# Motion Coupling at the Cervical Vertebral Joints in the Horse—An Ex Vivo Study Using Bone-Anchored Markers

## TL;DR

This study examines how the horse's neck joints move together with ligaments intact, revealing strong motion coupling that could improve training and treatment for neck issues.

## Contribution

The study provides new insights into equine cervical joint motion with ligaments intact, revealing detailed coupling patterns not previously documented.

## Key findings

- Most cervical joints showed strong correlations between yaw, pitch, and roll movements.
- The atlanto-occipital joint exhibited complete correlation between movement axes.
- C5–C6 and C6–C7 joints showed significantly lower correlation coefficients compared to other levels.

## Abstract

The horse’s neck is highly flexible and vital for balance, vision, and breathing. Many horses develop neck problems, but detailed motion of each neck joint is still poorly understood. Most past research removed the neck’s ligaments to make measurements easier, even though these tissues help the neck store and release energy during trotting or cantering. The present study looked at how different joint movements are linked with the ligaments still in place. Using donated horse bodies placed upright in a wooden frame, markers were fixed onto the head, and onto small pins in each neck bone and the first bone of the chest. The bones were then tracked as the head was turned, nodded, and tilted by hand. A strong link was found between movements; when the head moves to the side, most neck joints also move sideways. Nodding motion was strongest at the “yes joint” between the head and the first neck bone and turning was strongest at the “no joint” between the first and the second neck bone. No joint in the neck moved independently. Understanding how the horse neck moves can help improve horse training and treatments for neck problems.

The influence of soft tissue structures, including ligaments spanning one or more intervertebral junctions and the nuchal ligament, on motion of the equine cervical joints remains unclear. The present study addressed this using four post-mortem horse specimens extending from head to withers with all ligaments intact. Three-dimensional kinematics was obtained from markers on the head and bone-anchored markers on each cervical and the first thoracic vertebra during rotation, lateral bending, flexion and extension of the whole head, and neck segment. Yaw, pitch, and roll angles in 8 cervical joints (total 32) were calculated. Flexion and extension were expressed mainly as pitch in 27 and 22 joints, respectively. Rotation appeared as predominantly roll in 13 joints, whereas lateral bending was represented as predominantly yaw in 1 and as roll or pitch in all other joints. Significant correlations between yaw, pitch, and roll were observed at individual cervical joints in 97% of all measurements, with the atlanto-occipital joint showing complete (100%) correlation. Most non-significant correlations occurred at the C5–C6 joint, while C6–C7 exhibited significantly lower correlation coefficients compared to other levels. The overall movement of the head and neck is not replicated at individual cervical joint levels and should be considered when evaluating equine necks in vivo.