Page 125 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

100 CHAPTER 1

VetBooks.ir osseous trauma, and even fracture, of the distal pha- early phase of ossification or in the presence of
stress injury or fracture of the distal phalanx, at the
lanx at the base of the ossified cartilage (see Collateral
base of the sidebone. Lameness may also be seen
ligament injury and Fractures of the distal phalanx).
following direct injury to a sidebone, with or with-
Clinical presentation out fracture.
Sidebone is usually an incidental finding on physi-
cal examination or radiography of the foot. Rarely, Differential diagnosis
horses with sidebone present with lameness in the None.

Diagnosis
1.173 The ungual cartilages are readily palpated immedi-
ately proximal to the coronet in the palmar half of
the foot. With marked ossification, the cartilages
are not as flexible as normal, although palpation
alone is unreliable at confirming sidebones. Under
rare circumstances in which the ossified ungual
cartilage is fractured, local heat, swelling and
pain on palpation can be expected. Ossification of
the ungual cartilages is readily identified on dorso-
palmar and lateromedial radiographs (Figs. 1.173,
1.174). Fractures of the distal phalanx or the
sidebone itself may only be visible on dorsolateral/
palmaromedial or dorsomedial/palmarolateral
oblique views, with the foot either weight bearing
1.174 or in flexion on a Hickman block. Separate centres
of ossification must be distinguished from frac-
tures. If an ossified ungual cartilage is considered
to be the source of the pain causing lameness, the
axial nature of the pain can be confirmed with a
uniaxial palmar digital nerve block. Ossification
of an ungual cartilage usually results in increased
radionuclide uptake during scintigraphy, more so
near the base than further proximally. Injury to
an ossified ungual cartilage or to the distal pha-
lanx at the base of a sidebone, resulting in lame-
ness, presents a much higher radionuclide uptake
in comparison with the contralateral unaffected
sidebone or the sidebones in the contralateral foot.
MRI is required to confirm the presence of osseous
trauma of the distal phalanx, or a stress fracture or
a collateral ligament injury related to the ossified
Figs. 1.173, 1.174 Sidebone. Lateral (1.173) ungual cartilage. Osseous trauma is characterised
and dorsoproximal/palmarodistal oblique (1.174) by the presence of marked bone oedema and scle-
radiographs of bilateral ossification in a non-lame rosis in the distal phalanx as well as the presence
horse. Note that in 1.174 the radiolucent line going of an incomplete or complete fracture line at the
through the base of the sidebone is an area of non- base of the ossified cartilage (see Fig. 1.164). In
fusion. In a lame horse it could be a fracture. some horses with foot lameness, MRI has shown