Sidebone is ossification of the collateral cartilages of the distal phalanx; it occurs most often in the lateral cartilage. It is most common in the forefeet of heavy horses working on hard surfaces. Repeated concussion to the quarters of the feet is purported to be the cause. Some cases arise from direct trauma. Sidebone is usually an incidental radiographic finding and rarely causes lameness. If sidebone is a cause of lameness, the lameness should entirely subside with a unilateral palmar digital nerve block on the affected side.
When lameness is present, corrective shoeing to promote expansion of the quarters and to protect the foot from concussion may be of value. Grooving the hoof wall on the affected side has been reported to help reduce lameness. If sidebone is documented as a cause of lameness, unilateral palmar digital neurectomy may be indicated if the horse does not respond to corrective shoeing and trimming.