April 24, 2018
Managing Navicular Disease
“Navicular disease” is a term that was historically used to describe horses with lameness originating from the foot thought to be due to pain caused by degeneration of the navicular bone. However, now that MRI is increasingly used to evaluate horses with foot pain we know that these horses often have damage to the soft tissue structures in and around the foot in addition to the navicular bone, and not just the navicular bone itself.
The soft tissue structure that is most commonly involved is the deep digital flexor tendon (DDFT), but other structures such as the distal sesmoidean impar ligament, the navicular suspensory ligaments, and the collateral ligaments of the coffin joint can also be injured. Foot pain can also be caused by arthritis of the coffin joint. Additionally, in horses with chronic foot pain, adhesions (scar tissue) can develop between the DDFT and the navicular bone. Finally, the navicular bone has a bursa associated with it-this is a small fluid-filled sac between the navicular bone and the DDFT. This bursa can become inflamed, and in chronic cases, scar tissue can also develop inside of the bursa. Therefore, what was once referred to as “navicular disease” has more recently been referred to as either foot/heel pain or caudal foot pain since many structures other than the navicular bone may be the source of pain.
Horses with foot pain may have damage to or degeneration of only one of these structures, but more commonly there are problems with many of the structures within the foot. The treatment for horses with foot pain can vary depending on which structures are involved. In order to know exactly where the pain is originating, most horses must undergo an MRI. Radiographs can identify arthritis of the coffin joint and may be able to diagnose horses with significant changes in the navicular bone, but they will not detect problems with any of the other soft tissue structures or horses with mild changes in their navicular bone. Ultrasound can’t always diagnose problems with the soft tissue structures in the foot because it cannot penetrate through the hoof wall (where most of the structures are). Therefore, if your horse has foot pain, radiographs should be taken to make sure there is no arthritis in the coffin joint or no obvious issues with the navicular bone, but “normal” radiographs do not mean that your horse doesn’t have “navicular disease” or foot pain.
Initial therapy for horses with foot pain typically includes a period of rest or restricted activity, a course of a non-steroidal anti-inflammatory drug (bute, banamine, or Equioxx®), and corrective shoeing. For these horses it is very important to make sure that the toes are kept short and that there is adequate support in the back of the frog and the heel. Many horses respond well to being placed in shoes with a small (2-3 degree) heel wedge. Additional support can be provided by using a pour-in, such as Equithane Equi-Pak, placed from the tip of the frog back to the heel, leaving the toe open. These horses may also benefit from injectable +/- oral joint supplements. If radiographs show arthritis of the coffin joint, then injecting the joint with hyaluronic acid and a steroid will provide some pain relief (although keep in mind that if the horse has damage to any of the other soft tissue structures this may not completely resolve the lameness). Joint injections with other substances such as IRAP may be used to slow the progression of arthritis.
The advantage of doing an MRI for horses with foot pain is that some treatments can target specific injuries. If the navicular bone, bursa, or DDFT are the primary problem, then injecting the navicular bursa with hyaluronic acid and steroids can be helpful. Other treatments such as shock wave therapy, platelet rich plasma (PRP), or tildren may be indicated, depending on which structures are involved, and can improve the prognosis for horses with foot pain.
Diagram cutline:(figure courtesy of University of Missouri Extension)
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