Comparison of Radiologic Signs and Clinical Symptoms of Spinal Stenosis

Transcription

1 SPINE Volume 31, Number 16, pp , Lippincott Williams & Wilkins, Inc. Comparison of Radiologic Signs and Clinical Symptoms of Spinal Stenosis C. Martina Lohman, MD, PhD,* Kaj Tallroth, MD, PhD,* Jyrki A. Kettunen, PT, PhD, and Karl-August Lindgren, MD, PhD Study Design. Clinical findings of spinal stenosis were compared to graded radiologic findings of dural sac narrowing. Objectives. To examine the changes of the dural sac area of the lumbar spine on computerized tomography (CT) performed without and with axial loading, and study the correlations between the radiologic findings and clinical symptoms suggestive of spinal stenosis. Summary of Background Data. Although several studies have been performed regarding the advantage of an external compression device in lumbar CT, to our knowledge, none of these studies have correlated radiologic findings with clinical symptoms. Methods. The cross-sectional areas of the dural sac at the 3 lowest lumbar intravenous spaces, measured by CT both without and with external compression, were correlated to the clinical symptoms suggestive of spinal stenosis in 117 patients and 351 intervertebral levels. Results. No statistically significant correlation between the severity of the clinical symptoms of spinal stenosis and dural cross-sectional areas was found. Neither did the use of an external compression device improve the correlation. Conclusion. Although an external compression simulates the dynamic condition in the back during standing position, it does not eliminate the need to compare the radiologic findings with the clinical symptoms of patients examined because of a suspected narrowing of the spinal canal. Key words: spinal stenosis, spine, radiology, tomography, spiral computed. Spine 2006;31: A disproportion in the spinal canal between the size of the neural elements and space available is called spinal stenosis. A compression of the neural elements may cause both pain and neural symptoms. If the compression is within the spinal canal, the condition is termed central spinal stenosis, lateral if it involves the individual spinal nerve roots. 1 By far, the most common cause of spinal stenosis is various degenerative changes, either in the discs, facet From the *Department of Radiology, Research Unit, and Rehabilitation Unit, ORTON Orthopaedic Hospital, Helsinki, Finland. Acknowledgment date: October 21, First revision date: April 30, Second revision date: October 9, Acceptance date: October 10, The device(s)/drug(s) is/are FDA-approved or approved by corresponding national agency for this indication. No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript. Address correspondence and reprint requests to C. Martina Lohman, MD, PhD, Department of Radiology, ORTON Orthopaedic Hospital, Tenholantie 10, Helsinki, Finland; martina.lohman@ fimnet.fi joints, or vertebral bodies. 2 Spinal stenosis may also be caused by several less common entities. 3 Congenital spinal stenosis is caused by short pedicles or a narrow interpedicular distance. 4 Narrowing of the spinal canal may also be a sequela of trauma. Any narrowing may be aggravated if degenerative changes are superimposed on preexisting conditions. Patients with spinal stenosis tend to have the most profound clinical symptoms when upright. Axial loading and hyperextension bending of the lumbar spine will typically worsen the clinical symptoms by causing additional narrowing of the spinal canal. The traditional method to evaluate the neural elements of the back is myelography. This study can also be performed as a functional examination with physiologic axial loading if the myelograms are taken with the patient in an upright position. Furthermore, dynamic flexion-extension myelograms can be obtained. 5 However, myelography is an invasive study with the possibility of complications, such as postoperative headache and inflammation. During recent years, the use of computerized tomography (CT) and magnetic resonance imaging (MRI) has increased to gain information about the neural structures within the spine. An advantage of CT and MRI compared to myelography is the possibility to get transaxial images. In CT, it is sometimes difficult to delineate the different structures within the spinal canal. Their visibility can be improved if the CT scanning is undertaken after an intrathecal contrast injection, a so-called postmyelo-ct. Normally, both CT and MRI examinations are performed with the patient supine, with the knees bent. This position corresponds to standing in a nonweight-bearing position, in which symptoms caused by spinal stenosis tend to be less severe. However, a physiologic normal weight-bearing condition in the upright position can be simulated in a supine position using an external compression device. Radiologically, the dural sac in the lumbar spine is considered narrowed on CT and MRI if the crosssectional area is less than 100 mm 2. The narrowing can be further subdivided into 2 groups according to the severity of the narrowing. Widely accepted radiologic borderlines for absolute spinal stenosis is a crosssectional area less than 75 mm 2, and for a relative 100 mm 2. These borderlines for spinal stenosis originate from an experimental study by Schönström and Hansson 6 made on cadavers. Originally, these measurements were described for the level of L3 L4 but have later been 1834

