MANAGEMENT OF LUMBAR SPINAL STENOSIS

Abstract

The term stenosis means a narrowing of the calibre of an orifice or a tube. It causes a decreased flow of fluids or gasses within the tube or compression of its solid contents (Verbiest 1976). In the case of the spinal canal, the term indicates a pathological condition causing compression of the contents of the canal, particularly the neural structures. If compression does not occur, the canal should be described as narrow but not stenotic. I have defined lumbar spinal stenosis as a “narrowing of the osteoligamentous vertebral canal and/or the intervertebral foramina causing compression of the thecal sac and/or the caudal nerve roots; at a single vertebral level, narrowing may affect the whole canal or part of it” (Postacchini 1983). This definition distinguishes between disc herniation and stenosis. A disc prolapse does cause stenosis, in the strictest sense, but the two conditions are so different in their pathogenesis and anatomical and clinical characteristics that they cannot be considered as a single pathological entity. The lumbar spinal canal consists of a central part, two lateral parts and a posterior part corresponding to the interlaminar angle. The central portion is the so-called central spinal canal, and each lateral part constitutes the nerve-root or radicular canal. The central spinal canal is rounded and occupied by the thecal sac. Stenosis of this portion is sometimes called central spinal stenosis to distinguish it from lateral spinal stenosis (nerve-root canal stenosis). This terminology implies that in central spinal stenosis the nerve-root canals may not be stenotic, but this is not the case. Stenosis of the central portion is almost always associated with stenosis of the lateral corners of the spinal canal. The term ‘spinal canal stenosis’ is therefore preferable to central spinal stenosis. The nerve-root canal is the semitubular structure through which the nerve root runs from the thecal sac to the intervertebral foramen. The proximal part of the canal, also called the subarticular or intervertebral portion, is limited anteriorly by the intervertebral disc and posterolaterally by the superior articular process and the facet joint. The distal part of the canal corresponds to the lateral recess, i.e., the lateral corner of the vertebral foramen at the level of the pedicle. Pathological narrowing of the nerve-root canal not associated with stenosis of the central spinal canal is called isolated nerve-root (or radicular) canal stenosis. The entrance and exit of the intervertebral foramen lie at the medial and lateral borders of the pedicle. Some authors (Wiltse 1984; Burton 1987) include the intervertebral foramen in the nerve-root canal, of which it is then the most distal portion. In my opinion there are valid anatomical reasons for distinguishing between the two and identifying stenosis of the intervertebral foramen as a separate condition.