Merck Manual

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Professional Version

Pyramidal Disease in Horses

(Extensor process fracture, Buttress foot)


James K. Belknap

, DVM, PhD, DACVS, Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Ohio State University

Reviewed/Revised Sep 2015 | Modified Oct 2022

Fragmentation of the extensor process of the distal phalanx is thought to occur due to trauma, osteochondrosis, or presence of separate centers of ossification. Forelimbs are more commonly affected than hindlimbs. The fracture fragments are usually intra-articular but are commonly nondisplaced; they may be adhered to the extensor tendon. The fragments may be incidental findings, but they may also cause lameness. The close association of the extensor process with the distal interphalangeal joint can result in secondary arthritis if the fragments are not removed. Fractures can be removed either via arthroscopy or arthrotomy; 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. Systemic anti-inflammatory medication may be beneficial.

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