Navicular disease, or navicular syndrome, is a complex condition affecting the horse's foot, in particular, the heel area. Damage can lead to chronic forelimb lameness in either limb, both limbs or a shifting lameness between the two. Sometimes a lameness is not obvious, but you may notice a shortened stride length with lameness accentuated when worked on hard surfaces.
Navicular disease is a chronic degenerative condition of the navicular bone and associated structures within the horse’s foot. The exact cause of the disease is unknown, however, it is likely due to a complex combination of biomechanics, conformation of the foot and distal limb, vascular and genetic components. The onset of disease is most commonly seen in mature riding horses from around 8 - 10 years of age. The biomechanical and conformational factors that are associated with an increased risk of developing navicular disease include a broken back hoof pastern axis, under-run heels and long toes. These conformational changes increase the weight-bearing area to the back portion of the foot, leading to increased concussive forces between the flexor tendon and navicular bone, thus increasing the incidence of disease.
Diagnosis
Diagnosis is usually made after collecting a detailed history and performing a thorough lameness examination with your veterinarian. Lameness is generally worse on hard surfaces and is exacerbated when the horse is lunged in a small circle, showing increased lameness to the foot on the inside of the circle. The lameness generally blocks out to a palmar digital nerve block, which numbs the back portion of the foot. Quite often the lameness will shift from the foot that’s been blocked out to the opposite side.
The next step would be radiographs, where we may see evidence of increased number of vascular channels, increased sclerosis (increased bony density) of the medullary cavity (inner part of the bone) or there may be enthesophytes (bony spurs) along the edges of the navicular bone.
Treatment
Treatment includes the use of short term NSAIDs (e.g Bute or Prevequine) +/- intra-articular or navicular bursa corticosteroid injections and corrective shoeing. Correct foot care is the key to managing these chronic cases. The aim of our trim and shoeing is to restore a normal hoof pastern axis and decrease the pressures to the navicular bone. Most often this is achieved via the use of a wedge shoe and rolling the toe which brings the breakover right back, further relieving pressure to the back portion of the foot. Egg bar shoes are also a good option to reduce the pressure on the back part of the foot when ridden on soft surfaces, as it reduces how far the heels sink down into the sand.
As navicular disease is a degenerative condition, the clinical signs will worsen over time. A carefully designed and followed therapeutic plan consisting of corrective shoeing, NSAIDs use and intra-articular injections can prolong the ridden careers of many competition and pleasure horses, however most affected horses will reach a point of non-responsiveness to treatment over time.