Clinical validity of the nerve root sedimentation sign in patients with …download.xuebalib.com/xuebalib.com.28233.pdf · fDepartment of Trauma Surgery, University of Greifswald,

The Spine Journal 14 (2014) 667–674

Clinical Study

Clinical validity of the nerve root sedimentation sign in patientswith suspected lumbar spinal stenosis

Thomas Barz, MDa, Lukas P. Staub, MD, PhDb,*, Markus Melloh, MD, PhDc,Gregor Hamann, MDd, Sarah J. Lord, MD, MScb, Mark D. Chatfield, MScb,

Patrick M. Bossuyt, PhDe, Joern Lange, MDf, Harry R. Merk, MDd

aDepartment of Orthopaedic Surgery, Asklepios Klinikum Uckermark, Auguststraße 23, 16303 Schwedt/Oder, GermanybNHMRC Clinical Trials Centre, University of Sydney, Locked Bag 77, Camperdown, Sydney, New South Wales 1450, Australia

cWestern Australian Institute for Medical Research (WAIMR), University of Western Australia, Hospital Avenue, Nedlands, Western Australia 6009, AustraliadDepartment of Orthopaedic Surgery, University of Greifswald, Ferdinand-Sauerbruch-Straße, 17475 Greifswald, Germany

eDepartment of Clinical Epidemiology, Biostatistics, and Bioinformatics, Academic Medical Centre, Meibergdreef 9, 1105 AZ Amsterdam, The NetherlandsfDepartment of Trauma Surgery, University of Greifswald, Ferdinand-Sauerbruch-Straße, 17475 Greifswald, Germany

Received 26 March 2012; revised 25 March 2013; accepted 29 June 2013

Abstract BACKGROUND CONTEXT: The nerve roo

FDA device/drug

Author disclosures

MM: Nothing to disc

close. MDC: Nothing

to disclose. HRM: No

1529-9430/$ - see fro

http://dx.doi.org/10.10

t sedimentation sign in transverse magnetic reso-nance imaging has been shown to discriminate well between selected patients with and withoutlumbar spinal stenosis (LSS), but the performance of this new test, when used in a broader patientpopulation, is not yet known.PURPOSE: To evaluate the clinical performance of the nerve root sedimentation sign in detectingcentral LSS above L5 and to determine its potential significance for treatment decisions.STUDY DESIGN: Retrospective cohort study.PATIENT SAMPLE: One hundred eighteen consecutive patients with suspected LSS (52%women, median age 62 years) with a median follow-up of 24 months.OUTCOME MEASURES: Oswestry disability index (ODI) and back and leg pain relief.METHODS: We performed a clinical test validation study to assess the clinical performance ofthe sign by measuring its association with health outcomes. Subjects were patients referred toour orthopedic spine unit from 2004 to 2007 before the sign had been described. Based on clinicaland radiological diagnostics, patients had been treated with decompression surgery or nonsurgicaltreatment. Changes in the ODI and pain from baseline to 24-month follow-up were compared be-tween sedimentation sign positives and negatives in both treatment groups.RESULTS: Sixty-nine patients underwent surgery. Average baseline ODI in the surgical group was54.7%, and the sign was positive in 39 patients (mean ODI improvement 29.0 points) and negative in30 (ODI improvement 28.4), with no statistically significant difference in ODI and pain improvementbetween groups. In the 49 patients of the nonsurgical group, mean baseline ODI was 42.4%; the signwas positive in 18 (ODI improvement 0.6) and negative in 31 (ODI improvement 17.7). A positive signwas associatedwith a smallerODI and back pain improvement thannegative signs (both p!.01 on t test).CONCLUSIONS: In patients commonly treated with decompression surgery, the sedimentationsign does not appear to predict surgical outcome. In nonsurgically treated patients, a positive signis associated with more limited improvement. In these cases, surgery might be effective, but thisneeds investigation in prospective randomized trials (Australian New Zealand Clinical Trial Regis-try, number ACTRN12610000567022). � 2014 Elsevier Inc. All rights reserved.

