Page 8 - Equine Matters - Spring 2011

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S P L I N T B O N E S
Veterinary Surgeon
Ben Sturgeon
XLVets Practice
Castle Veterinary
Surgeons, Durham
7
EQUINE MATTERS
M
etacarpal and metatarsal bones II and IV (splint bones) are rudimentary ancestral structures found
pairing each cannon bone. Anatomically the bones support the lower rows of hock and knee bones
and are attached to the cannon by a thin interosseous ligament. Fractures of the splint bones are a relatively
common injury. They may result from direct external trauma (usually kicks) but may also be secondary to
abnormal internal forces, most commonly associated with suspensory ligament desmitis (swelling of the
ligament), particularly in horses that race over fences.
Splint Bone Fractures
Ben Sturgeon BVM&S, BSc, CertEP, MRCVS
Castle Veterinary Surgeons
The fractures can theoretically occur on any
of the splints, although those associated with
internal forces are more commonly found in
the forelimbs, with the left fore being more
frequent on the outside splint and the right fore
on the inside splint. This may be associated
with counter-clockwise work (most research has
been carried out in racing Thoroughbreds)
resulting in increased loading on these areas.
Here the distal ends of the splints attach to the
proximal sesamoid bones by fibrous bands
which may stretch during fetlock hyper or
overextension commonly when the leg is fully
weight bearing and the fetlock is at its lowest
point of the stride. This resulting ‘tug of war’
stresses the attachments predisposing to fracture
generally in the lower third of the bone.
Suspensory desmitis may also precede or go
hand in hand because of similar stresses being
placed on the structure, the resultant swelling
creating a ‘bowstring’ effect from the enlarged
suspensory leading to a progressive deviation
of the splint away from the cannon. Poor
knee and/or foot conformation will further
exacerbate or predispose to the condition.
Kicks are the more common presentation with
wounds often being open and discharging
with heat and swelling and the horse will
be obviously and acutely lame. Occasionally,
a chronic low grade lameness or discharging
tract are found weeks after a trauma which
prompts investigation and the finding of
a fracture.
Irrespective of the aetiology, wound assessment
and classification of the fracture itself, along
with any potentially involved surrounding
structures are vital before any treatment is
discussed and implemented. This is primarily
achieved by radiographic evaluation combined
with ultrasound of the ligamentous attachments.
X-rays will invariably reveal the fracture often in
pieces (comminution) although the basic axial
alignment of the bone and fragments is still
usually present, the presence of infection,
displacement of the fractured portion and
involvement of the cannon can also be
discerned. Furthermore, x-rays may reveal
pre-existing abnormalities of the splints (callus
formation) suggestive of long-term suspensory
ligament problems.
Irrespective, the first and most important
consideration to be made (from the
radiographs) is whether the affected splint
is stable or not. Fractures of the upper portion,
invariably due to kicks, may result in instability
of the carpus or hock (particularly of the inner
splints of the forelimbs), long term resulting in
interosseous ligament damage, osteoarthritis
of the joints or even avulsion (dislocation) of
the upper portion of the splint. In such cases
surgical fixation would be necessary to fix
the splint to the cannon bone using a
combination of screws and steel plate (figures
1 and 2.) Where infection is present or
suspected, fixation techniques may be
withheld until the infection is cultured and
resolved by use of appropriate antibiosis.
Figure 1: Fractured head of splint
Figure 2: Post-operative radiograph
following stabilisation