Sidebone and Coffin Bone Fractures (AAEP 2010)

Normal View

This proton density dorsal plane image through the navicular bone shows normal (not ossified) ungual cartilage.

When it comes to lame horses, things aren't always simple--the injuries/problems don't always come one at a time. Take sidebone, for example--in a recent study presented at the 2010 American Association of Equine Practitioners Convention (held Dec. 4-8 in Baltimore, Md.) researchers described a series of cases with sidebone, coffin bone fractures, and associated soft tissue problems.

"The ungual or collateral cartilages in the foot (on either side of the coffin bone, thought to function in hoof expansion/shock absorption) start out as (soft) hyaline cartilage, then can ossify (harden into bone, termed sidebone or ossified collateral/ungual cartilage) with age or other factors," explained Kurt Selberg, MS, DVM, a veterinary resident at Colorado State University (CSU). "The causes are unknown, but might include concussion (from working on hard surfaces), ligament strain, poor farriery, or other factors. Clinical signs include a shortened stride and obscure lameness, perhaps because the ossified cartilages don't function in their normal expanding and contracting manner (with each step)."

Selberg and coauthor Natasha Werpy, DVM, Dipl. ACVR, assistant professor of imaging at the Gail Holmes Equine Orthopaedic Center at CSU, described MRI findings in 22 horses from nine equine hospitals that had both ossified collateral cartilages and coffin bone fractures (23 affected feet). All cases had these problems in the forefeet, equally distributed between right and left forefeet.

Ossified View

This dorsal plane image through the navicular bone and shows severely ossified ungual cartilages.

He reported that the fractures were simple and nondisplaced, originated at the base of the ossified collateral cartilage in all cases, and involved the fossa of the collateral ligament on the coffin bone (depression on the bone where the ligament attaches) in 17 of the 23 affected feet. Also, adjacent ligaments and other soft tissues were compromised in all cases. A limited number of cases had long-term follow-up information, and in those horses fractures healed completely by 14 months after the initial case presentation.

Radiographs can detect the fractures, noted Selberg, but not the soft tissue problems. "MRI highlighted these injuries quite well," he said. "Injury of the ligaments associated with the cartilages was thought to be contributing to these cases' lameness.

"Injuries of the ligaments associated with ossified collateral cartilages have the potential to be a source of lameness," he concluded. "The routine site of fracture in this study at the base of the ossified collateral cartilage extending into the distal phalanx suggests a biomechanical cause or focal stress point from cycling. Are sclerotic ossified cartilages more likely to fracture? At this point we don't know for sure, but it seems that way."

"We are grateful for the contribution and effort of the hospitals involved in this study," commented Werpy. "It was possible to examine a larger number of cases than any one hospital could provide, which helped us arrive at a better understanding of this condition."

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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