Keywords: Lumbar spinal stenosis; Diagnostic test; Sensitivity and specificity; Diagnostic imaging; Nerve root sedimentation

status: Not applicable.

: TB: Nothing to disclose. LPS: Nothing to disclose.

lose. GH: Nothing to disclose. SJL: Nothing to dis-

to disclose. PMB: Nothing to disclose. JL: Nothing

thing to disclose.

TB and LPS should be considered co-first authors.

* Corresponding author. NHMRC Clinical Trials Centre, University of

Sydney, Locked Bag 77, Camperdown, New South Wales 1450, Australia.

Tel.: (61) 2-9562-5088; fax: (61) 2-9565-1863.

E-mail address: [email protected] (L.P. Staub)

nt matter � 2014 Elsevier Inc. All rights reserved.

16/j.spinee.2013.06.105

ContextThe sedimentation sign helps to identify patients with

severe stenosis. The authors assessed whether the sign

was predictive of clinical outcomes.

ContributionIn surgically treated patients, the sign was not predictive

of outcomes. In nonsurgically treated patients the out-

comes were worse when a positive sign was present.

ImplicationsThe findings are helpful for informed consent as patients

decide between operative and nonoperative treatments.—The Editors

668 T. Barz et al. / The Spine Journal 14 (2014) 667–674

Introduction

Lumbar spinal stenosis (LSS) is one of the most com-mon disorders of the spine in elderly patients [1]. SinceLSS was first described by Verbiest [2], an important re-search focus has been on the evaluation of clinical, radio-logical, and other diagnostic criteria to better describethis condition [3–9]. One major problem is that imagingfindings do not always correlate with clinical symptoms[10]. Consequently, no consensus exists on radiological orpathologic criteria that define a symptomatic LSS.

Furthermore, there is an ongoing debate on what diagnos-tic criteria can aid decisions about the use of conservative orsurgical treatment and the selection of specific surgical pro-cedures. Randomized controlled trials comparing conserva-tive with surgical treatment exist [11–15], and a recentsystematic review of this evidence suggests that decompres-sion surgery is associated with reduced pain, improved func-tion, and better quality of life compared with conservativetreatment [16]. However, the reviewers pointed out that theincluded studies used different radiological criteria to defineLSS, some but not all studies included patients with spondy-lolisthesis, and not all defined neurogenic claudication as anabsolute inclusion criterion. Although the evidentiary basisfor the benefits of decompression surgery is growing, the un-certainty around the indication for surgery and the differentsurgical procedures remains.

The nerve root sedimentation sign has recently been de-scribed. In transverse magnetic resonance imaging (MRI)scans in supine position of patients with severe LSS, lum-bar nerve roots do not sediment to the dorsal part, as a resultof gravity, but remain in the ventral and central part of thedural sac [17]. The initial report of the sedimentation signshowed that this test discriminates well between cases withsymptomatic LSS and controls with nonspecific low backpain. The next step in the evaluation of the sign involvesmeasuring the clinical value of the new test in

a representative patient population, to demonstrate whetherthe sedimentation sign can improve the identification of pa-tients with clinically relevant central LSS.

Because of the lack of a clear definition of LSS, there isno accepted reference standard for this condition [18], anda meaningful diagnostic accuracy study is not feasible forthe reporting of test sensitivity and specificity [19,20].When a perfect reference standard does not exist, the idealstudy design is a clinical test validation study that measuresthe associations between test results and relevant down-stream outcomes, such as the success of surgery [21]. Usingthese concepts, we designed a retrospective blinded chartreview of the clinical validity of the sedimentation sign.The aim of this study was to determine whether the sedi-mentation sign may provide valuable clinical informationthat can be used to aid treatment decisions and thereby im-prove health outcomes. We investigated associations be-tween the sedimentation sign and patient history, clinicalexamination, cross-sectional area (CSA) of the dural sacin transverse MRI scans, and changes in disease severityscores before and after decompression surgery or nonsurgi-cal treatment.

