SPINE Volume 41, Number 4, pp E205–E210

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DIAGNOSTICS

Slump Test: Effect of Contralateral Knee Extensionon Response Sensations in Asymptomatic Subjectsand Cadaver Study

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Michael Shacklock, MPT, FACP,�,�� Brian Yee, MPhty, FAAOMPT,y Tom Van Hoof, MSc, PhD,z

Russ Foley, PT, MSc,y Keith Boddie, DPT,§ Erin Lacey, DPT,{ J. Bryan Poley, DPT,jj

Marinko Rade, MSc (Orthop Med),yy,� Markku Kankaanpaa, MD, PhD,zz

Heikki Kroger, MD, PhD,§§ and Olavi Airaksinen, MD, PhD�

Results. Part 1: Reduction of stretch sensations occurred in the

Study Design. Part 1: A randomized, single-blind study on the

effect of contralateral knee extension on sensations produced by

the slump test (ST) in asymptomatic subjects. Part 2: A cadaver

study simulating the nerve root behavior of part 1.Objective. Part 1: Test if contralateral knee extension consist-

ently reduces normal stretch sensations with the ST.

Part 2: Ascertain in cadavers an explanation for the results.Summary of Background Data. In asymptomatic subjects,

contralateral knee extension reduces stretch sensations with the

ST. In sciatica patients, contralateral SLR also can temporarily

reduce sciatica. We studied this methodically in asymptomatic

subjects before considering a clinical population.Methods. Part 1: Sixty-one asymptomatic subjects were tested

in control (ST), sham, or intervention (contralateral ST) groups

and their sensation response intensity compared.

Part 2: Caudal tension was applied to the L5 nerve root of 3

cadavers and tension behavior of the contralateral neural tissue

recorded visually.

right © 2016 Wolters Kluwer Health, Inc. Unau

he �Department of Physical and Rehabilitation Medicine, Kuopiosity Hospital, Kuopio, Finland; yMercer University Physical Therapym, Atlanta, Georgia; zGhent University, Ghent, Belgium; §AmedisysHealthcare, Duluth, Georgia; {Gentiva Health Services, Seattle,

ngton; jjRestore Health Group, Rosewell, Georgia; ��Neurodynamicdynamic Solutions, Adelaide, South Australia, Australia; yyJosip Jurajayer University of Osijek, Faculty of Medicine, Orthopaedic and

ilitation Hospital ‘‘Prim. dr.Martin Horvat’’, Rovinj, Croatia;rtment of Physical and Rehabilitation Medicine, Tampere Universityal, Tampere, Finland; §§Department of Orthopaedic, Traumatologyand Surgery, Kuopio University Hospital, Kuopio, Finland.

wledgment date: January 20, 2015. First revision date: April 3, 2015.revision date: July 2, 2015. Acceptance date: August 29, 2015.

anuscript submitted does not contain information about medical(s)/drug(s). No funds were received in support of this work. Not financial activities outside the submitted work.

s correspondence and reprint requests to Michael Shacklock, FACP,26 Erskine Street, Adelaide, SA 5034, Australia; E-mail: michael@ynamicsolutions.com

0.1097/BRS.0000000000001218

intervention group but not in control and sham groups

(P�0.001).

Part 2: Tension in the contralateral lumbar nerve roots and dura

reduced in a manner consistent with the responses in the

intervention (contralateral ST) group.Conclusion. Part 1: In asymptomatic subjects, normal thigh

stretch sensations with the ST reduced consistently with the

contralateral ST, showing that this is normal and may now be

compared with patients with sciatica.

Part 2: Contralateral reduction in lumbar neural tension with

unilateral application of tension-producing movements also

occurred in cadavers, supporting the proposed explanatory

hypothesis.Key words: contralateral, dura, low back pain, lumbar nerveroots, neurobiomechanics, neurodynamic tests, neurodynamics,sciatica, slump test.Spine 2016;41:E205–E210

iagnosis of low back pain and sciatica is a key issue

D in which physical tests for nerve root tension signs,such as the straight leg raise (SLR) and slump test

(ST), are commonly performed clinically. Here, we focus onthe ST, which is inexpensive and has been shown to bereliable1–6 and has good diagnostic efficacy ratings for discprotrusion.7

The clinically applied ST utilizes spinal flexion and lowerlimb movements to apply tension to the neural tissue of thelumbar spine.8–21 The recipient is seated whilst the spine isflexed and the knee extended.22–28 Cervical flexion isreleased to ascertain whether any responses produced bythe test change, whether they be a normal stretch sensation(eg, posterior thigh), or symptoms such as back pain andsciatica. At its end position in asymptomatic subjects, thetest typically produces sensory responses and here we use theterm ‘‘evoked sensations’’ to denote what asymptomaticsubjects report.

