Bit & Bridle

Equine Sacroiliac Joint Disease

Equine Sacroiliac Joint Disease is one of the most significant and underdiagnosed causes of poor performance, reluctance to work, and hindlimb lameness in horses. The sacroiliac (SI) joint, where the sacrum of the spine articulates with the ilium of the pelvis, is subject to enormous forces during athletic activity. When this joint becomes painful, stiff, or unstable — through injury, degeneration, or inflammation — it can affect a horse's movement, jumping ability, straightness, and willingness to work in ways that are often dismissed or misattributed to poor training or behavioural issues.

Other Names

  • Sacroiliac pain
  • SI joint dysfunction
  • Pelvic pain in horses
  • Hunter's bumps (a specific associated sign)
  • Sacroiliac subluxation

What Is Equine Sacroiliac Joint Disease?

The sacroiliac joint is a large, weight-bearing joint connecting the sacrum (the fused vertebrae at the base of the spine) to the ilium (the largest bone of the pelvis) on each side of the body. Unlike most joints, it has very limited range of motion and is primarily a transmitter of propulsive forces from the hindquarters to the spine and back to the rider. It is stabilised by an extremely strong ligamentous complex.

Sacroiliac disease encompasses a spectrum of conditions: acute traumatic injury, chronic strain and overload, joint degeneration (osteoarthritis), enthesopathy (damage to ligament attachment sites), and sacroiliac subluxation (partial dislocation). The condition is well recognised in jumping horses, eventers, dressage horses, and racehorses, though it occurs across all disciplines. Accurate diagnosis requires modern imaging technology, and the condition was historically underdiagnosed due to the difficulty of accessing the joint clinically.

Causes

Sacroiliac disease can be caused by a single traumatic event or develop gradually through repetitive overloading. Common causes and risk factors include:

  • Falls or slips: Landing awkwardly, falling in a jump-off, or slipping in a field can cause acute traumatic injury to the SI joint and ligaments
  • Asymmetric loading: Repetitive work on one rein, poor rider position, or compensatory movement from hindlimb lameness elsewhere
  • Pelvic fractures: More severe trauma can fracture the ilium or sacrum
  • Conformational factors: Horses with very steep croup conformation or those that engage their hindquarters intensely in collected work are thought to be at increased risk
  • Heavy competition load: High-intensity athletic demand without adequate recovery time
  • Secondary to hindlimb lameness: Altered gait mechanics from a distal limb problem can overload the SI joint over time
  • Advancing age: Degenerative joint changes increase in middle-aged and older horses

Symptoms and Signs

Sacroiliac disease often presents insidiously and its signs are frequently non-specific. Owners and trainers may notice a gradual decline in performance before overt lameness is apparent. Signs include:

  • Poor performance: Reluctance to collect, difficulty maintaining impulsion, loss of spring in the canter, or inability to perform previously mastered movements
  • Hindlimb stiffness: Reduced flexion of the hindquarters, particularly at the start of work
  • Asymmetric hindlimb movement: One hindlimb may swing out laterally, drag, or show a reduced arc of flight
  • Discomfort when ridden: Pinning ears, tail swishing, threatening to buck, or actual bucking — particularly on transitions and uphill work
  • Hunter's bumps: Asymmetric or prominent tubera sacrale (the bony points either side of the croup) — this is a classic visual sign associated with SI ligament injury and subluxation
  • Muscle atrophy: Wasting of the gluteal (rump) muscles, often asymmetrically
  • Pain on palpation: Deep pressure applied over the SI region produces a pain response — the horse dips away, tenses, or kicks
  • Reluctance to stand for farriery: Difficulty holding one hindlimb up for the farrier, suggesting pain in the contralateral SI joint
  • Back stiffness or resentment to grooming along the topline

Diagnosis

Diagnosis of SI joint disease is notoriously challenging due to the joint's depth and limited accessibility on clinical examination. A stepwise diagnostic approach is required:

  • Clinical examination: Thorough assessment of gait, movement, pelvic symmetry, muscle symmetry, back and hindquarter palpation, and response to ridden exercise. Hindlimb flexion tests may reveal asymmetry.
  • Diagnostic analgesia: Ultrasound-guided injection of local anaesthetic into or around the SI joint is the most definitive way to confirm SI pain as a source of the clinical signs. Improvement after injection confirms the diagnosis.
  • Transrectal palpation: Manual palpation of the ventral surface of the sacroiliac joint and sacrum from inside the rectum — can detect crepitus, asymmetry, or pain responses. Requires sedation.
  • Ultrasonography: Percutaneous ultrasound examination of the dorsal SI region can identify enthesophytes, ligament damage, bony proliferations, and irregularity of the joint surfaces.
  • Nuclear scintigraphy (bone scan): Identifies areas of increased bone turnover (active remodelling or inflammation). Particularly useful for detecting stress fractures of the pelvis and sacrum.
  • Radiography: Standard X-ray has limited value due to the depth and oblique orientation of the joint, but may reveal severe bony changes or fractures.
  • CT or MRI: Where available, cross-sectional imaging provides the most detailed assessment of bony and soft tissue structures, though accessing the SI region in a standing horse under sedation is technically demanding.