Materials and methods

The rationale and design of this study have been de-scribed previously [20]. In brief, we assessed the sedimen-tation sign’s ability to detect clinically relevant LSS byevaluating its association with clinical outcomes in a broadpatient group with suspected LSS. A prospective evaluationof the sign independent of the currently used diagnostictests would be ideal but was not possible because knowl-edgeable clinicians can detect the sign at a glance. There-fore, we performed a retrospective review of MRI scansof patients undergoing treatment before the sedimentationsign had been described. This study was approved by theparticipating clinic’s ethics committee.

All patients referred to our orthopedic spine unit betweenJanuary 2004 and December 2007 were assessed for eligibil-ity. Included were patients in whom LSS was suspectedbased on patient history and physical examination. We ex-cluded patients who had contraindications for surgery orhad undergone previous spine surgery, patients with an acutespinal disorder (eg, disc herniation), specific low back painother than LSS, a history of inflammatory disease of thespine, primary or metastatic malignant disease in the spine,other musculoskeletal impairments compromising walkingability (eg, severe coxarthrosis/gonarthrosis), polyneurop-athy, or peripheral arterial disease.

Using the method described by Barz et al. [17], the sed-imentation sign was measured in transverse MRI scans oflevel L1/L2–L4/L5. The measurement was performed atthe approximate mid-height of the vertebral body aboveor below the maximal stenosis (for stenosis level L1/L2 al-ways below, for stenosis level L4/L5 always above). A pos-itive sedimentation sign was defined as the presence of

669T. Barz et al. / The Spine Journal 14 (2014) 667–674

nerve roots being located in the ventral or central part of thedural sac. A negative sedimentation sign was defined as allnerve roots being located in the dorsal part of the duralsac—except for the two ventral nerve roots that leave thedural sac one level below the stenosis (Fig. 1).

One investigator gathered clinical information from pa-tient charts, including patient history and self-assessment(Oswestry disability index [ODI] [22], visual analog scale[VAS] for back and leg pain), physical examination, tread-mill test, and imaging (MRI with CSA measurement of thedural sac), and treatment administered (decompression sur-gery with or without fusion or nonsurgical treatment). Theinvestigator also collected clinical information and patientself-assessment from the reports of follow-up examinations24 (612) months after the first presentation. Two other in-vestigators, both spine surgeons, independently rated thesedimentation sign on baseline MRI scans performed atthe time of first presentation. They were not treating physi-cians of study patients and were blinded to all other clinicalinformation. Before further analyses, discordant initial sed-imentation sign ratings of the two investigators were re-solved in a consensus meeting. All data were entered intoa relational Microsoft Access database to blind investiga-tors to other study information.

The primary outcome measures were ODI and pain VASchange between baseline and follow-up examinations.These health outcomes were compared between sedimenta-tion sign positives and negatives, in separate analyses forpatients treated with decompression surgery (surgicalgroup) and patients treated nonsurgically (nonsurgicalgroup). On-treatment analyses were performed; thus, pa-tients initially not planned for surgery but receiving delayeddecompression surgery at the same level during the follow-up interval (ie, crossover from nonsurgical to surgicaltreatment) were assessed in the surgical group. Secondaryoutcomes included calculation of the rates of delayed sur-gery, cross-classification of the sedimentation sign with

Fig. 1. Measuring the nerve root sedimentation sign. Magnetic resonance imagin

permission from Barz et al. [17].

existing tests, and the interrater reliability of the initial sed-imentation sign ratings of the two investigators.

We used median and interquartile range (IQR525th to75th percentile) to summarize the study results. In bothtreatment groups, we tested for a difference in the meanwithin-patient change in ODI and pain VAS between sedi-mentation sign positives and negatives using Student t test.Cohen kappa was calculated to assess interrater agreementbetween the initial sedimentation sign ratings of the two in-vestigators. A statistical significance level of 5% was used.Statistical analyses were conducted with the use of the Stata11 software package (Stata, College Station, TX, USA).

Results

Patients

A total of 175 patients presenting with possible LSS dur-ing the observation period met the inclusion criteria. Ofthese, 54 did not have a follow-up examination within thedefined interval, and 3 had to be excluded because of miss-ing outcome values (Fig. 2). The final study sample com-prised 118 patients with a median age of 62 years (IQR53–69) and 61 (52%) women.

