Ringbone is new bone growth on the last three bones
in a horse's leg, the
phalanges. Definitive diagnosis is by radiograph. Ringbone is classified
as "high" when it involves the distal end of the first phalanx (P1) and/or
the proximal end of the second phalanx (P2); or "low" when it involves
the distal end of the second phalanx (P2) and the proximal end of the third
phalanx (P3), especially at the extensor process.
Ringbone is further classified as "periarticular",
meaning the new bone is
around a joint, but does not involve a joint surface; and "articular" when
the new bone involves a joint surface. Articular ringbone is often
accompanied by osteoarthritis in the affected joint.
The joints affected by ringbone are the pastern
interphalangeal joint, PIJ) and the coffin joint (distal interphalangeal
Ringbone is usually caused by trauma and is often
found in horses with
poor conformation that causes them to stress one aspect of a joint more
than the other. Ringbone can also be caused by any insult that disturbs
the periostium of the bone (esp., wire cuts). Ringbone most often
affects fronts, but is sometimes found in hinds.
Horses with periarticular ringbone are often asymptomatic;
articular ringbone are usually lame to some degree.
All mechanical treatment for articular ringbone
consists of trimming
methods and/or the application of shoes and/or wedge pads that lessen
the articulation of the affected joint.
Trimming to lessen the articulation of the affected
leaving as much heel as possible while cutting as much toe as possible
without causing a leak. Trimming, by itself, is not as effective as the
application of therapeutic shoes and any trimming method that reduces
phalangeal angulation is counterproductive as this increases
articulation of the affected joints.
Typical "ringbone shoes" are aluminum or half rounds
set under as far as
possible, or rocker toes forged from wide web stock - often with
exaggerated wedge or roller calks at the heels, sometimes applied with
one of more wedge pads. (An effective quick and dirty ringbone shoe can be
made by welding a piece of 3/4" pipe across the heels of a keg shoe.)
Most effective ringbone shoes usually cause a choppy, mincing, action at
any gait because they can cause the foot to begin turnover prematurely
as the fetlock begins to ascend in what would normally be a support phase,
before the shoulder passes over the foot.
According to most veterinary texts, the prognosis
for articular ringbone
in fronts is unfavorable; for periarticular ringbone, guarded.