SPINE Volume 31, Number 16, pp 183418402006, Lippincott Williams & Wilkins, Inc.

Comparison of Radiologic Signs and ClinicalSymptoms 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 werecompared to graded radiologic findings of dural sac nar-rowing.

Objectives. To examine the changes of the dural sacarea of the lumbar spine on computerized tomography(CT) performed without and with axial loading, and studythe correlations between the radiologic findings and clin-ical symptoms suggestive of spinal stenosis.

Summary of Background Data. Although several stud-ies have been performed regarding the advantage of anexternal compression device in lumbar CT, to our knowl-edge, none of these studies have correlated radiologicfindings with clinical symptoms.

Methods. The cross-sectional areas of the dural sac atthe 3 lowest lumbar intravenous spaces, measured by CTboth without and with external compression, were corre-lated to the clinical symptoms suggestive of spinal steno-sis in 117 patients and 351 intervertebral levels.

Results. No statistically significant correlation be-tween the severity of the clinical symptoms of spinalstenosis and dural cross-sectional areas was found. Nei-ther did the use of an external compression device im-prove the correlation.

Conclusion. Although an external compression simu-lates the dynamic condition in the back during standingposition, it does not eliminate the need to compare theradiologic findings with the clinical symptoms of patientsexamined because of a suspected narrowing of the spinalcanal.

Key words: spinal stenosis, spine, radiology, tomog-raphy, spiral computed. Spine 2006;31:18341840

A disproportion in the spinal canal between the size ofthe neural elements and space available is called spinalstenosis. A compression of the neural elements may causeboth pain and neural symptoms. If the compression iswithin the spinal canal, the condition is termed central spi-nal stenosis, lateral if it involves the individual spinal nerveroots.1

By far, the most common cause of spinal stenosis isvarious degenerative changes, either in the discs, facet

joints, or vertebral bodies.2 Spinal stenosis may also becaused by several less common entities.3 Congenital spi-nal stenosis is caused by short pedicles or a narrow in-terpedicular distance.4 Narrowing of the spinal canalmay also be a sequela of trauma. Any narrowing may beaggravated if degenerative changes are superimposed onpreexisting conditions.

Patients with spinal stenosis tend to have the mostprofound clinical symptoms when upright. Axial loadingand hyperextension bending of the lumbar spine willtypically worsen the clinical symptoms by causing addi-tional narrowing of the spinal canal. The traditionalmethod to evaluate the neural elements of the back ismyelography. This study can also be performed as afunctional examination with physiologic axial loading ifthe myelograms are taken with the patient in an uprightposition. Furthermore, dynamic flexion-extension my-elograms can be obtained.5 However, myelography is aninvasive study with the possibility of complications, suchas postoperative headache and inflammation.

During recent years, the use of computerized tomog-raphy (CT) and magnetic resonance imaging (MRI) hasincreased to gain information about the neural structureswithin the spine. An advantage of CT and MRI com-pared to myelography is the possibility to get transaxialimages. In CT, it is sometimes difficult to delineate thedifferent structures within the spinal canal. Their visibil-ity can be improved if the CT scanning is undertakenafter an intrathecal contrast injection, a so-called post-myelo-CT.

Normally, both CT and MRI examinations are per-formed with the patient supine, with the knees bent. Thisposition corresponds to standing in a nonweight-bearingposition, in which symptoms caused by spinal stenosistend to be less severe. However, a physiologic normalweight-bearing condition in the upright position can besimulated in a supine position using an external com-pression device.

