Fractures of the distal phalanx (also known as the third phalanx, pedal bone, or coffin bone) are not uncommon in horses. They are named on the basis of their configuration and whether they exit through the distal interphalangeal joint (DIP joint), or coffin joint. Distal phalanx fractures can occur in forelimbs or hindlimbs after a concussive injury during exercise or turnout. They can occur in hindfeet if the horse kicks a wall or other solid structure.
Horses with distal phalanx fractures may have mild to severe lameness of the affected limb. Most affected horses have sensitivity to hoof testers, and horses with more severe fractures may resent tapping on the hoof wall with hoof testers. In horses with mild to moderate lameness, diagnostic analgesia of the palmar or plantar digital nerves usually localizes the lameness to the foot.
Radiography is typically used to identify the fracture (see articular fracture image), and multiple projections may be needed for identification and full evaluation. In some cases of severe lameness in horses (lameness at the walk or non-weight-bearing lameness) and when the extent of the fracture line (or lines) is hard to evaluate, CT may be needed to help determine treatment and prognosis.
Courtesy of Dr. Valerie J Moorman.
For horses with distal phalanx fractures that do not involve the joint (nonarticular fractures), conservative treatment with an extended period of rest and confinement (often approximately 6 months) and support of the hoof can result in a good longterm outcome. Hoof support with either a foot cast or a bar shoe with a rim or multiple clips can prevent expansion of the hoof, stabilizing the healing fracture.
Fractures are likely to heal with a fibrous union and may be evident on radiographs even after the horse regains soundness.
Fractures that involve the DIP joint tend to have better outcomes if they are treated surgically.
Smaller articular fractures that occur at the extensor process can be removed arthroscopically.
Larger fractures may be amenable to fixation using the lag screw technique, which can compress the fracture. Surgical compression of these fractures with a lag screw requires an approach through the hoof wall, increasing the risk of infection, which can develop months after surgery. Infection may necessitate screw removal after the fracture heals.
Both small and large articular fractures can also lead to the development of osteoarthritis of the DIP joint, which may require longterm treatment.
Fractures that are comminuted and also involve the DIP joint have the worst prognosis compared with other types of distal phalanx fractures. Horses with these fractures tend to be more lame, and comfort can be hard to achieve because of the fracture instability. In addition, these fractures are too complex for lag screw fixation. In these cases, euthanasia may be necessary.
See Regional Anesthesia in Horses for discussion of specific anesthetic techniques used to localize lameness.
