SPINE Volume 18, Number 13, pp 1839-1849·© 1993, J. B. Lippincott Company

Efficacy of Flexion and ExtensionTreatments Incorporating Braces forLow-Back Pain Patients WithRetrodisplacement, Spondylolisthesis, orNormal Sagittal Translation

Kevin F. Spratt, PhD,* James N. Weinstein, DO,* Thomas R. Lehmann, MD,tJoyce Woody,* and Hutha Sayre, RN*

Radiographic instability seemingly enjoys the status of awell-defined clinicaI syndrome. The concept is widelyused, and specific treatments, usually spinal fusion, areroutinely performed based on the diagnosis. The min-imum standards necessary to establish radiugraphic in-stability as a legitimate clinical syndrume have not beenestablished, however. The primary purpose of this studywas to determine if treatment invoking bracing, exer-cise, and education controlling either flexion orextension postures, would result in a distinctive patternof favorable or unfavorable results, depending on thetype of radiographic instability (retrodisplacement orspondylo isthesis). Fifty-six patients meeting strict studyinclusion and radiugraphic evaluation criteria were as-signed to a bracing treatment (flexion, extensiun, place-bo-control) accurding to a randomization scheme, de-signed to ensure equal representation of translation cat-eguries (retro, normal, spondy) across treatment groups,and assessed at admission and 1-month follow-up. Thesample was relatively evenly divided between men(46%) and women (54%), and by age. Translation classi-fication was related to bothoth gender and age, with menmore likely classified as retro and women more likelyspondy, and patients in their 20's having lower incidenceof spundy and higher incidence of normal translation.Translation classification was not related to selected in-dices of low-back pain history. Brace treatments werenot shown to reduce patient range of motion or lessentrunk strength. A significant treatment by time interactionfur the modified pain interference (VAS) scale indicatedimprovement for patients in extensioncomparedompared withpatients in flexion and control-placebo treatments. Inconjunction with no significant three-way interaction be

From the *Spine Diagnostic and Treatment Center, Department ofOrthopaedic Surgery, University of Iowa Hospitals and Clinics, IowaCity, Iowa and the +Louisville Orthopedic Clinic, Louisville, Kentucky.Supported in part by NIH grant #AR 34344-03 and Camp Interna-tional, Inc (J. Weinstein, principle investigator).Accepted for publication May 11, 1992.

tween treatment, translation classification, and time, itwas hypothesized that radiographic instability mightmore appropriate1y be considered a corroborative signof advanced discogenic problems. Improvement inextension treatment, regardless of the type ofradiographic abnormality, suggests that the treating clini-cian might consider extension treatment for chroniconiclow-back pain patients. Causes and Implications Implications for thefailure of this study to provide support for consideringradiographic instability as a clinicaI syndrome areconsidered and future directions for this area of researchsuggested. [Key words: bracing, spondylolisthesis, ret-rodisplacement, low-back pain, instability]

The precise diagnosis is unknown in 80-90% of patientspresenting with disabling low-back pain. In a populationstudy, Valkenburg and H a a n e n screened more than6,000 men and women and were able to documentobjective evidence of disc prolapse or lumbago in fewerthan 10% of their sample. In a general practice study,Dillane et al5 found that 79% of men and 89% of womenpresenting with a first episode of low-back pain wereclassified as having low-back pain of unknown origin.Nachemson et a 1 have estimated that only 15% ofchronic low-back pain cases have some demonstratedpatho-anatomic explanation.

Research studying the efficacy of various therapies forpatients experiencing low-back pain has suffered fromthe lack of an accepted classification system for low-backpain. Thus, modalities that may be efficacious for a selectsubset of patients suffering from a specific but undetectedpathology causing their low-back pain fail to demon-strate that efficacy when applied to populations of“idiopathic” low-back pain patients with heterogeneouspathologies.

Instability of the lumbar spine is a condition that hasbeen described since the advent of lumbar surgery butstill lacks sufficient scientific definition to be included in

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1840 Spine l Volume 18 l Number 13 l 1993

many epidemiology studies. Lumbar fusions have beenand continue to be performed because of this radio-graphic abnormality when accompanied by chronic pain,despite the fact that there is no universally accepteddefinition of instability. Even when surgery is notindicated, the diagnosis of instability may effect disabilityawards. Therefore, establishing an objective definition ofinstability may be essential to conducting meaningfulepidemiologic studies and clinical trials as well as to themonitoring of clinical practice related to low-back pain.

Biomechanically, the definition of instability dependson the determination of abnormal motion to appliedloads.30 Because there are three axes of rotation andthree planes of translation for movement to occur, thereis potential for several types of instability or observableexcessive motions. Historically, interest and clinicaltreatment has focused on excessive translation in thesagittal plane.