Radiologically, the dural sac in the lumbar spine isconsidered narrowed on CT and MRI if the cross-sectional area is less than 100 mm2. The narrowing canbe further subdivided into 2 groups according to theseverity of the narrowing. Widely accepted radiologicborderlines for absolute spinal stenosis is a cross-sectional area less than 75 mm2, and for a relative100mm2. These borderlines for spinal stenosis originatefrom an experimental study by Schonstrom and Hans-son6 made on cadavers. Originally, these measurementswere described for the level of L3L4 but have later been

From the *Department of Radiology, Research Unit, and Rehabili-tation Unit, ORTON Orthopaedic Hospital, Helsinki, Finland.Acknowledgment date: October 21, 2004. First revision date: April 30,2005. Second revision date: October 9, 2005. Acceptance date: Octo-ber 10, 2005.The device(s)/drug(s) is/are FDA-approved or approved by correspond-ing national agency for this indication.No funds were received in support of this work. No benefits in anyform have been or will be received from a commercial party relateddirectly 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, 00280 Helsinki, Finland; E-mail: martina.lohman@fimnet.fi

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used also for studies of lower intervertebral levels.Schonstrom et al7 also proved the effect of flexion andextension on the size of the dural sac in the lumbar region(i.e., regularly, a narrowing of the dural sac can be seenin extension, a widening in flexion).

The relationship between clinical symptoms of spinalstenosis and its radiologic manifestations is uncertain.Despite a significant spinal narrowing, patients may haveminute or no clinical symptoms. The opposite situationis also common (i.e., patients have clinical symptoms ofspinal stenosis but insignificant or no radiologic find-ings).8 Although patients often have relief of symptomsafter decompressive surgery, this is not always the case.Within a retrospective postoperative study, no differencein outcome could be found between operatively and con-servatively treated patients with spinal stenosis.9 Hernoet al10 did not find any difference in the clinical outcomeof operated and nonoperated patients in a matched-pairstudy. Another study by Amundsen et al11 showed abetter outcome for operated patients. A discrepancy be-tween the postoperative subjective disability and radio-logic results has also been established. The aim of ourstudy was to study the dural sac without and with axialloading, and correlate these radiologic findings to theclinical symptoms suggestive of spinal stenosis. Our hy-pothesis was that the decrease of the size of the dural sacproduced by axial loading would increase the correlationbetween clinical findings and the findings on CT.

Materials and Methods

Patients. During a period of more than 3.5 years (January 15,1997September 19, 2000), 117 patients were referred fromprimary health service to the ORTON Rehabilitation Centre,Invalid Foundation because of chronic low back pain and aclinical suspicion of spinal stenosis. None of the patients hadneurologic deficits. Of these 117 patients, 46 fulfilled in theirregular CT the radiologic criteria7 for absolute spinal stenosis(group A, dural cross-sectional area of 074 mm2), 25 forrelative spinal stenosis (group B, dural cross-sectional area of7599 mm2), whereas 46 had no narrowing of the dural sacarea (group C, dural cross-sectional area of 100 mm2). Ex-clusion criteria were inflammatory arthritis, spinal tumors andmetabolic disease affecting the spine, as well as arteriosclerosisand neurologic disorders. Patients with spinal anomalies werenot 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 patientswere male and 25 female. In group B, there were 15 males and10 females, and in group C, there were 25 males and 21 fe-males. 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 Cit was 79.3 kg (SD 13.1).

Radiologic Methods. The 3 lowest lumbar intervertebralspaces were scanned with 4-mm contiguous slices, extendingfrom the pedicle above proximal to the pedicle below the levelin question. Altogether, 351 disc levels were investigated. Foreach intervertebral space, an optimal slice in the middle of the

disc was selected for measurement of the dural sac. The samelevel was also scanned with axial compression.

The axial compression was achieved using an external, com-mercially available compression device, DynaWell (Billdals-vagen 2, SE 42736; Billdal, Sweden).1217 This consists of acompression 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 tosimulate the weight bearing of the lumbar spine in a standingposition. The compression force applied was approximately40% of the patients body weight, and the loading was com-menced 5 minutes before CT. To simulate a normal standingposition, the scanning both in the loaded and nonloaded posi-tion was undertaken with straight knees. The straps were care-fully positioned to follow the imagined gravity lines in an up-right position.

