Os coxae (Pelvis)
The pelvis (os coxae) is formed by the fusion of three bones: ilium, ischium, and pubis. The two hip bones are joined ventrally at the pelvic symphysis and dorsally articulate with the sacrum. The ilium is the largest component, with the tuber coxae ("point of the hip") and tuber sacrale as important palpable landmarks. The acetabulum, formed at the junction of all three bones, creates the socket of the hip joint. The ischial tuberosities ("pin bones") are prominent at the caudal aspect.
Pelvic fractures are diagnosed via rectal palpation, transrectal ultrasound, and scintigraphy. Assess external landmarks for symmetry.
Developmental orthopedic disease where cartilage fails to convert to bone properly, creating flaps or loose fragments. Stifle (lateral trochlear ridge of femur) and hock (tibial tarsal bone) are most
Fractures of the pelvis from slipping, falling, or running into objects. The tuber coxae (point of hip), floor of the pelvis, and ilial wing are most common sites.
Incomplete fractures of the tibia from repetitive concussion, most common in racehorses. The caudal tibial cortex is typically affected.
Tears of the meniscal cartilages in the stifle (knee). The medial meniscus is more commonly injured. Can occur from hyperextension, twisting, or degenerative changes.
Fractures of the tarsal bones, most commonly slab fractures of the third tarsal bone or central tarsal bone. Common in racehorses and sport horses.
Pelvic fractures (ilium, ischium, or pubis)
Tuber coxae fracture ("knocked-down hip")
Sacroiliac joint disease involves pain and dysfunction in the joint where the sacrum meets the pelvis. It is one of the most common causes of poor hindlimb impulsion and performance problems in sport
Stress fractures of the ilium (racehorses)
Hip dysplasia (rare in horses)
Degenerative joint disease of the lower hock joints (centrodistal and tarsometatarsal joints). Very common cause of hind limb lameness and poor performance.
The patella catches over the medial trochlear ridge and cannot release, locking the hindlimb in extension. Common in young, unfit horses and certain breeds. Related to the stay apparatus.
Developmental orthopedic disease where cartilage fails to convert to bone properly, creating flaps or loose fragments. Stifle (lateral trochlear ridge of femur) and hock (tibial tarsal bone) are most common sites. Signs include: Joint effusion (puffy joints) in young horses; lameness that may be mild or intermittent; stiffness; often bilateral; commonly found on pre-purchase radiographs; may be asymptomatic until work begins; responds to arthroscopic surgery.
Fractures of the pelvis from slipping, falling, or running into objects. The tuber coxae (point of hip), floor of the pelvis, and ilial wing are most common sites. Signs include: Acute severe hindlimb lameness; may be unable to bear weight; asymmetric pelvis (dropped or absent tuber coxae with wing fracture); muscle atrophy; crepitus; confirmed on rectal palpation or ultrasound; prognosis depends on location.
Incomplete fractures of the tibia from repetitive concussion, most common in racehorses. The caudal tibial cortex is typically affected. Signs include: Hindlimb lameness that worsens with exercise; localized pain on tibial palpation; may have heat and soft tissue swelling; diagnosed on nuclear scintigraphy (bone scan) before visible on radiographs.; Consult veterinarian for specific symptoms.
Tears of the meniscal cartilages in the stifle (knee). The medial meniscus is more commonly injured. Can occur from hyperextension, twisting, or degenerative changes. Signs include: Stifle effusion; hindlimb lameness; positive to stifle flexion; clicking or catching during movement; hindlimb circumduction; confirmed on ultrasound or arthroscopy; chronic cases show thigh muscle atrophy.
Fractures of the tarsal bones, most commonly slab fractures of the third tarsal bone or central tarsal bone. Common in racehorses and sport horses. Signs include: Acute hock lameness; hock effusion; pain on hock flexion; may see subtle lameness that worsens with work; diagnosed on radiographs (may need special views); surgical repair with lag screws for articular fractures.
Pelvic fractures (ilium, ischium, or pubis) Signs include: Consult veterinarian for specific symptoms.
Tuber coxae fracture ("knocked-down hip") Signs include: Consult veterinarian for specific symptoms.
Sacroiliac joint disease involves pain and dysfunction in the joint where the sacrum meets the pelvis. It is one of the most common causes of poor hindlimb impulsion and performance problems in sport horses. The condition can result from strain, subluxation, or osteoarthritis of the sacroiliac joint and its supporting ligaments. ## What it is The sacroiliac joints are low-motion synovial joints that transfer propulsive forces from the hindlimbs to the axial skeleton. Strong ligaments surround the joints and provide stability. Dysfunction can arise from acute trauma, repetitive stress, poor conformation, or degenerative changes. The joint is difficult to image directly, so diagnosis often relies on clinical signs, response to diagnostic analgesia, and exclusion of other causes of hindlimb lameness. ## Signs and symptoms - Poor hindlimb impulsion and engagement - Hunter's bump (prominent tuber sacrale on one or both sides) - Asymmetric gluteal muscle development - Difficulty with collection, lateral work, or jumping - Pain on palpation or manipulation of the sacroiliac region - Cross-cantering or reluctance to canter on one lead - Chronic cases may show muscle atrophy or compensatory back pain ## Causes and risk factors Sacroiliac joint disease is often associated with repetitive stress in sport horses, conformational issues (especially asymmetry), poor saddle fit, and previous trauma. Young horses in intense training and horses with weak core muscles appear to be at higher risk. The condition can also develop secondary to other sources of pain that alter gait mechanics. ## How it is diagnosed Diagnosis is challenging and usually involves a combination of clinical examination, palpation, and diagnostic analgesia (blocking the sacroiliac region). Radiographs and ultrasound have limited value for the joint itself but can rule out other problems. Nuclear scintigraphy (bone scan) is often helpful for identifying increased uptake in the sacroiliac region. A positive response to local anesthesia in the sacroiliac area supports the diagnosis. ## Treatment and management Treatment typically includes a period of rest or modified exercise, physiotherapy and core strengthening, shockwave therapy, and anti-inflammatory medication. Some horses benefit from sacroiliac joint injections (corticosteroids or regenerative therapies). Long-term management focuses on improving core strength, correcting any saddle fit issues, and addressing conformational or biomechanical contributors. Many horses can return to previous levels of work with appropriate management. ## When to call the vet Contact your veterinarian if your horse shows persistent poor impulsion, asymmetric muscle development, or resistance to collection that does not improve with basic training adjustments. Early intervention often leads to better outcomes. ## Prevention Prevention focuses on maintaining good core strength and symmetry through appropriate conditioning, ensuring proper saddle fit, and avoiding sudden increases in workload. Regular assessment of young horses in training can help identify issues early. ## Frequently asked questions **Is sacroiliac joint disease the same as kissing spines?** No, but the two conditions can occur together and both cause back pain and poor performance. **Can a horse with sacroiliac joint disease still compete?** Many horses return to successful competition with proper management, though some require ongoing treatment and modified training. **How long does recovery take?** Recovery timelines vary. Some horses improve significantly within weeks of targeted treatment, while others require months of rehabilitation. This information is for educational purposes only. Always consult with a licensed veterinarian for diagnosis and treatment of your horse. Signs include: Poor hindlimb impulsion and engagement; hunter's bump (prominent tuber sacrale on one or both sides); asymmetric gluteal muscle development; difficulty with collection, lateral work, or jumping; pain on palpation or manipulation of the sacroiliac region; cross-cantering or reluctance to canter on one lead; chronic cases may show muscle atrophy or compensatory back pain
Stress fractures of the ilium (racehorses) Signs include: Consult veterinarian for specific symptoms.
Hip dysplasia (rare in horses) Signs include: Consult veterinarian for specific symptoms.
Degenerative joint disease of the lower hock joints (centrodistal and tarsometatarsal joints). Very common cause of hind limb lameness and poor performance. Signs include: Consult veterinarian for specific symptoms.; Insidious onset hindlimb lameness; worse at start of work, improves with warming up; positive to distal limb flexion test (spavin test); shortening of hind stride; resistance to collection; bony swelling on medial hock in advanced cases; hock stiffness.
The patella catches over the medial trochlear ridge and cannot release, locking the hindlimb in extension. Common in young, unfit horses and certain breeds. Related to the stay apparatus. Signs include: Consult veterinarian for specific symptoms.; Hindlimb locked in extension (cannot flex); leg drags behind; sudden release with a jerk or click; intermittent in mild cases; worse at walk and when starting from standstill; may catch momentarily then release; improves with fitness.; Hindlimb locks in full extension and cannot flex; the horse drags the toe or hops until it releases with an audible click; may be intermittent; worse at walk and when tired; improves with fitness; common in young ponies and gaited breeds.
Pelvic fractures are diagnosed via rectal palpation, transrectal ultrasound, and scintigraphy. Assess external landmarks for symmetry.
See the Pelvis (Os Coxae) on our interactive 3D horse model. Open 3D Model