Navicular syndrome, once feared as a career-ending diagnosis, can now be managed more effectively, despite ongoing challenges.

In a 1989 study renowned equine sports medicine veterinarian Tracy Turner, DVM, Dipl. ACVS, Dipl. ACVSMR, partner in Turner Wilson Equine Consulting, in Stillwater, Minnesota, stated a stark statistic: “One can expect about 50% of horses diagnosed with navicular syndrome to be usably sound for one year after treatment, no matter what treatment is used. The disease is progressive, and affected horses eventually will need to be retired because of lameness.” If your own equine partner has recently been diagnosed with “navicular,” don’t panic just yet.

In this article we’ll cover the massive progress that’s been made in the past 35 years when it comes to managing navicular syndrome—a condition renamed podotrochlosis in that time frame. Despite diagnostic and therapeutic advancements, coping with a progressive disease for a horse’s entire life remains a significant challenge for horse owners and veterinarians alike.

The Plight of the Navicular Horse

A dreaded diagnosis amongst horsemen, navicular syndrome refers to inflammation and sometimes degeneration of the podotrochlear apparatus, which is located in the heel of the equine foot. Podotrochlosis became the anatomically correct term once practitioners understood this degenerative condition encompassed much more than the navicular bone itself.

In fact, anything in the horse’s heel is fair game—this includes the navicular bone, bursa, and associated ligaments, the coffin joint (where the coffin and short pastern bones meet) and its own collateral ligaments, and the distal (lower portion of the) deep digital flexor tendon, or DDFT, as it moves across the navicular bone and inserts on the bottom of the coffin bone². The horse’s navicular apparatus acts as a pulley system serving two primary roles: help lift the foot off the ground and dissipate the mechanical forces of movement.

Understanding the Navicular Apparatus

In a 2021 study Michelle Osborn, MA, PhD, of Louisiana State University School of Veterinary Medicine, in Baton Rouge, and her co-authors across several institutions described the equine navicular apparatus as having the same structural adaptations to mechanical stress as the human Achilles tendon complex. “When everything works as intended, these adaptations efficiently dissipate force away from the tendon’s bony attachment site, thereby protecting it from failure,” they wrote.

Osborn is a functional comparative anatomist and associate professor. Her co-authors on the study were Elizabeth Uhl, DVM, PhD, Dipl. ACVP, a veterinary pathologist and professor at the University of Georgia School of Veterinary Medicine, in Athens, and Jean Luc Cornille, master of the Cadre Noir de Saumur (now the French Horse and Riding Institute), FEI-level trainer and international competitor and the founder of “Science of Motion,” a training and therapy based on identifying and correcting the specific gait abnormalities in each horse. Together, the trio is studying the complex relationship between posture, movement, forces, and tissue degeneration as it relates to equine podotrochlosis.

Horses diagnosed with what was known as navicular syndrome just 30-40 years ago carried a guarded prognosis due to the limited understanding of the condition and lack of available treatments. “Navicular disease was once thought to warrant immediate retirement,” says Chris White, DVM, an equine sports medicine consultant at Cornwallis Veterinarians LTD, in Kentville, Nova Scotia, Canada. White is currently pursuing certification through the International Society of Equine Locomotor Pathology (ISELP).

While science hasn’t found a way to reverse degenerative damage to the podotrochlear apparatus, our equine athletes today benefit from more research-based, effective therapies than they did in the 1980s. “A lesion anywhere in the navicular apparatus can result in heel pain and lameness,” White says. “But nowadays, the sport horse patients that I diagnose with podotrochlosis are not retiring by any means. Rather, getting a diagnosis is only the first step in figuring out how to help that horse.”

Improvements in Identifying Podotrochlosis

You can’t fix a problem if you don’t know it exists. Nowadays, recognizing and addressing podotrochlosis early plays a pivotal role in our ability to slow down the progression of the disease and keep affected horses sound and in work longer. Jessica Martin, DVM, cIVCA, associate veterinarian at Mountain Pointe Equine Veterinary Services, in Long Valley, New Jersey, credits advances in diagnostic imaging for our improved ability to pick up on subtle initial podotrochlear changes. “As veterinarians, we are diagnosing podotrochlosis earlier and more often because we have access to higher-quality imaging.” She points specifically to digital radiography (X rays) that can be done on the farm and to MRI performed at a referral center.

