Developmental orthopedic diseases of horses are an important group of conditions that includes osteochondritis dissecans, physeal dysplasia, acquired angular limb deformities, flexor tendon deformities, and cuboidal bone malformations.
Osteochondritis dissecans is one of the more common developmental orthopedic diseases of horses. The condition mainly affects joint growth cartilage; however, bone shape and length can be disturbed. It can lead to cysts (see Bone, Joint, and Muscle Disorders in Horses: Cysts beneath the Cartilage (Subchondral Cysts)), an abnormal narrowing of the vertebral canal and, ultimately, an inability to coordinate muscle movements.
There are many causes of osteochondritis dissecans, such as rapid growth, overnutrition, mineral imbalance, and biomechanical problems (for example, trauma to cartilage). Inherited conditions have been noticed in some breeds, such as Standardbreds and Swedish Warmbloods.
The signs of osteochondritis dissecans are varied due to the wide range of causes and sites involved. The most common sign is a nonpainful joint swelling (for example, gonitis and bog spavin). Horses affected by osteochondritis dissecans do not typically become lame, except in cases of damage to particular sites. In severe cases, signs typical of other developmental orthopedic diseases also may be present. In cases involving trauma, joint damage may alter the performance of the horse and cause pain and lameness.
In foals younger than 6 months of age, the first sign noted is often a tendency to spend more time lying down. This is accompanied frequently by joint swelling, stiffness, and difficulty keeping up with other animals in the paddock. An additional sign may be the development of upright conformation of the limbs, presumably as a result of rapid growth. Osteochondritis dissecans of the fetlock is particularly seen in younger foals (less than 6 months old).
The main signs in yearlings or older horses are stiffness of joints, pain when the joint is bent, and varying degrees of lameness. These signs are usually associated with the onset of training, suggesting a preexisting biomechanical problem that the training aggravates.
A diagnosis can often be made on the basis of a detailed physical examination. More definitive diagnosis may require the use of x-rays, ultrasonography, or exploratory surgery using an endoscope.
Treatment and Outlook
Management of osteochondritis dissecans depends on the location and severity of signs. Mild cases recover spontaneously, and a conservative approach may be appropriate. In young animals (less than 12 months old) this involves several weeks of restricted exercise and a reduced diet to slow the growth rate. Particular care should be taken to ensure appropriate mineral supplementation. (Copper deficiency can be a problem.) Veterinarians debate whether correcting the diet, once signs have developed, actually assists in resolving the condition, but it may limit further cases on stud farms. Medicating the joint with hyaluronic acid may help, and injections of long-acting corticosteroids may reduce swelling and inflammation of the joint membrane.
When surgery is necessary, it is usually performed using an endoscope. This technique has been successful in most affected sites, particularly the hock, stifle, and fetlock. Damaged cartilage and loose pieces of bone below the cartilage (known as joint mice) are removed, and the joint is flushed extensively. The outlook for recovery should be good except in cases of severe joint disruption or degenerative joint disease.
Shoulders are often more problematic to treat surgically because endoscopic access is more difficult, and there is usually more extensive bone damage below the cartilage, often with formation of many cysts. Therefore, the outlook for recovery is guarded.
Physitis involves swelling around the growth plates of certain long bones in young horses. It can occur along with osteochondritis dissecans. Suggested causes include nutritional imbalances, defects in conformation, faulty hoof growth, toxicosis, and compression of the growth plate. Physitis is frequently seen in fast-growing foals (often 4 to 8 months of age) or in young horses (18 to 24 months of age) that have begun training. Foals affected are often those fed high-grain or high-protein diets.
The condition is characterized by swelling at the level of the growth plate, giving a “boxy” appearance to the affected joints when seen on x-rays. The bones most often affected include the radius, tibia, third metacarpal or metatarsal bone, and the first phalanx. The amount of lameness varies.