2 Comparison of Radiologic Signs and Clinical Symptoms of Spinal Stenosis Lohman et al 1835 used also for studies of lower intervertebral levels. Schönström et al 7 also proved the effect of flexion and extension on the size of the dural sac in the lumbar region (i.e., regularly, a narrowing of the dural sac can be seen in extension, a widening in flexion). The relationship between clinical symptoms of spinal stenosis and its radiologic manifestations is uncertain. Despite a significant spinal narrowing, patients may have minute or no clinical symptoms. The opposite situation is also common (i.e., patients have clinical symptoms of spinal stenosis but insignificant or no radiologic findings). 8 Although patients often have relief of symptoms after decompressive surgery, this is not always the case. Within a retrospective postoperative study, no difference in outcome could be found between operatively and conservatively treated patients with spinal stenosis. 9 Herno et al 10 did not find any difference in the clinical outcome of operated and nonoperated patients in a matched-pair study. Another study by Amundsen et al 11 showed a better outcome for operated patients. A discrepancy between the postoperative subjective disability and radiologic results has also been established. The aim of our study was to study the dural sac without and with axial loading, and correlate these radiologic findings to the clinical symptoms suggestive of spinal stenosis. Our hypothesis was that the decrease of the size of the dural sac produced by axial loading would increase the correlation between clinical findings and the findings on CT. Materials and Methods Patients. During a period of more than 3.5 years (January 15, 1997 September 19, 2000), 117 patients were referred from primary health service to the ORTON Rehabilitation Centre, Invalid Foundation because of chronic low back pain and a clinical suspicion of spinal stenosis. None of the patients had neurologic deficits. Of these 117 patients, 46 fulfilled in their regular CT the radiologic criteria 7 for absolute spinal stenosis (group A, dural cross-sectional area of 0 74 mm 2 ), 25 for relative spinal stenosis (group B, dural cross-sectional area of mm 2 ), whereas 46 had no narrowing of the dural sac area (group C, dural cross-sectional area of 100 mm 2 ). Exclusion criteria were inflammatory arthritis, spinal tumors and metabolic disease affecting the spine, as well as arteriosclerosis and neurologic disorders. Patients with spinal anomalies were not included in the study. The mean age of the patients in group A was 49.3 years (standard deviation [SD] 6.3), group B was 49.0 years (SD 7.0), and group C was 46.1 years (SD 7.5). In group A, 21 patients were male and 25 female. In group B, there were 15 males and 10 females, and in group C, there were 25 males and 21 females. The mean weight of the patients in group A was 81.6 kg (SD 19.1). In group B, it was 81.2 kg (SD 14.0), and in group C it was 79.3 kg (SD 13.1). Radiologic Methods. The 3 lowest lumbar intervertebral spaces were scanned with 4-mm contiguous slices, extending from the pedicle above proximal to the pedicle below the level in question. Altogether, 351 disc levels were investigated. For each intervertebral space, an optimal slice in the middle of the disc was selected for measurement of the dural sac. The same level was also scanned with axial compression. The axial compression was achieved using an external, commercially available compression device, DynaWell (Billdalsvägen 2, SE 42736; Billdal, Sweden) This consists of a compression device attached to a harness resembling a vest. The harness is attached to the compression device by 2 straps. By tightening the straps, the axial pulling force is adjusted to simulate the weight bearing of the lumbar spine in a standing position. The compression force applied was approximately 40% of the patients body weight, and the loading was commenced 5 minutes before CT. To simulate a normal standing position, the scanning both in the loaded and nonloaded position was undertaken with straight knees. The straps were carefully positioned to follow the imagined gravity lines in an upright position. The CT images were obtained in the plane of each of the 3 lowest intervertebral discs separately. Both during standing and axial loading, the lumbar lordosis tends to increase. Therefore, a new scout image was obtained in the axially loaded position, and the slices were again scanned in the plane of each individual disc. The cross-sectional area of the dural sac at the 3 lowest lumbar intervertebral spaces in every single patient was separately calculated with the measurement program in our Picker PQ 2000 CT scanner (Philips Medical, Cleveland, OH). The change in the dural sac size during external axial loading was assessed for every individual intervertebral space (Figure 1). Pain During CT. The severity of pain occurring either during the loaded examination or afterwards was questioned using a questionnaire scale with 4 classes. Grade A indicated no change compared to the normally occurring possible discomfort in the supine position. Grade B represented a discomfort or slight pain similar to that in the standing position. Grade C had moderate pain, more than the pain normally occurring in the standing position. Grade D indicated severe pain. Persistence of the pain for more than 30 minutes was recorded separately. Clinical Methods. At clinical examination, the following information of the clinical symptoms was registered. The duration of low back symptoms (in years) and the walking distance (in meters), as reported by the patient, was noted. Everyday functional disability was measured using the original Oswestry index questionnaire (ODI), 18 in which 0% to 20% corresponds to minimal functional disability, 21% to 40% to moderate, and 41% to 60% to severe functional disability. An even higher percentage of 61% to 80% indicates a crippled patient, and 81% to 100% designates that the patient is bedridden. The ODI questionnaire deals with problems caused by pain, and includes personal care, mobility, gender, social life, etc. Pain was measured with a linear visual analog scale (VAS), in which the patient estimates the severity of the pain on a linear scale. 