The CT images were obtained in the plane of each of the 3lowest intervertebral discs separately. Both during standing andaxial loading, the lumbar lordosis tends to increase. Therefore, anew scout image was obtained in the axially loaded position, andthe slices were again scanned in the plane of each individual disc.The cross-sectional area of the dural sac at the 3 lowest lumbarintervertebral spaces in every single patient was separately calcu-lated with the measurement program in our Picker PQ 2000 CTscanner (Philips Medical, Cleveland, OH). The change in the du-ral sac size during external axial loading was assessed for everyindividual intervertebral space (Figure 1).

Pain During CT. The severity of pain occurring either duringthe loaded examination or afterwards was questioned using aquestionnaire scale with 4 classes. Grade A indicated no changecompared to the normally occurring possible discomfort in thesupine position. Grade B represented a discomfort or slightpain similar to that in the standing position. Grade C had mod-erate pain, more than the pain normally occurring in the stand-ing position. Grade D indicated severe pain. Persistence of thepain for more than 30 minutes was recorded separately.

Clinical Methods. At clinical examination, the following in-formation of the clinical symptoms was registered. The dura-tion of low back symptoms (in years) and the walking distance(in meters), as reported by the patient, was noted. Everydayfunctional disability was measured using the original Oswestryindex questionnaire (ODI),18 in which 0% to 20% correspondsto minimal functional disability, 21% to 40% to moderate, and41% to 60% to severe functional disability. An even higherpercentage of 61% to 80% indicates a crippled patient, and81% to 100% designates that the patient is bedridden. TheODI questionnaire deals with problems caused by pain, andincludes 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 alinear scale.19A VAS of zero corresponds to no pain, and a VASof 100 to nonbearable pain. VAS was recorded separately forback pain and pain radiating to the lower limbs.

Statistical Methods. Statistical analysis was performed usingSystat statistical software (Systat Software, Inc., Point Rich-mond, CA). One-way analysis of variance was used to comparegroups means. Gender distribution within the 3 groups wastested using th Pearson 2 test. For the age distribution, dura-tion of symptoms, patient weight, compression force, pain dur-ing the compression, walking distance, ODI, and VAS in back

1835Comparison of Radiologic Signs and Clinical Symptoms of Spinal Stenosis Lohman et al

and legs, the 2-sample t test was used. In addition, the results ofthe ODI, VAS tests, and walking distance in the 3 groups werecorrelated using the Spearman correlation matrix, both with-out and with axial loading. The correlation between the reduc-tion in the dural sac area at the 3 levels during compression andthe different clinical symptoms was correlated using the Pear-son 2 test.

Results

PatientsThe number of patients with absolute spinal stenosis in-creased, and the number of patients with no spinal ste-nosis decreased when external compression was used(Figure 2). Of 25 patients with relative stenosis, 17

Figure 1. Example of the mea-surements performed. CT of L4L5intervertebral disc. Before (A)and after (B) compression. Mea-surement of A (C). Measurementof B (D). In compression, there isbulging of the disc and folding ofthe flavum ligaments, changingthe cross-sectional area of thedural sac from 88 to 39 mm2. Inthis case, the relative spinal ste-nosis has changed to an abso-lute spinal stenosis with externalcompression.

Figure 2. Number and percent-age of patients with absolute spi-nal stenosis, relative spinal ste-nosis, and no spinal stenosis inregular CT without compression(A) and CT during compression (B).

1836 Spine Volume 31 Number 16 2006

moved to the category of absolute spinal stenosis duringaxial compression. Of those patients without any nar-rowing of the dural sac on regular CT, 2 had absoluteand 14 had relative spinal stenosis after compression.

Dural Sac Areas at Intervertebral SpacesThe number of intervertebral segments with a normaldural sac decreased, and the number of stenotic onesincreased in compression (Figure 3). A normal area of thedural sac was seen at 219 intervertebral levels withoutcompression, decreasing to 179 levels after compression.The number of intervertebral levels with absolute steno-sis increased from 73 to 108 with compression. Thenumber of intervertebral levels showing relative narrow-ing increased by 5 after compression.

