By Siun Griffin, Vet Physio and LCAO Community Manager
In the intricate biomechanics of horses, understanding the musculature is crucial for ensuring their well-being and performance. Among the myriad muscles contributing to equine locomotion and posture, the splenius muscle holds significant importance.
Anatomy of the Splenius Muscle
The splenius muscle is located in the neck region of the horse. It is divided into two parts: the splenius capitis and the splenius cervicis.
Its origin is the spinous processes of T3–5 by means of thoracolumbar fascia and the nuchal ligament (the withers). The insertion is at the nuchal crest and mastoid process of temporal bone and transv. processes of C2–5. (the poll area)
Its innervations are by the dorsal branch of local spinal nerves, and dorsal branch of the accessory nerve.
It is part of the dorsal chain muscles. Specifically the epaxial muscles, which are extensor muscles of the vertebral column. It is a superficial muscle.
Function of the Splenius Muscle
The splenius muscle plays a crucial role in maintaining posture and facilitating movement in horses. Its primary functions include:
1. Head and Neck Extension
The splenius muscle aids in extending and elevating the head and neck, allowing the horse to maintain balance. By its action of elevating the head and neck it facilitates forelimb protraction during the walk.
During the trot it ‘acts before and during the first part of the stance phase of each forelimb to limit lowering of the neck.’
At the canter, it again limits the neck from lowering and creates neck extension ‘during the leading stance phase.’
2. Lateral Flexion
Working in conjunction with other neck muscles, the splenius muscle facilitates lateral flexion of the neck, enabling the horse to bend and turn effectively.
3. Stabilisation
The splenius muscle provides stability to the cervical and thoracic spine.
Innervation of the Splenius Muscle
The splenius muscle receives innervation from branches of the cervical spinal nerves, primarily the dorsal branches of cervical nerves 3 to 8 (C3-C8). These nerves supply motor fibres to the muscle, controlling its contraction and relaxation.
Clinical Considerations
1. Muscle Strain
Like any other muscle, the splenius muscle is susceptible to strain, particularly during strenuous physical activity or sudden movements. Signs of splenius muscle strain in horses may include lameness, reluctance to bend or extend the neck, and sensitivity to touch along the muscle.
2. Equine Performance
Dysfunction or injury to the splenius muscle can impact the horse's performance, compromising its ability to engage in activities such as dressage, jumping, or racing. Proper conditioning, warm-up, and cooldown routines can help prevent splenius muscle injuries and optimise equine performance.
3. Diagnostic Imaging
In cases of suspected splenius muscle injury or dysfunction, diagnostic imaging techniques such as ultrasound or magnetic resonance imaging (MRI) may be employed to assess the extent of damage and guide treatment decisions.
The splenius muscle plays a vital role in the biomechanics of horses, contributing to posture, movement, and overall performance. Understanding its anatomy, function, and innervation is essential for veterinarians, trainers, and owners in maintaining equine health and well-being.
Sources:
Adams and Stashak’s Lameness in Horses, 7th Edition
Anatomy of the Horse, Fifth, revised Edition
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