Navicular bones are subject to many different problems, but one area that seems particularly susceptible to injury and degeneration is a tiny fluid-filled sac called the navicular bursa. The bursa is a pillow-like sac of lubricant that cushions the bone and tendon. Its most basic job is to fill a space, and keep the structures on either side of it moving smoothly. Much of what we know about the navicular bursa has come to us not by studying navicular lameness directly, but by seeing catastrophic injury to the horse's foot when a puncture wound, such as a nail or spike, penetrates the back part of the foot and damages the bursa, allowing infection to set in. The horse suddenly is in great pain and unable to flex the tendon in the normal way.
Many horses never regain soundness after such an injury to the bursa.
If a puncture wound can cause that much of an impact to a soft tissue in the horse's foot, it must be an important structure. Still, until recently, researchers and practitioners alike chose to argue over the bone degeneration vs. loss of blood supply schools of navicular lameness etiology. Only in the past ten years, with the work of pathologists like Roy Pool, PhD, and James Rooney, DVM, has the bone taken a backseat to the other structures in and around the joint. One of the more recent changes in the overall care of our lame horses is the increase in neurectomies being performed. This controversial surgery is a last resort for some horses, many of whom have undergone other surgeries and a long list of therapies and corrective shoeing.