19 A VAS of zero corresponds to no pain, and a VAS of 100 to nonbearable pain. VAS was recorded separately for back pain and pain radiating to the lower limbs. Statistical Methods. Statistical analysis was performed using Systat statistical software (Systat Software, Inc., Point Richmond, CA). One-way analysis of variance was used to compare groups means. Gender distribution within the 3 groups was tested using th Pearson 2 test. For the age distribution, duration of symptoms, patient weight, compression force, pain during the compression, walking distance, ODI, and VAS in back

3 1836 Spine Volume 31 Number Figure 1. Example of the measurements performed. CT of L4 L5 intervertebral disc. Before (A) and after (B) compression. Measurement of A (C). Measurement of B (D). In compression, there is bulging of the disc and folding of the flavum ligaments, changing the cross-sectional area of the dural sac from 88 to 39 mm 2.In this case, the relative spinal stenosis has changed to an absolute spinal stenosis with external compression. and legs, the 2-sample t test was used. In addition, the results of the ODI, VAS tests, and walking distance in the 3 groups were correlated using the Spearman correlation matrix, both without and with axial loading. The correlation between the reduction in the dural sac area at the 3 levels during compression and the different clinical symptoms was correlated using the Pearson 2 test. Results Patients The number of patients with absolute spinal stenosis increased, and the number of patients with no spinal stenosis decreased when external compression was used (Figure 2). Of 25 patients with relative stenosis, 17 Figure 2. Number and percentage of patients with absolute spinal stenosis, relative spinal stenosis, and no spinal stenosis in regular CT without compression (A) and CT during compression (B).

4 Comparison of Radiologic Signs and Clinical Symptoms of Spinal Stenosis Lohman et al 1837 Distribution of dural sac areas number of intervertebral segments no spinal stenosis relative spinal stenosis absolute spinal stenosis 59 Figure 3. Number of dural sacs showing no spinal stenosis, relative spinal stenosis, and absolute spinal stenosis, with and without axial loading. 73 before compression 108 after compression moved to the category of absolute spinal stenosis during axial compression. Of those patients without any narrowing of the dural sac on regular CT, 2 had absolute and 14 had relative spinal stenosis after compression. Dural Sac Areas at Intervertebral Spaces The number of intervertebral segments with a normal dural sac decreased, and the number of stenotic ones increased in compression (Figure 3). A normal area of the dural sac was seen at 219 intervertebral levels without compression, decreasing to 179 levels after compression. The number of intervertebral levels with absolute stenosis increased from 73 to 108 with compression. The number of intervertebral levels showing relative narrowing increased by 5 after compression. Before compression, a narrowing of the dural sac, either relative or absolute, was seen in 71 of the 117 patients. Narrowing was seen at 3 levels in 18 patients, 2 levels in 25, and 1 level in 28. No narrowing at any of the 3 lowermost lumbar levels was seen in 46 patients. The mean decrease of the dural cross-sectional area was in L3 L mm 2, in L4 L mm 2, and in L5 S mm 2 (Figure 4). Pain During Compression in the 3 Groups The mean compression force used was 43% of the body weight in group A, 47% in group B, and 46% in group C. The pressure applied was dependent on how well the patient tolerated the compression. There was no group difference in mean intensity of pain during external compression (P 0.59). During the compression, 67 patients had no pain at all, 33 had slight, 9 had moderate, and 8 had severe pain. There were 2 patients who had pain for more than 30 minutes. No correlation could be found between the area of the dural sac before or during compression and the patient s subjective estimation of pain during compression. Correlation Between Radiologic Findings and Clinical Symptoms When we compared the data for those patients who after compression had absolute or relative narrowing of the dural sac in at least 1 intervertebral level to those with no narrowing at any level, the results were the same for both ODI and VAS for the back and leg. The patients with normal dural sac areas had even more symptoms of pain measured by VAS and disability measured by Oswestry. The Spearman correlation coefficient was calculated for the maximum walking distance, ODI, and VAS for the back and leg pain before and after the external compression. The correlation coefficients were between and 0.174, indicating no linear correlation between the tested clinical parameters and dural sac area, either with or without axial loading no spinal stenosis mm L3-L4 L4-L5 L5-S1 relative spinal stenosis absolute spinal stenosis Figure 4. The changes of the dural sac areas at the intervertebral levels, which were grouped according to the initial degree of width, as a result of axial loading.

