One deformity seen frequently in newborn foals is tightness in the flexure tendons. On some large breeding farms, as many as 25 percent of the foals will be born with varying degrees of tightness. The foals appear to be buckling at the knees with straight pasterns, and the tendons on the back of the leg are extremely tight. This is commonly called tendon contracture even though tendons don't actually contract. Rather, it is generally a soft tissue problem that involves the flexure tendons, the muscles, ligaments and joint capsules.
Congenital contracture (flexural deformity) is usually present on both sides and largely affects the fetlock joints or knees. The degree of contracture varies from slight, where the foal can stand on her own unassisted, to severe, where the foal cannot stand on her own. In a slight contracture the foal may appear to stand more upright in the pasterns, or a little buckled at the knees. In severe contracture the foal may buckle over at the fetlock or even walk on the front surface of the pastern. Difficulty in foaling may occur with severe knee contracture. This makes nursing very difficult because the foals roll forward on their buckled legs and have difficulty positioning the legs while suckling.
The cause of this deformity is not entirely clear. The milder contractures are often attributed to uterine malpositioning. Ingestion of toxic plants such as Astragalus mollisimus and Sudan grasses by the mare during gestation has also been implicated. In one study, 5 of 7 foals with hyperplastic goiter presented with forelimb contracture. Genetic factors have been suggested in the cause of this deformity.
The tendinous structures involved in the increased fetlock flexion include the superficial and deep flexors and possibly the suspensory ligament. Just superficial flexure tendon involvement alone results in knuckling over of the fetlock. Deep flexure contracture manifests as a flexural deformity of the coffin joint. Foals may have a club-footed appearance. Many structures appear to be involved with increased knee flexion. In one study, the severing of flexor tendons plus removal of some of the joint structures was necessary before a contracted carpus was able to be straightened at post mortem.
It is important to make the diagnosis of flexural contracture as soon as possible after birth. Without swift intervention, some severe cases can be life threatening Radiographs of the affected joint should be taken to ensure there is no bone malformation or arthritis present. Since the cause is unknown, there is no reason to treat the mare or pursue further diagnostic tests unless the newborn exhibit other signs.
The therapeutic measures to be taken to correct the malformation depend on the degree of severity of the contracture and the structures that are involved.
Mild flexural contractures may correct on their own within a few days of birth. Application of a leg wrap will hasten the progress. The placement of splints or casts on the young foal will induce a degree of hyperextension carpal and fetlock joints. The bandages should extend from the coronary bands to above the carpus (knee) and they should be changed on a daily basis. Corrective shoeing with a toe extension may be useful in some instances.
High doses of intravenous oxytetracycline in the young foal have been shown to relax the contracture. This treatment can be repeated on a successive day. Combining support wraps of the legs from the coronary band to above the carpus with the oxytetracycline therapy improves the contracture more quickly. Caution – on a rare occasion, foals may develop life threatening, kidney compromise from the oxytetracycline. Your veterinarian may choose to dilute the oxytetracycline in sterile saline to decrease the likelihood of kidney damage.
The prognosis for mild to moderate flexural deformities is excellent. If there is no response to splint/casting, then surgery is an alternative but the prognosis is less favorable.
Home Care & Prevention
Exercise is important in foals with mild contracture. A few hours in a small paddock daily will help to correct this deformity. If the contracture is moderate to severe, it is important to avoid too much exercise since the extensor tendon has increased stress and can rupture. This appears as a hard swelling below the knee.
Physical therapy consisting of straightening the leg or stretching the tendons several times a day may be helpful in correcting this problem.
Because flexural deformities may prevent the foal from standing and nursing, you may need to hold the foal up to nurse or feed her with a bottle until she is more mobile. It is extremely important that the foal receive colostrum, the antibody-rich, first milk that the mare makes, within three hours of birth.
There is no preventive care for this abnormality.