Damage to, or disease (infection and inflammation) of the internal structures of the foot are an extraordinarily common cause of lameness.

Investigations

The cause of lameness can be isolated to the foot by the use of nerve blocks (palmar digital and abaxial sesamoid), a coffin joint block or a navicular bursal block. The following four conditions can then be diagnosed by X-ray (but sometimes an MRI is necessary).

i – Pedal bone fractures

These can be caused by concussion sustained by jumping, injury while turned out, or by deep nail penetration. They are usually detected by X-ray but sometimes an MRI is necessary. Ultrasound cannot penetrate the hoof capsule.

Treatment is supportive farriery (such as fitting a hospital plate) and box rest. The prognosis is usually fair, although less so if the coffin joint is involved or the fracture is comminuted.

ii – Pedal ostitis

This is inflammation of the coffin bone, P3.  Although much less diagnosed since the advent of  MRI, it remains a potential problem, particularly with overwork on hard ground.

Treatment is rest, the use of padding on the sole, and oral NSAIDs.

iii – Side Bone

The bulbs of the heel are internally supported by the lateral cartilages —  attached to the inside and outside wings of the pedal bone (see diagram). If there is any uneven pressure on the foot due to poor foot balance, poor conformation or simply unperceivable causes, then these cartilages may ossify and become bone.  Large side bones can fracture due to the bone’s inflexibility and this can cause acute lameness.  Note that a lameness blocked to the foot may not be due to side bone seen on X-ray.

Treatment is rest and corrective/supportive shoeing.

iv – Coffin joint arthritis

Joint inflammation, or arthritis, encompasses inflammation of the joint capsule (synovitis), through to marked new bone formation within the joint. Often bone chips eg from the pyramidal process of the the pedal bone (P1) may be involved in coffin joint arthritis.  Synovitis is not visible on x-ray, and is classified under navicular syndrome (see below).

Treatment, depending on severity, age and use of the horse, includes joint medication, NSAIDs, joint supplements, rest and controlled exercise. Arthroscopic surgery may be recommended. Long-term prognosis is guarded.