There are no conclusive clinical data to support acause-and-effect relationship between a radiographicfinding of excessive translation in the sagittal plane(instability) and a low-back pain syndrome. Other thanradiographic evidence, no set of objective clinical criteriaare available to corroborate a diagnosis of radiographicinstability. Given the recent evidence suggesting thepotential for misclassifying radiographic translations inthe sagittal plane,34 it seems especially important todevelop corroborative clinical evidence associated withradiographic instability.

The necessary conditions for establishing a low-backpain syndrome have been well documented10,44:

1 .

2.

3 .

The incidence of the abnormality should behigher in a patient population than in a normalpopulation.A reproducible pattern of historical or physicalexamination findings should characterize the low-back pain syndrome.Stimuli specifically designed to exacerbate the con-dition should result in aggravation of symptoms ortreatment specifically designed to aid the conditionshould result in alleviation of or palliation ofsymptoms. l Materials and Methods

Regarding the incidence of the radiographic abnor-mality, Knutsson17 described excessive displacement in34% (48/140) of his clinical sample, and an additional8% (11/140) were classified as spondylolytic spondylolis-thesis. Morgan and King25 classified 29% (143/500) ofpatients with chronic low-back pain as having insta-bility, with 10% (50/500) having spondylolisthesis.Schmorl and Junghanns,32 in cadaver studies, determinedthe incidence of retrodisplacement as 1.5% (9/600)and degenerative spondylolisthesis as 2.3% ( 14/600).32Roentgenograms of these specimens were not assessed inflexion and extension, however. Friberg and Hirsch’placed cadaver spines in flexion and extension anddetermined that 15% (15/100) of the specimens demon-

strated roentgenographic instability. In their clinicalcases, however, the incidence of instability was 27%(578/2104). Thus, this body of evidence suggests that theincidence of radiographic abnormality is greater in alow-back pain population relative to asymptomatic orgeneral populations.

There are reports in the literature suggesting there areclinical signs corroborating the radiographic finding ofexcessive translations.2,20,25 A reproducible pattern ofpain or symptom aggravation or relief in response tomechanical maneuvers or general activities of daily livinghas not been established, however. Work attempting toestablish such links is underway but is not the focus ofthis report.

There are several reports of patients who haveundergone lumbar fusion in response to radiographicfindings of instability with favorable outcome.4,9,14,22,25These results were from uncontrolled clinical trials,however, and thus provide limited validity for thehypothesis that instability represents a clinical syndrome.Because fusion is seen by many as the obvious andperhaps best treatment for instability because it surgicallyaddresses the inherent abnormality, a prospective con-trolled clinical trial might be considered an excellentapproach for establishing instability as a clinical syn-drome. Given the nature of open surgery, however,application of fusion to necessary control groups, such aslow-back pain patients without radiographic signs, isdifficult.

The primary purpose of this study was to determine ifa nonoperative treatment, involving bracing, exercise,and education controlling either flexion or extensionpostures, would result in a distinctive pattern of fa-vorable or unfavorable results, depending on the type ofsagittal translation abnormality. Specifically, it was hy-pothesized that patients with retrodisplacement (retro-listhesis), spondylolisthesis, and “normal” translationwould respond differentially to treatments associatedwith flexion and extension posture. A secondary goal wasto establish more objective criteria for prescribing bracesfor low-back pain patients.

Materials. A series of forms were developed to evaluate thepatient at admission and at l-month follow-up. Specifically,forms were developed that detailed the patient’s generaldemographics and medical history; low-back pain history;radiographic evaluation summary; a physical examination,35including nonorganic signs42; and measures of trunk strengthand range of motion.

The general demographics, medical history, and physicalexamination at initial presentation were used to establishgeneral admission criteria to the study. The low-back painhistory and evaluation of patient trunk strength and range ofmotion provided the outcome criteria for the study. Trunkstrength and spine range of motion were evaluated usingstandard protocols. l9

The primary outcome measure was a self-report version of

Bracing Efficacy l Spratt et al 1841

the pain interference scale developed by Million et al24 andoften referred to in the literature as the “Visual Analog Scale”(VAS). This scale was developed as an outcome measure foruse in clinical trial studies and, in fact, was used initially toevaluate the efficacy of a corset treatment. The content ofthe 15 items was retained with slight modification and theinstructions were modified to allow the scale to be completedby the patient. Each of the scales were made into lo-pointvisual analog scale. After completion, some items were reversescaled so that high scores reflected greater wellness. Thecomposite or total score was computed as the average of the15 visual analog scale items. Thus, a patient’s score couldrange frominterference,

1 to 10, wi th largeror greater wellness.

scores indicating less pain

The original pain interference VAS was computed by“standardizing” each item as a z-score (mean, 0, and standarddeviation, 1) and then summing these 15 z-scores to obtain acomposite. Although the rationale for this procedure waspresented in the

functioning relative to the specific group measured. In other

original

words, a patient’s VAS score reflected a relative position in the

report, the benefits associated withallowing each item in the scale to contribute equally to the totalwas not seen as sufficient to outweigh the costs. Specifically, thisapproach forces the given study group to be its own norm

group because a patient’s score simply reflects individual

group without consideration of the overall impairment status ofthat group. This approach makes it very difficult to use the VASto compare results across studies. In addition, longitudinalassessments using this measure provide evidence about apatient’s relative improvement or worsening compared withthe with no notion of a patient’s absolute improvementor worsening. As an example, consider a group of 10 patientsassessed with the VAS at admission and at l-month follow-up.Suppose that nine of the patient showed marked improvementand one patient stayed the same. The traditional VAS score forthe patient who did not improve would be lower at follow-up,which might be interpreted as a sign of worsening. In othercircumstances, a lower VAS score at follow-up could occur evenif the patient showed improvement, but of a lessor magnitudethan the cohort or a higher VAS score at follow-up could occurif a patient worsened, but less so than others in the cohort.

Radiographic Criteria. A frame designed to maximize flexionand extension postures while simultaneously avoiding obliquityfrom a true lateral projection was used to standardize theradiographic procedures used to obtain flexion and extensionfilms for each patient. Two raters measured each flexion andextension film for relative translation in the sagittal plane at theL3-L4, L4-L5, and L5-S1 l e v e l s u s i n g t h e L e h m a n nmethod,18 described in detail by Shaffer et al.34

There are two commonly used methods for classifyingradiographic instability, the maximum translation18 and theexcursion approaches.1,13,38 Stokes and Frymoyer37 wereunable to detect large amounts of anteroposterior excursionwith biplanar radiographic techniques, nor able to correlateexcursion with clinical symptoms and signs. Pearcy andShepherd29 also was unable to detect large amounts ofexcursion in patients with spondylolisthesis. In pilot testingleading to this study, relative angular motion at each motionsegment (Hanley method12) and excessive excursion (differ-ence between anteroposterior translation measurements) didnot correlate with clinical symptoms. When instability was

defined as maximum displacement away from absolute verticalalignment on the flexion and extension films (i.e., eitherposterior [retrodisplacement] or anterior [spondylolisthesis]),interesting clinical features were observed. Specifically, retro-displacement occurred more often in young men involved withlifting compared with spondylolisthesis, which occurred moreoften in older women, less involved with heavy lifting.Additionally, certain items, such as “leg pain with twisting”,were associated with spondylolisthesis. As a result of thesefindings, the maximum translation approach was adopted toclassify patient instability. This definition is consistent withsurgical practices in which patients generally receive lumbarfusion for the presence of spondylolisthesis rather thanexcessive mobility of a motion segment. In addition, theoriginal works describing “instability” by Knutsson, l7 Morganand King,25 and Friberg and Hirsch’ used a qualitativedefinition considering the relative alignment of the adjacentvertebral bodies (“retroposition”, ‘ ‘pseudospondylolisthesis")rather than a quantitative definition related to excursion orhypermobility.

The rules for classifying translations as retrodisplacement(retrolisthesis), normal, or spondylolisthesis at each level aresummarized below:

Classification Rules for Maximum Sagittal Translation (NotExcursion)

Level Retro Normal SpondyL3-L4 5 -4 mm -2 mm-2 mm 2 3.5 mmL4-L5 5 -4 mm -2 mm-2 mm 2 3.5 mmL5-Sl 5 -6 mm -2 mm-2 mm 2 3.5 mmValid translation categorization required both raters to

agree in their classification. Thus, if one rater classified a patientat normal and the other rater classified the patient as outside thenormal range, then classification at that level for that view wascoded as ambiguous, and patient inclusion and overall classi-fication became dependent on classifications at other levels orfrom the other view of that level. In addition, if a translationwas outside the normal range, but not in the retro or spondyrange (e.g., 2.5 mm of translation), that classification was codedas ambiguous. Although these rules were considered quitestrict, it was decided that such strictness was necessary tominimize the chances of erroneous patient classification. Morerecent work in the laboratory has demonstrated that a moreconservative cut point may be necessary (i.e., displacementgreater than 6 mm), especially when films of inferior qualitymust be interpreted.34 The current study, however, wasdesigned and implemented before the availability of this morerecent work. Inevitably, some misclassification will occur, nomatter how conservative the cut points are made. Pilot workindicated that by eliminating those patients with displacementsin the ambiguous zones, and by requiring two independentraters to classify each patient the same, misclassifications wouldbe minimized. Overall, a patient rated as normal at all threelevels was classified as “normal”; patients rated as retro at oneor more levels, with no spondy ratings, were classified as retro;and patients rated as spondy at one or more levels were ratedas spondy. Additionally information was coded for patientsclassified as having instability. For those classified as retro,additional information was included that indicated if the retroclassification was based on an extension (RE) or a flexion (RF)posture. For those classified as spondy, additional informationwas included that indicated if the spondy was degenerative (SD)or isthmic (SI).