5 1838 Spine Volume 31 Number No correlation could be found between the severity of the spinal narrowing at the individual levels and number of levels with narrowing. In addition, the number of levels with absolute or relative spinal stenosis did not correlate to the clinical symptoms. A significant correlation was detected between the change in the dural sac area at L4 L5 level with compression and the severity of pain radiating to the leg, graded by the patients using the VAS scale. At L3 L4 and L5 S1, no such positive correlation was found between the pain radiating to the leg and the change in dural sac area during compression. Discussion The results in our study indicate that unclear, confusing clinical findings resembling spinal stenosis are also relatively common in patients who have mild or no narrowing of the spinal canal on CT. The mean age of our patients (48 years) is younger than that of the average patient with a radiologic narrowing of the spinal canal. The patients were referred to the Rehabilitation Clinic because of chronic back symptoms consistent with neurogenic claudication and a clinical suspicion of spinal stenosis, as well as for evaluation of their ability to work. However, CT examination without compression verified narrowing of the spinal canal in only 61% of patients and with axial compression in 74%, which reflects the overlapping clinical signs in different spinal disorders. A possible correlation of socioeconomic factors with symptoms or diagnoses was not investigated in our study. Patients with spinal malformations or developmental anomalies were not included in the study. To reduce the radiation load, the images were obtained at the level of the 3 lowest intervertebral discs. Because the vertebral bodies were not scanned, we are not able to compare the area of the dural sac at the level of the intervertebral disc to the area of the dural sac at, for example, the pedicle above the disc space. The relatively low age of the study population indicates that patients with congenitally short pedicles may be overrepresented compared to the population in general. According to a recent study with patients of quite a similar age, external compression was most beneficial for the diagnosis in persons with symptoms suspicious for neurogenic claudication (in 69%) than in patients with sciatica (in 14%) or low back pain (in 0%). 15 This same study showed that in patients with a suspicion of clinical spinal stenosis, the percentage having radiologic spinal narrowing increased to 35% with the use of compression. In our study, the percentage of symptomatic patients having dural sac areas less than 100 mm 2 in at least 1 of the 3 lowermost levels increased by 13% (from 61% to 74%) when axial compression was used. Furthermore, in the prior study, the percentage of patients having radiologic spinal stenosis when axial compression was used is quite similar to our results. However, in our study, more patients with a clinical suspicion of spinal stenosis actually had a narrow dural sac. In another prior study, 9% of the asymptomatic persons and 24% of the symptomatic patients had a significant decrease in the area of the dural sac in external compression, changing the area of the dural sac under the limits of radiologic normal (i.e., less than 100 mm 2 ). 13 Our study showed a 13% increase of patients having spinal stenosis when compression was used. Although achievements in the development of MRI scanners have produced the first upright MRI scanner in which the patients can be scanned in a real upright position, these scanners are not yet in common use. However, an upright position can be simulated in the supine position using an external compression device. Plain CT or MRI in conjunction with complementary axial compression combines the advantages of plain CT and upright myelography for the evaluation of the dural sac, yet, without the invasiveness of myelography. We studied the 3 lowermost intervertebral spaces. In our study, axial compression changed 40 of the 219 (18.2%) normal dural sacs to stenotic in 16 different patients (13.7% of all individuals studied). Even absolute spinal stenosis increased in 10% of the intervertebral spaces (35/351) in 17 different patients (14.5%) using axial compression. In 2 studies, 11,13 an absolute decrease in the cross-sectional area of more than 15 mm 2 has been considered statistically relevant in patients with clinically suspected spinal stenosis, regardless of the area of the dural sac. In our study, the mean narrowing at the intervertebral spaces ranged from 13.4 to 18.5 mm 2. However, the clinical relevance of a certain narrowing is complex, depending on the initial size of the dural cross-sectional area. If the cross-sectional area in the noncompressed situation is wide, a narrowing of about 15 mm 2 does not decrease the area to a critical