Dynamic Effects on the Lumbar Spinal Canal

STUDY DESIGN: In patients with sciatica or neurogenic claudication, the structures in and adjacent to the lumbar spinal canal were observed by computed tomographic myelography or magnetic resonance imaging in psoas-relaxed position and during axial compression in slight extension of the lumbar spine. OBJECTIVES: To determine the mechanical effects on the lumbar spinal canal in a simulated upright position. SUMMARY OF BACKGROUND DATA: For years, functional myelographic investigation techniques were shown to be of value in the evaluation of suspected encroachment of the spinal canal. Since the advent of computed tomography and magnetic resonance imaging, there have been few clinical and experimental attempts that have imitated these techniques. The data indicate that the space within the canal is posture dependent. METHODS: Portable devices for axial loading of the lumbar spine in computed tomographic and magnetic resonance examinations were developed. Fifty patients (94 sites) were studied with computed tomographic myelography, and 34 patients (80 sites) with magnetic resonance in psoas-relaxed position followed by axial compression in slight extension. The dural sac cross-sectional area at L2 to S1, the deformation of the dural sac and the nerve roots, and the changes of the tissues surrounding the canal were observed. RESULTS: In 66 of the investigated 84 patients, there was a statistically significant reduction of the dural sac cross-sectional area in at least one site during axial compression in slight extension. Of the investigated patients, 29 passed the borderlines for relative (100 mm2) or absolute stenosis (75 mm2) in 40 sites. In 30 patients, there was deformation of the dural sac in 46 sites. In 11 of the patients investigated with magnetic resonance imaging, there was a narrowing of the lateral recess in 13 sites, during axial compression in slight extension. CONCLUSIONS: Axial loading of the lumbar spine in computed tomographic scanning and magnetic resonance imaging is recommended in patients with sciatica or neurogenic claudication when the dural sac cross-sectional area at any disc location is below 130 mm2 in conventional psoas-relaxed position and when there is a suspected narrowing of the dural sac or the nerve roots, especially in the ventrolateral part of the spinal canal in psoas-relaxed position. The diagnostic specificity of the spinal stenosis will increase considerably when the patient is subjected to an axial load.