Anatomy of lumbar radicular compression: anatomic and radiological thoughts about failures of decompressive surgery

Improvement in pre and post-operative imaging has modified the diagnosis of lumbar radicular compression. CT scanning and MRI led to the advent of bodysection anatomy which allows an optimal analysis of the relation between container and content, in regard to the lumbar radicular canal. However, myelography remains an important method of analysis of dynamic obstructions.The authors report the retrospective analysis of 102 cases of failures in surgery for lumbar radicular release frequently difficulties in diagnosis are due to a lack of precision in anatomic and radiological interpretation of the clinical situation. This analysis is based on the classical radicular segmentation with 4 zones. 1. The osteo retro discal space: This segment is both the place for discal and articular dynamic conflicts. Degenerative alterations of this spaces modifies anatomic relations and insufficient decompression leads to some failures in "fenestration" surgery through posterior approach. 2. The para pedicular space: In the arthro-pedicular zone, the root is jammed in a confined area. This recess can be very easy to release, on the contrary a trefoil arrangement can lead to partial articular resection. In all cases, the evaluation of arthro-pedicular impigement is necessary even if the major compression is a disk hernia. Studying the posterior segment through CT scan has a predictive value in decision for systematic fenestration through the interlamellar space. Along the isthmo-pedicular segment, the root gets moulded on the inferior side of the pedicle. The morphometric criteriae of narrowing of the lumbar vertebral canal have been described at this particular bone level. Measuring gives relative values : even if constitutional narrowings of the lumbar vertebral canal can be explained when short pedicles are noted, arthrosic narrowing is the most frequent pathology and its static and dynamic impediments are found at the other levels. 3. The foraminal segment: The root sticks tightly to the walls of this foraminal \ldcanal\rd which is itself divided into two compartments, a superior one in contact with the postero lateral edge of the vertebra, and an inferior one at the disk level. Two horizontal scanner or MRI body sections (complementary to the parasagittal MRI sections) are essential for accurate analysis of the foramen. Intervertebral osteosynthesis with pedicular fixation now allows large intervertebral distractions ; but with a risk due to radicular adhesion on the walls of this defile 4. The extra foraminal space: This area was previously unrecognized. Exploration by MRI shows a very great vascular environment and the conflicts with ilio transversal ligaments and extraforaminal herniae. The course of the L5 root is vulnerable under the L5 transversal apophysis up to the anterior wall of the sacrum.

The analysis of failures of radiculâr decompression requires a very precise analysis. A same root can be involved in two disk conflict levels, the osteo retro discal space for classical conflicts and the foraminal level. Similarly, the same root can be involved at two articular impediment levels, one at the level of the arthropedicular segment, and the other at the level of the foraminal canal. Whatever, the impediments are disk, bone, articular, degenerative or constitutional, we must stress the significant part played by destabilization, hyper mobility or micromobility.