Before compression, a narrowing of the dural sac, ei-ther relative or absolute, was seen in 71 of the 117 pa-tients. Narrowing was seen at 3 levels in 18 patients, 2levels in 25, and 1 level in 28. No narrowing at any of the3 lowermost lumbar levels was seen in 46 patients. Themean decrease of the dural cross-sectional area was inL3L4 18.5 mm2, in L4L5 16.7 mm2, and in L5S113.4 mm2 (Figure 4).

Pain During Compression in the 3 GroupsThe mean compression force used was 43% of the bodyweight 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 groupdifference in mean intensity of pain during external com-pression (P 0.59). During the compression, 67 patientshad no pain at all, 33 had slight, 9 had moderate, and 8had severe pain. There were 2 patients who had pain formore than 30 minutes. No correlation could be foundbetween the area of the dural sac before or during com-pression and the patients subjective estimation of painduring compression.

Correlation Between Radiologic Findingsand Clinical Symptoms

When we compared the data for those patients who aftercompression had absolute or relative narrowing of thedural sac in at least 1 intervertebral level to those with nonarrowing at any level, the results were the same for bothODI and VAS for the back and leg. The patients withnormal dural sac areas had even more symptoms of painmeasured by VAS and disability measured by Oswestry.The Spearman correlation coefficient was calculated forthe maximum walking distance, ODI, and VAS for theback and leg pain before and after the external compres-sion. The correlation coefficients were between 0.041and0.174, indicating no linear correlation between thetested clinical parameters and dural sac area, either withor without axial loading.

Distribution of dural sac areas

73108

5964

219179

before compression after compression

nu

mber of intervertebral

segme

nts

no spinal stenosisrelative spinal stenosisabsolute spinal stenosis

Figure 3. Number of dural sacsshowing no spinal stenosis, rela-tive spinal stenosis, and absolutespinal stenosis, with and withoutaxial loading.

0

5

10

15

20

25

L3-L4 L4-L5 L5-S1

mm

2

no spinal stenosis

relative spinalstenosisabsolute spinalstenosis Figure 4. The changes of the du-

ral sac areas at the interverte-bral levels, which were groupedaccording to the initial degree ofwidth, as a result of axial loading.

1837Comparison of Radiologic Signs and Clinical Symptoms of Spinal Stenosis Lohman et al

No correlation could be found between the severity ofthe spinal narrowing at the individual levels and numberof levels with narrowing. In addition, the number of lev-els with absolute or relative spinal stenosis did not cor-relate to the clinical symptoms. A significant correlationwas detected between the change in the dural sac area atL4L5 level with compression and the severity of painradiating to the leg, graded by the patients using the VASscale. At L3L4 and L5S1, no such positive correlationwas found between the pain radiating to the leg and thechange in dural sac area during compression.

Discussion

The results in our study indicate that unclear, confusingclinical findings resembling spinal stenosis are also rela-tively common in patients who have mild or no narrow-ing of the spinal canal on CT. The mean age of ourpatients (48 years) is younger than that of the averagepatient with a radiologic narrowing of the spinal canal.The patients were referred to the Rehabilitation Clinicbecause of chronic back symptoms consistent with neu-rogenic claudication and a clinical suspicion of spinalstenosis, as well as for evaluation of their ability to work.However, CT examination without compression verifiednarrowing of the spinal canal in only 61% of patientsand with axial compression in 74%, which reflects theoverlapping clinical signs in different spinal disorders. Apossible correlation of socioeconomic factors with symp-toms or diagnoses was not investigated in our study.

Patients with spinal malformations or developmentalanomalies were not included in the study. To reduce theradiation load, the images were obtained at the level ofthe 3 lowest intervertebral discs. Because the vertebralbodies were not scanned, we are not able to compare thearea of the dural sac at the level of the intervertebral discto the area of the dural sac at, for example, the pedicleabove the disc space. The relatively low age of the studypopulation indicates that patients with congenitallyshort pedicles may be overrepresented compared to thepopulation in general.

