Page 501 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Distal Limb 467

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A B

Figure 4.32. Small (A) and large (B) type IV P3 fractures involving the extensor process.

Figure 4.33. CT image of a type V comminuted fracture of P3.
Fracture lines were present on both the lateral and dorsoplantar
radiographs. Figure 4.34. Type VI fractures are also referred to as solar
margin fractures of P3 (arrow).
with ossified ungual cartilages and a P3 facture found
that all fractures occurred at the base of the ossified car- relatively young horses, and can be observed radio-
tilage suggesting a biomechanical cause or focal stress graphically as an incidental finding in horses that are
point from cycling. The fractures involved only one of clinically normal (Figure 4.32). 9,15,30
57
the lateral processes and were articular.
Type IV extensor process fractures may occur due to
excessive tension on the common digital extensor ten- Clinical Signs
don, resulting in an avulsion fracture. Overextension of Generally the clinical signs are similar during the
the DIP joint may cause contact of the extensor process acute phases for all types of P3 fractures. A history of an
with the middle phalanx, and trauma to the dorsal acute onset of a moderate to severe lameness (grade 4–5
aspect of the foot has also been proposed as a cause. 30,62 out of 5) is common. In some cases the lameness will
5,6
The development of a separate center of ossification or worsen within the first 24 hours after injury, presumably
an osteochondrosis lesion of the extensor process may due to increased pressure within the hoof capsule sec-
also occur. 30,56,62 Supporting a theory of a developmental ondary to inflammation and swelling. Exceptions to this
lesion is the fact that lesions are often bilateral, occur in are solar margin fractures, type VII fractures in foals,