[Morphology and function of the interspinal ligaments and the supraspinal ligament of the lumbar portion of the spine].

The collagenous bundles of fibres in the lumbar interspinous spaces belong to different anatomical structures: the true interspinous ligaments, connecting two neighboured spinous processes in a postero-cranial direction, and fibres, lying in the dorso-caudal part, belonging to the thoracolumbar fascia (aponeurosis of the sacrospinal muscle). In the lumbo-sacral segment there are additional fibres arising from the dorsal part of the 5th lumbar spinous process and descending in a postero-caudal direction, interlacing with the thoracolumbar fascia. Superficial to the thoracolumbar fascia the fibres of the supraspinous ligament pass several spinous processes and form a longitudinal cord. Caudally the supraspinous ligament ends normally at the 4th lumbar spinous process. Below the caudal end of the supraspinous ligament the fibres of the thoracolumbar fascia cross to the opposite side and form a scissor-latticed structure. The interspinous ligaments limit the ventral-flexion of the lumbar spine; they can be extended in extreme retro-flexion, too. Downwards of L4 the fibre-texture of the thoracolumbar fascia permits a greater extent of ventral-flexion. In these segments the erector spinae muscle has to ensure the stability of the spine motion segments instead of a longitudinal ligamentous connection.