After baseline assessment, 55 (47%) patients werescheduled to undergo surgery. Median time from baselineassessment to surgery was 1.6 months (IQR 0.0–2.6). Inthe remaining 63 patients, no surgery was planned; theirtreatment generally included physical therapy and oral painmedication [23]. In 14 of the 63 patients initially notplanned to have surgery, the treatment decision was revisedduring the follow-up period, and these patients receivedsurgery and their median time interval between baseline as-sessment and delayed surgery was 8.3 months (IQR 4.4 to22.1). In patients who did not receive surgery, the mediantime between baseline and follow-up examination was

g scans with a negative sign (left) and a positive sign (right). Adapted with

Patients with possible LSSn=175

Included in studyn=118

Excluded (n=57)- 54 no follow-up at 24 months- 3 missing ODI or VAS values

Decompression surgeryn=55

No decompression surgeryn=63

Delayed surgeryn=14

Surgical group (n=69)

- 28 Decompression alone- 41 Decompression plus fusion

Non-surgical group (n=49)

Fig. 2. Study profile of included participants.

670 T. Barz et al. / The Spine Journal 14 (2014) 667–674

24.2 months (IQR 21.7–26.0). The median time interval be-tween surgery and follow-up examination was 22.3 months(IQR 18.3–26.5) in the immediate surgery group and 12months (IQR 0.5–16.8) in the delayed surgery group.

Hence, for outcome assessment, there were 69 patientsin the surgical group, of whom 28 received decompressionsurgery alone and 41 underwent decompression surgeryplus fusion, and 49 patients in the nonsurgical group(Fig. 2). In the surgical group, fusion surgery was addedon to decompression when preoperative back pain exceeded5 VAS points, in cases of degenerative spondylolisthesis,degenerative scoliosis, instability in functional imaging,multisegment stenosis, and a central stenosis that was ac-companied by bilateral foraminal stenosis. Baseline charac-teristics of the included patients are given in Table 1.

Table 1

Baseline patient characteristics in patients planned for decompression surgery an

Characteristic Decompression surgery (n555)

Female sex 54%

Age* 66 (54–71)

VAS back pain* 7 (5–8)

VAS leg pain* 8 (5–8)

Loss of strength in legs 54%

Paresthesia 78%

ODI* 54 (44–66)

CSA* (mm2) 90 (60–140)

Treadmill*,y (m) 40 (13–120)

VAS, visual analog scale; ODI, Oswestry disability index; CSA, cross-sectio

* Values are expressed as median (interquartile range).y Not available in all patients: decompression surgery, n542; delayed surge

Outcomes

Table 2 presents the baseline values and improvement inoutcome in the two treatment groups, contingent on thesedimentation sign result. The changes from baseline tofollow-up are depicted in Figs. 3–8. Nearly all patients re-ceiving decompression surgery improved after treatment,whereas the outcomes in the nonsurgical group were lessfavorable. There were no statistically significant differencesin outcome improvements among patients undergoing de-compression alone or decompression plus fusion surgery.

In the 69 patients in the surgical group, the sedimenta-tion sign was positive in 39 patients and negative in 30.In patients with a positive sign, the ODI improved on aver-age by 29.0 points, compared with 28.4 points in sign neg-atives. The difference between sign positives and negativeswas not statistically significant. Similarly, back pain onVAS improved on average by 3.9 in sign positives and3.0 in sign negatives, and leg pain improved by 4.2 in signpositives and 4.3 in sign negatives. These differences inchange of pain between sign positives and negatives wereagain not statistically significant (Table 2).

