- Osteochondrosis: The underlying disorder
- Osteochondritis: The inflammatory response to the disorder
- Osteochondritis dissecans: The separation of an area of cartilage and/or bone, forming a flap
What causes osteochondritis dissecans?
OCD occurs when the bone fails to develop normally in a growing animal and is unable to repair itself.
Bone development in horses
Bone development in horses occurs through a process called endochondral ossification, where bone starts as a cartilage scaffold and transitions to bone. This process begins during fetal development and continues throughout the foal’s growth.
Disease process overview
The OCD disease process is multifactorial and is proposed to involve several factors:
- Endochondral ossification: This process can lead to irregularities due to the delicate vascularization in horses, resulting in chondronecrosis, a condition involving cartilage death.
- Genetic susceptibility and environmental factors: These determine the size and severity of the irregularities.
- Lesion formation and repair: Once a lesion forms, the horse’s natural metabolic activity facilitates repair. However, as the horse ages, this metabolic activity declines, making repair more difficult.
- Progression to articular defects: Lesions that are not repaired can develop into significant articular defects.
Environmental influences
Exercise and nutrition are environmental influences that may lead to OCD and determine the size and severity of the abnormalities. Proper exercise is essential for musculoskeletal development. However, both overloading and underloading can lead to joint injuries. Consistency is better than peaks of loading. To mitigate environmental influences that may lead to OCD, complete pasture turnout is preferable to stall confinement or mixed turnout/stall arrangements.
Nutrition also plays a role. High-energy feeds can alter growth hormones and the metabolism of juvenile cartilage. Additionally, growth rates vary genetically, and high-carbohydrate diets can exacerbate growth rates. Mineral and trace element imbalances, such as low copper levels or improper calcium/phosphorous ratios, can impact bone metabolism, while excessive phosphorus can contribute to OCD.
Genetic factors
OCD prevalence varies among breeds, as does heritability. Genomic studies have linked OCD to two-thirds of the 33 chromosomes in horses.
OCD prevalence among breeds:
- Standardbreds: 10.5-35%
- Thoroughbreds: 23%
- Warmbloods: 15-44%
- Feral Horses: 2.5%
Clinical presentation and detection
When it comes to joint abnormalities in horses, symptoms can vary significantly based on age. Yearlings may experience joint effusion (swelling within the joint), which can manifest without lameness. In contrast, young foals often exhibit stifle effusion accompanied by noticeable lameness, which signals a more immediate concern. For older horses, symptoms may not surface until they begin training. To detect OCD, radiographs (X-rays) are considered the gold standard, while ultrasound and CT can be useful for spotting atypical lesions that might otherwise go unnoticed.
OCD can affect various joints, including:
- Hocks (common in Warmbloods and Standardbreds)
- Stifle (common in Thoroughbreds)
- Fetlock joints
- Cervical intervertebral facets
- Shoulder and elbow joints
- Frequently bilateral (same joint in opposite legs)
How to treat OCD in horses
Treatment options for OCD include conservative or surgical management depending on the severity of the condition. Conservative management may be utilized in very young horses or in very mild cases; it involves limited exercise to alleviate stress on the affected joint, alongside the use of NSAIDs to reduce pain and inflammation. Joint injections can provide relief and help improve function, although, should be used with caution.
In cases where conservative methods are insufficient, surgical management may be necessary. This can include the arthroscopic removal of OCD fragments, which helps to eliminate loose bodies causing pain, or the reattachment of OCD flaps.
Prognosis and recovery
The prognosis for horses with OCD is generally favorable, especially with surgical management. Studies in racing breeds (Thoroughbreds and Standardbreds) show a 65-90% return to athletic activity or racing. However, the prognosis can vary based on the grade and number of lesions.
Recovery period:
- Initial rest: Stall rest and bandaging for about two weeks until suture removal
- Gradual exercise: Stall rest with hand walking or small turnout for one month, followed by larger turnout for one to three months
- Training: Start or resume training after a satisfactory recheck exam
OCD is a multifactorial and complex disease. Understanding OCD and its early detection can help owners manage the disease successfully to ensure their horses lead healthy, active lives. If you suspect your horse may have OCD, consult with your veterinarian or CSU Veterinary Health System Equine Surgery and Lameness service for proper diagnosis and treatment.
This information was derived from Equine Surgery, Fifth Edition.