gms | German Medical Science

Objective: Recessal stenosis is traditionally considered a result of bony narrowing due to osteophytic appositions on the superior articular process. Clinical experience reveals that significant additional compression of the neural structures is due to degenerative hypertrophy of the adjacent ligamentum flavum. Therefore, microanatomical and neuroradiological investigations were performed to determine the microtopography of this ligament, especially with respect to its lateral extension.

Method: Lumbar spine specimens of 15 mid-aged human cadavers (mean age 34.5 years) were collected, and MRI studies with T1-weighted images were performed. The specially embedded specimens were dissected at the level of the spinal ganglion (slice thickness: 2 mm). Microsurgical neuroanatomical and morphometric data using a crossover-technique were collected in order to define the reachability of the capsular and extraforaminal segment of the ligamentum flavum in three bilateral levels, i.e. 90 operative sites.

Results: The distance between midline and extraforaminal extension of the ligamentum flavum showed a mean value of 17 mm. The distance increased to 19 mm when the lateral insertion was correlated to the origin of the ligamentum flavum at the anterior margin of the lamina. The farthest lateral segment of the ligamentum flavum was determined in each case; it covered the synovial cavity of the lumbar facet joint in the direction of the extraforaminal segment of the intervertebral canal.

Conclusions: Due to this anatomical situation a hypertrophic ligamentum flavum may contribute significantly to nerve root compression at the level of the lateral spinal recess. Measurements from mid-aged cadavers show the extent of the ligamentum flavum including its intra- and extraforaminal parts. This has to be kept in mind during surgical decompression, which might be incomplete unless these hypertrophied parts are completely removed. Furthermore, the rational background of this anatomical study finds an important aspect in the surgical practice and suggests performing the operative procedure controlateral to the lesion in order to achieve a complete decompression.