Distal Phalanx (Plll) Fractures

Stephen E. O'Grady, DVM, MRCVS

Presented at the Equine Practitioners Group Congress in South Africa

Fracture of the distal phalanx is not an uncommon injury in equine practice. Although this fracture is most common in racehorses, it can occur in any breed. Causes could be racing on hard track, kicking an unyielding object, landing on blunt objects while exercising and penetration of the hoof by a foreign body. Other hoof problems such as pedal osteitis, bone infections, flat feet and improper trimming and/or shoeing may predispose the horse to this type of injury.

Classification:

Fractures of the distal phalanx have been classified according to their configuration.

The involvement of the coffin joint influences the outcome of the case and the future soundness of the animal. Fractures that involve the articular surface usually account for increased lameness, a longer length of convalescence and a poor prognosis for a return to full athletic ability. On the other hand, non-articular wing fractures carry a much better prognosis.

Diagnosis:

Affected horses will show a moderate to severe supporting limb lameness that is acute in onset. Trotting on a hard surface will generally accentuate the lameness. Increased digital pulse, sensitivity to hoof testers over the sole and swelling around the coronary band are noted. With time, the sensitivity of the hoof testers will become localized to the area of the fracture. Clinical signs are similar to those displayed by horses with a sub solar abscess or a severe sole bruise. Once the clinical examination has isolated a foot-related problem and no abscess is found, high quality radiographs are necessary to confirm the presence of a fracture. It is the author's opinion that digital nerve anesthesia should not be used prior to radiographs in acute lameness situations, even if clinical signs are minimal, as full weight bearing on the foot may cause the fracture line to increase in length, become comminuted, or cause non-articular fractures to become articular. Radiographic examination should consist of several views of the coffin bone. Several oblique views are often required to position the primary x-ray beam directly over the fracture site. When an articular fracture is suspected, this can be confirmed many times with a straight-on anterior-posterior view, which will reveal a "step" in the distal inter phalangeal joint as a result of the fracture. If the clinical signs indicate a possible fracture of the distal phalanx but the initial radiographs are negative, the horse should be stall confined for 7 to 10 days and subsequent radiographs may demonstrate the fracture line due to bone demineralization at the site of the initial injury. A Plll fracture can be diagnosed in the acute stage using nuclear scintigraphy if the initial radiographs are negative.

Treatment:

If the diagnosis is made quickly and appropriate treatment is initiated, most fractures in young horses less than a year old heal with resolution of the lameness. All types of distal phalangeal fractures described above can occur in foals and heal very nicely with no more than initial stall confinement and then controlled exercise until bony healing is complete.

In older horses with all types of fractures, basic therapy would consist of strict stall confinement, the judicial use of nonsteroidal anti-inflammatory drugs (NSAIDs) and therapeutic shoeing.

Surgical intervention consisting of internal fixation can be considered in type ll and III sagittal articular fractures. In these cases, a cortical bone screw is placed perpendicular to the fracture line.

Arthroscopic surgery can be useful to remove small bone fragments from the extensor process in type IV fractures. A larger fracture fragment involving the extensor process should be considered a candidate for internal fixation. Both of the above procedures can be performed through a small incision over the extensor tendon above the coronary band.

Nonsteroidal anti-inflammatory drugs should be given in such a dosage as to decrease inflammation but not entirely eliminate pain, as this may cause further damage at the fracture site and it may be difficult to evaluate the effectiveness of the surgery or the therapeutic shoe. If the fracture invades the joint, the administration of intramuscular Adequan? on a weekly basis would appear to be rational therapy.

Therapeutic Shoeing:

A Plll fracture can be stabilized in the acute stage through the use of 2 or 3-inch fiberglass casting tape, which is easily applied to the circumference of the outer hoof wall. A piece of felt is attached at the bulbs of the heels and the entire hoof is encircled with the casting tape. Caution is necessary because if the tape is left on too long. Marked contracture of the heels will take place.

Therapeutic shoeing consists of a full bar shoe with a continuous rim attached to the perimeter of the shoe, encasing the basal border of the hoof wall to prevent or limit expansion of the hoof wall, decrease the independent movement of the heels and provide stabilization to the third phalanx. This author is packing the solar surface of the foot with silastic material along with the continuous rim shoe for the following reasons. Firstly, when any form of restrictive shoe is applied to the outer hoof wall, the foot tends to contract, especially at the heels, over a short period of time. Solar/frog support in any form appears to lessen this process quite markedly. Secondly, the coffin bone descends in a distal palmar/plantar direction when weight is born on the limb with no form of support from the ground surface. Also, if the fracture is articular with the larger fragment being displaced ventrally, this added support may increase the stabilization in this direction. The full rim shoe is relatively easy to construct. Whatever type of bar shoe that is chosen should fit the circumference of the hoof in the quarter and heel area, but should be fit slightly full in the toe area. The shoe should extend beyond the heels to provide palmar/plantar support. A piece of aluminum foil acts as a template to construct the rim for the shoe. The template is fitted to the distal edge of the hoof wall and extends 1.5 inches past the widest part of the foot. The template is used to trace a pattern on a piece of 16 ga. metal that is then cut out, formed and welded to the shoe. The shoe is then attached to the foot using one or two mails on either side. When made properly, the rim will fit the perimeter of the foot and can be tapped gently in place with a hammer. The rim can also be fit so there is space present between the rim and the hoof wall. This space is then filled with an acrylic substance to provide a uniform fit. By mixing Technovet? hardener with Justi? powder the final solution is almost liquid and can be readily poured in the space between the rim and hoof wall. With the hoof off the ground, the rim is tapped gently into place while the solution hardens. Tightening the rim while the foot is non-weight bearing will minimize expansion when weight is again applied to the limb. The solar region is filled with firm impression material which, when completed, must be level with the ground surface of the shoe.

Recently this author as glued the shoes on a limited number of fracture cases. An aluminum straight bar shoe is fitted to the foot. The shoe is attached to the solar surface of the foot and the excess composite is used to create a rim around the perimeter of the foot. The results seem promising. One major advantage is that it provides a non-traumatic method to attach a shoe.

Marginal fractures (type V) occur at any site along the solar margin of the distal phalanx and are commonly secondary to another condition such as chronic sole bruising, pedal osteitis, chronic laminitis or osteomyelitis, which may all represent a type of avascular necrosis. In general, these solar margin fractures are not of primary concern themselves, but rather an indication of another underlying condition. These horses respond to shoeing with a wide web bar shoe that is well concaved (using a grinder) on the inner solar surface of the shoe.

Prognosis:

Non-articular wing fractures (type I) carry a good prognosis. With 3 to 6 months of stall rest and therapeutic shoeing, most of these horses can return to their former use. A few horses may require an ipsilateral palmar digital neurectomy to resolve any residual lameness. Articular wing fractures (type II) and midsagittal fractures (type lll) carry a guarded to poor prognosis, as many develop degenerative joint disease. Unsoundness remains even after extended periods of rest. Palmar digital neurectomies have been performed on these cases but because the articular surface of the join is involved, there usually incomplete resolution of the lameness following the surgery.