Q.I recently bought a young prospect who passed a fairly rigorous prepurchase exam (PPE). When she got home my farrier came to shoe her and told me he believes she has “pyramidal disease.” I’d never heard of this hoof condition before but have found a few references to it online. How do I know she has this condition, what causes it, why wouldn’t it have been included in the PPE, and what’s the long-term prognosis for her as a sport horse?
A.Pyramidal disease is a form of osteoarthritis in horses which affects the coffin joint (low ringbone) or the pastern joint (high ringbone). Specifically, pyramidal disease is the fragmentation of the extensor process of the distal phalanx (coffin bone, or P3). It is thought to occur due to trauma, osteochondrosis, or presence of separate centers of ossification. Forelimbs are more commonly affected than hind limbs.
In many cases, pieces of the bone can fracture and chip away, causing a great deal of pain. The fracture fragments are usually intra-articular (in the joint) but are commonly nondisplaced; they may adhere to the extensor tendon. The fragments might be incidental findings, but they could also cause lameness. When pyramidal disease involves a joint, it is more likely to cause lameness than when it doesn’t involve a joint (non-articular).
The close association of the extensor process with the distal interphalangeal joint (the coffin joint) can result in secondary arthritis if the fragments aren’t removed. Veterinarians can remove fractures either via arthroscopy or arthrotomy (where the surgeon cuts the joint open with a scalpel to find and remove the chips); arthroscopic removal of small fragments carries a good prognosis. With large, untreated fractures, an enlargement of the toe region just above the coronary band is usually present, which results in the “buttress foot” or “pyramidal” appearance to the foot.
Pyramidal disease can be caused by damage within the joint (articular), or from damage to the structures that surround and support the joint (periarticular), such as the joint capsule or ligaments.
Horses with poor conformation and/or hoof alignment issues are predisposed to developing pyramidal disease later in life. Poor conformation traits that can contribute to this condition include upright pasterns, club foot, toed-in or toed-out, or improper hoof angle. These flaws exert stress on the horse’s joints. Horses participating in certain equestrian disciplines are also more at risk of developing ringbone. For example, horses used for jumping (landing after the jump); barrel racing (sharp, high-speed turns); roping (sudden hard stops); and/or carriage driving, parades, or police horses (working on pavement) might be at risk.
Recognizing and treating pyramidal disease is important, because it can change the shape of the foot over time and cause your horse a great deal of undue stress and pain. With a close examination of the foot, a veterinarian should be able to easily diagnose buttress foot. This is because as the disease worsens, the shape of the foot changes significantly and becomes more narrow and square.
Systemic anti-inflammatory medication might be beneficial.
Clinical signs can be difficult to catch in the early stages of the disease. While riding, horses may develop a short, shuffling, or choppy gait; stop performing activities they used to normally do (such as jumping, performing sharp turns, or sudden stops); or appear less willing to move forward. Clinical signs might vary from day to day and will differ depending on whether one or both legs are affected. After a short rest period, lameness might appear to have resolved only to return once work is restarted.
Diagnosis of pyramidal disease is through radiography and is important for verifying whether the associated bony changes involve a joint or not, as treatment and prognosis are dependent on this finding.