A Pain In The Neck

Diagnosing areas of discomfort in this complex structure can be challenging, as Dr Sue Dyson FRCVS explains

- Dr Sue Dyson

THE equine neck consists of seven vertebrae, which articulate in different directions via intercentral joints and articular process or facet joints.

The greatest range of motion — extension and flexion, lateral bending and rotation — occurs between the fifth cervical and the first thoracic vertebrae. Even clinically normal horses will show X-ray abnormalities involving the articular process joints between these vertebrae, reflecting osteoarthritis.

Various muscles and ligaments attach to the neck vertebrae and influence their movement. In most horses, there is left-right symmetry between the vertebrae and the muscular attachments. Some, however, are born with an asymmetry of both the bones and the soft tissues. Suffice to say, some world-class horses have had such abnormalities with no associated clinical signs.

The spinal cord lies within a central channel in each vertebra called the vertebral foramen. The cervical nerve roots, which supply the horse’s neck and forelimbs with nerves, pass through additional passages at the level of the articular process joints, known as intervertebral foramina.

Narrowing of these channels by new bone formation or soft tissue proliferation can result in abnormal pressure on nerve roots and either neurological dysfunction, such as stumbling, or pain that causes forelimb lameness. Pressure on the spinal cord can cause ataxia (wobbliness).

TAKING SHAPE

THE horse’s neck is mobile and its position has a major influence over his movement. If his neck is too high, the back will be forced into extension and will hollow, so the range of motion of the back will be reduced. If his neck is too flexed and his chin is too close to his chest or sternum, forelimb step length will be shortened.