Flexural limb contracture results in the inability to extend a limb fully. In neonatal foals, this condition is due to disparity in the length of the musculotendinous unit relative to the length of the bone. Uterine malposition, teratogenic insults (arthrogryposis), and genetic defects have been implicated as causes in neonates. Neonatal foals (especially premature or dysmature foals) can also show flexor tendon laxity or digital hyperextension due to weakness or relaxation of the flexor tendons.
The acquired form of flexural limb contracture is more common and is a result of chronic pain in the affected limb. Pain can arise from physitis, osteochondrosis, degenerative joint disease, pedal bone fracture, or soft tissue wounds and infection. Pain induces reflex muscle contraction with shortening of the flexor musculotendinous units. An affected horse will walk on its toe or knuckle over in the fetlock.
Abnormalities of bone ossification and growth (ie, osteochondrosis and physitis) are intimately associated with flexural limb deformities and must be evaluated and addressed as part of treatment. (Also see Flexural Limb Deformities and Angular Limb Deformities.)
Clinical Findings of Flexural Deformities in Horses
Clinical signs of flexural deformities vary widely in neonatal foals. Some foals cannot stand, some attempt to walk on the dorsum of their fetlocks, and others can stand but knuckle in the fetlocks or carpi. One foal might improve spontaneously, while another foal that was seemingly healthy at birth might progressively worsen.
In older foals, onset tends to be rapid, causing them to walk on their toes with their heels off the ground. Slower onset is characterized by an upright hoof with an elongated heel and concave toe.
Physitis is frequently also evident in horses with contracted tendons. Involvement of both forelimbs is common, and one leg tends to be worse than the other (see image). Toe abscesses are a common complication of hoof and locomotion changes, and they add to the pain and deformity.
Courtesy of Dr. Chris Whitton.
Older horses (1–2 years old) can also develop partial contracture in the metacarpophalangeal joints. Yearlings usually are more severely affected and more difficult to treat than are younger patients.
It is important to attempt to identify any underlying bone or joint disease; however, doing so is often difficult, and the disease might have already resolved.
Treatment of Flexural Deformities in Horses
For congenital flexural deformities: splints, systemic NSAIDs, IV tetracycline, and stall rest
For acquired flexural deformities: nutritional management, corrective farriery, analgesia, and sometimes surgery
Mild flexural deformities in neonatal foals often need no treatment. More severe cases require supportive care; the use of splints necessitates careful fitting and management, because rub sores are common and can be severe. Casts are generally safer, if used only for short periods (5–7 days).
A single high dose of oxytetracycline (30 mg/kg, IV, in 500–1,000 mL of fluids) is commonly administered in foals with flexural deformities as it can aid in tendon relaxation when administered during the early stages.
Early acquired cases of flexural deformities in older foals and weanlings can be managed conservatively with nutritional correction, proper hoof trimming/manipulation (toe extension), and analgesia; however, once the deformity is present for a prolonged duration, this approach is rarely successful.
Surgical treatment can be simple or complex, depending on the degree of involvement:
Desmotomy of the accessory ligament of the deep digital flexor tendon (inferior check ligament desmotomy) is the most successful and most commonly used procedure for distal interphalangeal joint contracture and does not interfere with future performance. Superior check ligament desmotomy might be included for horses with fetlock contractures.
For carpal deformities, sectioning of the tendons of insertion onto the ulnaris lateralis and flexor carpi ulnaris is performed.
In hindlimbs, tenotomy of the medial head of the deep digital flexor is performed, because the inferior check ligament is often vestigial. In severe cases, tenotomy of the deep digital flexor tendon can be used as a salvage procedure.
Nutritional correction, proper foot trimming, and analgesia are integral to recovery when surgery is performed. The prognosis is fair to good for horses diagnosed early and managed properly.
Key Points
Congenital flexural deformities most commonly involve the distal interphalangeal (DIP) joints, carpus, and fetlock joints.
Mild to moderate congenital flexural deformities respond to physical therapy via corrective shoeing, combined with bandaging or splints.
Acquired flexural deformities occur most frequently before the second year of life, affecting the DIP joint at 3–6 months of age, carpus at 1–6 months, and fetlock at 9–18 months.
DIP joint deformity unresponsive to medical treatment for 1–2 months can be treated via desmotomy of the accessory ligament of the deep digital flexor tendon (inferior check ligament).
For More Information
Hunt RJ. Flexural limb deformities in foals. In: Ross MW, Dyson SJ. Diagnosis and Management of Lameness in the Horse. 2nd ed. Elsevier/Saunders; 2011:645–649.
Kidd JA. Flexural limb deformities. In: Auer JA, Stick J, Kümmerle JM, Prange T, eds. Equine Surgery. 5th ed. Elsevier; 2019:1490–1508.
Also see pet owner content regarding flexural deformities in horses.