What Causes Podotrochlosis? Nature vs. Nurture

Ongoing debate exists regarding contributing factors of the disease. Quarter Horses, Warmbloods, and Thoroughbreds are overrepresented in podotrochlosis cases³, but the condition can affect any horse breed or sex, although geldings have a greater risk than stallions or mares. Conformation remains an important predictor, because proportionally small feet supporting large bodies appear to increase the weight and strain placed on the pototrochlear apparatus. In fact, at the 2006 American Association of Equine Practitioners (AAEP) Convention, Turner presented data showing that horses developing hoof lameness are 7.5 times more likely to have small feet for their body weight⁴ than horses that remain sound.

As for Osborn and her colleagues, they have a working theory for the pathophysiology of podotrochlosis—in other words, the functional changes that accompany the condition. It begins by considering lameness a warning sign of impending tissue damage. “We’ve found that horses with podotrochlosis often have a pastern joint in a state of pathologic hyperextension (extending past its normal range of motion),” the researchers say, referring to their 2021 study on the topic. “This upsets the balance of the apparatus and its ability to manage the mechanical forces impacting it². The entire apparatus is affected, and the damage is progressive unless the mechanical overloading is corrected.” They speculate that many of the damaging forces on the navicular apparatus result from forelimb overloading caused by unbalanced body posture and biomechanics.

Looking at the current body of research, scientists blame both genetic (intrinsic) and acquired (extrinsic) factors in the development and progression of podotrochlosis in horses and suggest structures proximal to (above) the foot could influence disease onset and progression.

Managing Podotrochlosis in Horses

“Reiterating our earlier point, since we do not have a cure for this disease and it is generally progressive in nature, podotrochlosis is a long-term management commitment for the owner and veterinarian,” says Martin. “Luckily, with advances in podiatry and veterinary care, we have been successful at maintaining comfort in even active horses.”

White agrees: “With podotrochlosis being a degenerative progress, I am not looking—or able to—cure the condition; I am simply trying to manage it.” Our sources recommend hoof care and medication as the primary lines of defense against the progression of navicular degeneration, emphasizing the need for an individualized treatment plan for each case.

The consensus is the course of treatment highly depends on the individual horse and whether any soft tissues are involved. “No two cases will respond exactly the same,” Martin explains. “Thus, there is no ‘cookie-cutter’ course of treatment for every horse. Management—and prevention—of this disease starts with skilled and regular hoof care, including corrective shoeing if needed. As the horse ages and the disease likely progresses, additional treatments to manage chronic pain may be instituted. These often include long-term non-steroidal anti-inflammatory (NSAID) therapy, bisphosphonates (Opshos or Tildren), and intra-articular therapy.”

Challenges With Long-Term Management

The unique challenge with podotrochlosis is the degenerative condition can easily span 15-20 years of a horse’s life, and some veterinary treatments are simply not meant to be administered regularly for such long periods of time.

Veterinarians routinely use intra-articular corticosteroid therapies (joint injections) to treat both synovitis—inflammation of the synovial membrane, or joint lining, which is the precursor to arthritis—and podotrochlosis. Injected into the coffin joint and navicular bursa of the horse, corticosteroids are powerful drugs that act quickly to combat the inflammatory cascade. They can effectively control the pain and inflammation that not only cause clinical lameness but can also contribute to the worsening of the disease.

“But long-term steroid use is not ideal,” says White. “Orthobiologics are much safer in the long run if we are doing repeated intra-articular injections throughout the horse’s life. These regenerative therapies are processed from the horse’s own blood, so they don’t have the deleterious effects that come with steroids,” he explains, pointing to an increase in circulating insulin, which can aggravate underlying metabolic problems, increase the risk of developing the debilitating hoof disease laminitis, and cause injury to the joint cartilage over time.

