Each horse has a natural set of inter-relationships involving the bones, joints, and supporting structures of the foot. The owner, by scheduling regular maintenance, and the farrier, by practicing good farriery, work to maintain these relationships within the physiological limits of the individual.
As long as the normal range of conformation remains within certain limits, the health of the navicular bone (which completes the back wall of the coffin joint and forms a pulley over which the deep flexor tendon runs) is maintained. The navicular bone becomes susceptible to the development of navicular disease when the structures of the foot are too upright or--more often--when the toe of the foot is too long and the heel of the foot becomes under-run.
Subsequently, although some horses may be conformationally predisposed, navicular disease is actually more an acquired condition than a disease, navicular disease is a condition in which the navicular bone has been traumatized (usually over a long period of time), resulting in alteration and/or deterioration.
Ultimately--despite our increasing knowledge base concerning pathology--determining if a horse is in fact navicular constitutes a judgement call which is influenced by numerous factors, including but not limited to: age, history, usage, conformation, radiographic quality, radiographic interpretation, environmental issues, and hoof capsule appearance.
- pointing one foot, thenthe other
- narrowing/contracting heels
- lameness whrn leaving stall or confined rest
- history of lameness
- lameness increased when worked in tight circle(s)
- pain with testers
- improvement with PDN (Palmar Digital Nerve Block)
- evidence of lameness in opposing limb with PDN
- radiographic evidence
- proper trimming and shoeing
- avoiding low angles (i.e., disproportional to pastern and shoulder angles)
- avoiding extensive work on excessively hard surfaces
Navicular problems evidence themselves over the long-term; subsequently, horses will often have other problems such as bone spavin, back pain, suspensory desmitis, etc. that have developed prior to / concurrently / compensatorily. Any of these will need to be treated concurrently for the best possible results.
The most commonly prescribed approach is to concave the sole of the foot and shoe the horse in square-toed eggbars of the lightest possible weight (the GE Navicular shoe is a poplular and effective appliance). Some practitioners will prescribe a pad or even a protective bar to protect the navicular area. Since many of these horses evidence a low angle, it is not uncommon for the practitioner to prescribe wedge pads or wedge shoes to increase angulation (although angulation can often be increased through educated trimming). Normally, the shoeing interval will be set to five weeks or so, to avoid any significant changes in toe length and/or angulation. In effect, the "therapeutic" shoeing prescription is basically to shoe the horse properly.
Ultimately, successful treatment depends upon how early the condition is detected and the type and consistency of therapeutic intervention.
Many conditions will mimic navicular problems: chronic subsolar bruising, pedal osteitis, under-run/crushed heels, sheared heels, digital flexor tendonitis, etc. Determining if a horse is in fact suffering from navicular disease is an involved and complicated process that requires extensive diagnostic and interpretive work performed by a qualified equine practitioner.