Flexural Limb Deformity

Also know as: Contracted Tendons

Introduction

Flexural limb deformities term applies to those in which the limb deviates from the normal vertical alignement in the sagittal plane.

The primary problem involves the soft tissues that support the various joints of the limb. Depending on the defect and on its severity and chronicity, the problem may involve one or more of the flexor muscles and the associated ligaments and fascia, or it may also involved the ligaments, fascia, joint capsule and synovial structures of the joints involved.

Flexural limb deformities are divided into two broad categories:

Flexor laxity: in which the joints are hyperextended due to loose supporting structures.

Flexor contracture: normal extension of joints is limited and the joints are permanently flexed due to tight supporting structures.

As for the aetiology of flexural limb deformities, the two categories are:

Congenital: the deformity is present at birth. Causes include: genetic predisposition, intrauterine malpositioning, teratogens.

The deformities commonly observed are: digital hyperextension and contractural deformities.

Congenital flexural deformities are common causes of dystocia in the mare.

Acquired: excessive intake and abrupt changes in quality and quantity of feed can lead to accelerated growth in foals. The longitudinal growth rate of the bones exceeds the ability of the tendons to extend passively, pulling the respective joint into flexion. Polyarthritis and trauma are painful conditions and can lead to a flexion reflex resulting in an acquired contractural deformity.

Joints involved include: distal interphalangeal joint, metacarpophalangeal joint, metatarsophalangeal joint and carpus.

Clinical Signs

Congenital contractural deformities:

Congenital digital hyperextension: toes lift off the ground due to flaccidity of the flexor tendons and the foot may rock back on the heel. More severe cases result with the foal walking on the palmar/plantar surface of the phalanges resulting in skin abrasions of the pastern and fetlock. It is more common in the hindlimbs.

Congenital contractural deformities: no voluntary extension of the affected limbs.

Distal interphalangeal joint contracture: the foal walks on its toes. The dorsal hoof wall is often concave in appearance with increased heel length (club foot)

Metacarpophalangeal joint contracture: the foal will have difficulty standing and knuckle over at the fetlock.

Carpal contracture: foal observed buckling forward.

Acquired contractural deformities:

Distal interphalangeal joint contracture: short toe and steep dorsal hoof wall angle. Boxy appearance over time. Stage I: angle of the dorsal hoof wall is less than 90°. Stage II: angle of the dorsal hoof wall is more than 90°.

Metacarpophalangeal/metatarsophalangeal joint contracture: straight angle to knuckled-over appearance at the fetlock. More common in the forelimbs.

Proximal interphalangeal joint contracture: dorsal subluxation with an audible click as the foal walks. Occurs bilaterally.

Diagnosis

A thorough history including nutritional management should be taken.

Radiography might reveal bony abnormalities such as osteochondrosis and degenerative joint disease.

The foal should be observed standing and walking. Its limbs should be manipulated and palpated in weight-bearing and non-weight bearing positions.

Palpation of the flexor tendons whilst attempting the straighten a limb with contracture can help determine which tendon is involved, as it will become taught.

Treatment

The aim is to progress towards a normal limb position.

Pain should be managed to encourage weight bearing.

Congenital deformities:

Digital hyperextension: Moderate exercise. Light bandaging to protect the phalanges. Heel-extension shoes.

Contracture deformities: encourage weight-bearing exercise or manipulate the limbs of a foal if it is recumbent

Oxytetracycline intravenously chelates calcium ions and is thought to aid in tendon relaxation. The foal's nutrition should also be corrected.

Toe extensions can be applied and splints and casts can be used to relax the muscle-tendon unit.

Acquired deformities:

Distal interphalangeal joint: balanced nutrition and exercise are important, and non-steroidal anti-inflammatories can be used to help the foal continue to exercise during the painful stretching of the tendons. Toe-extensions and casts have also been used to correct the deformity.

Metacarpophalangeal joint: a combination of a balanced diet, physical therapy, NSAIDs can be used. Corrective shoeing including wedges to raise the heel to bring the fetlock into a more normal position.

Carpal joint: use of physical therapy and splints

Proximal interphalangeal joint: trimming of the hoof.

Surgical therapy is an option for acquired contractures or severe congenital deformities, and includes:

Distal interphalangeal joint contracture: desmotomy of the superior or inferior check ligament, depending on if the deep or the superficial digital flexor palpates tighter.

Tenotomy of the deep digital flexor tendon can be considered as a salvage procedure in stage II deformities.

Metacarpophalangeal joint contracture: desmotomy of the superior or inferior check ligament as above. Additional transection of the suspensory ligament might be necessary in severe cases, however the prognosis for athleticism is poor.

Carpal joint contracture: tenotomy of the ulnaris lateralis and flexor carpi ulnaris tendons

Proximal interphalangeal joint: transection of the inferior check ligament. If subluxation of the pastern is not reducible, surgical arthrodesis may be necessary.

Prognosis

Mild congenital deformities respond within several days and the prognosis is generally good. Surgery should be considered if there is no response to medical therapy.

Desmotomy of the inferior check ligament in the treatment of distal interphalangeal joint contracture is reasonable.

Stage II contractural deformity and non-reducible carpal contractures hold a poor athletic prognosis.

Flexural Limb Deformity Learning Resources
Flashcards Test your knowledge using flashcard type questions	Equine Orthopaedics and Rheumatology Q&A 21

References

Floyd, A. (2007) Equine podiatry Elsevier Health Sciences

Stashak, T. (1996) Practice guide to lameness in horses Wiley-Blackwell

Barr, A. (1994) Developmental flexural deformities in the horse In practice July 182-188

Lavoie, J-P. (2009) Blackwell's Five-Minute Veterinary Consult: Equine John Wiley and Sons