The horse is an athletic animal, designed to move in forward motion at high speeds. Repetitive high-strain movements outside of their ordinary range of motion, such as jumping, can make the horse’s back and limbs susceptible to injuries. [1]

A hunter’s bump, or sacroiliac subluxation, is a hump on the horse’s lower back that develops above the croup. It is most apparent when viewing a horse in motion from behind.

Hunter’s bumps are usually caused by the displacement or dislocation of a sacroiliac (SI) joint in the lower back. The condition can affect one or both sides, depending on the horse’s conformation and the severity of the injury.

Signs of a hunter’s bump can be improved with supportive treatment and careful management practices. A combination of stall rest, medication and alternative therapies reduce SI joint pain in the horse and promote healing.

If you think your horse could be developing a hunter’s bump or SI joint pain, contact your veterinarian to obtain a diagnosis.

Hunter’s Bump in Horses

A hunter’s bump can occur when ligaments in the SI joint are torn or strained due to repetitive stress or a traumatic event, such as a pelvic fracture.

This causes a bony prominence of the pelvis (tuber sacrale) to be pushed upwards, creating a bump in the horse’s back.

A hunter’s bump can also occur naturally due to pelvic asymmetry or the horse’s conformation. Horses with naturally long hip bones may have a prominent bump on the rump, which does not hinder performance. [2]

Sacroiliac subluxation is very common in jumping sports, which is where the condition gets the name “hunter’s” or “jumper’s” bump. [3]

Picture of Hunters Bump in Horses

Sacroiliac Joints

The sacroiliac (SI) joints are low-motion joints in the horse’s lower back, situated on either side of the spine. These joints link the lower part of the spine to the pelvis, acting as shock absorbers for propulsive forces and supporting the back during motion. [4]

The SI joint is found under 8-11 cm below overlying muscles. This makes it difficult to palpate for diagnosis and to provide effective treatment. [5]

Risk Factors

SI joint injuries are most common in performance breeds, such as Thoroughbreds, Standardbreds and Warmbloods.

Unconditioned and young horses that begin high-level performance training without an appropriate adjustment are likely to develop SI joint pain or discomfort. Sudden, excessive strain on the SI joint during hindlimb flexion can lead to ligament tears and dislocation.

Horses with muscle wasting along the topline or croup are more likely to injure their sacroiliac joints. [3]

Senior horses are more susceptible to joint degeneration, loss of flexibility in the back and loss of muscle strength. They also have slower recovery from injuries, making them susceptible to musculoskeletal abnormalities due to overcompensation. [6]

Overweight horses carry a heavier load, which makes them more likely to strain muscles and joints.

Horses with poor symmetry between pelvic bones may be more susceptible to developing a hunter’s bump and regional pain, but more research is needed.

Clinical Signs

Hunter’s bumps are not inherently painful, although they are often accompanied by back pain.

Mild bumps are referred to as blemishes and not a source of lameness, as they don’t necessarily cause discomfort for the horse or affect performance. [2]

Horses with poor muscle definition in the back and hind end may have a more prominent bump.

Severe Hunter’s Bump

Severe bumps and accompanying sacroiliac or back pain can be identified by the following clinical signs: [4][5]

  • A prominent unilateral or bilateral bump above the croup
  • Poor performance
  • Gait abnormalities (ie. shortened strides, disunited canter, “bunny-hopping”)
  • Reluctance to move and jump
  • Lack of impulsion

If your horse is displaying signs of back pain or developing a bump above the croup, contact your veterinarian for examination and diagnosis.

Diagnosis

Back pain can be difficult to diagnose in the horse, due to the inaccessibility of the structures of the spine and pelvis. Some structures in the lumbar-sacral region can be palpated to help determine the affected area, but the SI joint is very deep under the skin. [7]

Pain or injuries in the lower hind limb can also transfer up the leg, into the pelvic region. This can cause secondary lumbar sacral injuries that are challenging to diagnose because the primary injury can be overlooked. [8]

SI joint displacement or inflammation rarely presents with typical lameness or pain symptoms, which further complicates diagnosis. SI joint abnormalities can go unnoticed for years. [4]

Examination & Imaging

Diagnosis of hunter’s bump involves a physical exam and diagnostic imaging. Ultrasonography and nuclear scintigraphy can be used to assess ligament injuries in the pelvis, while x-ray is used to visualize the bones.

These images are often difficult to interpret due to significant natural variation in structures and the depth of pelvic structures below muscle.

Currently, a dorsal image of the sacrum is considered the best option for comparing SI joints and making a diagnosis. [6]

Other Causes of Back Pain

If you suspect your horse has hunter’s bump, your veterinarian will perform a full lameness exam to rule out other conditions or injuries.

In a report of 443 horses with back pain, only 15% had chronic SI joint problems. [9] Other common causes of back or pelvic pain include:

  • Osteoarthritis
  • Pelvic stress fractures
  • Ilial wing fractures
  • Sacral fractures
  • Sarcoiliac sprain
  • Aortoiliac thromboembolism
  • Exertional rhabdomyolysis (“tying-up“)
  • Trochanteric bursitis
  • Impinged dorsal spinous processes (“kissing spine“)