Morphogenesis, anatomy and histology of the ligamentum flavum

Spinal ligaments play a very important role in the mechanics of the spine. Curiously the ligamentum flavum (LF) has been the object of few specific studies. First a study on LF of foetuses has been carried out with anatomical, histological (classic staining techniques, immunohistochemistry and ultrastructural study) and radiological techniques. The LF is very different from the other spinal ligaments. It derives very early from a mesenchymeal tissue and not from the primitive muscular structures. Its development, its relations are very closed with lamina, capsules and tendons of spinal muscles. It is quickly an innervated and vascularized ligament with a predominance of elastic fibres. It is from a structural and functional point of view, by its two layers, the equivalent of a capsule and an articular ligament. Second, an ultrastructural and immunohistochemical study has been realized on adult LF to specify the kind of its innervation. It is innervated by fibres of great diameter, with myelin sheath. The positive immunomarking with neuropeptid Y is in favour of the proprioceptive type of this innervation. The LF has a specific and active role within the vertebral building, at the level of the spinal joints. Its characteristics described above confirm its neurological role especially for proprioceptive control. On the whole, this ligament is both mobilizing, stabilizing and adviser. The implications in spinal physiopathology are numerous