Page 578 - Adams and Stashak's Lameness in Horses, 7th Edition

544 Chapter 4

Severe fractures involving the sesamoid bones and
metacarpophalangeal/metatarsophalangeal joints are
VetBooks.ir injuries in racing Thoroughbreds and Quarter
one of the most common types of fatal musculoskeletal
In a recent study in Thoroughbred race-
horses.
7,46,68,77
horses, fractures of the proximal sesamoid bones repre-
sented 55% of all catastrophic fractures, while the most
common noncatastrophic fractures involved the carpus
and first phalanx. 91
Fractures of the apical portion of the sesamoid bone
are the most common, comprising more than 88% of
sesamoid fractures. In Thoroughbred racehorses 2 years
or older, 64% involve hindlimbs and 36% forelimbs.
78
Sesamoid fractures are most common (53.4%) in 2‐
year‐olds, and then 3‐year‐olds (23%). 78,79 Apical frac-
tures are frequently articular, singular, rarely comminuted
and usually involve less than one‐third of the bone
(Figure 4.125). Apical fractures occur most frequently in
the lateral sesamoid bone of the left hindlimb (42.8% of
fractures) compared with the right hindlimb (36.6%) in
Standardbreds, whereas a more equal distribution is
observed in Thoroughbreds.
Basilar fractures are less common (6% of sesamoid frac-
tures in Standardbreds). They represent an avulsion frac-
ture associated with the DSLs and may be comminuted.
These fractures are more common in the Thoroughbred
than in the Standardbred and can be small articular, trans-
verse articular, or nonarticular (Figure 4.126). 15,84,92
Abaxial fractures are uncommon in Standardbreds
(3%), and more common in Thoroughbreds and Quarter
horses. 84,92 These fractures can either be articular or
nonarticular and can be difficult to diagnose and may
require an additional tangential projection on the radio-
graphic examination to identify their exact location, or Figure 4.126. DP radiograph of a Thoroughbred racehorse with
they can be identified on the dorsopalmar/plantar a thin fracture of the base of the proximal sesamoid (arrow). Also
projection. 8,66 note the other degenerative changes present in the fetlock (marked
Midbody transverse sesamoid fractures are seen most sclerosis of the palmar condyles of the distal third metacarpal bone,
frequently in Thoroughbreds, older Standardbreds remodeling of the fetlock joint space; primarily on the side of the
(mean age 6.5 years), and young foals under 2 months base sesamoid fragment).

A B
Figure 4.125. (A) Oblique radiograph of a Standardbred racehorse with a large, displaced apical sesamoid fracture (arrow).
(B) Arthroscopic image of a horse with a large apical sesamoid fracture (arrows are fragment; arrowheads are fracture line).