Musculus gluteus medius
The gluteus medius is the largest muscle in the horse. It originates from the gluteal surface of the ilium, the gluteal fascia, the sacrum, and the sacroiliac and sacrosciatic ligaments, and inserts on the greater trochanter of the femur. Its primary actions are to extend the hip joint and abduct the hind limb. It is the principal extensor of the hip and the major propulsive muscle of the hindquarters. Innervation is via the cranial gluteal nerve (roughly L5–S2). Because it is so large and powerful, it is responsible for the bulk of the forward drive generated by the hind limbs. Asymmetry or atrophy of the gluteal muscles is often visible and can result from sacroiliac joint problems, nerve damage, or chronic lameness. “Hunter’s bumps” (prominence of the tuber sacrale) may follow sacroiliac strain, but most horses with sacroiliac region pain have symmetrical tubera sacrale; hindquarter muscle asymmetry is more common. The trochanteric bursa deep to the accessory gluteal tendon can become inflamed (trochanteric bursitis).
Origin: Gluteal surface of the ilium, gluteal fascia, and sacroiliac ligament
Insertion: Greater trochanter of the femur (trochanteric fossa)
Action: Extends the hip joint; primary driver of propulsion; abducts the hindlimb
Innervation: Cranial gluteal nerve (L5-S2)
Gluteal atrophy is a common finding with sacroiliac dysfunction, pelvic fractures, or cranial gluteal nerve lesions. Hunter’s bumps may be conformational or secondary to sacroiliac ligament strain. Trochanteric bursitis produces pain over the greater trochanter. Ultrasound and advanced imaging can evaluate the muscle and surrounding structures.
## Overview Gluteal myopathy or tying-up is exertional rhabdomyolysis affecting the hindquarter muscles. During or after exercise the muscles become firm and painful, the stride shortens, and the hor
## Overview Sacroiliac joint strain is damage to the ligaments supporting the joint between the spine and pelvis. It is a common cause of poor hindquarter performance. Signs include difficulty engagi
## Overview Gluteal atrophy is loss of muscle mass in the hindquarter secondary to chronic disuse from hind-limb lameness or neurologic disease. Viewed from behind, the affected side appears smaller.
Asymmetry of the hindquarter muscles, a prominent bump over the croup, or reduced hind-limb engagement should be evaluated. Sudden loss of hindquarter muscle after a fall or trailer accident needs prompt veterinary attention. Chronic mild asymmetry is common and may or may not be clinically significant.
## Overview Gluteal myopathy or tying-up is exertional rhabdomyolysis affecting the hindquarter muscles. During or after exercise the muscles become firm and painful, the stride shortens, and the horse may sweat excessively. Myoglobinuria (dark urine) and elevated muscle enzymes confirm muscle damage. ## Causes Exercise beyond conditioning, electrolyte imbalance, or underlying genetic myopathies (polysaccharide storage myopathy, recurrent exertional rhabdomyolysis). ## Diagnosis Clinical signs plus markedly elevated creatine kinase and aspartate aminotransferase. Urinalysis for myoglobin. Genetic testing when recurrent. ## Treatment Immediate rest, fluids, pain control, and prevention of kidney damage from myoglobin. Long-term management addresses diet and exercise for underlying myopathies. ## Recovery and Prognosis Good for single episodes with prompt care. Recurrent cases need ongoing management. ## Prevention Gradual conditioning, appropriate diet, and electrolyte balance. Signs include: firm painful hindquarters during or after exercise; shortened stride; sweating; dark urine; elevated muscle enzymes
## Overview Sacroiliac joint strain is damage to the ligaments supporting the joint between the spine and pelvis. It is a common cause of poor hindquarter performance. Signs include difficulty engaging the hindquarters, reluctance to canter on one lead, and poor impulsion; hip height (the tubera sacrale) is usually symmetrical. Some horses react to pressure over the tubera sacrale. ## Causes Repetitive stress or acute trauma, especially in jumping horses. ## Diagnosis Clinical examination, diagnostic analgesia, and sometimes scintigraphy or ultrasound. ## Treatment Rest, anti-inflammatories, physiotherapy, and gradual rehabilitation. Injections may be used in some cases. ## Recovery and Prognosis Fair to good with appropriate management. The hunter’s bump may remain. ## Prevention Progressive conditioning, especially for young jumping horses. Signs include: difficulty engaging hindquarters; reluctance to canter one lead; poor impulsion; some horses react to pressure over the tubera sacrale
## Overview Gluteal atrophy is loss of muscle mass in the hindquarter secondary to chronic disuse from hind-limb lameness or neurologic disease. Viewed from behind, the affected side appears smaller. It is a sign of prolonged reduced use rather than a primary disease. ## What It Indicates Chronic pain or neurologic dysfunction in the ipsilateral hind limb leading to disuse. ## Diagnosis Visual asymmetry plus identification of the underlying lameness or neurologic deficit. ## Treatment Treat the primary cause. Controlled exercise and physiotherapy help restore muscle once the horse is comfortable. ## Recovery and Prognosis Muscle can rebuild if the underlying problem is resolved. Long-standing atrophy recovers slowly. ## Prevention Early treatment of hind-limb lameness. Signs include: visibly smaller hindquarter on one side; asymmetric muscling; persistent mild hind-limb lameness; reduced power
Gluteal atrophy is a common finding with sacroiliac dysfunction, pelvic fractures, or cranial gluteal nerve lesions. Hunter’s bumps may be conformational or secondary to sacroiliac ligament strain. Trochanteric bursitis produces pain over the greater trochanter. Ultrasound and advanced imaging can evaluate the muscle and surrounding structures.
Asymmetry of the hindquarter muscles, a prominent bump over the croup, or reduced hind-limb engagement should be evaluated. Sudden loss of hindquarter muscle after a fall or trailer accident needs prompt veterinary attention. Chronic mild asymmetry is common and may or may not be clinically significant.
See the Gluteus Medius on our interactive 3D horse model. Open 3D Model