34th Annual Scientific Meeting proceedings

Congenital flexural deformities (FDs)
A congenital FD of the distal interphalangeal joint (DIPJ) is easily recognized in most cases. Unlike angular limb deformities, which can often be monitored, a congenital FD should be addressed as quickly as possible. Some FDs noted at the time of parturition can be splinted or cast within 30 to 45 minutes of birth with good results. The splints or casts are left in place for 24 hours and then reset if needed. Some FDs may be overlooked in recumbent foals if the joints can be manually straightened, but they should become apparent once the foal is assisted to stand. Distal limb FDs in foals on deep bedding or in long grass may go unnoticed, so foals should be examined in a setting that allows the entire distal limb to be visible. Joints should be manipulated to see if manual straightening is possible. Radiography is rarely required for FDs. Treatment principles for congenital DIPJ FDs include analgesics, farriery or splints/casts. Analgesics are required if the foal is reluctant to rise, ambulate or nurse.

For the DIPJ a technique called “active tension-extension splinting” can be used and was first described by Compston and Payne. This technique involves casting the lower limb in a sedated foal and then bivalving the cast to use only the dorsal portion. The toe end of the half cast is reinforced with resin or acrylic and wires are passed through the foal’s hoof at the toe and the lower end of the reinforced cast and tightened. The half cast is then secured to the limb which extends the affected joints. A similar construct can be made by a farrier using a dorsal metal strut attached to a cuff.

Farriery options are discussed below.

Acquired FDs of the DIPJ
Pain is considered to be the primary inciting factor associated with acquired FDs. Any painful condition could trigger a flexion withdrawal reflex and the resultant muscle contraction, leading to an altered stance. It is also common for lameness in the affected limb to precede the development of an acquired flexural deformity but this lameness can go un-noticed.

Early diagnosis is important to increase the chance of complete resolution, but it may be made difficult because the foal is out at pasture with the mare as DIPJ deformities can be hidden by the grass. Regular examination on a hard, level surface will aid early detection which improves the prognosis.

Opinions differ on the role of exercise in the treatment of FDs, but it seems reasonable that if the deformity is secondary to a painful condition, then exercise limitation and analgesics would be beneficial. Uncontrolled exercise may exacerbate the painful stimuli and the deleterious loading of the contralateral limb. Controlled physiotherapy to encourage extension of the affected region would allow more controlled loading of the area, but scientific documentation in the literature is lacking.

Both the inciting cause and treatment of acquired FDs are painful processes. To aid the foal or yearling in standing and ambulating, NSAIDs are given at low doses. Foals with painful limbs tend to lie down for longer periods, which can aggravate the flexural problem and underscores the need for analgesics.

Acquired FDs of the DIPJ occur primarily in foals between 1 and 4 months of age and almost always affect the forelimbs. The condition is usually bilateral, although one limb may be more severely affected. Deformities of the DIPJ involve the DDFT, because this tendon inserts on the solar surface of the distal phalanx and is responsible for flexion of the DIP joint. Initially, the dorsal hoof wall assumes a more vertical angle, and the heels may not contact the ground if the condition occurred acutely. Two sequelae are associated with a foot in this conformation. First, the heels overgrow because of the lack of ground contact, and the foot appears “boxy” as the heels approach the length of the toe. Second, the toe is under greater stress and wear, which can widen the white line and lead to flaring of the distal hoof wall. In more slowly developing cases, the heels may maintain contact with the ground and overgrow. The deformities are divided into stages I and II.

DIPJ FDs in which the foal is bearing weight on the toe generally benefit from some controlled exercise on a firm surface to allow stretching of the deep digital flexor musculotendinous unit (MTU) combined with analgesics; however, the toe region must be protected to prevent excessive wear and possible development of an infectious process. Turnout in a yard that is sufficiently small to prevent uncontrolled exercise is probably a reasonable choice.

The overlong heels of DIP FDs occur when the heels do not contact the ground and can then overgrow, giving the typical “boxy” conformation to the foot. The heels should be rasped back gradually. Radical trimming of the heel only increases strain forces on the dorsal toe by increasing strain on the deep digital flexor MTU, combined with localized force through weight-bearing in the toe. Similarly, if the heel has been lifted off the ground by the deformity, the heels should not be rasped because this only applies greater forces and leverage to the dorsal laminae and the distodorsal aspect of the distal phalanx. However, judicious trimming of the heel combined with application of a toe extension and protection can be an effective treatment.

Application of a toe extension or a glue-on rubber shoe is effective for many FDs of the DIPJ by increasing tension in the DDFT, although some clinicians and farriers do not agree that their use is always beneficial. Another useful purpose of toe extensions is protection of the toe and prevention of excessive wear in that region. Simple application of a shoe can provide adequate protection. The argument against toe extensions is that if the flexural deformity is secondary to a painful stimulus, further tension on the DDFT will exacerbate the pain. Some clinicians support elevation of the heel to reduce pain, encourage relaxation in the DDFT, and change the weight-bearing surface of the foot from the toe to the entire hoof wall. There is likely a subset of cases of DIP FDs that respond to a toe extension and another subset that respond to heel elevation. Another option involves a 2- to 3-degree wedge placed under the toe but not extending dorsally beyond the hoof wall. This has the effect of creating a lever arm without placing distractive forces on the dorsal hoof wall.

Surgical intervention is indicated in foals unresponsive to conservative treatment and in severely affected foals. Corrective trimming and application of a toe extension can be carried out when the foal is anesthetized or post-operatively. A desmotomy of the ALDDFT can be a very effective surgical treatment options but is not always a straight forward surgery and the ALDDFT can be larger than the DDFT in young horses. Ultrasound guided mapping of the borders with needles is a useful technique.

Acquired FDs in Mature Horses
This is a frequently overlooked condition in mature horses. They usually occur in the forelimbs but hindlimbs can be affected. This condition cannot be cured with farriery and shoeing and that overaggressive management with the erroneous idea to “correct“ the club foot will usually cause a clinical deterioration in these horses. Even though desmotomy of the ALDDFT has been described to treat this condition in adult horses, chances to achieve correction are guarded. Most horses are best managed conservatively by adhering to the following principles of hoof care and shoeing: keeping the angle between P3 and the ground constant, maximizing the area that contacts the ground, setting the point of breakover back palmar to the deformed dorsal hoof wall, preserving the sole horn under the tip of the distal phalanx, and in, some cases, using rocker shoes. Cases in the hindlimbs of mature horses involving chronic pathology of the ALDDFT more commonly result in a flexural deformity of the DIP joint but the MTP joint can also be involved. In the diagnostic work-up, ultrasonography of the ALDDFT is indicated because thickening of this ligament from desmopathy is commonly detected in these horses. The ALDDFT of the hindlimb is much less prominent than that of the front limb but is always present. Injuries of the ALDDFT of the hindlimb occur mainly in middle-aged horses and can lead to lameness and/or flexural deformity of the DIPJ that can be accompanied by flexural deformity of the MTPJ. Performing a desmotomy or desmectomy of the ALDDFT in the hindlimb to treat adult horses with a flexural deformity secondary to desmopathy of the ALDDFT is associated with a guarded prognosis with 90% remaining lame and only a minority regaining a normal posture in one study.