Named for the sport in which it often occurs, hunter’s (or jumper’s) bump is a sometimes painful pelvic condition that affects performance and gait. It’s tricky to diagnose, occurs in horses which do many different disciplines, and can be an acute or chronic condition. Hunter’s bump is a prominence of the tuber sacrale, a part of the hip bone that lies at the highest point of both sides of the horse’s croup.

(Hunter’s bump anatomy) “The pelvic bones consist of three distinct anatomical regions—ilium, pubis, and ischium,” explains Nathan Slovis, DVM, Dipl. ACVIM, an internist at the Hagyard-Davidson-McGee referral hospital in Lexington, Ky. “The ilium consists of a wing and body. The wing can have normal anatomical variations. The dorsal (top) aspect of the ilium forms what is called the tuber sacrale. Normally the tuber sacrale is covered by fat and muscle, which could make it difficult to see on obese and/or well-muscled horses. Loss of fat or muscle will make the tuber sacrale more pronounced. A prominent tuber sacrale could be caused by a luxation or subluxation (dislocation or partial dislocation) of the sacroiliac joint.”

The sacroiliac joints are designed to combine firmness of attachment between the sacrum (a specific anatomical section of the spinal column) and the wing (ilium) of the pelvis. “The sacroiliac joint aids in a shock-absorbent capacity by transferring hind limb propulsive forces to the vertebral column,” Slovis states. This dissipates the load placed upon the vertebral column from shear (created by two objects sliding parallel to each other), tension, and compression forces.

However, the sacroiliac joint is not meant to be mobile; stresses that produce motion might produce subluxation or tearing of the muscles/ligaments that hold the joint in place, resulting in distinct hind limb lameness