title: Low Back Pain on Passive Straight Leg Raising: The Anterior Theca as a Source of Pain The Longitudinal Assessment of Imaging and Disability of the Back (LAIDBack) Study: Baseline Data Recurrent low back pain and early disc degeneration in the young. Spinal stenosis, back pain, or no symptoms at all? A masked study comparing radiologic and electrodiagnostic diagnoses to the clinical impression. Pain Drawings in the Assessment of Nerve Root Compression: A Comparative Study With Lumbar Spine Magnetic Resonance Imaging Raynaud's phenomenon, vibration induced white finger, and difficulties in hearing The Diagnostic Accuracy of Magnetic Resonance Imaging, Work Perception, and Psychosocial Factors in Identifying Symptomatic Disc Herniations Interobserver and Intraobserver Variability in Interpretation of Lumbar Disc Abnormalities: A Comparison of Two Nomenclatures Are first-time episodes of serious LBP associated with new MRI findings? Magnetic resonance imaging of the lumbar spine in people without back pain. Interobserver reliability in the interpretation of diagnostic lumbar MRI and nuclear imaging. Self reported health status and magnetic resonance imaging findings in patients with low back pain
abstract: Study Design . A prospect i ve clinical and radiologic investigation of two groups of patients presenting with either acute back pain only or acute leg pain only , yet similar restriction in straight leg raising ( SLR ) . Objectives . To highlight a group of patients presenting with acute low back pain only , yet a restricted SLR normally associated with leg pain ( sciatica ) caused by a posterolateral disc prolapse . To determine the anatomic source of the pain in the low back pain only group . Summary of Background Data . A restricted SLR is commonly associated with leg pain ( sciatica ) due to compression of a nerve root by an intervertebral disc prolapse . Previous studies investigating pain patterns on SLR have suggested that central disc prolapses tend to induce back pain whereas the more lateral prolapses induce leg pain . Such research work has involved patients presenting with typical sciatic pain investigated by myelography and undergoing decompressive surgery . There are no studies specifically investigating patients presenting with low back pain only and reduced SLR . Methods . Two groups of patients , one with acute low back pain only and one with acute leg pain only , yet showing similar restriction in SLR underwent MR imaging .  The scans were review ed “ blind ” by an experienced spinal radiologist and imaging features recorded according to a detailed protocol . The MR findings were then compared . Results . Significant disc prolapses were seen equally in both groups . The disc prolapses in the back pain only group were more likely to be central , smaller , to compress the theca only , and to be at a higher lumbar level as compared with the leg pain only group . Conclusions . Acute low back pain associated with significant restriction in SLR is likely to be caused by a disc prolapse compressing the anterior theca Study Design . Prospect i ve cohort study of r and omly selected Veterans Affairs ( VA ) out patients . Objective . To determine the prevalence of  magnetic resonance imaging ( MRI ) findings in the lumbar spine among persons without current low back pain or sciatica and to examine which findings are related to age or previous back symptoms . Summary of Background Information . Previous studies of patients without low back pain have not explored the possible association of various MRI findings to past symptoms . Methods . We r and omly selected an age-stratified sample of subjects without low back pain in the past 4 months from clinics at a VA hospital . We collected information on demographics , comorbidity , functional status , and quality of life .  MR images were obtained using a st and ardized protocol through each of the five lumbar disc levels . Results . Of 148 subjects , 69 ( 46 % ) had never experienced low back pain .  There were 123 subjects ( 83 % ) with moderate to severe desiccation of one or more discs , 95 ( 64 % ) with one or more bulging discs , and 83 ( 56 % ) with loss of disc height . Forty-eight subjects ( 32 % ) had at least one disc protrusion and 9 ( 6 % ) had one or more disc extrusions . Conclusion . Many MR imaging findings have a high prevalence in subjects without low back pain . These findings are therefore of limited diagnostic use . The less common findings of moderate or severe central stenosis , root compression , and extrusions are likely to be diagnostically and clinical ly relevant STUDY DESIGN A prospect i ve 9-year follow-up study involving r and omized matched subgroups of 15-year-old schoolchildren with or without low back pain at baseline . OBJECTIVES To evaluate the long-term persistence of initially reported recurrent low back pain , and to examine the significance of abnormalities found in magnetic resonance imaging of lumbar discs in individuals 15 and 18 years of age as possible contributors to persistently recurrent low back pain . SUMMARY OF BACKGROUND DATA In surveys among children and teenagers during the past few years , as many as half of all children in a community report a history of low back pain . The current results , in accordance with previous findings , indicate that there is a subgroup of adolescents with more chronic symptoms which , in the authors ' opinion , deserves more attention . Disc disease accompanying low back pain is a key issue both in research and clinical practice . The significance of early degenerative findings in the lumbar discs is not known . METHODS In the survey of 14-year-olds ( n = 1503 ) , a subgroup ( 7.8 % ) with recurrent low back pain was found . A r and om sample of individuals with recurrent low back pain ( n = 40 ) and an equal number of completely asymptomatic control subjects were selected for a comparative study . The selected groups were examined by magnetic resonance imaging at 15 and 18 years of age . The participation rate of youth at 14 , 18 , and 23 years of age for all three question naires was 82 % ( 29 boys and 33 girls ) . Imaging data were interpreted by two blinded