Jan Willén

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, 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.

The effects of external compression by three different retractors on pressure in the erector spine muscles during and after posterior lumbar spine surgery in humans.

Study Design. An experimental study on patients undergoing posterior lumbar spine surgery. Objectives. To study the relation between external compression and muscle strain induced by spinal retractors and intramuscular pressure in the dorsolumbar compartment during posterior spinal surgery. Summary of Background Data. Pressures were studied as a function of the distance between the retractor blades during surgery. Methods. Intramuscular pressure was measured bilaterally in the erector spinae muscle with intermittent microcapillary infusion technique in 12 patients undergoing posterior lumbar spine surgery during 271 (range 90‐420) minutes. Three self‐retaining retractors were tested; the McCulloch, the Viking, and the Richard retractors. Results. Intramuscular pressure was 7.7 mm Hg before surgery. It varied between 35 mm Hg and 69 mm Hg during surgical exposure of the laminas and facet joints. Intramuscular pressure varied between 61 mm Hg and 158 mm Hg depending on which retractor was used and on the distance between the retractor blades. Intramuscular pressure never exceeded 30 mm Hg at rest after the operation. Conclusions. External compression and muscle strain from retractor blades during surgery increased intramuscular pressure in the paravertebral muscles to levels that, according to other studies, induce ischemia in the muscles.

The Diagnostic Effect From Axial Loading of the Lumbar Spine During Computed Tomography and Magnetic Resonance Imaging in Patients With Degenerative Disorders

Study Design. Patients with low back pain, sciatica, and neurogenic claudication were observed during computed tomographic myelography or magnetic resonance imaging in psoas-relaxed position and axially compressed supine position of the lumbar spine. Objective. To estimate the clinical value of axially loaded imaging in patients with degenerative disorders of the lumbar spine. Summary of Background Data. Computed tomography and magnetic resonance imaging still are performed with the lumbar spine in a supine relaxed position, which results in unloading of the spine and enlargement of the canal. Methods. A device for axial loading of the lumbar spine in computed tomography and magnetic resonance imaging was used. Altogether, 172 patients were examined in psoas-relaxed position and axially compressed supine position of the lumbar spine: 50 patients with computed tomographic myelography and 122 patients with magnetic resonance imaging. If a significant decrease (>15 mm2) in the dural sac cross-sectional area to values smaller than 75 mm2 (the borderline value for stenosis) was found during examination in axial loading, or if a suspected disc herniation, narrow lateral recess, narrow intervertebral foramen, or intraspinal synovial cyst changed to being obvious at the axial loading examination, this was regarded as additional information important for the treatment. Results. Additional valuable information was found in 50 of 172 patients (29%) during examination in axial loading. In the different diagnostic groups, additional valuable information was found in 69% of the patients with neurogenic claudication, in 14% of the patients with sciatica, and in 0% of the patients with low back pain. The percentage of additional valuable information increased to 50% in the patients with sciatica, if recommended inclusion criteria for examinations in axial loading were used. A narrowing of the lateral recess causing compression of the nerve root was found at 42 levels in 35 patients at axial loading. Conclusion. According to the study results, axially loaded imaging adds frequent additional valuable information, as compared with conventional imaging methods, especially in patients with neurogenic claudication, but also in patients with sciatica if defined inclusion criteria are used.

Imaging lumbar spinal stenosis.

The entire concept of spinal stenosis is based on the assumption that there is a minimal space necessary for the function of the neural content of the spinal canal, and this space, under certain circumstances, gets too small. This may seem self evident, but it was not until the middle of the previous century that there was sufficient focus on this concept to establish the diagnosis of lumbar spine stenosis.

Optoelectronic movement analysis to measure motor performance in patients with chronic low back pain: test of reliability.

OBJECTIVE To assess test-retest reliability of the Posturo-Locomotion-Manual(PLM) test in patients with chronic low back pain. DESIGN A controlled study in which the PLM test was used repeatedly on patients with chronic low back pain and persons without back pain. SUBJECTS Twelve patients with treatment-resistant chronic low back pain, selected by 2 orthopaedic spine surgeons and 12 age- and sex-matched individuals with no back pain history. METHODS An optoelectronic camera and a computer were used to quantify the performance during a simple test in which subjects picked up an object from the floor and transported it up to a shelf, thereby forcing the body through postural, locomotor and manual movements. The outcome measures were: movement time, simultaneity index and phase times for postural, locomotion and arm movement phases. Statistical analyses regarding intra-individual agreement between the measurements (reliability analysis) and changes over time were carried out. RESULTS The effect of test movement habituation was minimized when the lowest mean value of any of 3 consecutive measures (tri-average) was used. In the control group, variation between test occasions was small. In the group of patients with chronic low back pain there was a random measurement error before intervention (sensory motor learning). After intervention the PLM test had the same precision in both groups. CONCLUSION When the tri-average measure is used, the influence of test movement habituation is minimized and the optoelectronic PLM test is found to be reliable and responsive. It proved to be a useful tool to quantify dynamic performance in freely moving patients with chronic low back pain.