Page 130 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.3 The foot 105

VetBooks.ir may be seen to point one foot or to heap up the bed- of navicular disease. A negative response to analge-
sia of the DIP joint and the navicular bursa makes it
ding to stand with the heels elevated, although these
features may be more typical of deep digital flexor
tendinopathy. unlikely that a lame horse has navicular disease.
Even though radiographs are too insensitive
The trot is bilaterally short-strided, with a short- to detect early bone or any soft-tissue or cartilage
ened cranial phase and the foot lands toe first. change, they remain the main diagnostic tool in
Lameness is mostly bilateral, but one limb is gener- practice to demonstrate morphological changes in
ally more painful than the other, which results in a the distal sesamoid bone and adjacent structures
visible head nod. Lameness is worse on hard ground (Figs. 1.184–1.187). However, radiography only
and on circles, especially when the lame limb is on the allows the recognition of advanced bone disease.
inside. Lameness may switch between limbs when a A minimum of three high-quality radiographic projec-
horse is exercised in different directions on a circle tions are required: a 60° dorsoproximal/palmarodistal
or following nerve blocks. Distal limb flexion tests
may be positive in the flexed limb or, occasionally,
the horse may trot off worse in the stance limb, pre- 1.184
sumably due to increased loading. Hyperextension
of the DIP joint with a wooden wedge or board (toe
elevation test) may also increase the severity of lame-
ness but the sensitivity and specificity of this test are
low for early disease. Heat, pain or swelling is not
present. The response to application of hoof testers
is generally unremarkable, except when the testers
are applied across the middle third of the frog in
some small footed horses. Pain may also be elicited
with hoof testers if navicular disease is accompanied
by poor foot balance. 1.185

Differential diagnosis
Any chronic bilateral forelimb lameness including
bruising, pedal osteitis, collateral desmitis and DIP
joint pain. Any source of chronic pain originating
from the heels including tendinopathy of the DDFT Figs. 1.184, 1.185 Dorsoproximal/palmarodistal
and collapsed, underrun and sheared heels. (1.184) and palmaroproximal/palmarodistal oblique
radiographs (1.185) demonstrating an increase in
Diagnosis number and size of the distal nutrient foramina/
A clinical diagnosis of navicular disease can only be synovial invaginations.
made if lameness is significantly improved or abol-
ished by a palmar digital nerve block, intra- articular 1.186
analgesia of the DIP joint and analgesia of the navic-
ular bursa, although many horses with deep flexor
tendinopathy will share the same blocking pattern.
Approximately 20% of horses with navicular disease
will be much improved or sound following intrabursal Fig. 1.186 Palmaroproximal/palmarodistal oblique
analgesia after they have first failed to improve to radiograph showing loss of the corticomedullary
intra-articular analgesia of the DIP joint. This means junction, increased radiodensity of the medullary
that a negative response to intra-articular analgesia cavity and erosion of the palmar cortex of the distal
of the DIP joint does not always exclude a diagnosis sesamoid centred on the sagittal ridge.