Treatment

Treatment depends on the nature and severity of the underlying pathology and may involve a combination of approaches:

  • Rest and controlled exercise: Acute injuries require a period of box rest followed by gradual, structured rehabilitation. Swimming or water treadmill therapy can be beneficial.
  • Intra-articular or peri-articular corticosteroid injections: Ultrasound-guided injection of corticosteroids (often combined with hyaluronic acid) directly into or around the SI joint is the most commonly used and effective treatment for inflammatory SI disease. Effects typically last 3–6 months.
  • Mesotherapy: Subcutaneous injection of a solution along the dorsal midline and back — used by some practitioners for non-specific back and SI pain
  • Physiotherapy and manual therapy: Mobilisation techniques, stretching, and targeted exercise therapy — delivered by a qualified equine physiotherapist — are an important part of long-term management
  • Shockwave therapy (ESWT): Extracorporeal shockwave applied to the SI region can reduce pain and stimulate healing in enthesopathy cases
  • Acupuncture: Used as an adjunct therapy by some practitioners for back and SI pain
  • Saddle fit assessment: An ill-fitting saddle can both cause and perpetuate SI pain. A professional saddle fit check is essential in any horse with back or SI pain.
  • Rider assessment: Asymmetric rider position can maintain asymmetric SI loading even after treatment. A riding coach or equine biomechanics expert can identify and correct these issues.

Prevention

SI joint disease cannot always be prevented, but the following measures reduce risk and promote resilience:

  • Ensure saddle fit is checked regularly by a qualified saddle fitter — at least annually and whenever the horse's topline changes
  • Balance training between both reins to avoid asymmetric loading
  • Maintain regular farriery to preserve optimal hoof balance — uneven feet directly affect hindquarter loading symmetry
  • Implement a progressive training programme with adequate recovery time between intense sessions
  • Address distal limb lameness promptly to prevent compensatory SI overloading
  • Ensure turnout on suitable surfaces — slippery fields or rutted ground increase fall and slip risk

Prognosis

The prognosis for return to athletic function depends on the underlying cause and severity. Horses with mild to moderate SI inflammation or ligament strain typically respond well to injection therapy and physiotherapy, with many returning to full work within 3–6 months. Horses with degenerative osteoarthritis or significant bony pathology carry a more guarded prognosis for high-level competition but may continue in light work indefinitely with appropriate management. Horses with acute pelvic fractures carry a variable prognosis depending on fracture severity and location.

When to Call the Vet

Consult your vet if your horse shows:

  • Unexplained decline in performance or willingness to work
  • Consistent hindlimb asymmetry or resistance to lateral work
  • Visible asymmetry of the tubera sacrale (hunter's bumps)
  • Gluteal muscle wasting, particularly if unilateral
  • Back pain or resentment to grooming/palpation of the hindquarters
  • Bucking or strong objections to collection, transitions, or canter work

For related conditions that should be considered in the differential diagnosis, see Equine Hoof Abscesses (which can cause compensatory gait changes) and Equine Laminitis. Our horse terminology guide on equine back and pelvic anatomy provides a useful anatomical framework for understanding where the SI joint sits within the body.

Frequently Asked Questions

How do I know if my horse's bucking is due to SI pain?

Bucking related to SI pain typically occurs in specific circumstances — during downward transitions, when asked to collect or engage the hindquarters, or on one particular rein. It is usually consistent and reproducible, rather than random. A horse with SI pain will often show other signs alongside bucking: pinned ears, tail swishing, reluctance to go forward, and asymmetric hindlimb movement. A veterinary examination is needed to determine whether pain is the cause — never assume bucking is purely behavioural without ruling out pain first.

What are hunter's bumps and do they mean my horse has SI disease?

Hunter's bumps are prominent, asymmetric tubera sacrale — the bony points at the top of the croup. They are caused by displacement or asymmetric remodelling of the ilium at the SI attachment, typically following trauma or subluxation of the SI joint. Their presence strongly suggests historical SI injury, but not all horses with hunter's bumps have current, active SI pain. Conversely, some horses with significant SI disease have no visible asymmetry. Clinical and imaging assessment is required to determine whether the condition is currently painful and limiting.

How long do SI joint injections last?

The duration of response to SI joint injections varies considerably between horses and depends on the underlying pathology. Many horses show 3–6 months of significant improvement after corticosteroid injection. Some horses require injections twice yearly as part of ongoing management. When combined with physiotherapy and appropriate training modifications, the interval between injections often lengthens over time. If a horse shows no response to injection, the diagnosis should be reconsidered.

Can poor saddle fit cause sacroiliac joint disease?

Yes. A saddle that sits too far back, is asymmetric, bridges (creating pressure at the pommel and cantle whilst leaving the middle of the back unsupported), or that causes the rider to sit asymmetrically can all create uneven and excessive loading of the SI region over time. Any horse with diagnosed SI disease should have its saddle assessed by a qualified saddle fitter as part of the overall treatment and prevention plan.