In the 14 patients with delayed surgery, the sedimenta-tion sign had been positive in six patients and negative ineight. In the six patients with a positive sign, the medianbaseline ODI was 46 (IQR 44–54) and the CSA 62.5 mm2

(IQR 60–65). In the eight patients with a negative sign,the median baseline ODI was 59 (IQR 45–67) and CSA152.5 mm2 (IQR 115–200). The risk of undergoing de-layed surgery was not significantly higher in sign posi-tives than in sign negatives (relative risk 1.22, 95%confidence interval 0.48–3.08). Five patients underwentdecompression surgery alone; the sedimentation signhad been negative at baseline in all of them. In nine pa-tients, decompression surgery plus fusion was performed,the sign had been positive in six and negative in three.Overall, the mean ODI improvement after delayed sur-gery was 24.3 points, back pain improved by 2.7 andleg pain by 4.1. There were no statistically significant dif-ferences in these outcomes between sign positives andnegatives.

d no surgery

Delayed surgery (n514) No surgery (n549)

21% 57%

56 (46–60) 63 (53–68)

7.5 (7–8) 6 (5–8)

8 (7–8) 5 (4–7)

43% 18%

64% 43%

51 (44–66) 40 (28–54)

100 (65–155) 130 (80–180)

80 (50–225) 40 (10–200)

nal area.

ry, n512; no surgery, n517.

Table 2

ODI and VAS measures according to sedimentation sign result, stratified by treatment group

Treatment group

Sedimentation sign positive Sedimentation sign negativeDifference of decrease

(95% CI) p ValueBaseline Follow-up Decrease Baseline Follow-up Decrease

Surgical group (n569)

ODI 55.67 26.67 29.00 53.47 25.07 28.40 0.60 (�7.21, 8.41) .88

VAS back pain 7.13 3.26 3.87 6.63 3.63 3.00 0.87 (�0.35, 2.09) .16

VAS leg pain 7.00 2.85 4.15 6.87 2.54 4.33 �0.18 (�1.66, 1.30) .81

Nonsurgical group (n549)

ODI 49.22 48.66 0.56 38.39 20.65 17.74 �17.19 (�27.41, �6.96) !.01

VAS back pain 6.28 5.89 0.39 6.26 3.91 2.35 �1.97 (�3.2, �0.73) !.01

VAS leg pain 5.72 5.16 0.56 4.94 2.97 1.97 �1.41 (�2.93, 0.10) .07

ODI, Oswestry disability index; VAS, visual analog scale; CI, confidence interval.

671T. Barz et al. / The Spine Journal 14 (2014) 667–674

In the 49 patients in the nonsurgical group, the sedimen-tation sign was positive in 18 patients and negative in 31. Insign positives, the ODI improved on an average by 0.6,whereas in sign negatives, it improved by 17.7. The ODIimprovement was significantly smaller in sign positivescompared with sign negatives (p!.01). Back pain improvedon an average by 0.4 VAS points in sign positives and 2.4points in sign negatives, again significantly less in sign pos-itives (p!.01). The improvement in leg pain was 0.6 in signpositives and was 2.0 in sign negatives, which were almoststatistically significant (Table 2).

Concordance of sedimentation sign with other tests

Baseline test results for subjects with a positive and neg-ative sedimentation sign are shown in Table 3. Patients witha positive sign more often had smaller CSA, shorter walk-ing distance on the treadmill, and more functional limita-tions in the ODI at baseline than patients with a negativesign. A loss of leg strength was more common in patientswith a positive sign; however, paresthesia in the lowerlimbs was more prevalent in sign negatives. Similar levels

Baseline

Follo

w-u

p

Surgical group Non-surgical group

ODI

100

001001

50

50 50

0

00

Fig. 3. Change in Oswestry disability index (ODI) from baseline to

follow-up in treatment groups. The diagonal line represents no change:

points below the line show ODI improvement and points above the line

show ODI deterioration (open circles denote sedimentation sign positives

and filled circles denote sign negatives).

of back and leg pain were observed regardless of sedimen-tation sign rating. Fifty-three percent of patients with a pos-itive sign indicated their preference for decompressionsurgery, whereas 66% of those with a negative sign pre-ferred nonsurgical treatment.

Interrater agreement of initial sedimentation signratings

The two spine surgeons who rated the sedimentationsign agreed in 111 of the 118 MRI scans (94%). Both clas-sified the sign as positive in 53 patients and negative in 58.The resulting kappa coefficient was 0.88 (95% confidenceinterval 0.80–0.97).

