Page 132 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

Musculoskeletal system: 1.3 The foot 107

VetBooks.ir of the navicular bone, identified on MR images. into the DIP joint or navicular bursa improves lame-
ness in mild to moderately affected horses for 2–6
Most of these horses become sound with 2–3 months
of stall rest with controlled hand walking.
Trimming is directed at improving the dorso- months. Intrabursal injection results in twice as
many horses becoming sound for approximately dou-
palmar and mediolateral hoof balance. There is no ble the time compared with intra-articular medica-
universal shoeing solution for navicular disease and tion. Repeat intrabursal injection of corticosteroids
it is important to try and meet the needs of the indi- appears to result in progressively shorter periods of
vidual horse. This may require some trial and error, remission of lameness and may lead to progressive
but once a satisfactory solution is found, then every- degenerative disease of the DDFT. An ultrasound-
thing should be done to maintain the equilibrium guided lateral injection technique has been devel-
and further shoeing changes can be detrimental. oped to avoid penetration of the DDFT with each
Potentially successful shoeing modifications include injection.
rolling of the toe, elevation of the heels and extend- Desmotomy of the collateral sesamoidean liga-
ing the ground surface contact with an egg-bar shoe. ments appears to have fallen out of favour, probably
Heel elevation by 6° was found to reduce the forces because of the unpredictable results and the high
acting on the navicular bone by 24%, but it may rate of recurrence of lameness around 6–12 months
increase impact forces on the heel during landing of after surgery. Palmar digital neurectomies are usu-
the foot and promote further heel collapse. Wedge ally effective for 1–2 years. They should be avoided
heel shoes or wedge pads are therefore generally in horses with core lesions and parasagittal tears of
considered to be only temporary aids. Egg-bar shoes the DDFT because of the high risk of recurrence of
have been shown to alter the rate of bone turnover lameness following return to normal exercise due to
in navicular bones and to be clinically effective in proximal extension of the tendon lesion. Progressive
reducing pain arising from the navicular apparatus. deterioration of pre-existing tendon damage due to
An egg-bar shoe has been considered the equivalent pain-free exercise may also lead to catastrophic ten-
of a 6.2° heel elevation when the horse is working on don rupture following neurectomy.
a normal arena surface.
Medication with oral phenylbutazone or other Prognosis
NSAIDs on an as-needed basis is helpful to main- If therapeutic shoeing and medical management
tain horses in regular daily exercise and appears to are insufficient to return a horse to its prior perfor-
be beneficial, but their use is highly restricted by mance, the horse may be returned to a lower level of
competition regulations. exercise or competition. Alternatively, a palmar digi-
The use of isoxsuprine (a vasodilator) may be tal neurectomy may be performed in horses in which
effective in milder cases. Its use is controversial, the intractable pain is not associated with pathology
as some controlled studies and anecdotal evidence of the DDFT and the rider is experienced.
suggest it improves lameness in some horses, while
other evidence suggests it is not absorbed and does FRACTURE OF THE DISTAL
not improve blood flow to the foot. Calcium dobesi- SESAMOID OR NAVICULAR BONE
late is a synthetic venoactive drug that has been used
experimentally to reduce venous congestion in sub- Definition/overview
chondral bone of arthritic joints. A recent pilot study The distal sesamoid bone usually fractures para-
suggested a beneficial effect on lameness in horses sagittally, approximately 1–2 cm medial or lateral
with high fluid signal in the spongiosa of the navicu- to the sagittal ridge. Fractures may be simple or,
lar bone, but further research is needed. rarely, comminuted. Comminuted fractures tend to
Tiludronate and clodronate are bisphosphonates be displaced. Congenital, non-fused centres of ossi-
that are widely used to treat navicular disease despite fication of the navicular bone may be confused with
the relative lack of data on their efficacy. Injection of a parasagittal fracture. The navicular bone may
corticosteroids, with or without sodium hyaluronate, have two (bi-partite) or three (tri-partite) separate