There are three known etiologies for these fractures: hyperextension injury, avulsion by the extensor tendon, and a separate center of ossification (osteochondrosis, which usually occurs bilaterally).
Radiographic examples of a small chip (left) and a large, fresh fragment (right).
Frieshian horses are frequently presented with very large fragments. This fracture configuration is rarely seen in other horse breeds.
Fractures of the distal phalanx - all fracture types
Fractures of the distal phalanx are diagnosed in horses of all ages, even very young foals (see left side).
Fractures of the distal phalanx are caused by acute trauma, such as a kick toward a hard, non-movable object. Most often fast or excessive work induces fractures of the distal phalanx. Laceration of the hoof capsule may result in fractures as well. The forelimb is more commonly involved than the hind limb.
Overview of fracture types
The following fracture types have be classified:
I. Abaxial fractures without joint involvement II. Abaxial fractures with joint involvement III. Axial/sagittal and perisagittal fractures IV. Fractures of the extensor process V. Multifragment (comminuted) fractures VI. Solar margin fractures
In this presentation the management of the different fracture types will be discussed in ascending severity and descending prognosis as listed in the human fracture classification: VI, I, IV, III, II, V. Note: The numbering of the fracture types in the distal phalanx does not follow the human system, where the fracture are numbered in increasing severity and decreasing prognosis.
The patient usually shows an acute, moderate to severe lameness accentuated during turns. The hoof and distal phalangeal region are warm to the touch, and an increased pulse can be palpated over the palmar or plantar arteries. Pressure exerted with the hoof testers usually elicits a positive response. Arthrocentesis of the DIP joint results in a blood-tinged synovial sample when there is articular involvement. Signs are relieved by regional anesthesia of the distal phalangeal region. In the differential diagnosis, a hoof abscess should be considered.
Radiographs conﬁrm the diagnosis in most cases. Additionally, the irregular border of the distal phalanx and debris on the hoof capsule can make recognition of the fracture difficult. It is important to take several radiographs from different angles. Abaxial nonarticular fractures are usually difficult to recognize because they are normally only minimally displaced.
However, in the acute case it is occasionally difficult to detect a fracture line initially because of minimal displacement.
If no fractures can be recognized and the animal is “fracture-lame” localized to the distal phalanx, the animal should be placed in a box stall and the radiographs repeated after 7 to 10 days.
It is important to distinguish vascular channels from potential fractures. The presence of thin lines crossing vascular channels at different angles indicates a fracture.
Scintigraphy, computed tomography (CT), and magnetic resonance (MR) imaging are often successful in delineating an obscure fracture. CT and MR are especially useful to assess articular fractures and to identify displacement of the fragments.