Navicular disease affects many horses and is especially common in quarter horses, thoroughbreds and warmbloods. Multiple treatments have been used for navicular disease with varied success. With the advent of MRI and ultrasound, it has been shown that some pain from the syndrome does not even involve the navicular bone but rather soft tissue structures around the bone. For this reason, the term navicular disease is no longer recommended and heel pain is the preferred term because the navicular bone may not be the only source of pain.
However, in cases in which the bone is believed to be involved, a bisphosphonate drug has been used. The two that are approved for horses are Tilden and Osphos. Dr. Niklas Drumm from England reported that bisphosphonates inhibit bone resorption by killing cells called osteoclasts that absorb bone tissue. The drugs have been shown to help some horses with disease of the navicular bone but will not be effective if other structures than the bone are involved; however, some believe the drug also provides anti-inflammatory and pain relief as well. The drugs do not provide a long-term effect but usually are effective for a few months in the horses that do respond. The bisphosphonates are commonly used along with routine therapy for heel pain including therapeutic shoeing and joint injections. Both of these drugs can cause potential side effects of kidney damage and colic, so their use is not without some risk. Also, the balance of bone production and bone removal is a normal process and by preventing normal bone resorption from occurring, other problems could develop with long-term use as one of these drugs is injected into the vein and the other in the muscle, so they affect the entire horse, not just the navicular bones.
Dr. Steven Colburn from California said in the Texas Equine Vet Association publication the Remuda that he previously treated all navicular cases with therapeutic shoeing, isoprene and aspirin, and then if they did not respond, he would inject the coffin joint with medication. However, he now uses Osphos and indicates up to 70% of his patients have improved. It is important for your vet to perform a complete exam with x-rays and blocking the feet to make sure of the diagnosis. In some cases, an MRI is required because heel pain can affect structures other than the navicular bone, such as ligaments around the bone. However, if x-rays indicate the bone is involved, Dr. Colburn treats the horse with Osphos (clodronate). Those inhibit bone resorption, which decreases loss of bone as bone loss is one thing that occurs in horses with navicular disease. Dr. Colburn recommends light work after the injection and you will need to stop using NSAIDs such as bute at the same time as both drugs can affect the kidneys. Some horses can develop colic after the injection, but it is usually mild and walking the horse after the injection can usually decrease symptoms. Rare signs after Osphos injection include a decreased appetite, lethargy, and injection site reactions.
The safe use of Osphos has not been studied in horses younger than 4 years old and should not be used in pregnant horses, lactating mares, or those used for breeding.