DYNAMIC EFFECTS ON THE LUMBAR SPINAL-CANAL - AXIALLY LOADED CT-MYELOGRAPHY AND MRI IN PATIENTS WITH SCIATICA AND OR NEUROGENIC CLAUDICATION/

Study Design. In patients with sciatica or neurogenic claudication, th e structures in and adjacent to the lumbar spine canal were observed b y computed tomographic myelography or magnetic resonance imaging in ps oas-relaxed position and during axial compression in slight extension of the lumbar spine. Objectives. To determine the mechanical effects o n the lumbar spinal canal in a simulated upright position. Summary of Background Data. For years, functional myelographic investigation tech niques were shown to be of value in the evaluation of suspected encroa chment of the spinal canal. Since the advent of computed tomography an d magnetic resonance imaging, there have been few clinical and experim ental attempts that have imitated these techniques. The data indicate that the space within the canal is posture dependent. Methods. Portabl e devices for axial loading of the lumbar spine in computed tomographi c and magnetic resonance examinations were developed. Fifth patients ( 94 sites) were studied with computed tomographic myelography, and 34 p atients (80 sites) with magnetic resonance in psoas-relaxed position f ollowed by axial compression in slight extension. The dural sac cross- sectional area at L2 to S1, the deformation of the dural sac and the n erve 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 a rea in at least one site during axial compression in slight extension. Of the investigated patients, 29 passed the borderlines for relative (100 mm(2)) or absolute stenosis (75 mm(2)) in 40 sites. In 30 patient s, there was deformation of the dural sac in 46 sites. In 11 of the pa tients investigated with magnetic resonance imaging, there was a narro wing of the lateral recess in 13 sites, during axial compression in sl ight extension. Conclusions. Axial loading of the lumbar spine in comp uted tomographic scanning and magnetic resonance imaging is recommende d in patients with sciatica or neurogenic claudication when the dural sac cross-sectional area at any disc location is below 130 mm(2) in co nventional psoas-relaxed position and when there is a suspected narrow ing of the dural sac or the nerve roots, especially in the ventrolater al 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.