Page 581 - Adams and Stashak's Lameness in Horses, 7th Edition

Lameness of the Distal Limb 547

Apical, articular abaxial, and basilar fractures Fractures of the sesamoid (typically axial) that occur
involving less than one‐third of the sesamoid bone in conjunction with fracture(s) of the metacarpal or
VetBooks.ir ment. 8,13,67,78,79,83,84,86,92 Nonarticular abaxial fractures identified with radiography because the prognosis for
metatarsal condyle are serious injuries that should be
are best treated by surgical removal of the frag-
may require removal, but horses often perform success-
returning to racing, even with repair of the condylar
fully without surgery. Midbody transverse fractures fracture, is poor. These fractures are usually sagittal and
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affecting the middle third and basilar transverse frac- axial and occur due to extreme pulling on the intersesa-
tures of the proximal sesamoid bones have been treated moidean ligament when the condylar fracture displaces.
successfully with lag screw fixation or circumferential These fractures suggest significant soft tissue injury to
wiring to provide postoperative bone compression and the fetlock joint and that OA is likely to ensue regardless
immobilization. 8,39,54,76,102,104,105 Lag screw fixation has of treatment (Figure 4.129).
been shown to have superior results in comparison
with other surgical options. Ideally, the fragment
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should be in one piece and should involve at least 30% Prognosis
of the bone for use of screw fixation repair. Casting is The reported prognosis for apical sesamoid fractures
recommended after surgery because the forces to bend is good to excellent (88% of Standardbreds and 77%
104
or cyclically fail the screw at the fracture site are high, of Thoroughbreds return to racing), for abaxial frac-
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particularly if anatomic reduction was not complete. tures is good (71% of Thoroughbreds or Quarter horse
Bone graft can be inserted into the fracture site just racehorses returned to racing), for basilar fractures is
86
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prior to tightening the screw. Bony union is expected fair (50%–60% of Thoroughbreds return to racing),
within 6 months and return to training at about 9 and for midbody fractures repaired by either lag screw
months. The screw does not need to be removed, even fixation or circumferential wiring is fair (44%–60%
if it breaks, as long as it is not infected. Approximately return to performance). 39,54 However, repair of midbody
44% of horses repaired with a 4.5‐mm lag screw fractures using lag screws is thought to provide a more
returned to race in one study. 18 favorable prognosis. In addition, a recent study indi-
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Surgery is easily performed with the horse in lateral cated that the size of apical fractures does not appear to
or dorsal recumbency under general anesthesia. Surgical influence the prognosis in racehorses. Reports of
47
removal of apical sesamoid fractures smaller than one‐ conservative treatment options are not available for
third of the length of the bone can be performed by comparison, but generally it is presumed that the prog-
arthroscopy or arthrotomy through the palmar/plantar nosis is guarded to poor for either basilar or midbody
recess of the fetlock joint. Arthroscopy offers the advan-
tage of more precise dissection and a faster return to
performance for small articular fractures without sus-
pensory involvement (3 weeks) and the ability to remove
more than one fracture from a joint with minimal inci-
sional morbidity. Lag screws are best directed from a
distal to proximal direction.
For basilar fractures, the arthroscope is similarly
placed in the fetlock recess, but the instrument portal
must be made into the distal fetlock recess such that
instruments can be placed parallel to the base of the
sesamoid. Abaxial fragments that lie entirely on the
basilar aspect (nonarticular) of the sesamoid bone can-
not be reached by any arthroscopic approach and must
be removed by incision directly over the fragment. Most
of these fractures do not need to be removed and heal by
fibrous union. Removal of nonarticular basilar fractures
can be performed between the DSLs for smaller frag-
ments or through the tendon sheath, and using intra-
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operative ultrasound to help locate these fragments has
been reported to be beneficial. 5
Biaxial midbody sesamoid fractures are a common
cause of breakdown in the Thoroughbred and Quarter
horse racehorse. 7,46,77 Due to the fact that the suspensory
apparatus is lost and distal limb vascular supply may be
disrupted, management is directed toward immobilizing
the fetlock joint for a sufficient time period to stabilize
soft tissue damage. Treatment options include surgical
arthrodesis or conservative ankylosis, although many of
these horses may be humanely euthanized. A major
complication to this “breakdown” injury is supporting
limb laminitis in the contralateral weight‐bearing limb.
See the section on traumatic suspensory rupture for Figure 4.129. Axial sesamoid fracture (arrows) in a horse with a
more information. lateral condylar fracture. Source: Courtesy of Dr. Wes Sutter.