Nuchal ligament

The nuchal ligament is a ligament at the back of the neck that is continuous with the supraspinous ligament. The nuchal ligament extends from the external occipital protuberance on the skull and median nuchal line to the spinous process of the seventh cervical vertebra in the lower part of the neck. From the anterior border of the nuchal ligament, a fibrous lamina is given off. This is attached to the posterior tubercle of the atlas, and to the spinous processes of the cervical vertebrae, and forms a septum between the muscles on either side of the neck. The trapezius and splenius capitis muscle attach to the nuchal ligament. It is a tendon-like structure that has developed independently in humans and other animals well adapted for running. In some four-legged animals, particularly ungulates and canids, the nuchal ligament serves to sustain the weight of the head. In Chiari malformation treatment, decompression and duraplasty with a harvested nuchal ligament showed similar outcomes to pericranial and artificial grafts. In sheep and cattle it is known as the paxwax. It relieves the animal of the weight of its head. The nuchal ligament is unusual in being a ligament with an elastic component, allowing for stretch. Most ligaments are mostly made of highly aligned collagen fibres which do not permit stretching. Structurally, the nuchal ligament is formed with the association of both elastin proteins as well as type III collagen (45%). The collagen fibrils share a consistent size as well as helical pattern which gives the ligament its tensile strength. The elastin on the other hand is a protein that allows for flexibility. These two elements of the nuchal ligament maintain a complex balance which allows the constant weight bearing of the head along with multidirectional movement without damaging the durability of the ligament through over-use/stretching. In most other mammals, including the great apes, the nuchal ligament is absent or present only as a thin fascia. As it is required for running, not all animals have one.