limit. However, if the cross-sectional area without compression is originally narrow, a further decrease may change the cross-sectional area to a clinically significant degree. Unfortunately, the decreased amount of liquor and the crowding of spinal nerves often seen in spinal stenosis are difficult to measure objectively from CT images. When lying supine with straight legs, the psoas muscle will cause a lumbar lordosis similar to that in the standing position. When a pillow is used under the knees, the position with the legs bent and back straightened differs from the normal standing position with a deeper lumbar lordosis. The nonloaded images have been obtained with bent legs in all but 1 17 prior study using the DynaWell compression device. In an attempt to simulate the normal standing and weight-bearing conditions as much as possible, we scanned our patients with straight legs, both without and with external compression. The clinical importance of this narrowing appears to be more complex and not directly related to either the area of the dural sac with or without axial loading. In our study, the reduction of the dural sac area did not correlate to the subjectively graded clinical symptoms. In addition, the use of axial loading did not increase the correlation between the clinical symptoms and radiologic findings. All patients in our study were symptomatic,

6 Comparison of Radiologic Signs and Clinical Symptoms of Spinal Stenosis Lohman et al 1839 some more and some less, with similar symptoms, but not all of these patients had radiologic narrowing of the dural sac. In 51 intervertebral spaces, the area of the dural sac increased during axial loading. In most of the disc spaces, the increase was only a few mm 2, which can be explained by the measurement technique. Only 9 disc spaces showed an increase more than 15 mm 2, all of these at the level of L5 S1. Either slight craniocaudal movement of the dural sac in relation to the disc space or movement in the transaxial plane in patients with instability of the lumbar spine may explain the paradoxical widening of the disc space during compression. Kimura et al 17 reported such changes of movement caused by external axial compression in the discs of healthy subjects. In their study, the L4 L5 disc showed a significant reduction in disc height but no change in the intervertebral angle. On the other hand, L3 L4 and L5 S1 showed no statistically significant reduction of disc height but, instead, a statistically significant change in the intervertebral angles. In prior studies, similar changes of controversial widening of the dural sac during compression can be seen in the graphs. 14 Spinal canal narrowing is considered to cause more problems when it occurs at several levels. 20 In our study, multilevel narrowing with an area of less than 100 mm 2 was seen in 43 patients without, increasing 33%, to 57 patients after axial compression. According to studies by Porter and Ward, 20 and Hamanishi et al, 21 the correlation between radiologic and clinical findings is more obvious in multilevel spinal narrowing compared to singlelevel spinal stenosis. This finding contradicts our study. We could not find any correlation between the number of levels with spinal stenosis (neither absolute or relative) and the clinical symptoms. The difference in the results is most likely explained by a difference in the study population. Despite clinical symptoms suspect of spinal stenosis, no radiologic narrowing of the spinal canal was found in some of our patients. However, a significant positive correlation was found between the reduction of the dural sac size at L4 L5 during compression and the severity of pain radiating to the leg. At L5 S1, olisthesis is most common, a fact that may affect the measurements at L5 S1 during compression. We have no explanation as to why a reduction at the L3 L4-level does not have the same correlation to the clinical symptom of pain radiating to the leg as that at the L4 L5 level. Studies using the DynaWell have been performed with different imaging methods, including CT, 12,14 both with and without intrathecal contrast, but also using MRI. 14 Side effects of the axial compression have also be been recorded. 