Navicular syndrome is a degenerative disease complex of horses that can encompass injuries to any of the structures within the navicular apparatus of the foot, including the navicular bone, navicular bursa, collateral sesamoid ligaments, distal impar ligament, or deep digital flexor tendon. Certain breeds are predisposed, and the condition is almost always bilateral. Diagnosis is based on clinical signs and evidence from radiographic or advanced imaging techniques. Treatment is palliative and relies on corrective farriery, intrasynovial medication, and NSAIDs. The condition is progressive, and the prognosis is guarded to fair.
Navicular syndrome is a degenerative condition of horses that affects any of the structures of the navicular apparatus. It is a very common cause of bilateral forelimb lameness in middle-aged horses. American Quarter horses, Thoroughbreds, and warmblood breeds are the most commonly affected breeds.
Etiology and Pathophysiology of Navicular Syndrome in Horses
Although the exact pathophysiology of navicular syndrome is unknown, multiple compounding forces within the navicular region are thought to play a role.
Horses that have narrow, upright feet with contracted heels and small, narrow frogs are the most commonly affected.
Horses with small hooves may also have larger bodies and thus are predisposed to this condition because of the high loads concentrated in their small feet.
Poor distal limb or hoof conformation, hoof imbalances (long toes or low heels), and poor hoof management or inappropriate shoeing (use of too small a shoe) are also thought to be predisposing factors.
In warmblood breeds, navicular syndrome also has a genetic component.
Clinical Findings and Diagnosis of Navicular Syndrome in Horses
Clinical signs
Radiography, CT, or MRI
Navicular syndrome is most commonly a bilateral forelimb lameness that can vary in intensity from mild to moderate to severe, and usually one forelimb shows more lameness than the contralateral limb. Horses with navicular syndrome may demonstrate a shortened stride, overt lameness, a shuffling gait, or stumbling.
Courtesy of Dr. Ronald Green.
Courtesy of Dr. Valerie J. Moorman.
It is not uncommon for owners to think that the lameness in navicular syndrome originates from the shoulder. Many horses with the disease demonstrate hoof tester sensitivity in the heel or across the frog. Some horses are positive to distal limb flexion, and many show exacerbation of lameness if made to stand on a toe wedge. The lameness most commonly shows marked improvement after a palmar digital nerve block, after which lameness in the contralateral forelimb often becomes apparent.
Diagnosis of navicular syndrome in horses is often supported by diagnostic imaging. Radiographic changes include osseous cystlike lesions, enlarged or numerous vascular channels at the distal margin (see enlarged vascular channels image), medullary sclerosis, enthesiophytes at the proximal margin, distal border fragments, or flexor cortex erosions (see navicular bone degeneration image). Horses that do not have notable radiographic changes may still have soft tissue injuries associated with the navicular apparatus.
Ultrasonography of the distal aspect of the pastern region between the heel bulbs can be used to image the proximal aspect of the navicular bursa. Ultrasonography through the frog can be used to image the distal aspect of the navicular bursa. However, the utility of ultrasonography for diagnosing navicular syndrome in horses is low, particularly with the advent of widely available advanced imaging techniques.
MRI delineates lesions within all structures of the podotrochlear apparatus and provides a comprehensive definition of each individual case. CT is also useful for the diagnosis of navicular syndrome; however, it provides less detail than MRI provides.
Treatment and Management of Navicular Syndrome in Horses
Trimming and shoeing changes
NSAIDs
Bisphosphonates
Intra-articular corticosteroids or biologics
Navicular bursoscopy and neurectomy of the palmar digital nerves
There are numerous treatment options for horses with navicular syndrome, which can be broken down into conservative (medical) management and surgical management.
Conservative (Medical) Management
Often the first conservative treatment of navicular syndrome in horses is to make shoeing changes (eg, rolling or rockering the toe of the shoe, or mounting the shoe more palmarly on the foot to decrease the breakover distance). Other conservative management methods include the following:
a regimen of rest
systemic NSAIDs such as phenylbutazone or firocoxib
intrasynovial injection of the distal interphalangeal joint (DIP joint) or navicular bursa with corticosteroids (triamcinolone acetate or betamethasone acetate) with or without the addition of hyaluronic acid
systemic bisphosphonates (tiludronate disodium or injected clodronate)
extracorporeal shock wave therapy
The injection of biologics such as mesenchymal stem cells, autologous conditioned serum, and platelet-rich plasma has been used in some cases with soft tissue lesions in the navicular region.
Surgical Management
Surgical treatments of navicular syndrome in horses include navicular bursoscopy and neurectomy of the palmar digital nerves.
Navicular bursoscopy can be used to debride dorsal tears of the deep digital flexor tendon (DDFT) or flexor cortex erosions on the navicular bone, and to break down adhesions within the proximal aspect of the navicular bursa.
Neurectomy of the palmar digital nerves is reserved for cases in which medical management has failed and there is no notable damage to the DDFT. If the DDFT shows appreciable injury, neurectomy of the palmar digital nerves can result in the horse overusing the limb, and potential rupture of the DDFT; thus, MRI evaluation is preferred before a neurectomy is performed.
Because nerves can regrow, horses treated with neurectomy eventually demonstrate a return of lameness, usually 1–2 years after surgery. Other potential complications of this surgery include the development of a painful neuroma and infection of the foot that can go unnoticed because of the horse’s lack of foot sensation. Owners of horses that undergo neurectomy should be instructed to closely monitor the horse’s feet, and many horses benefit from being shod with full pads.
Because clinical signs of navicular syndrome tend to progress, lifelong treatment is often necessary, and some horses fail to respond positively to treatment as the disease progresses.
See Regional Anesthesia in Horses for discussion of specific anesthetic techniques used to localize lameness.
Key Points
Navicular syndrome is a common cause of bilateral forelimb lameness in middle-aged horses. Many horses have pain in the heel region, which can be elicited by hoof testers. Most horses show marked improvement in lameness with a palmar digital nerve block.
Many treatments are available. The most common are shoeing changes, rest, systemic anti-inflammatory drugs, and medication of synovial structures (distal interphalangeal joint or navicular bursa). Treatment is usually lifelong.
Navicular syndrome is a degenerative condition, and although many horses respond positively to treatment, they may fail to improve with time.
For More Information
Baxter GM, ed. Adams and Stashak’s Lameness in Horses. 7th ed. Wiley-Blackwell; 2020.
Also see pet health content regarding navicular disease in horses.
