[The lumbar ligamentum flavum. Anatomic characteristics with reference to microdiscotomy]

One important step in lumbar discotomy is the safe penetration and exact partial removal of the Lig. flavum. This is a crucial prerequisite for the selective and gentle removal of prolapsed and sequestrated intervertebral disc tissue. Extensive lancing of the Lig. flavum should be avoided, to minimize intraoperative and postoperative complications, such as injuries to the nerves and the Dura mater, instabilities, bleeding and scarring. As there has up to now been insufficient information on the anatomy of the Lig. flavum especially regarding microdiscotomy, an analysis of the Ligg. flava L2/L3 to L5/S1, guided by this aim, was carried out on 36 corpses kept in formaline (16 f, 20 m; 52-78 y). Preparations showed the lumbar Ligg. flava to be embodied in the Foramina interarcualia in a characteristic configuration. There also proved to be defined insertion areas on the laminae of the vertebral arches, which must be taken into consideration during the operative exposure. The Lig. flavum rises from the cranial vertebral arch from the ventral surface of the lamina (6.8 mm) whilst the insertion area on the caudal lamina covers the dorsal and the ventral surface. The extent at the ventral surface is 2.2 mm in average. Taking the insertion proportions into account we would suggest the Lig. flavum to be divided as follows: Pars interspinalis, which clearly differs from the Lig. interspinale (and from the M. interspinalis), and which houses venous anastomoses in its dorsal, ridge-shaped extension. Pars interlaminaris, which starts at the laminae and constitutes the target area for flavotomy in its lateral section, and Pars capsularis, which merges into the capsular structures of the facets. In all levels examined, there proved to be dorso-ventrally a typical change in the direction of the course of the fibres in the Pars interlaminaris. Whilst the direction of the fibres dorsally is oriented cranio-medially to caudo-laterally at an angle between 15 degrees and 30 degrees to the median line, the ventral fibres of the Lig. flavum are strictly aligned cranio-caudally. The changes in the directions of the fibres are continuous with the fibres being very closely intertwined, without there being any spatium at all. The texture of the Lig. flavum is, therefore, a mirror image of that of the autochthonuous muscular system of the back, even if the overlapping angle area is considerably smaller. The different segment levels show a segment-specific thickness profile. The analysis has provided anatomic information about the Ligg. flava L2/L3 to L5/S1. These data represent important prerequisites for a selective, gentle and safe intraoperative procedure for discotomy.