Discussion

This study evaluated the clinical meaning of the nerveroot sedimentation sign in detecting central LSS aboveL5. After the initial report of the sign, which demonstratedits ability to detect LSS under ideal circumstances [17], thepresent study moves the evaluation of the sign a step furtherby assessing the clinical implications of a positive and neg-ative test finding in a broader patient group. In patients

−80

−60

−40

−20

0

20

Surgical group Non−surgical group

sign pos sign neg

OD

I diff

eren

ce

sign pos sign neg

Fig. 4. Change of Oswestry disability index (ODI) in treatment groups ac-

cording to sedimentation sign classification.

Follo

w−u

p

0

5

10

0

5

10

0 5 10 0 5 10

VAS back

Baseline

Surgical group Non-surgical group

Fig. 5. Change of visual analog scale (VAS) back pain from baseline to

follow-up in treatment groups. The diagonal line represents no change:

dots below the line show pain improvement and dots above the line show

pain deterioration (open circles denote sedimentation sign positives and

filled circles denote sign negatives). The size of dots corresponds to the

number of patients.

0

5

10

0 5 10 0 5 10

0

5

10

VAS legs

Surgical group Non-surgical group

Follo

w−u

p

Baseline

Fig. 7. Change of visual analog scale (VAS) leg pain from baseline to

follow-up in treatment groups. The diagonal line represents no change:

dots below the line show pain improvement and dots above the line show

pain deterioration (open circles denote sedimentation sign positives and

filled circles denote sign negatives). The size of the dots corresponds to

the number of patients.

672 T. Barz et al. / The Spine Journal 14 (2014) 667–674

treated with decompression surgery or nonsurgical treat-ment, changes in ODI and pain from baseline to 24-month follow-up were compared between sedimentationsign positives and negatives. Patients in the surgical grouphad similar outcomes regardless of the sign. In contrast, inthe cohort receiving nonsurgical treatment, patients witha positive sign showed less improvement than patients witha negative sign. Compared with the results of other diag-nostic tests, the sedimentation sign was consistent in iden-tifying patients suggestive of LSS; on average, their CSA ofthe dural sac was small, and they were only able to walkshort distances. The independent sedimentation sign ratingsof two spine surgeons showed excellent agreement.

The most intriguing result of this study concerns the pa-tients with a positive sedimentation sign who were nottreated with surgery. Conservative treatment showed

−10

−5

0

5

VAS

back

diff

eren

ce

Surgical group Non−surgical group

sign pos sign neg sign pos sign neg

Fig. 6. Change of visual analog scale (VAS) back pain in treatment

groups according to sedimentation sign classification.

virtually no change in the outcome in these patients,whereas conservative treatment in patients with a negativesign was associated with improved outcomes. In contrast,the results of the sedimentation sign were not associatedwith different outcomes after surgery. Decompression sur-gery (with or without fusion) was effective in nearly all pa-tients, including those who were initially treatedconservatively but received delayed surgery (with similarimproved outcomes recorded at shorter follow-up time).

The existence of a difference in nonsurgically treated pa-tients, in the absence of similar differences after surgerywhere all patients seem to improve, suggests that those witha positive sedimentation sign represent a group of patientsin whom surgery might be effective. In addition to the pos-itive sign, these patients also had higher ODI and higher legpain levels at baseline (albeit not statistically significant),

−10

−5

0

5

VAS

leg

diffe

renc

e

Surgical group Non−surgical group

sign pos sign neg sign pos sign neg

Fig. 8. Change of visual analog scale (VAS) leg pain in treatment groups

according to sedimentation sign classification.

Table 3

Comparison of sedimentation sign results with other diagnostic tests at

baseline

Test

Sedimentation sign

positive (n557)

Sedimentation sign

negative (n561)

CSA* (mm2) 65 (50–90) 145 (115–200)

Treadmill*,y (m) 41 (15–120) 56 (10–200)

ODI* 54 (44–66) 44 (32–56)

VAS back pain* 7 (5–8) 7 (5–8)

VAS leg pain* 7 (5–8) 6 (4–8)

Loss of strength in legs 48% 28%

Paresthesia 57% 66%

Patient preference for surgery 53% 34%

CSA, cross-sectional area; ODI, Oswestry disability index; VAS, visual

analog scale.

