The Longissimus Dorsi Muscle in the Horse: Anatomy and Function

The Longissimus Dorsi Muscle in the Horse: Anatomy and Function

The longissimus dorsi is one of the most significant muscles in the equine musculoskeletal system. As part of the epaxial muscles, it plays a crucial role in movement, stability, and performance. Understanding its anatomy, function, and clinical relevance is essential for veterinarians, osteopaths, and equine bodyworkers.

Location and Structure

The longissimus dorsi is the largest and longest muscle of the horse’s back. It runs along both sides of the vertebral column, It is not just found in the back. It actually begins in the neck at c4 and goes to the sacrum. It also has branches that extend all the way up to the head and back to the tail. The neck sections of the longissimus are called the longissimus cervicis muscle. The longissimus dorsi muscle is part of the longissimus system, which belongs to the erector spinae group and is divided into three sections: (1)

• Longissimus lumborum – located in the lumbar region.
• Longissimus thoracis – extending along the thoracic vertebrae.
• Longissimus cervicis – continuing into the cervical region towards the head.

Origin and Insertion

• Origin: Arises from the sacrum, ilium, lumbar vertebrae, and thoracic vertebrae.
• Insertion: Attaches to the transverse processes of the vertebrae, and ribs vertebrae. (2)

Function

The longissimus dorsi plays a vital role in spinal movement and support. Its functions include:

• Extension of the spine – dorsiflex
• Lateral flexion – bending the spine to one side.
• Stabilisation of the vertebral column – crucial for maintaining balance and posture.
• Transmission of force from the hindquarters – essential for locomotion, jumping, and collection in dressage movements.
• Absorption of mechanical power – acting eccentrically to control spinal motion during movement.

(3)

Nerve Supply

All sections of the longissimus are innervated by the dorsal rami of the spinal nerves. With the thoracic section innervated by the dorsal rami of the thoracic and lumbar spinal nerves. The capitis and cervicis sections are innervated by the dorsal rami of the cervical spinal nerves. (4)

These nerves emerge providing motor and sensory signals to the muscle.

Biomechanics and Movement

The biomechanics of the horse's back depend on the interaction between the spinal column and the spinal musculature. (5) The longissimus dorsi muscle performs different functions along its length, contributing to the movement and stabilisation of different spinal segments. It plays an essential role in:

• Flexion-extension cycles – vital during locomotion.
• Load transmission between the limbs and spine – particularly in trotting and cantering.
• Back motion stability – ensuring controlled movement and force absorption.

Clinical Relevance

• Muscle tension and pain: Common in performance horses due to overuse, poor saddle fit, or incorrect training methods.
• Weakness or atrophy: Can result from lack of use, neurological issues, or improper conditioning.
• Osteopathic treatments: Techniques such as massage, stretching, and osteopathic adjustments can help maintain flexibility and function.
• Diagnostic importance: Palpation, thermography, and ultrasound are useful tools for assessing muscle health and detecting injuries.

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The longissimus dorsi is a key muscle in equine biomechanics, affecting movement, performance, and overall well-being. Understanding its anatomy, function, and common issues allows professionals to optimise horse care, prevent injuries, and improve equine athletic performance. Future research integrating 3D anatomical analysis and muscle activity measurements could further enhance our understanding of its function and clinical applications.

References

1. Journal of Applied Animal Science, 8(3), 9-26. Díaz Delgado, O. B., Louro, L. F., Rocchigiani, G., Verin, R., Humphreys, W., Senior, M., & Campagna, I. (2021). Ultrasound-guided erector spinae plane block in horses: A cadaver study. Veterinary Anaesthesia and Analgesia, 48(4), 577–584. Available at: ScienceDirect
2. Grösel, M., Zsoldos, R. R., Kotschwar, A., Gfoehler, M., & Peham, C. (2010). A preliminary model study of the equine back including activity of longissimus dorsi muscle. Equine Veterinary Journal, 42(5), 444–450.

beva.onlinelibrary.wiley.com

3. Piermattei's Atlas of Surgical Approaches to the Bones and Joints of the Dog and Cat (Fifth Edition), 2014, Longissimus Muscle. ScienceDirect
4. Study.com. Longissimus Muscle - Function, Origin & Insertion
5. Ritruechai, P. (2016). A Review on the Functions of the Horse Back and Longissimus Dorsi Muscle. Journal of Applied Animal Science, 8(3), 9-26.
6. Spinal Biomechanics and Functional Anatomy by Jean-Marie Denoix (2019). Published in Veterinary Clinics: Equine Practice.
7. Muscle Fibre Architecture of Thoracic and Lumbar Longissimus Dorsi Muscle in the Horse" by Dietrich et al. (2021). This study examines the intramuscular architecture of the longissimus dorsi, providing insights into its role in spinal stability and locomotion.

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