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DIAGNOSTICS Slump Test � Shacklock et al

During the ST, the change of normal evoked sensations orclinical symptoms with cervical movements does not differ-entiate normal from abnormal. Instead, in both situations,such a change provides support for a neuromechanicalmechanism because, on account of anatomical connectivity,cervical flexion/extension produces tension changes in thelumbar neural tissues, which links the change in evokedsensations or clinical symptoms to the neural system.

A key aspect of diagnosis with the ST is to show differ-ences between the normal evoked (stretch) sensations thatoccur in asymptomatic subjects and reproduction of patientsymptoms. Normal evoked sensations for the ST have beenestablished in asymptomatic subjects, one of which consistsof ipsilateral posterior thigh stretch at the end of the finalknee extension/dorsiflexion phase and this decreases withrelease of cervical flexion.1–5,26,27 Interestingly, eventhough the stretch sensation in the posterior thigh changeswith cervical movements, the tension and myoelectricactivity in the hamstrings have been shown not to change.2

Hence, the likelihood of myofascial tissues in the posteriorthigh producing evoked sensations reduces and other struc-tures come into focus, namely the lumbar neural tissues.

A new variation on the ST is to perform certain move-ments contralaterally or bilaterally.28 The contralateral STis when the usual ST is performed and, whilst holding thisposition stable, contralateral knee extension is added. Inperforming this on subjects presumed to be healthy, we haveobserved that, surprisingly, a typical response to contrala-teral knee extension is reduction in the original (ipsilateral)thigh stretch sensation. Furthermore, in some patients withunrelenting sciatica, sometimes, the sciatica can be relievedtemporarily with such a similar movement, for instance, thecontralateral SLR in supine. The mechanism for this effect isnot understood and, before investigating it directly, there isa need to ascertain scientifically whether it is artifactual, orsomething that is significant and consistent that may war-rant more detailed investigation.

Hence, the purposes of this study were to first investigateevoked stretch sensations to the contralateral ST (ContraST)in asymptomatic subjects to establish a normal response forfuture clinical comparison; second, as part of an ongoingline of investigation,18–20 we needed to test scientifically

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TABLE 1. Subjective Exclusion Criteria

Under 18 years of ageNo pain, altered sensation, pins and needles, weakness, or any otheprevious 12 monthsAny injuries to the spine, neck, back, hips, legs, ankles, or feet in thCondition of the spine, including ankylosing spondylitis, Schmorl’s nosteoporosis, spondyloarthrosis/opathy, spondylolisis or spondylolistArthritis or any autoimmune diseasePrevious surgery or malignancyDiabetes or thyroid conditionCondition of the nervous system, including spina bifida, hydrocephaChiariPrevious or current psychiatric or mental illness

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whether this effect is consistent. If so, further investigationin patients with low back pain and sciatica may be war-ranted. Finally, the third purpose was to develop an explan-atory mechanical hypothesis for the findings in the form of acadaver study to establish whether the lumbar neural tissuesbehave in a manner consistent with the results in asympto-matic subjects.

MATERIALS AND METHODS

Part 1: Slump Test Response Sensations inAsymptomatic SubjectsThis part of the study passed ethical scrutiny by the Uni-versity Institutional Review Board and was performed inaccordance with the Declaration of Helsinki. Informedconsent and participation were obtained local universityvolunteers. All were informed of the upcoming proceduresin plain language and an explanation of their rights wasgiven, specifically that they could terminate their participa-tion at any time without reason or prejudice. Subjectsanswered questions (Table 1) and were tested with activeand passive movement in relation to exclusion criteria(Table 2). Subjects were excluded if they satisfied any ofthe exclusion criteria.

Sixty-one asymptomatic subjects (age range 22–43 years,19 males, 42 females) were included. An explanation wasgiven that certain maneuvers would be performed andsubjects may or may not experience response sensations.If subjects did report any sensations, they were asked toindicate their location and verbally rate their intensity on anumeric pain rating scale (NPRS) between 0 and 10. Sub-jects were blinded to the research hypothesis and whetherany specific movements would or would not produceany changes.

The ST procedure and methods were the same as pre-viously published.1,2 The prevention of crossover muscu-loskeletal effects with contralateral knee extension due topotential for pulling of the hamstrings on the ischial tuber-osities, thereby affecting pelvis position, was achieved byplacing books between subjects’ sacrum and the laboratorywall, after Herrington et al1 and Lew and Briggs.2 Foradded measure, we used pressure biofeedback (Chatanooga

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r discomfort in the spine, hip, or either lower extremity in the

e previous 12 monthsodes, disc protrusion, spinal stenosis, tumors, tuberculosis,

hesis, stenosis

lus, syrinx or cysts, multiple sclerosis, tethered cord, or Arnold

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TABLE 2. Physical Tests for Exclusion

Standing Sitting Supine

Trunk flexion Cervical flex, ext Hip flexion, extension

Trunk extension Cervical rot—right, left Knee flexion, extension

Trunk side bend right, left Cervical lat. flex—right, left Ankle dorsiflexion, plantarflexion

Ankle dorsiflexion, plantarflexion

DIAGNOSTICS Slump Test � Shacklock et al

Stabilizer) between the subjects’ sacrum and the spacers.The pressure cuff readout was placed behind the subjectssuch that they could not see it and the examiner looked backover subjects’ shoulders at the readout to ensure that thepressure remained stable at 20 PSI. For fixation of the spine,shoulders, and thighs, seat belts were then placed under thetable firmly and comfortably positioned over the subjects’shoulders and around their thighs.

Slump Test ProceduresAll subjects underwent the standard clinical ST procedurethat consisted of

Co

Fig(C)

Spi

(1)

pyr

ureInte

ne

being seated comfortably on the table with theirthighs parallel, knees against the edge of the table,and legs relaxed down at approximately 90 degreesknee flexion;hands resting on the couch behind the subjects’ back;

(2)

(3)

full comfortable lumbar, thoracic cervical spine flex- ion;right knee extension to the point of comfortable (4)

production of sensations in the ipsilateral limb;release and reapplication of cervical flexion to ascer-

(5)

tain whether any evoked sensations in the limbchanged;maintenance of the response position for 30 seconds;

(6)

(7)

subjects reported the intensity of their sensations in verbal NPRS form at the beginning and end ofthe 30-second duration and the data recorded.

Before this, subjects were randomlyassigned into 3 groups:control (n¼20), sham (n¼21), and intervention (n¼20).

ight © 2016 Wolters Kluwer Health, Inc. Unau

1. Slump testing in 3 groups: (A) Standard end range slumprvention: slump test and passive knee extension with ankle in plan

Control GroupTo control for the possibility that sensations during the testmight change over time or per chance, data were collectedfrom a control group and compared with the other 2 groups(sham and intervention). This control group experiencedsolely the ST to the response sensation at end range for30 seconds and their sensations recorded at the beginningand end of the 30 seconds (Figure 1A).

Sham GroupSubjects in the sham group followed the same procedure asthe control group except that, during the 30 seconds inwhich the ST was maintained at the end of symptomaticrange, the contralateral ankle was dorsiflexed passivelywhilst the contiguous knee remained in 90-degree flexion(Figure 1B). Hence, the dorsiflexion was actually a neuro-dynamic movement, but one that did not move the lumbo-sacral nerve roots (ie, sham), as the contiguous knee was in90-degree flexion and the forces of the dorsiflexion wouldnot be transmitted proximally along the sciatic nerve, pre-venting the mechanical effects of dorsiflexion reaching thelumbosacral nerve roots.

Intervention GroupThe subjects in this group also received the same procedureas the control group (ST held for 30 seconds) except that,during the 30 seconds, the contralateral knee was passivelyextended to end range whilst the ankle was held in theplantargrade position (Figure 1C). As knee extension wasmoved, the effects would spread along the sciatic nerve tothe nerve roots as would occur with the SLR. This would

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test, (B) Sham: slump test and passive contralateral dorsiflexiontargrade.

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DIAGNOSTICS Slump Test � Shacklock et al

draw the cord caudally and produce the intendedexperimental effects.

Reliability was tested on 10 subjects. The procedure forthe control group was performed at the same time on 2different days and agreement in the values of the NPRSwas calculated.

Statistical AnalysisPercentage agreement between the NPRS sensation valueson the 2 occasions was used to evaluate reliability.

The 1-tailed hypothesis to be tested was that responseswould decrease with the contralateral maneuvers performedin the study. This was because, in our experience in testingthe maneuver on numerous persons with normal STresponse sensations, whenever any sensations changed withcontralateral testing, they typically decreased ratherthan increasing.

One-way analysis of variance (ANOVA) was used to testfor significance of differences in self-reported NPRS valuesbetween groups, whilst the Tukey posthoc test for multiplecomparisons was used to test for differences between thecontrol and sham groups, intervention and sham groups, andintervention and control groups. The alpha value was setat 0.05.

Part 2: Lumbar Neural Tissue Behavior in CadaversThe use of cadavers in this part of the study was approved bythe Centre of Education and Research in Anatomical Sci-ences, Department of Basic Medical Sciences, University ofGhent, Belgium.

The objective here was solely to ascertain what mechan-isms may operate in the lumbar nerve root and dura on oneside during manually applied distal traction of the lumbarnerve root on the other, simulating the effects of the Con-traST and SLR. The mechanism was tested in 3 cadavers, 2processed with the Thiel method, in which the soft tissuesremain soft and pliable, and 1 embalmed cadaver. Thelumbar spine was opened from the posterior directionand the dura and cauda equina exposed. The dura was thenopened and forceps placed around the right L5 nerve root.The root was manually drawn caudally in the canal towardits intervertebral foramen and the effects on the other sideobserved. The events were recorded audiovisually.

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Figure 2. Reduction in tension in the contralateral lumbar nerve roots duarrows—L5 nerve root. Thin arrows—filum terminale. Before distal tractroots are generally straight. Caudal traction on L5 nerve root—contralater

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RESULTS

Part 1: Asymptomatic Subject Response SensationsData were collected from 61 subjects (20 males, 41 females),with an average age 25.3 years. Twenty subjects were in thecontrol group, 21 in the sham group, and 20 in theintervention group.

Reliability testing on the control group resulted in a 91%test–retest agreement of the NPRS measures.

All subjects except 2 (96.7%) reported stretch sensationsin the posterior thigh and knee. One of those 2 subjectsreported sensations in the calf and the other in the toes andboth of these subjects reported their sensations to changewith cervical movements. Taking into account the totalsample (n¼61), all but 4 (93.4%) reported a change withcervical flexion.

Comparisons were made with the average change inNPRS for each of the control, sham, and interventiongroups.

Even though not all subjects in the control and shamgroups reported a reduction in evoked sensations, theaverage for all groups did show a small reduction. How-ever, compared with the intervention group, the change inintensity of response sensations (reduction) in the controland sham groups was negligible. Average changes inNPRS were 0.65 for the control group (n¼20), 0.62for the sham group (n¼21), and 3.80 for the interventiongroup (n¼20). All subjects in the intervention groupreported the change in sensations to be a reduction.One-way ANOVA resulted in a significant differencebetween groups (P�0.001). The Tukey posthoc test formultiple comparisons revealed no significant differencebetween the control and sham groups (P¼0.996), but asignificant difference was demonstrated between the inter-vention and sham groups (P�0.001) and intervention andcontrol groups (P�0.001).

Hence, the reduction in evoked sensations in the ipsilat-eral limb with the end-range ST was directly linked tocontralateral knee extension.

Part 2: Cadaver ExperimentAll 3 cadavers demonstrated the events shown in Figure 2. Indrawing the nerve root caudally, all the neural tissues on the

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ring caudal traction on L5 nerve root. Thick arrows—dura. Mid-sizedion on L5 nerve root—filum terminale, dura, and contralateral nerveal nerve roots and dura become looser.

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DIAGNOSTICS Slump Test � Shacklock et al

opposite side became looser. Loosening too of the filumterminale illustrated that the cord had displaced caudally(see Video, Supplemental Digital Content 1, http://links.lww.com/BRS/B38).

DISCUSSIONThe data in this study agree with other studies on severalcounts; excellent reliability in relation to response sensationswith the ST,2,3 all subjects reported evoked sensations(stretch) in the posterior thigh,1,2,4,26,27 and 93.4% of sub-jects reported a change in these responses with cervicalmovements.1–3

During the ST to end range, 100% of subjects reported adecrease in the stretch sensation in the ‘‘held’’ (ipsilateral)side with contralateral knee extension.

Clearly, these results warrant caution and raise questions.The sample may have been influenced by the fact thatsubjects were from a university wherein their health mayhave been better than other asymptomatic populations.Conversely, what supports the sample is that it may haveconsisted of subjects who were closer to ‘‘ideal’’ and bettersuited to investigation of this model. Therefore, we wouldagree that the effect found in this study is likely to diminishin a broader sample; however, it is likely to remain sub-stantial.

The idea that the measured reduction in intensity ofevoked sensations may have been due to relaxation of thesoft tissues in the thigh must be considered. However, wethink this not to be the case because it was controlled forwith randomization, sham and control groups in whichsubjects and the magnitude of the reduction in responsesin the control and sham groups was not statistically signifi-cant. Furthermore, Lew and Briggs2 measured hamstringbehavior mechanically and electromyographically, showingthat these aspects did not change with the ST and duringcervical movements.

An explanatory hypothesis is that the 100% of subjectsreporting a reduction in responses with contralateral kneeextension correlated with the lumbar neural tissue behavior,as previously described.28 As the path of the lumbar nervesroots between the cord and foramina approaches vertical,the nerve roots will draw the cord caudally and thereforeproduce reduction in tension in the roots on the other side,assisting each other in distribution of tension. In vivo, Radeet al18–20 have shown that this crossover mechanism existsby using the bilateral SLR, which produces virtually doublethe caudal cord excursion compared with the unilateral,supporting the hypothesis we propose. However, eventhough it is not possible to measure lumbar neural tensionin conscious humans, we can think of no other structure ortissue that could produce mechanical events that matchedthe subject responses in this study. However, we acknowl-edge that this remains a hypothesis and more direct study isnecessary for verification.

This study naturally raises questions in relation to thecrossed SLR sign. Symptom provocation with the crossedSLR clearly constitutes an abnormal response that may now

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be compared with the ContraST. However, an instan-taneous reduction in response sensations with the Con-traST may not in itself differentiate normal fromabnormal, particularly if the ContraST were to be foundto have an anatomical basis that occurs in both situations.Instead, it may assist in decisions on whether the responsehas a neural aspect generally and whether it may or maynot respond to various interventions. However, moreinvestigation is required before such conclusions couldbe entertained.

What is of more immediate benefit in this study is that theresponses with the ContraST were consistent, highly signifi-cant, and are now documented as a normal response sen-sation that may be compared with those in patients with lowback pain and sciatica.

CONCLUSIONIn asymptomatic subjects, the passive ContraST was reliableand produced a reduction in the posterior thigh stretchsensations to the ST in all asymptomatic subjects of theintervention group (P�0.001), whereas no significantchanges occurred in the control and sham groups(P¼0.996).

The reduction of the evoked posterior thigh sensationswith the ContraST is now documented as a normal event.Further investigation of the causal mechanism is warrantedwhereby there may be potential for it to be tested clinicallyin patients with low back pain and sciatica and there may bea need for more direct investigation of an explanatorymechanism.

An explanatory hypothesis derived from cadaver simu-lation has been presented in which tension in the lumbarneural tissues reduced during application of the contrala-teral neurodynamic movement.

th

Key Points

ori

The commonly used ST for diagnosis of nerve roottension signs was performed on asymptomaticsubjects and the effect of contralateral kneeextension on the evoked stretch sensationsinvestigated in asymptomatic subjects.

Contralateral knee extension reduced evokedsensations in the intervention group but not inthe sham and control groups.

Reduction of evoked sensations with contralateralknee extension during the ST is now a normalfinding and can be used to compare in patientswith sciatica.

Simulation of nerve root behavior in cadaversshowed that the contralateral nerve root and duraloosen with caudal tension applied to L5 nerve root.

Further investigation on potential benefits couldconsider that such responses might be used indecisions on conservative management ofpatients with sciatica due to disc protrusion.

ze

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DIAGNOSTICS Slump Test � Shacklock et al

Supplemental digital content is available for this article.Direct URL citations appearing in the printed text areprovided in the HTML and PDF version of this article onthe journal’s Web site (www.spinejournal.com).

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