Distal phalanx: Solar margin fractures

Solar margin fractures do occur regularly and are underdiagnosed. Direct or blunt trauma, possibly caused when the horse kicks a hard, immobile object, are common causes of solar margin fractures.

In the spring of the year in some climates, when freezing and thawing produces hard uneven ground in the mornings, these fractures are prone to occur. These fractures can also develop as a result of chronic laminitis at the dorsal rim.

The fractures develop in different sizes and at different locations along the solar rim.

Occasionally an abscess may develop that eventually will drain through the sole. Through this an initially sterile abscess will become infected. During the process of abscess formation the lameness becomes more severe but once draining starts, the pressure is relieved and the lameness decreases. Gas pockets on the radiographs are indicative of disruption of the sole.

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.

Clinical signs

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.

Imaging

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.