According to a recent study with patients of quite asimilar age, external compression was most beneficial forthe diagnosis in persons with symptoms suspicious forneurogenic claudication (in 69%) than in patients withsciatica (in 14%) or low back pain (in 0%).15 This samestudy showed that in patients with a suspicion of clinicalspinal stenosis, the percentage having radiologic spinalnarrowing increased to 35% with the use of compres-sion. In our study, the percentage of symptomatic pa-tients having dural sac areas less than 100 mm2 in at least1 of the 3 lowermost levels increased by 13% (from 61%to 74%) when axial compression was used. Further-more, in the prior study, the percentage of patients hav-ing radiologic spinal stenosis when axial compressionwas used is quite similar to our results. However, in ourstudy, more patients with a clinical suspicion of spinalstenosis actually had a narrow dural sac.

In another prior study, 9% of the asymptomatic per-sons and 24% of the symptomatic patients had a signif-icant decrease in the area of the dural sac in externalcompression, changing the area of the dural sac underthe limits of radiologic normal (i.e., less than 100mm2).13 Our study showed a 13% increase of patientshaving spinal stenosis when compression was used. Al-though achievements in the development of MRI scan-ners have produced the first upright MRI scanner inwhich the patients can be scanned in a real upright posi-tion, these scanners are not yet in common use. How-ever, an upright position can be simulated in the supineposition using an external compression device. Plain CTor MRI in conjunction with complementary axial com-pression combines the advantages of plain CT and up-right myelography for the evaluation of the dural sac,yet, without the invasiveness of myelography.

We studied the 3 lowermost intervertebral spaces. Inour study, axial compression changed 40 of the 219(18.2%) normal dural sacs to stenotic in 16 differentpatients (13.7% of all individuals studied). Even abso-lute spinal stenosis increased in 10% of the intervertebralspaces (35/351) in 17 different patients (14.5%) usingaxial compression. In 2 studies,11,13 an absolute decreasein the cross-sectional area of more than 15 mm2 has beenconsidered statistically relevant in patients with clinicallysuspected spinal stenosis, regardless of the area of the duralsac. In our study, the mean narrowing at the intervertebralspaces ranged from 13.4 to 18.5 mm2. However, the clini-cal relevance of a certain narrowing is complex, dependingon the initial size of the dural cross-sectional area. If thecross-sectional area in the noncompressed situation is wide,a narrowing of about 15 mm2 does not decrease the area toa critical limit. However, if the cross-sectional area withoutcompression is originally narrow, a further decrease maychange the cross-sectional area to a clinically significantdegree. Unfortunately, the decreased amount of liquor andthe crowding of spinal nerves often seen in spinal stenosisare difficult to measure objectively from CT images.

When lying supine with straight legs, the psoas musclewill cause a lumbar lordosis similar to that in the stand-ing position. When a pillow is used under the knees, theposition with the legs bent and back straightened differsfrom the normal standing position with a deeper lumbarlordosis. The nonloaded images have been obtained withbent legs in all but 117 prior study using the DynaWellcompression device. In an attempt to simulate the nor-mal standing and weight-bearing conditions as much aspossible, we scanned our patients with straight legs, bothwithout and with external compression.

The clinical importance of this narrowing appears tobe more complex and not directly related to either thearea of the dural sac with or without axial loading. In ourstudy, the reduction of the dural sac area did not corre-late to the subjectively graded clinical symptoms. In ad-dition, the use of axial loading did not increase the cor-relation between the clinical symptoms and radiologicfindings. All patients in our study were symptomatic,

1838 Spine Volume 31 Number 16 2006

some more and some less, with similar symptoms, butnot all of these patients had radiologic narrowing of thedural sac.

