Orthopaedic problems in young Thoroughbreds

Helping these future athletes achieve a protective conformation is vital with respect to their welfare, athletic career and sales potential: Orthopaedic conditions have the potential to blight a promising athletic career and prevent young horses reach their full potential. Early diagnosis and management are critical if horses are to be given the best chances of a successful and long career. And this, of course, depends on horsemen being able to pick up on problems as early as possible so they can be dealt with effectively. The Beaufort Cottage Educational Trust is a charity that aims to help disseminate knowledge in the Thoroughbred breeding and racing communities with the ultimate goal of improving horse welfare.

Each year, the charity organizes the Gerald Leigh Memorial lectures which are fantastic resources for horsemen. The lecture series is supported by the Gerald Leigh Trust in honor of Mr. Leigh's passion for the Thoroughbred horse and its health and welfare. Most years, the lectures are presented in person in an event at the UK’s National Horseracing Museum in Newmarket; but for 2021, an in-person gathering was not possible and instead, the lectures are available online. For 2021, the charity chose the theme of orthopaedic problems, which are such a common challenge in young Thoroughbreds.

Angular Limb Deformities: Evaluation and treatment in foals and yearlings

Recognizing, diagnosing and understanding angular limb deviations in young Thoroughbreds are critical skills for horsemen and an important part of both stud management and veterinary care. Angular limb deformities (ALD) refer to deviation of the limb in its frontal plane, or side to side when evaluating the individual from the front or back. A varus deformity is a medial deviation of the limb below the location of the problem (e.g., toeing in), whereas a valgus deformity is a lateral deviation of the limb below the location of the deformity (e.g., toeing out). Angular limb deformities must be distinguished from a flexural limb deformity, which is in the sagittal plane, i.e., from front to back when evaluating the individual from the side.  

How do ALD occur?

ALD can be both congenital and acquired. Congenital means the condition has been present from birth and causes include incomplete ossification or immaturity of the small cuboidal bones, which make up the hocks and knees as well as weakness of the ligaments supporting the joints and periarticular laxity. These issues tend to result in valgus knees and hocks. We also know that ALD can be inherited and that as a breed, Thoroughbreds tend to be varus (toe in). 

Acquired ALD develop after birth and come about through overloading of the physis (growth plate), which is usually caused either from hard ground, an over-conditioned foal or a combination of the two. The biomechanics of equine limb lead horses to bear more weight through the inside of the leg; therefore, the inside of the growth plate, which is inhibited more than the outside and when there is overloading the net effect is that the foal will toe in.

How do ALD impact a foal’s future career?

Carpal and fetlock injuries in racing Thoroughbreds account for a large majority of the reasons racehorses spend time out of training. Intervening while foals are growing and developing to help them achieve a protective conformation gives them the best chance of maximizing their potential and enjoying their racing career. 

Diagnosis of ALD

Evaluating young stock is certainly best achieved using a team approach involving owners/managers, farriers and veterinarians. Regular evaluation from a young age is key, as is examination of the foal while static and while walking. Severe deviations should also be evaluated radiographically.

Treatment of ALD

Conservative treatment options can include exercise restriction, corrective farriery and nutritional management. Hoof correction and toe extensions can be extremely helpful in managing foals and yearlings with minor deviations; and farriery can often correct such issues without needing to resort to surgical treatment options.

The surgical treatment of choice for correcting ALD is the transphyseal screw. In general, it achieves the most effective and cosmetic outcome of the surgical options. The procedure involves placing a screw across the growth plate on the side of the leg that is growing too fast. For example, for a foal that is toeing in, the screw is placed on the outside of the leg. This allows the inside of the growth plate to grow faster and so correct the deviation. The screws are placed under a short general anesthetic. The screw does need to be removed to avoid over-correction, but often they can be removed with the horse standing using a mild sedative once the desired correction is achieved.

Osteochondrosis – recent advances and diagnosis

Osteochondrosis is one of the most important developmental diseases in young athletic horses. It occurs in young, large-breed horses, including Thoroughbreds, and can cause a variety of clinical signs. The age at which the disease starts to cause clinical signs varies from a young foal to horses over 10 years old. This is because lesions can remain silent and only cause clinical signs later on in life. But even in the absence of any clinical signs, the pathological lesions will have been present since the horses reached skeletal maturity. 

How does osteochondrosis affect athletes?

Osteochondrosis often starts to cause problems when the horse is put into training—when they are athletically challenged. This age will differ for different populations, starting earlier in Thoroughbred racehorses than in Warmbloods destined for sports horse disciplines. Often the horse will be sound, or can experience different degrees of lameness and may present with joint effusion. This disease affects more than one joint in an individual in over 50% of cases, and it usually occurs in the same joint on the contralateral limb; but it can also affect multiple different joints. 

How does osteochondrosis develop?

In foals, areas of growth cartilage within the joints will continue to ossify (become bone) after birth. When this process is complete and the animal is skeletally mature, a thin layer of normal articular cartilage will remain supported by subchondral bone. Osteochondrosis is caused by a “failure of endochondral ossification,” which simply means the growth cartilage fails to become healthy bone. A defect, with or without a fragment, is then created in the articular surface of the bone. This dynamically changing area is susceptible to trauma or high biomechanical loads. Recent advances in research, carried out in Norway by Dr. Olstad, suggest that failure of endochondral ossification is likely caused by loss of blood supply to these areas of growth cartilage, which prevents it from ossifying. This has been linked to a heritable predisposition, among other factors such as rapid growth, dietary imbalance, exercise, environment and prior joint sepsis.

Diagnosis of osteochondrosis

Thorough clinical examination and radiography remain at the forefront of osteochondrosis diagnosis. This disease occurs at joint-specific predilection sites as a result of site-specific biomechanical forces and differences in the age at which that site becomes skeletally mature. For example, in the femoropatellar joint (pictured), the most common site of osteochondrosis is the lateral trochlear ridge of the femur. This is predilected by the thick cartilage surface, later age of maturation/ossification, and by the shear forces the patella exerts on the ridge as the stifle flexes and extends. Ultrasonography can also be very sensitive in detecting osteochondrosis in the stifle. Research performed by Dr. Martel in Canada suggests early detection of subclinical lesions in the stifle have been found in foals aged 27-166 days old.  

Management of osteochondrosis

Lesions can spontaneously resolve, and the majority will have done so by 12 months old. Otherwise, management recommendations to limit lesion development include keeping horses exclusively at pasture up to 1 year old, not using rough terrain, in large group sizes (>3 brood mares) or in a large pasture size (large pasture size > 1 hectare before 2 weeks old and > 6 hectare before 2 months old). Strict box rest is discouraged, and a convalescence paddock of 33ft x 56ft (10m x 17m) for 60-90 days may help stabilize lesions. 

Conclusion

Gerald Leigh was an incredibly successful Thoroughbred breeder and owner based in the UK. The 2021 lectures honoring his passion for the Thoroughbred provide a useful update for horsemen on two common conditions of the young Thoroughbred and add to the contribution the charitable trust established by Mr. Leigh’s family, which continues to make in supporting the Thoroughbred industry.

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