Page 562 - Adams and Stashak's Lameness in Horses, 7th Edition

528 Chapter 4

oriented lateral to the midline in the forelimb. This may
be due to a smaller lateral articular surface of P1 in the
VetBooks.ir position of the center of the sagittal groove lateral to the
forelimb compared with the hindlimb. The consequent
17
midline may dictate that fractures propagate down that
side of the bone in the forelimb. In contrast, sagittal
fractures that extend distal or medial to the midline are
approximately twice as common in the hindlimbs as in
the forelimbs. The relationship between the slope of
17
the proximal and distal articulations of P1 may also
account for the different fracture configurations between
the fore‐ and hindlimb. 17
Parasagittal P1 fractures in the athletic horse may
occur as part of a chronic pathological process character-
ized as bone maladaptation or fatigue‐type fractures. In
support of maladaptation etiopathogenesis, P1 fractures
can occur during normal events without unusual trauma,
at a consistent and site a specific location along dorso-
proximal P1 with repeatable configurations and with
prodromal signs such as periostitis. These so‐called
fatigue fractures are usually only seen in performance
horses and often represent an area of bone weakness
related to stress remodeling. As microdamage accumu-
lates from repetitive loading of P1, the bone weakens or
“fatigues,” predisposing to fracture. This same scenario
can occur in multiple locations in performance horses
(humerus, metacarpus, tibia, pelvis, etc.). Radiographically
silent short incomplete parasagittal P1 fractures have
been seen on MRI and scintigraphy, 51,53 and these may
Figure 4.107. Lateral radiograph of the fetlock demonstrating a precede the development of a radiographic apparent sag-
fracture of the palmar eminence of P1. This fracture was an acute ittal P1 fracture or may predispose to a comminuted
injury and was repaired by lag screw fixation. Smaller, chronic fracture. Stress fractures tend to occur most commonly
fractures are more common in this location and are often removed if in the midsagittal groove at the proximal aspect of the
they are problematic. bone, the same area where most P1 fractures originate.

A B
Figure 4.108. Lateral (A) and dorsopalmar (B) radiographs of a horse with a severely comminuted fracture of P1. Internal fixation is not
possible with these types of fractures, and transfixation pin casts or external fixators are usually used to attempt salvage of these horses.