12 However, the pain related to the use of the external compression device has not been correlated to the grade of disc degeneration or facet joint osteoarthrosis, which often causes pain in this patient group. The subjectively graded pain experienced by the patients during the compression did not correlate to the area of the dural sac, so the use of this compression device also appears to be safe for patients with suspected spinal stenosis. Subjective back pain can be measured only subjectively with the use of question forms, like the VAS for pain intensity and the Oswestry questionnaire for subjective functional disability. Because we also considered the maximal walking distance on a treadmill as a somewhat subjective test, we decided to rely on the patient s own statement about the maximal walking distance. Radiologic measurements of the dural sac area are performed in an attempt to grade findings objectively that may explain the pain and disability experienced by the patient. In addition, the radiologic evaluation of the morphology is especially important in patients considered for operative treatment. The insignificant correlation between the radiologic data and clinical symptoms may be because of the fact that the pain may be to some extent related to factors that we are not able to identify, localize, and grade radiologically, or to even yet unknown factors. However, it is important to remember that the subjective symptoms, and clinical and radiologic findings may be different. Conclusions Although external compression simulates the weightbearing condition in the back during upright positioning it does not eliminate the need to compare the radiologic findings to the clinical symptoms when examinations caused by suspected narrowing of the dural sac are undertaken. It is assumed that narrowing of the spinal canal inevitably causes entrapment of the neural structures and may require operative treatment. In this study the narrowing of the spinal canal did not correlate with the severity of clinical symptoms suggesting that there may be also other factors contributing to the clinical symptoms, more difficult to grade or yet to be investigated. Key Points Compression of the lumbar spine significantly changed the area of the dural sac. CT findings suggesting spinal stenosis need to be compared to clinical symptoms. No significant correlation was found between the area of the dural sac in axially loaded CT and the clinical symptoms of spinal stenosis. References 1. Epstein JA, Epstein BS, Lavine LS, et al. Lumbar nerve root compression at the intervertebral foramina caused by arthritis of the posterior facets. J Neurosurg 1973;39: Kirkaldy-Willis WH, Wedge JH, Yong-Hing K, et al. Pathology and pathogenesis of lumbar spondylosis and stenosis. Spine 1978;3: Tallroth KSD. Spinal stenosis subsequent to juvenile osteochondrosis. Skeletal Radiol 1990;19: Lutter LD, Longstein JE, Winter RB, et al. Anatomy of the achondroplastic lumbar canal. Clin Orthop Relat Res 1977;126: Sortland O, Magnaes B, Hauge T. Functional myelography with metriz-

7 1840 Spine Volume 31 Number amide in the diagnosis of lumbar spinal stenosis. Acta Radiol Suppl 1977; 355: Schönström N, Hansson T. Pressure changes following constriction of the cauda equina. An experimental study in situ. Spine 1988;13: Schönström N, Lindahl S, Willen J, et al. Dynamic changes in the dimensions of the lumbar spinal canal: an experimental study in vitro. J Orthop Res 1989;7: Amundsen T, Weber H, Lilleas F, et al. Lumbar spinal stenosis. Clinical and radiologic features. Spine 1995;20: Herno A, Airaksinen O, Saari T, et al. Lumbar spinal stenosis: A matchedpair study of operated and non- operated patients. Br J Neurosurg 1996;10: Herno A, Partanen K, Talaslahti T, et al. Long-term clinical and magnetic resonance imaging follow-up assessment of patients with lumbar spinal stenosis after laminectomy. Spine 1999;24: Amundsen T, Weber H, Nordal HJ, et al. Lumbar spinal stenosis: Conservative or surgical management? A prospective 10-year study. Spine 2000;25: Danielson BI, Willen J, Gaulitz A, et al. Axial loading of the spine during CT and MR in patients with suspected lumbar spinal stenosis. Acta Radiol 1998; 39: Danielson B, Willen J. Axially loaded magnetic resonance image of the lumbar spine in asymptomatic individuals. Spine 2001;26: Willen J, Danielson B, Gaulitz A, et al. Dynamic effects on the lumbar spinal canal: Axially loaded CT- myelography and MRI in patients with sciatica and/or neurogenic claudication. Spine 1997;22: Willen J, Danielson B. The diagnostic effect from axial loading of the lumbar spine during computed tomography and magnetic resonance imaging in patients with degenerative disorders. Spine 2001;26: Schönström N, Willen J. Imaging lumbar spinal stenosis. Radiol Clin North Am 2001;39: Kimura S, Steinbach GC, Watenpaugh DE, et al. Lumbar spine disc height and curvature responses to an axial load generated by a compression device compatible with magnetic resonance imaging. Spine 2001;26: Fairbank J. Use of Oswestry Disability Index (ODI). Spine 1995;20: Price DD, McGrath PA, Rafii A, et al. The validation of visual analogue scales as ratio scale measures for chronic and experimental pain. Pain 1983; 17: Porter RW, Ward D. Cauda equina dysfunction. The significance of twolevel pathology. Spine 1992;17: Hamanishi C, Matukura N, Fujita M, et al. Cross-sectional area of the stenotic lumbar dural tube measured from the transverse views of magnetic resonance imaging. J Spinal Disord 1994;7: