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NeuroradiologyA Journal Dedicated to Neuroimagingand Interventional Neuroradiology ISSN 0028-3940Volume 57Number 6 Neuroradiology (2015) 57:583-588DOI 10.1007/s00234-015-1513-9

Hidden spondylolisthesis: unrecognizedcause of low back pain? Prospective studyabout the use of dynamic projections instanding and recumbent position for theindividuation of lumbar instabilityAlessandro Landi, Fabrizio Gregori,Nicola Marotta, Pasquale Donnarumma,et al.

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DIAGNOSTIC NEURORADIOLOGY

Hidden spondylolisthesis: unrecognized cause of low back pain?Prospective study about the use of dynamic projectionsin standing and recumbent position for the individuationof lumbar instability

Alessandro Landi1 & Fabrizio Gregori1 & Nicola Marotta1 & Pasquale Donnarumma1 &

Roberto Delfini1

Received: 18 November 2014 /Accepted: 13 March 2015 /Published online: 26 March 2015# Springer-Verlag Berlin Heidelberg 2015

AbstractIntroduction Dynamic X-rays (DXR) are widely recognizedas an effective method to detect lumbar instability (LI). Theyare usually performed with the patient in standing position(SDXR). In our opinion, standing position inhibitsmicromovements of the lumbar segment interested by thelisthesis, thanks to paravertebral muscles antalgic contractionand augmented tone. We aim to demonstrate that DXR inrecumbent position (RDXR), reducing the action ofparavertebral muscles, can discover hypermovements not ev-idenced in SDXR.Methods Between January 2011 and January 2013, we stud-ied 200 consecutive patients with lumbar degenerative diseasewith MRI, SDXR, and RDXR. We aimed to find a correlationbetween low back or radicular pain and the presence of aspondylolisthesis not showed by the SDXR, but showed bythe RDXR.Results We analysed 200 patients: of the 133 not path-ologic in SDXR, 43 patients (32.3 %) showed anhypermovement in RDXR (p=0.0001) without any sig-nificant correlation between hidden listhesis and age,sex, or level involved.Conclusions The aim of our study is to determine whether inpatients with lumbalgywithout evidence of listhesis in SDXR,pain can be attributed to a faccettal syndrome or to a

spondylolisthesis. Consequence of pain is augmentedmuscular tone of the paravertebral musculature, particu-larly in standing position. Augmented muscular tonetries to inhibit the pain generator, attempting to limitthe slippage of the involved segment. In patients exam-ined in RDXR, the tone of paravertebral musculature isreduced, showing the hidden spondylolisthesis.

Keywords Lumbar instability . Dynamic X-rays .

Recumbent dynamic X-rays . Spondylolisthesis . Low backpain

Introduction

Vertebral instability has been widely discussed in litera-ture during the years. The most cited definitions arethose of Pope and Panjabi [1] and Frymoyer andSelby [2]: Ba loss of motion segment stiffness, such thatforce application to that motion segment produces ab-normally great motion compared to that of a normalspine) and of Watters et al. [3] (an acquired anteriordisplacement of one vertebra over the subjacent verte-bra, associated with degenerative changes, without anassociated disruption or defect in the vertebral ring),according to Leone et al. [4].

The execution of dynamic X-rays (DXR) in flexionand extension is commonly used in clinical practice andis widely recognized as an effective method to detectthe presence of lumbar instability (LI) and to obtainqualitative and quantitative data regarding this condition[5, 6]. At the same time, there is not an unanimousconsensus on this technique [7]. In clinical practice,DXR in standing position (SDXR) are often used to

* Alessandro Landidott.alessandro.landi@gmail.com

1 Department of Neurology and Psychiatry, Division of Neurosurgery,BSapienza^ University of Rome - Policlinico Umberto I, viale delPoliclinico 155, 00181 Rome, Italy

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disclose LI and to plan the surgical strategy: the sur-geon’s choice for an instrumented fusion or not is usu-ally based on the results of SDXR and of MRI and/orCT obtained with the patient in supine position, avail-able in every centre of spinal surgery [6].

The roentgenogram is generally obtained in a latero-lateral position, with the patient standing and in a posi-tion of maximal flexion forward and then extensionbackward of the trunk, because the standing position,according to some authors [5, 8–10], can evocate agreater segmental slip if compared to the recumbentposition.

The range of segmental vertebral mobility is relativelywide, but a sagittal translation ≥4 mm or ≥8 % and a sagittalrotation ≥10° in L1–L5 and ≥2° in L5–S1 are usually consid-ered pathological for LI and widely accepted by many authors[11–16].

During the years, many techniques have been studiedand developed to identify pathological movements ofthe lumbar spine needing surgical treatment [17], butnone of them are currently performed in spinal surgerycentres, because of the lack of standardization for thetechniques and the technical difficulty related to thoseprocedures, and for the controversial results obtained insome cases [8, 18–20].

In our opinion, the standing position in which theroentgenogram is routinely performed, in some casesworks as a limit to micromovements of the lumbar seg-ment interested by the listhesis hiding its presence, asexposed by Wood [5] and Pearcy [21]. According to us,the paravertebral muscles act as a stabilizer of thehypermovement that generates instability because oftheir antalgic contraction and augmented muscular tone.Therefore, this phenomenon can reduce sagittal transla-tion and Bhide^ LI.

The aim of our study is to demonstrate that DXR inflexion and extension performed in recumbent position(RDXR), with the patient lying along his side, reducesthe augmented muscular tone of the paravertebral mus-cles in patients with low back pain or sciatic pain andmight discover hypermovements hidden by antalgic con-tractions when investigated with DXR obtained instanding position.

Materials and methods

In the period between January 2011 and January 2013, inthe Neurosurgery Department of BSapienza^ University ofRome, 200 consecutive patients with lumbar degenerativedisease have been studied. The mean age of the studiedpatients was 59.8 years (range 45–82). The patients were117 males and 83 females. All patients have been studied

with lumbosacral MRI or TC when MRI could not beperformed (i.e., patients with pacemaker or prosthesisnot compatible with MRI) and DXR performed in bothstanding and recumbent position, obtaining a maximalmovement of both flexion and extension.

RDXR have been obtained with the patient lying on hisside (generally the right side). For the projections in maximalflexion, the patients flexed the hips; for the projections inmaximal extension, the patients had their hips extended.

In all cases, the SDXR and RDXR were performed at aconstant source-to-film distance of 1 m to avoid inaccuraciesthat result from magnification and obtain standardized imagesin all cases.

We considered as pathological the movements of sagittaltranslation ≥4 mm or ≥8 % of the antero-posterior diameter ofthe vertebral body and sagittal rotation ≥10° in L1–L5 and ≥2°in L5–S1, as proposed by many authors [11–16].

All roentgenograms were reviewed by consensus of tworadiologists and two neurosurgeons. All measurements weremade with digital measuring tools.

The aim of our study is to find a correlation between clin-ical symptom (low back pain or radicular pain) and the pres-ence of a spondylolisthesis not showed by the SDXR, butshowed by the RDXR, demonstrating how a spondylolisthesisnot discovered by SDXR, can cause low back pain in patientswith non-diagnostic SDXR.

Results

We analysed 200 patients. Fifty-three patients (26.5 %)showed LI at SDXR but not in RDXR; 43 patients (21.5 %)showed LI in RDXR but not in SDXR; 90 patients (45 %)showed no LI in both SDXR and RDXR; and 14 patients(7 %) showed LI in both SDXR and RDXR.

The L3–L4 segment was involved in 7 % of cases, L4–L5was involved in 54 % of cases, and L5–S1 was involved in39 % of cases. In 98 patients, the only symptom complainedwas lumbalgy; in 102 cases, the complained symptom waslumbalgy associated with radicular pain or neurogenicclaudication.

One hundred thirty-three patients did not show LI inSDXR. Among them, 43 patients (32.3 %) showed a LI inthe RDXR. This result was statistically relevant (p=0.001,McNemar test; k=0.422 with confidence interval (C.I.) be-tween 0.301 and 0.543). Statistical analysis did not showany correlation between LI showed in RDXR and age, asemerges from literature [20], dividing the patients in twogroups (≥60 and <60 years), sex and level involved.

We calculated the values of sensibility, specificity, positivepredictive value (PPV), and negative predictive value (NPV)for SDXR and RDXR separately, assuming as gold standardthe results of the combination of the two techniques.

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The values obtained for SDXR are the following:

– Sensibility 50.8 % (C.I. from 42.6 to 60.9 %)– Specificity 88.9 % (C.I. from 80.7 to 93.9 %)– PPV 85.1 % (C.I. from 74.7 to 91.7 %)– NPV 60.2 % (C.I. from 53.0 to 69.5 %)

The values obtained for RDXR are the following:

– Sensibility 77.3 % (C.I. from 68.6 to 84.1 %)– Specificity 87.8 % (C.I. from 79.4 to 87.8 %)– PPV 88.5 % (C.I. from 80.6 to 93.5 %)– NPV 76.0 % (C.I. from 66.9 to 83.2 %)

The C.I. was calculated with Wilson method.

Discussion

The concept of LI, introduced for the first time by Knutsson in1944 [22], has been object of many revisions and critics frommany authors during the years. An operative definition, accept-ed by the North American Spine Society (NASS) refers to LI asBan acquired anterior displacement of one vertebra over thesubjacent vertebra, associated with degenerative changes, with-out an associated disruption of defect in the vertebral ring^ [3].

Flexion and extension dynamic roentgenograms of thelumbar spine represent the method of choice for the study ofthe LI in the interested segment. During the years, many tech-niques have been studied and proposed to study the lumbarspine and its pathological mobility [17], without a universalconsent and procedural uniformity.

The rationale of this study is to determine whether in pa-tients without evidence of LI at the SDXR and with lumbalgy,the pain can be attributed to a faccettal syndrome or to aspondylolisthesis not showed by the SDXR. In patients withspondylodiscarthrosis, it has not been well established whatcan be the source of pain.

According to Panjabi et al. [23], three elements contributeto determine stability: spine, muscles, and the neural controlunit. Under normal conditions, the three subsystems work inharmony and provide the needed mechanical stability.

The stiffness of the spine varies with the load: it is flexibleat low loads and stiffens with increasing load. This concepthas been exposed by the authors with the Bball-in-a-bow anal-ogy,^ giving a graphic explanation to the concepts of range ofmotion (ROM) and neutral zone (NZ). The muscles act as guywires in stiffening the spine and, thus, increasing its criticalload and stability and reducing the neutral zone.

As a response to the painful stimulation of the mechano-receptors situated in the ligaments, the muscle activation pat-tern is altered by the neural control unit [23–26].

This biomechanical mechanism is the basis of our hypoth-esis, assuming that the listhesis is the pain generator. The painoriginating from the listhesis produces an antalgic hypertonusof the paravertebral musculature, which is elicited by theweight bearing (in an orthostatic position) [11, 27], in themoment in which the intervertebral disc and the vertebral ar-ticulations are mostly solicited and have more possibilities togive rise to a listhesis. The aim of the antalgic hypertonuswould be to limit the pathological movement of the interestedsegment [6], inhibiting the pain generator and neutralizing thesource of pain.

This hypothesis is valid in a setting of low-gradespondylolisthesis (phase I of the degenerative cascade—unsta-ble dysfunction), in which the capacity of containment of thedisc and of the capsuloligamentous structures are not complete-ly compromised, so that the disc and the articular masses main-tain most of their functions, even if they are damaged.

One theory is that the damage of the intervertebral disc,associated to the stretch and the compression of thesinuvertebral nerve of Luschka, generates the pain and is re-sponsible for low back pain. In addition to this is associatedthe stretch of the articular capsule of the articular masses,incurring in diastases in the moment in which they loose con-tinence, after the degeneration. In this context, the antalgichypertonus is not identified as a cause of lumbalgy, but as adefensive system against the pain evoked by the stretch of theLuschka sinuvertebral nerve.

Otherwise, when the degenerative cascade evolves towardsphase II (frank segmental instability), the shear force acting onthe disc cannot be overwhelmed by the contraction of the coremusculature and can not contain anymore the vertebralslippage.

Studying patients with roentgenograms in flexion andextension position while they lie on their side reduces boththe hypertonus of the paravertebral musculature [5, 6] thathides the listhesis and the basal postural muscular tone ac-tivated by the gravity force, revealing, when present, the

Fig. 1 The RDXR shows an L4–L5 listhesis not showed by the SDXR.Note that the patient has an isthmic lysis

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Bhidden^ spondylolisthesis. This phenomenon is evocableparticularly in those patients having much pain whileflexing or extending their trunk during the execution ofthe SDXR. The intervertebral disc, when posed under theload of gravity generates pain because the straining of theannulus fibrosus fibres, stimulates the pain receptors. Thisnervous pathway determines an augmentation of the pos-tural tone of the muscles: multifidus, psoas, ileocostalis,longissimus, and quadratus lumborum. Posing the patientin a recumbent position can eliminate or at least reduce thisaugmented muscular tone.

In Figs. 1, 2, and 3, we show three patients whose LI inRDXR is, respectively, present in RDXR and not in SDXR,augmentation of the LI showed in SDXR, and movement of alisthesis considered stable. In particular, the patient in Fig. 1has an isthmic lysis, and the listhesis becomes evident only inRDXR, endorsing our hypothesis.

Our study is not focused on a quantitative identification ofthe listhesis, but has been centred the diagnostic sensibility ofthe radiologic exam. A diagnostic examination, to be of anyvalue, has to have good values of sensibility and specificity.

Using the combination of the results of SDXR and RDXR asgold standard, we have determined that the specificity of bothexaminations is high, but SXDR has inferior values of sensibil-ity if compared to RDXR; Wood has found similar results [5].

Despite those results, the execution of SDXR cannot beoverlooked: 14 patients on a total of 110 with LI (12.7 %)did not show LI on RDXR but only on SDXR. SDXR canevocate a major segmental translation of the listhetic segmentaccording to the literature [5, 9, 10], but its sensibility is infe-rior if compared with RDXR, because it cannot discover allthe cases of LI.

The 43 patients positive for LI at the RDXR but not at theSDXR had a MRI scan that suggested a lumbar discarthrosisthat, with a SDXR not evidencing a LI, would orient the sur-gical treatment for a decompression without instrumentation.

The identification of a Bhidden^ spondylolisthesis maychange the therapeutic course of a patient. In most spinal sur-gery centres, patients with lumbar spondylodiscarthrosic dis-ease with the suspect of LI, are usually examined with MRIand SDXR [6]. Patients without signs of LI in SDXR arepreferentially treated with spinal decompression without in-strumentation. If those patients present a Bhidden^ listhesis,not showed by SDXR, a decompressive-only treatment mightnot lead to an improvement of the lumbalgy. The naturalcourse of this clinical condition should lead to a worseningof the instability with an augmentation of the pain symptomsand a worse clinical condition.

The choice of surgical or conservative treatment for pa-tients with spondylolisthesis is suggested by the NorthAmerican Spine Society (NASS) 2014 guidelines [28] andby the Journal of Neurosurgery (JNS) 2014 guidelines [29].The role of RDXR can have in orienting the surgical strategyremains unclear.

RDXR can be performed as a diagnostic supplement inthose cases in which the clinical symptoms (low back painalone or combined with radiculopathy or neurogenic claudi-cation), associated with the MRI radiological evidence of in-direct signs of instability and a SDXR negative for LI, aresuspect for the presence of spondylolisthesis. The MRI is an

Fig. 2 The RDXR shows an augmentation of the listhesis if compared toSDXR

Fig. 3 The RDXR shows anaugmentation of the listhesis in alisthesis considered stable

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examination executed in recumbent and static position, posi-tion in which the patient is often symptom-free. In our expe-rience, it is the careful clinical examination to guide the diag-nostic procedure: a patient with positional lumbalgy (variationof pain at the variation of position) and with negative SDXRhas to be examined in a more detailed way with an adjunctiveradiological exam. If the clinical symptom is supported byMRI and SDXR, the RDXR are not to be performed.

Chaparian et al. [30] had an estimation of the effectiveexposure to radiations for a lumbar X-ray: 0.226±0.046 mSv in posterior-anterior (PA) projection and 0.557±0.121 mSv in lateral-lateral (LL) from the right side. The ex-posure to this amount of radiations can have mean REIDvalues (per million) of 7.75±1.59 for men and 7.43±1.52for women in PA projection, and 19.55±4.25 for men and22.75±4.93 for women in LL projection with the source ofradiations placed on the right side of the patient.

The ideal projection to obtain to reduce the exposure toionizing radiations, as explained by Chaparian [30], is PAand LL from the right side to the left side for men and LLfrom left to right for women.

In patients who undergo surgery, the exposure to ionizingradiations can be reduced if the follow-up roentgenograms at 1and 6months (not the early postoperative) are obtained only inLL projection, avoiding to perform the PA projection, com-pensating the adjunctive exposure to radiations needed to per-form the RDXR. PA projection offers a minor amount of in-formation to the surgeon, so it can be sacrificed.

Studying the patients in the way we showed, with the ex-ecution of a supplementary roentgenogram, a low-cost examand with a reasonable cost-benefit ratio, we highlighted a hid-den clinical condition that may require a different surgicaltreatment from the one planned over the execution of SDXR.

Our study aims to suggest a diagnostic adjunction in de-generative spondylolisthesis. RDXR has not to substituteSDXR, but has to be a diagnostic integration in daily clinicalpractice in doubtful cases, to avoid a misdiagnosis of a clinicalcondition whose treatment is mainly oriented towardsarthrodesis.

Further studies on whether LI evidenced by RDXR mightinfluence or not the surgical strategy are needed.

Conclusions

In literature, the definition of LI and the options available to itscorrect diagnosis are still controversial. Adding to theroutinary clinical study, based upon the execution of SDXR,the execution of RDXR (exam with high sensibility andspecificity and low-cost) in doubtful cases (suspect for LI)and with negative SDXR, a higher percentage of cases withLI can be diagnosed.

Ethical standards and patient consent We declare that this manu-script does not contain clinical studies or patient data.

Conflict of interest NM consults for B-Braun.

References

1. Pope MH, Panjabi M (1985) Biomechanical definitions of spinalinstability. Spine (Phila Pa 1976) 10:255–256

2. Frymoyer JW, Selby DK (1985) Segmental instability. Rationalefor treatment. Spine (Phila Pa 1976) 10:280–286

3. Watters WC, Bono CM, Gilbert TJ et al (2009) An evidence-basedclinical guideline for the diagnosis and treatment of degenerativelumbar spondylolisthesis. Spine J 9:609–614. doi:10.1016/j.spinee.2009.03.016

4. Leone A, Guglielmi G, Cassar-Pullicino VN, Bonomo L (2007)Lumbar intervertebral instability: a review. Radiology 245:62–77.doi:10.1148/radiol.2451051359

5. Wood KB, Popp CA, Transfeldt EE, Geissele AE (1994)Radiographic evaluation of instability in spondylolisthesis. Spine(Phila Pa 1976) 19:1697–1703

6. Cabraja M, Mohamed E, Koeppen D, Kroppenstedt S (2012) Theanalysis of segmental mobility with different lumbar radiographs insymptomatic patients with a spondylolisthesis. Eur Spine J 21:256–261. doi:10.1007/s00586-011-1870-y

7. Hammouri QM, Haims AH, Simpson AK et al (2007) The utility ofdynamic flexion-extension radiographs in the initial evaluation ofthe degenerative lumbar spine. Spine (Phila Pa 1976) 32:2361–2364. doi:10.1097/BRS.0b013e318155796e

8. Otani K, Okawa A, Shinomiya K, Nakai O (2005)Spondylolisthesis with postural slip reduction shows different mo-tion patterns with video-fluoroscopic analysis. J Orthop Sci 10:152–159. doi:10.1007/s00776-004-0877-1

9. Penning L, Blickman JR (1980) Instability in lumbarspondylolisthesis: a radiologic study of several concepts. AJRAm J Roentgenol 134:293–301. doi:10.2214/ajr.134.2.293

10. Lowe RW, Hayes TD, Kaye J et al (1976) Standing roentgenogramsin spondylolisthesis. Clin Orthop Relat Res :80–84.

11. Dupuis PR, Yong-Hing K, Cassidy JD, Kirkaldy-Willis WH (1985)Radiologic diagnosis of degenerative lumbar spinal instability.Spine (Phila Pa 1976) 10:262–276

12. Kanemura A, Doita M, Kasahara K et al (2009) The influence ofsagittal instability factors on clinical lumbar spinal symptoms. JSpina l Disord Tech 22:479–485. doi :10 .1097/BSD.0b013e31818d1b18

13. Posner I, White AA, Edwards WT, Hayes WC (1982) A biome-chanical analysis of the clinical stability of the lumbar and lumbo-sacral spine. Spine (Phila Pa 1976) 7:374–389

14. Morgan FP, King T (1957) Primary instability of lumbar vertebrae asa common cause of low back pain. J Bone Joint Surg (Br) 39-B:6–22

15. Boden SD, Wiesel SW (1990) Lumbosacral segmental motion innormal individuals. Have we been measuring instability properly?Spine (Phila Pa 1976) 15:571–576

16. Hanley EN (1995) The indications for lumbar spinal fusionwith and without instrumentation. Spine (Phila Pa 1976) 20:143S–153S

17. Kälebo P, Kadziolka R, Swärd L (1990) Compression-traction ra-diography of lumbar segmental instability. Spine (Phila Pa 1976)15:351–355

18. Friberg O (1987) Lumbar instability: a dynamic approach bytraction-compression radiography. Spine (Phila Pa 1976) 12:119–129

Neuroradiology (2015) 57:583–588 587

Author's personal copy

19. Pitkänen M, Manninen HI, Lindgrer KA et al (1997)Limited usefulness of traction-compression films in the ra-diographic diagnosis of lumbar spinal instabi l i ty.Comparison with flexion-extension films. Spine (Phila Pa1976) 22:193–197

20. Friberg O (1991) Instability in spondylolisthesis. Orthopedics 14:463–465

21. Pearcy M, Portek I, Shepherd J (1985) The effect of low-back painon lumbar spinal movements measured by three-dimensional X-rayanalysis. Spine (Phila Pa 1976) 10:150–153

22. Knutsson F (1944) The instability associated with disc degenerationin the lumbar spine. Acta Radiol 25:593–609

23. Panjabi MM D1992] The stabilizing system of the spine. Part I.Function, dysfunction, adaptation, and enhancement. J SpinalDisord 5:383–389, discussion 397

24. Panjabi MM (2003) Clinical spinal instability and low back pain. JElectromyogr Kinesiol 13:371–379. doi:10.1016/S1050-6411(03)00044-0

25. Panjabi MM D1992] The stabilizing system of the spine. Part II.Neutral zone and instability hypothesis. J Spinal Disord 5:390–396, discussion 397

26. Panjabi MM, Goel VK, Takata K (1982) Physiologic strains in thelumbar spinal ligaments. An in vitro biomechanical study 1981Volvo Award in Biomechanics. Spine (Phila Pa 1976) 7:192–203

27. Kirkaldy-Willis WH, Farfan HF (1982) Instability of the lumbarspine. Clin Orthop Relat Res :110–123

28. Kreiner S, Shaffer WO, Baisden J, Gilbert T, Summers J,Toton J, Hwang S, Mendel R RC (2014) Evidence-based clin-ical guidelines for multidisciplinary spine care diagnosis andtreatment of degenerative lumbar spinal stenosis. North Am.Spine Soc

29. Eck JC, Sharan A, Ghogawala Z, Resnick DK (2014)Guidelines for the performance of fusion procedures for de-generative disease of the lumbar spine. Part 7: intractablelow-back pain without stenosis or spondylolisthesis. JNeu rosurg Sp ine 2 :670–672 . do i :10 .3171 /2014 .4 .SPINE14270

30. Chaparian A, Kanani A, Baghbanian M (2014) Reduction of radi-ation risks in patients undergoing some X-ray examinations byusing optimal projections: a Monte Carlo program-based mathe-matical calculation. J Med Phys 39:32–39. doi:10.4103/0971-6203.125500

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