"Sidebone" is the common term for ossification of the collateral cartilages of the distal phalanx in a horse.
Etiology and Pathophysiology of Sidebone in Horses
Although the exact etiology is unknown, sidebone is believed to be associated with concussive forces. It is most common in the forefeet of heavy horses or of horses with poor conformation.
In sidebone, ossification usually starts at the base of the cartilage and extends proximally, or it can originate from a separate center of ossification. Ossification is commonly more extensive in the lateral cartilage than in the medial cartilage. Substantially ossified collateral cartilages of the hoof are associated with injury to the collateral ligament of the distal interphalangeal joint (DIP joint) or to the distal phalanx.
Clinical Findings of Sidebone in Horses
Sidebone is rarely the primary source of lameness in horses. The ossification is usually an incidental finding on physical examination or radiographic evaluation of the foot.
Diagnosis of Sidebone in Horses
In cases of sidebone with extensive ossification, the lack of flexibility of the cartilages can be palpated immediately proximal to the coronet in the palmar/plantar aspect of the horse's hoof. The ossification can be identified on dorsopalmar or dorsoplantar and lateral radiographs of the foot (see sidebone radiographic image).
Courtesy of Dr. Brian Beasley.
In rare cases, the ossified cartilage fractures. Fracture of ossified collateral cartilage often results in local heat, swelling, and pain on palpation. Separate centers of ossification should be distinguished from fractures. In horses with lameness, all other causes should be excluded before the lameness is attributed to sidebone.
Treatment and Management of Sidebone in Horses
There is no need to treat subclinical ossification of collateral cartilages. If sidebone is deemed to be the cause of lameness in a horse, rest and NSAIDs are indicated. In cases of acute or chronic lameness, any hoof imbalances should be evaluated and addressed. Unilateral neurectomy or surgical excision of the cartilage may help horses with persistent lameness that cannot be controlled by conservative measures.
Overall, the prognosis for sidebone in horses is good unless the nature of the lameness requires surgery, in which case the prognosis is guarded.
For More Information
Also see pet health content regarding sidebone in horses.
