Named after the type of equine athlete it usually affects—the hunter/jumper—a hunter’s bump is a characteristic upward protrusion at the horse’s hindquarters over the sacroiliac (SI) region. This bump is often more than just a simple blemish. The cause, impact on performance, and appropriate treatment of a hunter’s bump varies greatly from rump to rump, so let’s take a closer look at this common, but sometimes misunderstood condition.

Etiology and Causes

What exactly is a hunter’s bump? The possible etiologies and various structures involved contribute to the confusion and myths surrounding the condition, because there are actually several types of hunter’s bumps, explains Coralie Morauw, DVM, CVSMT, associate veterinarian at Chicago Equine Medical Center, in Wauconda, Illinois, and faculty of Veterinary Spinal Manipulative Therapy (VSMT) at the Healing Oasis Wellness Center, in Sturtevant, Wisconsin.

“To start with a bit of anatomy, the sacroiliac joint connects the hind limb with the spine where the sacral vertebrae and ilium (pelvis) meet,” says Morauw. “Its main function is forward propulsion. Tons of important soft tissue structures surround the SI joint, notably the lateral sacroiliac, dorsal sacroiliac, and sacrosciatic ligaments, as well as major muscle groups including the gluteal and iliopsoas muscles.”

When a hunter’s bump is not present, both tuber sacrales—the top eminences of the ilium—follow the silhouette of the croup smoothly, without protrusion. In contrast, a hunter’s bump is a protuberance of one or both tuber sacrales. Such protrusion can be unilateral or bilateral and is generally linked to one of five main causes, says Morauw, which are often interconnected:

1. Conformation. Two big conformation flaws that predispose a horse to a “rump bump” are a flat rump—one lacking angulation—and a straight hind leg. In these cases, the tuber sacrales protrude upward even though there is nothing physiologically wrong with them.
   
2. Musculature variation. Any asymmetry in the gluteal muscles can result in a hunter’s bump appearance. A unilateral increase in musculature can cause the opposite side to appear decreased, revealing a protruding tuber sacrale on one side only.
   
3. Related to cause No. 2, muscle neuropathy from diseases such as equine protozoal myeloencephalitis (EPM) or nerve entrapment can contribute to hind-end muscular asymmetries. Beyond the nefarious effects of the neuropathy itself, the resulting muscle atrophy (wasting) increases the risk of strain and injury to the sacroiliac region, making the horse more vulnerable to hind-end pain and lameness.

4. Altered stance stemming from a pain response. Horses can adjust their posture to reduce pressure in a painful area. This can cause the ilium to shift upward, resulting in the apparition of a hunter’s bump. Asymmetrical movement due to pain can also lead to asymmetrical muscle development, linking back to cause No. 2. Chronic overuse of the SI joint, muscles, and/or ligaments in the region can all lead to pain and inflammation and create a hunter’s bump. This bump might appear, for example, when the sacroiliac ligaments are strained.
   
5. Subluxation or luxation. A subluxation is a partial dislocation, and a luxation is a full dislocation of the SI joint, where the latter is usually traumatic and carries a poor prognosis. Subluxations are common in jumping disciplines and result in hypomotility (reduced range of motion) of the joint. In the case of a hunter’s bump, the sacroiliac joint is restricted in a fashion that the tuber sacrale is more dorsal (further up toward the head) than normal.

Effect on Soundness and Performance

The presence of a hunter’s bump does not always automatically bother a horse, which is good news for concerned owners. “Lameness is not pathognomonic to those cases,” says Morauw,  adding that while the bump itself might not be painful, it’s nonetheless important to consider its impact on the entire horse. “Compensatory changes and abnormal movement (of the sacroiliac region) often causes secondary thoracic and lumbar back pain,” says Morauw. “In these cases, finding the root cause of the hunter’s bump is key in determining the course of action. For example, if back pain stems from direct misuse of the sacroiliac region versus from secondary misuse of the hocks due to the chronic hunter’s bump, there will be different treatment options for the different affected joints.”

Treatment

Morauw and other veterinarians agree the first-line treatment for a hunter’s bump is rest and pain medications, usually the non-steroidal anti-inflammatory drug (NSAID) phenylbutazone (Bute). Depending on the condition’s cause and duration, some cases might require a combination of the following therapies and modalities:

• Muscle relaxers such as methocarbamol.
• Chiropractic care.
• Mesotherapy.
• Intra-articular therapy.
• Extracorporeal shock wave therapy.
• Photobiomodulation therapy.
• Pulsed electromagnetic (PEMF) therapy.
• Acupuncture/aquapuncture (acupuncture complemented by vitamin B12 injection).
• Physical and massage therapy.

Here again, we must consider the entire animal when making a plan to address an individual horse’s hunter’s bump. “In addition to treating secondary muscle or spinal pain, it is essential to rule out any discomfort stemming from the sacroiliac region itself,” says Morauw. Remember the affected tissues can vary because joints, bones, muscles, and ligaments all make up the sacroiliac region – that’s why we don’t have a one-size-fits-all treatment for hunter’s bumps.

Spinal manipulation might apply to some horses’ treatment plans. “In my experience, chiropractic care is essential in managing hunter’s bumps,” says Jesslyn Bryk-Lucy, DVM, cAVCA, owner of Leg Up Equine Veterinary Services, and resident veterinarian and an assistant professor of equine science at Centenary University, in Hackettstown, New Jersey. “I’ve had several cases where I examined a horse with a hunter’s bump and thought that a return to performance was impossible. While the severe cases never look ‘normal’ again, I have been surprised every time at how much the hunter’s bumps had improved with chiropractic adjustments, both in their visual appearance and in the owners’ reports that the horse felt better under saddle.”

Prevention

The best treatment for a hunter’s bump is prevention. “Management of horses with a developing hunter’s bump is a key component in preventing further issues associated with sacroiliac dysfunction,” says Bryk-Lucy. “Proper conditioning of the hind end is essential for the muscles in the area to stabilize the joint and carry the load.” She recommends hill work, cavalettis, and transitions to strengthen the hind end, reminding owners to start with easy exercises and work up slowly to avoid soreness as the horse increases his fitness level.

Final Thoughts

If you notice the characteristic bump forming on your horse’s rump during your training, don’t push him. Give your horse time to rest, and create a plan with your veterinarian to minimize discomfort and maximize the likelihood the bump will resolve without complications.