* Values are expressed as median (interquartile range).y Not available in all patients: sign positive, n537; sign negative,

n534.

673T. Barz et al. / The Spine Journal 14 (2014) 667–674

indicating more severe LSS compared with sign negatives,who improved after nonsurgical treatment.

In this study, the rate of delayed surgery was not associ-ated with a positive sedimentation sign. Factors other thanthe clinical severity of LSS, such as patient preference, mayhave played an important role in the initial decision againstsurgery. Furthermore, other indications for surgery, for ex-ample, segmental instability, kyphosis, or foraminal steno-sis, were the reason for a later decision to perform surgeryin some of these patients.

The results of this study suggest that the sedimentationsign provides additional information to other diagnostictests and can help in identifying patients who may benefitfrom decompression surgery. Given that almost all patientsreferred to a spine specialist with suspected LSS undergoMRI examination, the sedimentation sign does not incuradditional costs. Its use is very simple, fast, and does notrequire taking any measurements. Moreover, the sign visu-alizes the stenosis in a way that can be clearly and simplyconveyed to patients when making recommendations aboutsurgery in clinical practice. It is a (qualitative) relative mea-sure of nerve root compression within the individual anat-omy of the spinal canal, unlike the (quantitative) absolutemeasure of the CSA of the dural sac, for which no thresholdcan be defined that is applicable to all patients. We believethat combining the sedimentation sign with CSA measure-ment and functional assessment using treadmill tests canimprove the diagnosis of clinically relevant LSS.

This study has some limitations. First, patients were se-lected into treatment groups based on conventional test re-sults and other factors; therefore, patient outcomes cannotbe used to draw conclusions about the relative effects ofsurgery versus conservative treatment. We were not ableto conduct an unbiased formal test for interaction to exam-ine whether the sedimentation sign can be used to definea patient group who are more or less likely to benefit fromsurgery. Even so, our analyses of the prognostic signifi-cance of the sign in patients selected to each treatment op-tion were valuable to explore the sedimentation sign’s

potential importance for treatment decisions. As such, thisstudy should be regarded as an exploratory pilot study,which has established that the sedimentation sign holds suf-ficient promise to warrant a larger definitive trial. Second,to reflect actual practice in which the sedimentation signis proposed to be used, we analyzed outcomes with anon-treatment approach. Even when comparing outcomesaccording to the intention-to-treat principle, based on theintended management after baseline assessment, a positivesign was associated with worse outcomes in the nonsurgicalgroup, albeit to a lesser extent (results not reported). Third,the timing of follow-up examinations could not be con-trolled, and we accepted follow-up intervals ranging be-tween 12 and 36 months. Too short follow-up may notallow enough time to demonstrate full recovery and benefitsafter spinal fusion, whereas too long follow-up may impairoutcomes because of adjacent segment degeneration andconsecutive instability or even spinal fractures. Most ofour patients were followed up between 20 and 26 monthsafter baseline examination. Furthermore, outcomes of de-compression surgery do not appear to change over time af-ter the initial postoperative improvements [24], andmultivariate analyses of our data showed no significant in-fluence of variations in follow-up interval on outcomes (re-sults not shown).

Further research of the nerve root sedimentation signneeds to demonstrate the applicability of our results to dif-ferent clinical settings. Retrospective studies similar to theone reported here are currently underway. More practicalguidance for clinicians is needed, detailing how the sedi-mentation sign should be read and interpreted in more com-plex cases such as multilevel LSS. In addition, a rigorouslyconducted reliability study of the sedimentation sign is es-sential [25]. Prospective studies that incorporate both test-ing and treatment should also be carried out. Unbiasedestimates of the effects of using the sedimentation signon patient health outcomes can ultimately only be obtainedin randomized controlled trials. The aim of such trialsshould be to properly assess the value of the sign as a pre-dictive marker for treatment selection.

Conclusions

In patients commonly treated with decompression sur-gery, the sedimentation sign does not appear to predict sur-gical outcome. In nonsurgically treated patients, a positivesign is associated with more limited improvement. In thesecases, surgery might be effective, but this needs investiga-tion in prospective randomized trials.

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