Learn to recognize the signs of Developmental Orthopedic Disease (DOD) so you can help your young horse before it’s too late.

Developmental Orthopedic Disease (DOD) is an umbrella term that encompasses a wide range of conditions in the juvenile horse. All these conditions involve cartilage, bone, or soft tissue (joint capsule, tendon, or ligament) in some way. Some issues are apparent at birth, while others only occur in older growing horses. The cause of DOD is multi-factorial, and as such, horses can have more than one condition at the same time.

Common causes of DOD

Rapid growth is one of the most common reasons for a foal to develop DOD. This can be due to excessively high dietary protein, either from grain or alfalfa hay. Feeding a ration with a nutritional imbalance of calcium and phosphorus will also lead to certain types of DOD. Some horses have a genetic predisposition for developing DOD, and the combination of a predisposed horse and an improper diet increases the risk.

Pain cannot be over-emphasized as a contributing factor in horses with DOD. Foals that grow too fast have tendons and ligaments that grow slower than their bones. Therefore, the tendons and ligaments are shorter than the bones, and as they stretch, significant pain results. Rapid growth can also lead to inflammation of the growth plates (epiphysitis), which is also painful and may prevent the weanling from walking correctly or even getting up and down properly. Painful horses that do not walk correctly and don’t fully bear weight on their legs will begin to contract their tendons and ligaments, leading to the deformities discussed below.

A look at the different types of DOD

The most common conditions under the DOD umbrella in foals less than six months of age are angular limb deformities and flexural limb deformities.

Angular limb deformities

Foals can be born with an angular deformity, or one can develop as the foal grows. One or both legs may be affected, and to differing degrees. The leg can angle outward, known as a valgus deformity; or inward, known as a varus deformity (Figure 1). The prognosis depends on the severity of the deformity, what joint is involved, the underlying cause, and the age of the foal at the time of veterinary examination.

The most frequently-affected joint and direction of deformity is a carpal valgus, or outward angulation of the “knee” of the forelimb. These angulations will often self-correct during the first 30 to 60 days of the foal’s life, especially if his feet are trimmed properly during this time and the foal is confined to a stall. Exercise is detrimental to a foal with an angular deformity. The bones are not in the correct alignment, and the pressure from exercise can permanently deform the foal’s soft bones so the limb cannot straighten.

Deformities of the carpus can be treated surgically up to six months of age with a good chance of obtaining a straight limb. However, if the pastern or fetlock (ankle) joints are involved, it is critical that the foal be examined by three to four weeks of age.  Surgical intervention is recommended at a much earlier age for deformities in this region, because after six to eight weeks of age, they become permanent. This variation is caused by the different rates of growth plate closure in the lower part of the limb versus the upper limb.

Flexural limb deformities

Flexural limb deformities such as a club foot (Figure 2) can be congenital (the foal is born with it) or they can develop over time if the foal grows too fast. In addition to the causes mentioned above, positioning within the uterus during pregnancy is also thought to contribute to some congenital flexural deformities.

Treatment for congenital deformities may be conservative, with supportive care to assist with nursing, exercise restriction, splinting, oxytetracycline administration, and pain management. If the deformity is severe enough at birth to prevent the foal from standing and nursing, colostrum must be milked from the mare and fed to the foal to avoid failure of passive transfer (see sidebar below). Continuous nutritional support will be required until the deformity is treated and the foal can stand unassisted. Oxytetracycline helps to relax the tendon fibers in neonatal foals, and must be administered intravenously very carefully to avoid damage to the vein and to the kidneys.

Stretching of the tendons and ligaments is painful, and lack of pain management leads to a vicious circle of continuing contraction. Proper trimming of the foot, and in some cases application of glue-on shoes, is also vital to success. If conservative therapy does not resolve the deformity, surgery is performed to transect the inferior check ligament. This will not affect soundness or athletic performance, but if proper post-operative bandaging is not performed, an unsightly scar may develop.

Developmental flexural deformities occur as weanlings and yearlings enter rapid growth spurts, and most often involve the fetlock (Figure 3). These deformities, if caught early and treated properly, can be resolved successfully without surgery. However, if they are allowed to progress beyond a few days, it is much more difficult to straighten the limb, and surgery is often required. Conservative therapy includes decreasing the caloric intake while still providing a balanced diet, pain management, and bandaging and splinting. Improper splinting will lead to pressure sores, and must be done under strict veterinary supervision to be successful.

If surgery is required to treat flexural deformities, it may involve cutting the inferior check ligament or, if the deformity is severe, the superficial digital flexor tendon may require transection. If so, the athletic potential of the horse may be jeopardized, pending the response to rehabilitation.

Epiphysitis

Epiphysitis is also extremely common in weanlings and yearlings, and is often a precursor to flexural limb deformities at the fetlock due to its painful nature. It is typically seen in youngsters that grow rapidly secondary to a high-protein diet. Treatment, therefore, requires that caloric intake be decreased until the inflammation in the growth plate subsides. Pain management is a vital component, because pain will lead to the deformities described above. Too much exercise in these horses causes fatigue and over-stretching of the tendons or ligaments, leading to pain as well as a vicious cycle that, unless broken with proper therapy, results in deformity.

Osteochondrosis dissecans (OCD)

As foals reach the six-month mark, signs of osteochondrosis dissecans (OCD) may occur.  OCD is a failure of the joint surface to form properly, resulting in a fragment of cartilage and bone that is separate from the normally smooth surface (Figure 4). This fragment leads to joint inflammation, which increases joint fluid production. The excess fluid makes the joint swell, which is the first sign of OCD. Hocks are the most common joint affected, and lameness is rare. Stifles and fetlocks are the next most common sites; lameness is common with OCD in these locations. However, OCD can occur in any joint, including the elbow, shoulder, and neck.

As soon as swelling in a joint is noted, x-rays should be taken to confirm the presence of OCD. Hock and fetlock OCD surgery should be done as soon as possible after diagnosis, as it involves a three-month healing period post-operatively. Stifle surgery is delayed until ten months of age, since bone in this location will continue to grow and change until that time.  The recovery time is much longer at six to 12 months. Proper post-operative bandaging is critical to success in hocks and fetlocks. These locations are easily contaminated by manure if the bandages slip, and this will lead to an infection. Infected joints are always more expensive to treat than the original surgery, and can be life-threatening if not treated aggressively.

The prognosis for soundness is very good for hocks with OCD. The sooner the fragment is removed, the less likely the hock will remain swollen after surgery. Stifle OCD often has a less favorable prognosis for soundness, and the prognosis for fetlock OCD depends on the location of the fragment and the horse’s age at the time of surgery. Your surgeon will give you a more specific prognosis for each horse when the x-rays are evaluated prior to surgery.

In summary

Foals, weanlings, and yearlings with most types of DOD can be successfully treated with a good outcome.  Early detection and proper management of the entire horse during treatment (such as making sure the foal with a deformity can stand and nurse) will lead to complete resolution in a majority of cases. Post-operative bandaging and care as directed by your surgical center will result in a good outcome for hock and fetlock OCD surgery. If you have a young horse with DOD, or are having trouble with post-operative care following surgery, contact your veterinarian or surgeon immediately. He or she can assist you in achieving a sound horse with minimal to no cosmetic blemishes.