Orthobiologics and Bisphosphonates: Innovative Treatments

Orthobiologics are autologous, which means they come from the horse’s own body. Common examples include interleukin-1 receptor antagonist protein (IRAP) and platelet-rich plasma (PRP).

It’s important to pause here and review how bone remodeling works, because bisphosphonates affect a player in the process. Cells called osteoclasts break down old bone, while osteoblasts create new bone.

“As for bisphosphonates, these are widely used and specifically labeled by the FDA for controlling clinical signs associated with navicular syndrome in horses,” says Martin. “These drugs inhibit osteoclastic activity. Because they work on bone, bisphosphonates are most appropriate for cases that have more bony involvement and minimal soft tissue damage.

“With judicious case selection, bisphosphonates can be beneficial,” she adds, referring to a 2019 study in which researchers saw lameness improve in six out of 11 horses (55%) with podotrochlosis within 90 days of one dose of clodronic acid (the active ingredient in Osphos) injected intramuscularly.

White says bisphosphonates “can be a godsend for horses with podotrochlosis.” As a precaution he does, however, recommend checking renal values to ensure kidney health before administering bisphosphonates to horses receiving them regularly (every six to 18 months) There is also a contraindication to not give them at the same time as NSAIDs.

Controversy exists regarding the widespread extra-label use of bisphosphonates in horses for various musculoskeletal conditions, evidenced by recent (2022) research cautioning against their administration in juvenile and exercising animals⁵. Bisophosphonates are labeled for use in horses ages 4 and older, and the USEF rules follow suit⁶.

“Bone formation and remodeling is a very complex process that we really do not know much about, and there is reason to question our assumptions about it,” say Osborn and her colleagues. “Osteoclasts are critical for the remodeling process, which occurs throughout life—the whole skeleton is turned over the span of approximately 15 years. Constant remodeling is critical for the ability of bone to adapt to mechanical forces and for the repair of damaged bone. Current research and legislation encourage veterinarians to use bisphosphonates judiciously and only when the benefits appear to outweigh the risks.”

Goals for Managing Navicular Long-Term

The goal when managing podotrochlosis is to prolong the soundness and usefulness of the horse. Some damage, such as remodeling of the navicular bone or arthritis of the coffin joint, can’t be undone. “As years and even decades pass, treatments that once worked wonderfully at the time of diagnosis may start to lose efficacy,” says White. “It’s unfortunately a common sequela in the disease, making it ever more important to keep your veterinarian and farrier involved long after initial diagnosis.”

“If the horse’s comfort can’t be maintained (even in retirement), then it becomes a quality-of-life discussion,” adds Martin.

Take-Home Message

What’s the long-term prognosis for the sport horse with podotrochlosis today? Much better than it was at the turn of the century. While veterinarians and horse owners still need to address the condition early and manage it for the duration of the animals’ lives, navicular syndrome is, in most cases, no longer a career-ending diagnosis. Our sources and authors on recent research agree that thanks to advances in diagnostic and treatment options, many horses with varying degrees of podotrochlosis can be comfortably managed into their golden years.

References

1. Turner TA. Diagnosis and Treatment of the Navicular Syndrome in Horses. Vet Clin North Am Equine Pract. 1989;5(1):131–144.
2. Osborn ML, Cornille JL, Blas-Machado U, Uhl EW. The equine navicular apparatus as a premier enthesis organ: Functional implications. Vet Surg. 2021;50:713–728.
3. Dyson S, Murray R, Blunden T, Schramme M. Current concepts of navicular disease. Equine Vet Educ. 2011;23:27–39.
4. Turner TA. How to subjectively and objectively examine the equine foot. Proceedings of the American Association of Equine Practitioners. 2006;52.
5. Vergara-Hernandez FB, Nielsen BD, Colbath AC. Is the Use of Bisphosphonates Putting Horses at Risk? An Osteoclast Perspective. Animals. 2022;12(13):1722.
6. United States Equestrian Federation. 2022 USEF Guidelines & Rules for Drugs and Medications. tinyurl.com/568njkzr