Os coxae (Pelvis)
The pelvis (os coxae) is formed by the fusion of three bones on each side: the ilium (cranially), the ischium (caudally), and the pubis (ventrally). These fuse at the acetabulum, which forms the socket of the hip joint. The two sides are joined ventrally at the pelvic symphysis and articulate dorsally with the sacrum at the sacroiliac joints. The ilium is the largest component and bears the tuber coxae (point of the hip) and tuber sacrale as important palpable landmarks. The ischial tuberosities (pin bones) are prominent caudally. The pelvis anchors the most powerful muscles in the body and transmits propulsive force from the hindlimbs through the sacroiliac joints to the spine. It also protects the pelvic organs.
Pelvic fractures, sacroiliac strain or injury, and hip dysplasia or luxation can cause significant hindlimb lameness. The tuber coxae and ischial tuberosities are common landmarks and sites of traumatic injury. Pelvic asymmetry or pain on rectal examination warrants further investigation.
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
## Overview Pelvic fractures result from slipping, falling, or impact, or from stress in racehorses. Common sites include the tuber coxae (point of hip), ilial wing, and pelvic floor. Signs are acute
## Overview Tibial stress fractures are incomplete cracks from repetitive concussion, most common in racehorses. The caudal tibial cortex is typically affected. Lameness worsens with exercise. Locali
## Overview Meniscal injury is a tear of the cartilage pads in the stifle. The medial meniscus is more commonly affected. Tears occur from hyperextension, twisting, or degeneration. Signs include sti
## Overview Tarsal slab fractures are articular fractures of the hock, most often involving the central or third tarsal bones. They occur in racehorses and other performance horses from hyperextensio
## Overview Pelvic fractures can involve the ilium, ischium, or pubis. Ilial wing and tuber coxae fractures are among the more common and often carry a better prognosis. Pubic and ischial fractures c
## Overview A tuber coxae fracture, commonly called a knocked-down hip, is a break of the point of the hip from impact with a gate, fence, or another horse. A fragment is often displaced, changing th
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
## Overview Stress fractures of the ilium are incomplete pelvic cracks from repetitive loading in racehorses. They cause hind-limb lameness that worsens with exercise and may present only as poor per
## Overview Hip dysplasia is abnormal development of the coxofemoral joint. It is rare in horses compared with dogs. When present, it causes hind-limb lameness, reduced range of motion, and radiograp
## Overview Bone spavin is osteoarthritis (degenerative joint disease) of the distal tarsal joints, principally the distal intertarsal and tarsometatarsal joints. Repeated compression and rotation da
## Overview Upward fixation of the patella occurs when the medial patellar ligament catches over the medial trochlear ridge and cannot release, locking the hind limb in extension. The leg drags behin
Hindlimb lameness that is worse on one side, asymmetry of the hips or croup, or reluctance to engage the hindquarters should be evaluated. Trauma to the point of the hip or pin bones needs veterinary assessment.
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.
