Musculus longissimus dorsi
The longest and largest muscle in the horse, running from sacrum to cervical vertebrae. THE muscle of the back -- essential for carrying a rider, stabilizing the spine, and transmitting hindquarter propulsion. Most commonly affected in equine back pain.
Origin: Iliac crest, sacrum, spinous/transverse processes of lumbar and thoracic vertebrae
Insertion: Transverse and articular processes of thoracic and cervical vertebrae; ribs
Action: Extends the back and loin; lateral flexion; stabilizes the vertebral column during locomotion
Innervation: Dorsal branches of thoracic and lumbar spinal nerves
The longissimus is the largest epaxial muscle and the principal extensor of the back. Back pain ('kissing spines', sacroiliac dysfunction) commonly manifests as pain and spasm in this muscle. Important for collection and impulsion in dressage.
The most common riding-related back problem. Caused by overwork, poor saddle fit, or rider imbalance.
Poorly fitted saddles create focal pressure points causing localized atrophy, pain, and behavioral changes.
Prolonged back pain leads to visible wasting creating a gutter along the spine. Recovery requires targeted rehabilitation.
Kissing spines, also known as overriding dorsal spinous processes, occur when the bony projections along the top of the horse's spine touch or overlap, causing pain and inflammation. This condition mo
The most common riding-related back problem. Caused by overwork, poor saddle fit, or rider imbalance. Signs include: Sensitivity along the back when palpated; hollowed back under saddle; resistance to transitions; short choppy stride; tail swishing when ridden; improved movement without rider.
Poorly fitted saddles create focal pressure points causing localized atrophy, pain, and behavioral changes. Signs include: Dry spots in sweaty saddle patch; white hairs along saddle region; muscle atrophy beside withers; cold-backed behavior; uneven saddle wear.
Prolonged back pain leads to visible wasting creating a gutter along the spine. Recovery requires targeted rehabilitation. Signs include: Visible groove alongside spinous processes; prominent spine; weak hollow back posture; inability to carry a rider comfortably.
Kissing spines, also known as overriding dorsal spinous processes, occur when the bony projections along the top of the horse's spine touch or overlap, causing pain and inflammation. This condition most commonly affects the thoracolumbar region (T13 to L2) and is seen on radiographs in 30 to 40% of horses, though not all show clinical signs. It is a frequent cause of back pain and poor performance in sport horses. ## What it is The dorsal spinous processes are the upward-pointing bony projections of the vertebrae. In kissing spines, these processes are too close together and impinge on each other during movement, leading to bone remodeling, inflammation of the interspinous ligaments, and pain. The condition is often associated with poor posture, weak core muscles, or conformational factors that increase extension of the back. While many horses have radiographic changes without pain, clinical kissing spines cause significant discomfort, especially under saddle. ## Signs and symptoms - Back pain or sensitivity when pressure is applied along the spine - Dipping away from pressure or hollowing the back under rider - Bucking, rearing, or resistance to collection - Poor performance or unwillingness to go forward - Muscle atrophy along the topline - Reluctance to canter or perform lateral movements - Extreme sensitivity at specific vertebral levels during grooming or saddling - Cross-cantering or difficulty maintaining a consistent gait ## Causes and risk factors Kissing spines develop from a combination of conformational, biomechanical, and management factors. Risk factors include weak abdominal and back muscles, repetitive extension of the spine (common in jumping and dressage), poor saddle fit, and genetic predisposition. Horses with long backs or weak toplines are more susceptible. The condition can also develop secondary to other sources of pain that cause the horse to hollow its back. ## How it is diagnosed Diagnosis combines clinical examination, palpation of the back, and imaging. Radiographs are the primary tool and show the proximity or overlap of the spinous processes. Nuclear scintigraphy (bone scan) can help identify active inflammation. Ultrasound evaluates the interspinous ligaments and soft tissues. Local anesthesia of the affected interspinous spaces is often used to confirm that the kissing spines are the source of pain. ## Treatment and management Treatment options range from conservative to surgical. Conservative management includes physiotherapy, core strengthening exercises, shockwave therapy, mesotherapy, and anti-inflammatory medication. Interspinous ligament injections or corticosteroid injections into affected spaces can provide relief. In refractory cases, surgical options such as interspinous ligament desmotomy or partial resection of the spinous processes are used with good success rates in appropriately selected horses. Saddle fit evaluation and rehabilitation are essential components of long-term management. ## When to call the vet Contact your veterinarian if your horse shows signs of back pain, resistance under saddle, or performance issues that do not resolve with basic management changes. Early diagnosis and a multimodal treatment plan offer the best chance of returning the horse to comfortable work. ## Prevention Prevention focuses on maintaining strong core and back muscles through appropriate conditioning and avoiding repetitive spinal extension without adequate strength. Regular saddle fit checks, good footing, and prompt attention to any signs of back discomfort help reduce risk. Horses with conformational risk factors benefit from proactive core strengthening programs. ## Frequently asked questions **Do all horses with kissing spines on X-rays have pain?** No. Many horses have radiographic changes without clinical signs. Diagnosis requires correlation with clinical findings and response to local anesthesia. **Can kissing spines be cured?** Surgical treatment can provide long-term improvement in many horses. Conservative management can control symptoms but may not eliminate the underlying bony changes. **Is surgery always necessary?** No. Many horses respond well to physiotherapy, injections, and rehabilitation. Surgery is usually reserved for cases that do not improve with conservative treatment. This information is for educational purposes only. Always consult with a licensed veterinarian for diagnosis and treatment of your horse. Signs include: Back pain or sensitivity when pressure is applied along the spine; dipping away from pressure or hollowing the back under rider; bucking, rearing, or resistance to collection; poor performance or unwillingness to go forward; muscle atrophy along the topline; reluctance to canter or perform lateral movements; extreme sensitivity at specific vertebral levels during grooming or saddling; cross-cantering or difficulty maintaining a consistent gait
The longissimus is the largest epaxial muscle and the principal extensor of the back. Back pain ('kissing spines', sacroiliac dysfunction) commonly manifests as pain and spasm in this muscle. Important for collection and impulsion in dressage.
See the Longissimus Dorsi on our interactive 3D horse model. Open 3D Model