In 51 intervertebral spaces, the area of the dural sacincreased during axial loading. In most of the disc spaces,the increase was only a few mm2, which can be explainedby the measurement technique. Only 9 disc spacesshowed an increase more than 15 mm2, all of these at thelevel of L5S1. Either slight craniocaudal movement ofthe dural sac in relation to the disc space or movement inthe transaxial plane in patients with instability of thelumbar spine may explain the paradoxical widening ofthe disc space during compression. Kimura et al17 re-ported such changes of movement caused by externalaxial compression in the discs of healthy subjects. In theirstudy, the L4L5 disc showed a significant reduction indisc height but no change in the intervertebral angle. Onthe other hand, L3L4 and L5S1 showed no statisticallysignificant reduction of disc height but, instead, a statis-tically significant change in the intervertebral angles. Inprior studies, similar changes of controversial wideningof the dural sac during compression can be seen in thegraphs.14

Spinal canal narrowing is considered to cause moreproblems when it occurs at several levels.20 In our study,multilevel narrowing with an area of less than 100 mm2

was seen in 43 patients without, increasing 33%, to 57patients after axial compression. According to studies byPorter and Ward,20 and Hamanishi et al,21 the correla-tion between radiologic and clinical findings is more ob-vious in multilevel spinal narrowing compared to single-level spinal stenosis. This finding contradicts our study.We could not find any correlation between the number oflevels with spinal stenosis (neither absolute or relative)and the clinical symptoms. The difference in the results ismost likely explained by a difference in the study popu-lation. Despite clinical symptoms suspect of spinal ste-nosis, no radiologic narrowing of the spinal canal wasfound in some of our patients. However, a significantpositive correlation was found between the reduction ofthe dural sac size at L4L5 during compression and theseverity of pain radiating to the leg. At L5S1, olisthesisis most common, a fact that may affect the measurementsat L5S1 during compression. We have no explanationas to why a reduction at the L3L4-level does not havethe same correlation to the clinical symptom of pain ra-diating to the leg as that at the L4L5 level.

Studies using the DynaWell have been performedwith different imaging methods, including CT,12,14 bothwith and without intrathecal contrast, but also usingMRI.14 Side effects of the axial compression have also bebeen recorded.12 However, the pain related to the use ofthe external compression device has not been correlatedto the grade of disc degeneration or facet joint osteoar-throsis, which often causes pain in this patient group.The subjectively graded pain experienced by the patientsduring the compression did not correlate to the areaof the dural sac, so the use of this compression device

also appears to be safe for patients with suspected spinalstenosis.

Subjective back pain can be measured only subjec-tively with the use of question forms, like the VAS forpain intensity and the Oswestry questionnaire for sub-jective functional disability. Because we also consideredthe maximal walking distance on a treadmill as a some-what subjective test, we decided to rely on the patientsown statement about the maximal walking distance. Ra-diologic measurements of the dural sac area are per-formed in an attempt to grade findings objectively thatmay explain the pain and disability experienced by thepatient. In addition, the radiologic evaluation of themorphology is especially important in patients consid-ered for operative treatment. The insignificant correla-tion between the radiologic data and clinical symptomsmay be because of the fact that the pain may be to someextent related to factors that we are not able to identify,localize, and grade radiologically, or to even yet un-known factors. However, it is important to rememberthat the subjective symptoms, and clinical and radiologicfindings may be different.

Conclusions

Although external compression simulates the weight-bearing condition in the back during upright positioningit does not eliminate the need to compare the radiologicfindings to the clinical symptoms when examinationscaused by suspected narrowing of the dural sac are un-dertaken. It is assumed that narrowing of the spinal canalinevitably causes entrapment of the neural structures andmay require operative treatment. In this study the nar-rowing of the spinal canal did not correlate with theseverity of clinical symptoms suggesting that there maybe also other factors contributing to the clinical symp-toms, more difficult to grade or yet to be investigated.

Key Points

Compression of the lumbar spine significantlychanged the area of the dural sac. CT findings suggesting spinal stenosis need to becompared to clinical symptoms. No significant correlation was found betweenthe area of the dural sac in axially loaded CT andthe clinical symptoms of spinal stenosis.

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