## Overview Pelvic fractures result from slipping, falling, or impact, or from stress in racehorses. Common sites include the tuber coxae (point of hip), ilial wing, and pelvic floor. Signs are acute severe hind-limb lameness, possible asymmetry of the pelvis, crepitus, and muscle atrophy. Diagnosis is by rectal palpation, ultrasound, or scintigraphy. ## Causes Trauma or fatigue failure. ## Diagnosis Rectal examination, ultrasound, and bone scan. Radiographs are difficult in adults. ## Treatment Strict stall rest for most fractures. Surgery is rarely feasible. Prognosis depends on the location and degree of displacement. Tuber coxae fractures often do well; more central fractures are more serious. ## Recovery and Prognosis Variable. Many tuber coxae and some ilial fractures heal with rest. Displaced acetabular or highly unstable fractures have a poor outlook. ## Prevention Safe footing and monitoring of racehorses for early stress changes. Signs include: acute severe hind-limb lameness; asymmetric pelvis; crepitus; muscle atrophy; confirmed on rectal palpation or ultrasound
## Overview Tibial stress fractures are incomplete cracks from repetitive concussion, most common in racehorses. The caudal tibial cortex is typically affected. Lameness worsens with exercise. Localized pain, heat, or soft-tissue swelling may be present. Bone scan diagnoses them before they are visible on radiographs. Rest prevents propagation to a complete fracture. ## Causes Cyclical loading. ## Diagnosis Nuclear scintigraphy. Radiographs often normal early. ## Treatment Strict rest, usually 8 to 12 weeks or longer. ## Recovery and Prognosis Excellent if rested before complete fracture. ## Prevention Training modifications when early lameness appears. Signs include: hind-limb lameness worse with exercise; localized pain on tibial palpation; possible heat and swelling; diagnosed on bone scan before radiographs
## Overview Meniscal injury is a tear of the cartilage pads in the stifle. The medial meniscus is more commonly affected. Tears occur from hyperextension, twisting, or degeneration. Signs include stifle effusion, hind-limb lameness, a positive flexion test, clicking or catching, and circumduction. Chronic cases show thigh-muscle atrophy. Diagnosis is by ultrasound or arthroscopy. ## Causes Trauma or degenerative change. ## Diagnosis Ultrasound and arthroscopy. ## Treatment Arthroscopic debridement of the torn portion. Prognosis depends on the extent of the tear. ## Recovery and Prognosis Fair for partial tears. Poor for extensive tears involving the meniscotibial ligaments. ## Prevention None specific. Signs include: stifle effusion; hind-limb lameness; positive stifle flexion; clicking or catching; circumduction; thigh atrophy in chronic cases
## Overview Tarsal slab fractures are articular fractures of the hock, most often involving the central or third tarsal bones. They occur in racehorses and other performance horses from hyperextension or fatigue. Signs include acute hock lameness and effusion. Surgical lag-screw repair is the treatment of choice for displaced articular slabs. ## Causes Acute overload or stress fracture propagation. ## Diagnosis Radiographs, often requiring multiple oblique views. Computed tomography provides detail. ## Treatment Lag-screw fixation for articular slabs. Conservative management for some non-displaced fractures. Prognosis is better with accurate reduction. ## Recovery and Prognosis Fair to good for properly repaired slabs. Osteoarthritis can develop. ## Prevention Training management to reduce fatigue injury. Signs include: acute hock lameness; hock effusion; pain on flexion; radiographic slab fracture
## Overview Pelvic fractures can involve the ilium, ischium, or pubis. Ilial wing and tuber coxae fractures are among the more common and often carry a better prognosis. Pubic and ischial fractures can affect the pelvic canal and weight-bearing. Diagnosis relies on rectal palpation, ultrasound, or scintigraphy because standard radiographs are limited in adults. ## Causes Trauma or stress. ## Diagnosis Rectal examination, ultrasound, bone scan. ## Treatment Strict stall rest for the majority. Surgical options are rare. ## Recovery and Prognosis Better for tuber coxae and some ilial fractures. More guarded for acetabular or highly displaced fractures. ## Prevention Safe environments and monitoring of at-risk racehorses. Signs include: hind-limb lameness; pelvic asymmetry; crepitus; muscle atrophy; site-dependent severity
## Overview A tuber coxae fracture, commonly called a knocked-down hip, is a break of the point of the hip from impact with a gate, fence, or another horse. A fragment is often displaced, changing the outline of the pelvis. It is the least damaging pelvic fracture because it does not involve a joint. Most horses return to work, though a permanent blemish remains. ## Causes Direct trauma. ## Diagnosis Visual asymmetry and ultrasound or radiographs. ## Treatment Rest. Surgery is rarely needed. Return to work is often possible in about 3 to 4 months. ## Recovery and Prognosis Excellent for athletic use. Permanent cosmetic change is expected. ## Prevention Safe stable and paddock design. Signs include: sudden lameness; swelling at the point of the hip; knocked-down hip appearance; asymmetric hip height
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
## Overview Stress fractures of the ilium are incomplete pelvic cracks from repetitive loading in racehorses. They cause hind-limb lameness that worsens with exercise and may present only as poor performance. Scintigraphy is the diagnostic method of choice. Strict stall rest is required because muscle pull can propagate the fracture. ## Causes Cyclical loading. ## Diagnosis Bone scan. Ultrasound may detect more advanced cracks. ## Treatment Complete stall rest, often 60 days or more. Hand-walking is usually avoided. ## Recovery and Prognosis Good if rested before complete fracture. ## Prevention Training monitoring. Signs include: hind-limb lameness worse with exercise; poor performance; diagnosed on bone scan; no obvious trauma
## Overview Hip dysplasia is abnormal development of the coxofemoral joint. It is rare in horses compared with dogs. When present, it causes hind-limb lameness, reduced range of motion, and radiographic evidence of shallow acetabulum or femoral-head malformation, usually recognized in young horses. ## Causes Developmental. Genetic factors are suspected but poorly defined in horses. ## Diagnosis Radiographs of the pelvis under appropriate positioning or anesthesia. Clinical signs of coxofemoral pain. ## Treatment Conservative management with anti-inflammatories and controlled exercise. Surgical options are limited. Many affected horses have restricted athletic careers. ## Recovery and Prognosis Guarded for athletic use. ## Prevention None established. Signs include: hind-limb lameness in a young horse; reduced hip range of motion; radiographic dysplasia of the coxofemoral joint
## Overview Bone spavin is osteoarthritis (degenerative joint disease) of the distal tarsal joints, principally the distal intertarsal and tarsometatarsal joints. Repeated compression and rotation damage cartilage, narrow the joint spaces, and stimulate new bone formation. The result is progressive hind-limb lameness that is one of the most common causes of performance limitation in sport horses. ## Causes Repetitive concussion, conformational faults (straight or sickle hocks), and athletic activities that heavily load the hocks (jumping, dressage, western performance) are the main drivers. Mineral imbalances have been suggested but evidence is limited. ## Diagnosis History of gradual hind-limb lameness that may warm out of, positive flexion tests, and a characteristic “stabbing” or short stride are suggestive. Radiographs show joint-space narrowing, sclerosis, and periarticular new bone. Diagnostic analgesia of the distal tarsal joints confirms the source of pain. ## Treatment Non-steroidal anti-inflammatory drugs, intra-articular corticosteroids, corrective shoeing, and workload modification are first-line measures. Chemical or surgical arthrodesis (facilitated ankylosis) can be considered when medical management fails and the goal is pain-free fusion of the low-motion joints. ## Recovery and Prognosis Many horses remain useful with medical management. Complete fusion, whether spontaneous or surgical, can restore comfort. Advanced bilateral disease may ultimately limit athletic career length. ## Prevention Selection for good hock conformation, balanced shoeing, and sensible training progression reduce risk but cannot eliminate it in high-level athletes. Signs include: gradual hindlimb lameness; shortened stride or toe dragging; positive hock flexion test; bony enlargement on the medial lower hock in advanced cases; stiffness after rest
## Overview Upward fixation of the patella occurs when the medial patellar ligament catches over the medial trochlear ridge and cannot release, locking the hind limb in extension. The leg drags behind until it suddenly releases with a jerk or click. It is common in young, unfit horses and those with straight hind-limb conformation. Mild cases are intermittent and worse at the walk or when starting out. Severe cases may remain locked for hours. ## Causes Poor quadriceps tone, straight conformation, or sudden reduction in fitness. ## Diagnosis Observation of intermittent or persistent locking. ## Treatment Conditioning and hill work for mild cases. Medial patellar ligament splitting or desmotomy for persistent cases. ## Recovery and Prognosis Excellent with appropriate management. ## Prevention Maintain fitness, especially in predisposed horses. Signs include: hind limb locked in extension; leg drags behind; sudden release with a jerk or click; intermittent in mild cases; worse at walk
Pelvic fractures, sacroiliac strain or injury, and hip dysplasia or luxation can cause significant hindlimb lameness. The tuber coxae and ischial tuberosities are common landmarks and sites of traumatic injury. Pelvic asymmetry or pain on rectal examination warrants further investigation.
Hindlimb lameness that is worse on one side, asymmetry of the hips or croup, or reluctance to engage the hindquarters should be evaluated. Trauma to the point of the hip or pin bones needs veterinary assessment.
See the Pelvis (Os Coxae) on our interactive 3D horse model. Open 3D Model