How to Manage the Club Foot—Birth to Maturity

A club foot results from a flexural deformity of the distal interphalangeal joint that is characterized by a shortening of the deep digital flexor tendon musculotendinous unit. Flexural deformities are a problem not only in foals but are also responsible for the club foot conformation seen in adult horses. Treatment is most successful when the cause is investigated and therapy is initiated as early as possible and when the biomechanical properties of the foot are thoroughly understood. Flexural deformities in foals to mature horses are addressed through appropriate farriery, often combined with surgery. Author’s address: Northern Virginia Equine, PO Box 746, Marshall, VA 20116; e-mail: sogrady@look.net. 

1. Introduction

A club foot can be defined as an upright conformation of the foot associated with a flexural deformity of the distal interphalangeal joint (DIPJ).1 Grossly, the dorsal hoof wall angle is upright or steep accompanied by a broken forward foot-pastern axis. A flexural deformity of the DIPJ can be defined as a shortening of the musculotendinous unit of the deep digital flexor tendon (DDFT) that results in hyper flexion of the joint.^{2– 8}  The mechanism of this shortening of the musculotendinous unit is not well understood, and the initiating cause is often undetermined but may be related to lameness, nutrition, or genetic predisposition. Flexural deformities are not only observed in foals but are also responsible for the club foot conformation seen in mature horses. The deformity may be congenital or acquired and in many instances may have a genetic basis.^{2– 4}  Treatment is most successful when the cause is investigated, therapy is initiated as early as possible, and when the biomechanical properties of the foot are thoroughly understood. Furthermore, knowledge of the anatomical changes that occur in a club foot and biomechanical principles will enhance interaction with the farrier whose input will be necessary for a successful outcome. Flexural deformities in foals to mature horses are addressed through appropriate farriery, which is often combined with surgery. Flexural deformities have been traditionally referred to as “contracted tendons”; however, the primary defect appears to be a shortening of the musculotendinous unit rather than a shortening of just the tendon structure, thus making “flexural deformity” the preferred descriptive term.^2,8  Shortening of the musculotendinous unit produces a structure of insufficient length to allow normal alignment of the distal phalanx (P3) relative to the middle phalanx, resulting in variable clinical signs ranging from an upright hoof angle to a club foot. As it seems many of the club feet seen in mature horses result from inappropriate management in the first year of life, this paper will discuss the management of club feet (flexural deformities) from birth to the adult horse. As a true club foot is synonymous with a flexural deformity, the terms will be used interchangeably throughout this paper.

2. Anatomy Review

In the antebrachium, the muscle bellies of the DDFT lie directly on the caudal aspect of the radius and are covered by the muscle bellies of the superficial digital flexor tendon (SDFT) and the flexors of the carpus. The deep digital flexor muscle consists of 3 muscle bellies (the humeral head, the inconsistent radial head, and ulnar head), which form a common tendon proximal to the carpus. This tendon, along with the SDFT, passes through the carpal canal and continues down the palmar aspect of the third metacarpal bone. Below the fetlock, at the level of the middle phalanx, the DDFT passes between the medial and lateral branches of the SDFT, continues distally, and inserts on the flexor surface of the distal phalanx (P3). A strong tendinous band known as the accessory ligament of the DDFT (AL-DDFT) originates from the deep palmer carpal ligament and fuses with the DDFT at the middle of the metacarpus (Fig. 1). The design and function of the anatomical structures is such that any prolonged shortening of the musculotendinous unit affects the position of the DIPJ. This palmar surface of the distal phalanx is pulled palmarly by this shortened musculotendinous unit, placing the DIPJ in a flexed position. The alignment of the bone within the hoof capsule remains constant while the hoof capsule is pulled with the distal phalanx. The flexed position of the DIPJ combined with the altered load on the foot leads to a rapid distortion of the hoof capsule and thus the club foot conformation. It can also be noted from the anatomy that transecting the AL-DDFT lengthens the musculotendinous unit either functionally or by allowing relaxation of the proximal muscle belly associated with the DDFT.
 

3. Classification of Club Feet

Traditionally, club feet or flexural deformities have been classified as type 1 where the hoof-ground angle is 90° or less and type 2 where the hoof-ground angle is greater than 90°.³ A recent method of classifying club feet using a grading system (grade 1– 4) has been proposed.^2,9 It would appear beneficial to classify the severity of the flexural deformity to devise an appropriate treatment plan and monitor the response to a given therapy. A grading system would also enhance record keeping as well as improve communication between the veterinarian, farrier, and owner with regard to treatment strategies and follow-up. A grade 1 club foot has a hoof angle 3° to 5° greater than the contralateral foot and a characteristic fullness present at the coronet. The hoof-pastern axis generally remains aligned rather than being broken forward. A grade 2 club foot has a hoof angle 5° to 8° greater than the contralateral foot, the angle of the hoof-pastern axis is steep and slightly broken forward, growth rings are wider at the heel than at the toe, and the heel may not touch the ground when excess hoof wall is trimmed from the heel. A grade 3 club foot has a broken-forward hoof-pastern axis, often a concavity in the dorsal aspect of the hoof wall, and the growth rings at the heels are twice as wide as those at the toe. A grade 4 club foot has a hoof angle of 80° or greater, a marked concavity in the dorsal aspect of the hoof wall, a severe broken-forward hoof-pastern axis, and the coronary band from the toe to the heel has lost all slope and is horizontal with the ground (Fig. 2). For simplicity, the author uses a grading system based on the severity or degree of flexion noted in the DIPJ on a well-positioned weight bearing lateral radiographic projection to classify flexural deformities. Any marked flexural deformity should be considered significant and treated accordingly.

4. Club Feet in the Young Horse

Club feet or flexural deformities in foals can be divided into congenital or acquired deformities. As such, congenital deformities are noted at birth, and acquired deformities generally occur from 2 to 8 months of age as the foal grows and develops.^2-4,10 [...]