Page 561 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Distal Limb 527

Thoroughbreds. 17,27,38,69 Dorsal frontal fractures are rel-
atively rare but usually occur in the hindlimb.
3
VetBooks.ir ing Thoroughbreds and Standardbreds. In a recent
Comminuted P1 fractures also occur commonly in rac-
report, 72% of horses with comminuted P1 fractures
32
sustained the injury during racing or race training.
However, comminuted P1 fractures may occur in other
types of performance horses (especially western perfor-
mance or polo) and may occur in any horse at pasture or
at exercise from a single traumatic event. 32,38 In one
report 27% of the horses sustained a comminuted frac-
ture while at pasture, and a smaller percentage devel-
oped the fracture while being used for showing or
pleasure riding. In a more recent report, 28% of all
38
comminuted P1 fractures were from nonracing causes. 32
Etiology
It appears that a combination of longitudinal com-
pression in conjunction with asynchronous lateral to
medial rotation of P1 or twisting of P1 in relation to the
metacarpus/metatarsus may be the cause of some frac-
tures. During normal weight‐bearing, the convex sagit-
tal ridge of the distal end of the third metacarpal or
metatarsal bone fits into the concave groove in the prox-
imal surface of P1. If this alignment is not perfect, the
convex sagittal ridge may act as a wedge to create the
fracture. Also, during limb flexion, there is a lateral to
medial rotation of P1 around its long axis. If the rotary
movement is accelerated, as would occur if the foot
slips, a P1 fracture may result. In most cases, a combina-
Figure 4.105. Dorsopalmar radiograph of the pastern region tion of axial weight‐bearing and torsional forces usually
demonstrating a complete sagittal fracture of P1 that exists in the
lateral cortex. This fracture was repaired with three lag screws contributes to P1 fractures.
through an open approach to the fetlock joint. Source: Courtesy of Nearly all midsagittal fractures begin at the concave
Dr. Jeremy Hubert. groove of the proximal aspect of P1 and tend to be

A B

Figure 4.106. (A) Oblique view of an incomplete dorsal fracture of P1. (B) Lateral view of a complete dorsal fracture of P1 that exits the
dorsal cortex. Source: Courtesy of Dr. Julie Dechant.