The Functions of the Nuchal and all Associated Ligaments

The equine neck and back is furnished with ligaments; nuchal, supraspinous, dorsoscapular and sacroiliac. They are important in helping to keep the individual vertebrae in place and provide the neck and back with strength, support and mobility.

Nuchal Ligament

The nuchal ligament (ligamentum nuchae) supports and holds the horses head and neck in position. It is one of the most important structures that influence the support of the horses back. The nuchal ligament functions to support and hold the horses head and neck in position and allows them to be raised and lowered. The ligament is strong, elastic and tendon-like in structure and consists of two parts: the funicular part and the lamellar part. The elasticity of the nuchal ligament minimizes muscular exertion when the horse lowers or raises its head during grazing (illustrated in figure 1).

The funicular part is a rope-like ligament that consist of two parallel cords that attach at the nuchal crest of the occipital bone of the horses skull and cross the ridge of the first and second cervical vertebrae (atlas and axis) spanning the crest of the neck to the withers. The cranial nuchal (atlanta) bursa contains lubricating synovial fliud and acts to prevent friction over the atlas (site associated with condition termed poll evil) and the caudal nuchal bursa acts to prevent friction over the axis. The supraspinous bursa lies between the second and fourth thoracic spinous processes and again acts to reduce friction between the nuchal ligament and underlying structures (site associated with condition termed fistulous withers). The caudal aspect of the funicular part of the nuchal ligament, flattens and merges with the supraspinous ligament.

The lamellar part of the nuchal ligament is made up of two sheets of fan-shaped, elastic soft tissue extensions. These elastic bands extend from the funicular part and the second and third thoracic spines to spines of the axis and C3 to C5 or C6. The lamellar part functions to restrain the movement of the dorsal spines and support the weight of the head, holding it in position.

When the cervical vertebrae are flexed, the nuchal ligament is tensioned. The effect extends along the back as far as the lumber spine, this is of great significance to the support of the horses back when the horse is working under saddle. The position of the head and neck determines the position of the vertebral column i.e. when the horse is riding in an outline the tension on the nuchal, supraspinous ligaments and abdominal muscles combine to lift the horses back. When the nuchal ligament functions efficiently, it enables the back muscles to contribute more to propulsion rather than support.

Supraspinous Ligament

The supraspinous ligament functions to restrain the movements of the dorsal spines and keep the vertebrae in place giving the back support, strength and stability. When working efficiently in conjunction with the nuchal ligament, it enables the back muscles to contribute more to propulsion rather than support and together with the abdominal muscles helps to lift the horses back.

The supraspinous ligament arises from the caudal part of the nuchal ligament at the withers. The nuchal ligament flattens caudally and merges with the suprapinous ligament then runs along the back until it reaches the last lumbar vertebrae. It joins together all the spinous processes of the lumber and thoracic vertebrae (illustrated figure 2)

Dorsoscapular Ligament

The dorsoscapular ligament is a tough fibrous tissue which functions to attach the axial skeleton to the appendicular skeleton at the dorsal aspect of the scapular. The ligament is a thickened part of the thoracolumbar fascia. The dorsal part arises from the spines of T3, T4 and T5 vertebrae and the ventral part attaches to the medial surface of the scapula between attachments of the ventral serrated muscle (illustrated figure 3).

Sacroiliac Ligaments

The 3 sacroiliac ligaments (dorsal, lateral & sacrosciatic) function to support the sacroiliac joint. They arise over the dorsal aspect of the sacrum, leaving a gap at the lumbosacral junction.