Meddleton Equine Hospital

A previous article, Lameness in the Foal, stressed the importance of early recognition and proper treatment of lameness in babies. This article will pick up at weaning age and cover common lameness issues encountered in developing horses (weanling through the first few years). Like foals, any young horse is at risk of trauma and infection, and any accident should be addressed promptly to ensure the best possible outcome. In addition, this age group is at risk for developmental orthopedic disease (DOD). DOD encompasses a number of disease entities including angular deformities, flexural deformities, physitis, and Osteochondrosis dissecans (OCD).

Angular limb deformities

As mentioned in the previous article, fetlock deformities (crooked at the ankle) should be addressed in the first 2 months of life since the growth plate that can be manipulated in order to straighten the legs closes early in life. Deformities of the Carpus (knee) and Tarsus (hock) can and should be corrected later in life. An exception would be a very severe deformity or one that is getting worse. A mild deformity, especially an outward deviation (valgus) of the Carpus, will usually self correct with exercise restriction as the foal matures and the chest broadens.

It is safe to wait until 6-9 months of age before fixing these deformities if they are mild and not getting worse. On the other hand, severe deformities will result in abnormal and asymmetric strain on the joints and ligaments of the leg. This can result in permanent damage to bones (crushing) and early arthritis if not addressed promptly and aggressively. Any limb deformity should be presented to a Veterinarian in order to determine the best course of action.

Physitis

This is a painful inflammation of the growth plates. It occurs most commonly in lower radius (above the knee) and lower canon bone. There will often be a visible swelling (hourglass shape) just above the fetlock. Physitis can result from infection, crushing injury (overuse or trauma), or asymmetric loading (in a crooked leg), but the cause is usually unknown. It most commonly affects rapidly growing horses.

Affected horses usually respond to exercise restriction, caloric restriction, balancing of the Calcium to Phosphorus ratio in the diet, and proper Copper and Zinc supplementation. The pain of physitis can result in an acquired flexural deformity (club foot, standing on tip of toes, buckling at fetlock).

Flexural deformity

Unlike *"contracted*" newborn foals (congenital flexural deformity), contracture that develops later in life is usually a response to pain. Physitis is a common culprit, but is not the only cause. Sometimes the cause remains unknown, but painful joint conditions such as OCD are also common causes. Young horses that develop this condition slowly will show progressive increase in the hoof angle (develop a club foot) and/or progressive straightening of the fetlock joint.

Acute contractures (presumably from a rapid and severe onset of pain) can result in sudden onset of walking on tip toe or even buckling forward at the coronary band (Coffin joint) or fetlock. Like physitis, these are managed with exercise restriction, caloric restriction, Ca:Phos balancing, and Zn/Cu supplementation. Judicious use of analgesics (Bute and Banamine) and therapeutic trimming are also important in managing this condition.

In severe cases, surgery is required in order to lengthen the musculotendinous unit (usually cut the distal and/or proximal check ligaments). Timely intervention is a key to successful management of these conditions. If it is left to progress to the point that the horse cannot stand without buckling (for fetlock deformities) or that the hoof angles has gone past 90 degrees (for club feet), the prognosis for normal function is poor.

Osteochondrosis dissecans (OCD)

OCD is a disease of the junction between bone and cartilage. It can affect any joint in the body, but certain joints are more commonly affected. There is a presumed inherited component, but it is a complicated inheritance pattern without predictable results. Foals will be born with the problem, but the problem typically does not become evident until the horse is close to adult weight and is beginning to train.

The problem is generally a weak adhesion between the bone and cartilage in addition to a weakened bone under the cartilage. Exercise on these abnormal joints often results in separation of cartilage and sometimes diseased bone from the joint. The exposed bone and collagen fibers will result in chronic inflammation of the joint. The portions of the joint that do not have cartilage cause intense pain during exercise, and the inflammation causes chronic pain and degrades the rest of the cartilage; this can lead to arthritis and loss of the cartilage that was originally healthy.

The first sign of OCD is joint effusion (swelling); it is often detectable before horses go into training and before there is a clinical lameness. Very severe cases of OCD will result in lameness and muscle atrophy (from lack of use) even in foals that have not begun to work. Horses that are mildly to moderately affected will generally develop a lameness at the onset of their training.

A lameness exam with flexion tests and radiographs is all that is generally needed to diagnose this condition. However, as is the case with lameness in general, mild cases will often require nerve and/or joint blocks to localize the source of pain, and advanced imaging modalities such as ultrasound, CT, or MRI may be required to identify the problem. Surgery to remove the diseased cartilage and bone is the treatment of choice for most cases.

Some lesions are self limiting and never cause a lameness or inflammation and do not require surgery. Some lesions respond to treatment with Adequan. On the other hand, some lesions are not accessible or are too large to treat without permanently crippling the horse. Unfortunately, some severely affected horses may never be usable even with adequate and timely medical or surgical intervention. The most commonly affected joints are the stifles, hocks, shoulders, and fetlocks. With the exception of the shoulder, swelling around the joint is commonly seen.

Any joint swelling and/or lameness in a young horse should prompt an immediate Veterinary evaluation. Most cases of OCD have a good outcome if operated on before significant damage has been done to the joint.

Cervical Vertebral Instability/Malformation (Wobbler syndrome)

The spinal cord is housed in a movable column of bone as it travels through the neck. The vertebrae of the neck (cervical) have to protect the cord while allowing a great deal of motion. In some horses the canal in which the cord resides is narrowed, or there is an abnormal joint that results in pinching of the cord when the neck is flexed or extended.

Pinching of the cord results in death of nerve cells effectively interfering with communication between the brain and the legs. Clinically, the horses will display muscle wasting and weakness (especially behind) and incoordination (stumbling, falling). This disease affects Thoroughbreds, Arabs and Warmbloods more commonly, but can happen in any breed. Abnormal muscle loss or *"clumsiness*" in the young horse are a cause for concern and should be presented for Veterinary inspection.

Radiographs of the neck are often enough for a presumptive diagnosis of Wobbler syndrome, but a Myelogram is required for definitive diagnosis. During a myelogram, a dye that shows up on x-rays is placed in the spinal canal and radiographs of the neck are obtained in neutral, extended, and flexed positions. This is done under general anesthesia and will show exactly where and when the spinal cord is being compressed.

Treatment is successful in mild to moderate cases that have been identified and treated early. It consists of surgical fusion of the abnormal cervical vertebral joints. The immobilized joints no longer pinch the cord and a degree of healing ensues. Horses usually spend up to 3 months in a stall with handwalking and do not fully recover for 6-12 months. The surgery is only routinely performed at a few large Equine private practices and Veterinary teaching hospitals in the country, but the diagnostics (cervical radiographs, myelogram) are available locally.

Any young horse displaying signs compatible with the above diseases should be examined as soon as problems arise. Most of these problems can be managed successfully if proper treatments and management are implemented before permanent changes have occurred.