Treatment consists of reducing food intake to reduce body weight or at least growth rate; confining exercise to a yard or a large, well-ventilated loose box with a soft surface (for example, peat moss, deep straw, shavings, or sand); ensuring that the feet are carefully and frequently trimmed; and correcting any imbalances in the diet. Your veterinarian can make appropriate recommendations for dietary changes and supplements.
As a preventive measure, the older foal or yearling that is fat or heavy-topped should be watched carefully for signs of physitis, especially when the ground is hard and dry. When these conditions exist, feed rations and exercise should be restricted.
Contracted Flexor Tendons
Flexor tendon disorders may be congenital (present at birth) or acquired. They are associated with postural and foot changes, lameness, and a lack of strength and energy. A foal that is malpositioned within the uterus, genetic defects, and toxic substances that the mare was exposed to may be causes of contracted limbs in newborn foals. In horses with acquired deformities, contracted tendons are most often a response to longterm pain. The pain may arise from physitis (see Bone, Joint, and Muscle Disorders in Horses: Physitis), osteochondritis dissecans (see Bone, Joint, and Muscle Disorders in Horses: Osteochondritis Dissecans), osteoarthritis (see Bone, Joint, and Muscle Disorders in Horses: Osteoarthritis), or soft-tissue wounds and infection. Pain may cause the horse to withdraw the limb, walking on its toes or knuckles in the fetlocks. This withdrawn position causes the tendon to contract. Nutritional imbalances that are known to cause problems with bone growth (as seen in osteochondritis dissecans and physitis) are also associated with the syndrome.
Signs vary widely in newborn foals. Some cannot stand, some attempt to walk on the upper part of their fetlocks, and others can stand but knuckle in the fetlocks or carpi. One foal may improve spontaneously, while another, seemingly healthy at birth, may become progressively worse. The onset of signs may be rapid in foals 3 to 12 months old; such animals may walk on their toes with their heels off the ground. A slower onset may produce a “boxy” hoof with an elongated heel and toe that curves inward. Physitis may also occur in these horses. Usually both forelimbs are involved, although one or the other tends to be worse. Sores on the toes are a frequent complication that adds to the pain and deformity.
Slightly older horses (1 to 2 years old) commonly knuckle in the fetlock joints, which swell and enlarge. These horses are upright and straight-legged in both fore- and hindlimbs. Yearlings usually are more severely affected and more difficult to treat than younger animals. A complete examination by a veterinarian is necessary to determine the specific tendons involved. Any underlying bone or joint diseases or nutrition problems must be identified and corrected.
Various types of splints and casts are used for foals with contracted tendons. Cases in foals less than 1 year old can be managed conservatively with nutritional correction, proper hoof trimming, and treatment to control pain. Surgically cutting the accessory ligament of the deep digital flexor tendon is the most successful and commonly used procedure and does not interfere with future performance. Other types of surgery, including surgical cutting of the tendon and tendon lengthening, tend to be less successful. In longterm cases, complications such as abnormal tightening of the joint membrane, malformation of accompanying ligaments, and bone involvement may prevent full recovery. Nutritional correction, proper foot trimming, and treatment to relieve pain are essential to proper healing, even when surgery is recommended. The outlook for recovery is fair to good for horses diagnosed early and managed properly.
Last full review/revision July 2011 by Russel R. Hanson, DVM, DACVS, DACVECC; Joerg A. Auer, DrMedVet, Dr h c, MS, DACVS, DECVS; Andrew P. Bathe, MA, VetMB, DACVS, DEO, MRCVS; Leo B. Jeffcott, MA, BVM, PhD, FRCVS, DVSc, VD; Svend E. Kold, DMV, MRCVS, RCVS Specialist in Equine Surgery (Orthopedics); C. Wayne McIlwraith, BVSc, PhD, DSc, FRCVS, DACVS; Dale A. Moore, MS, DVM, MPVM, PhD; Sheldon Padgett, DVM, MS, DACVS; Tracy A. Turner, DVM, MS, DACVS, DABT; Stephanie J. Valberg, DVM, PhD, DACVIM; John F. Van Vleet, DVM, PhD