Page 473 - Adams and Stashak's Lameness in Horses, 7th Edition

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CHAPTER

Lameness of the Distal Limb

NAVICULAR REGION/PALMAR FOOT

Randy B. EgglEston and gaRy M. BaxtER

NAVICULAR SYNDROME/DISEASE
However, a significant number of affected horses had
Navicular disease or syndrome remains one of the normal radiographic findings, which led to the suspicion
most controversial and common causes of intermittent of soft tissue injuries, giving rise to the term navicular
forelimb lameness in horses between 4 and 15 years of syndrome. 2,100,101 Many horses with bilateral foot pain
age. 35,115,121 It is estimated that the syndrome is responsi- have concurrent soft tissue and navicular bone abnor-
ble for one‐third of all chronic forelimb lameness in malities, also suggesting that navicular syndrome may
horses. 23,115 Quarter horses, Thoroughbreds, and be more appropriate in the majority of horses. The term
Warmbloods, particularly geldings, appear to be at “palmar foot syndrome” has also been recommended
greatest risk, whereas the syndrome is rarely diagnosed based on the variety of pathological entities that can be
in ponies or Arabian horses. 35,115 A recent study that identified in lame horses that improve following PD
evaluated a large population of horses with foot lame- anesthesia (Box 4.1). 35,46,96 This diagnosis seems most
ness in the United Kingdom also indicated that there appropriate for those horses that do not have definitive
was increased risk of foot pain associated with breed, navicular bone involvement or disease. Making a diag-
occupation, age, and body weight–height ratio. The nosis of navicular syndrome or palmar foot syndrome is
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disease has been shown to have a hereditary predisposi- a bit arbitrary, but it avoids labeling horses as having
tion possibly due to limb conformation of the horse or navicular disease when the lameness could be due to
to the specific shape of the navicular bone. 12,30,31 The many other sources in the foot. As our imaging capabili-
shape of the proximal border of the navicular bone has ties have improved, there has been a growing apprecia-
been determined to be inherited in Dutch Warmblood tion for the variety of soft tissue abnormalities that are
horses, and horses with an undulating or concave proxi- associated with palmar foot lameness, with or without
mal border are more predisposed to the disease. 30,31,96 concurrent navicular bone involvement. 39,100,101
Other factors such as faulty conformation, hoof imbal- Navicular disease/syndrome has been defined as a
ances, improper or irregular shoeing, and exercise on chronic forelimb lameness associated with pain arising
hard surfaces are also believed to predispose and aggra- from the navicular bone and closely related structures
vate the condition. 88,115,121 Although the hindlimbs can including the collateral suspensory ligaments (CSLs) of
be affected, it is rare, and navicular disease is primarily the navicular bone, distal sesamoidean impar ligament
considered a problem of the forelimbs. (DSIL), navicular bursa, and the deep digital flexor ten-
There is some debate as to the proper nomenclature don (DDFT). 35,36,42,100,101 Horses with primary DDF tend-
to use when diagnosing a horse that blocks to palmar initis within the foot are usually not considered to have
digital (PD) anesthesia. The early diagnosis of navicular navicular disease/syndrome. The disease is character-
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disease (“disease” implies a specific sign or symptom ized by degenerative changes in the structure, composi-
and a specific location) was based on abnormalities pre- tion, and mechanical function of the cartilage,
sent on the navicular bone seen radiographically. subchondral bone, and surrounding soft tissues of the

Adams and Stashak’s Lameness in Horses, Seventh Edition. Edited by Gary M. Baxter.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/baxter/lameness
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