radiologists experienced in low-field-strength magnetic resonance imaging . In calculations of relative risks , the participants reporting recurrent low back pain in all phases of the study were compared with participants who had no persistently recurrent pain . RESULTS Eleven participants ( 35 % ) in the original group with low back pain persistently reported recurrent pain . In 15-year-old participants with disc degeneration , the relative risk of reporting recurrent low back pain up to the age of 23 years was 16 ( 95 % confidence interval 2.2 - 118 ) compared with those having no disc degeneration . In addition , disc protrusion and Scheuermann-type changes at 15 years contributed to the risk of persistently recurrent low back pain . CONCLUSIONS The authors ' earlier findings already favored the hypothesis of a causal relation between the early evolution of a degenerative process of lower lumbar discs and recurrent low back pain in the near future . The current results further strengthen this hypothesis , indicating that individuals with disc degeneration soon after the phase of rapid physical growth not only have an increased risk of recurrent low back pain at this age , but also a long-term risk of recurrent pain up to early adulthood OBJECTIVE To assess the relations between clinical ly recognized lumbar spinal stenosis and the conclusions of masked radiologists and electrodiagnosticians . DESIGN Prospect i ve , masked , double-controlled trial . SETTING University spine center . PARTICIPANTS One hundred fifty persons age 55 to 80 years with or without back pain and with or without magnetic resonance imaging (MRI)-demonstrated stenosis , screened for neuropathy risk , previous surgery , or cancer . INTERVENTIONS Question naires on pain and function ; ambulation testing and physical examination ; and masked electrodiagnotics and MRI . MAIN OUTCOME MEASURE Diagnostic impressions of the examining clinician , radiologist , and electrodiagnostician . RESULTS Following application of post hoc exclusion criteria and elimination of patients due to incomplete or inadequate test data , the clinical diagnosis was lumbar stenosis in 50 subjects , back pain in 44 subjects , and no pain in 32 subjects . Radiologic and clinical impression had no relation ( P = .80 vs asymptomatic , P = .99 vs back pain controls ) . Electrodiagnostic impression trended to relate to clinical impression ( P = .14 vs asymptomatic , P = .09 vs back pain ) . Retrospective application of age-related electrodiagnostic norms for paraspinal electromyographic and limb motor unit changes , established in this study , reclassified 13 of the 17 asymptomatic persons whom the electrodiagnostician thought had stenosis . The clinical impression did correspond to history and physical examination findings typically associated with spinal stenosis and to the independent impression of a neurosurgeon who examined MRI and clinical , but not to the electrodiagnostic data . CONCLUSIONS The impression obtained from an MRI scan does not determine whether lumbar stenosis is a cause of pain . Electrodiagnostic consultation may be useful , especially if age-related norms obtained in this study are applied Study Design . Prospect i ve comparative study of pain drawings with findings on lumbar spine magnetic resonance imaging . Objectives . To assess the ability of the  pain drawing  to predict the presence of nerve root compression . Summary of Background Data . Most research work has concentrated on the ability of the pain drawing to act as a screening method for psychological distress with less work directed at the influence the anatomic abnormality has on the pain drawing . Methods . One hundred thirty‐four consecutive out‐ patients attending for lumbar magnetic resonance imaging in the investigation of back and leg pain completed pain drawings and psychological testing immediately before the examination . The pain drawing was analyzed by previously reported criteria , and the magnetic resonance imaging was assessed independently for the presence of nerve compression by three radiologists . Multivariate stepwise discriminant analysis was used to identify patients with nerve compression on the basis of their pain drawing . Results . Nerve compression was predicted by numbness in the anterolateral aspect of the foot . There was considerable overlap in the appearances of the pain drawings between patients with and without nerve compression , and the pain drawing correctly classified only 58 % of patients with nerve compression . Conclusions . The pain drawing is not a good predictor of nerve compression on magnetic resonance imaging in a group of patients investigated for back and leg pain . It should be interpreted with caution and in light of the full clinical picture Background : An association has previously been reported between finger blanching and hearing difficulties , but only in workers with exposure to noise and h and transmitted vibration ( HTV ) . Aims : To explore the association in a community sample , including cases who lacked occupational exposure to noise or HTV . Method : A question naire was mailed to 12 606 subjects aged 35–64 years , chosen at r and om from the age – sex registers of 34 British general practice s. Inquiry was made about years of employment in noisy jobs , lifetime exposure to HTV , hearing difficulties and tinnitus , and lifetime history of cold induced finger blanching . Subjects were classed as having severe hearing difficulty if they used a hearing aid or found it difficult or impossible to hear conversation in a quiet room . Associations of finger blanching with hearing difficulties and tinnitus were analysed by logistic regression . Results : Among 8193 respondents were 185 who reported severe hearing difficulty and 1151 who reported finger blanching .  After adjustment for age and years of work in noisy jobs , hearing difficulty was about twice as common in men and women who reported finger blanching , including those who had never been importantly exposed to noise and in those never exposed to HTV . Conclusions : These data support an association between finger blanching and hearing loss , which is not explained by confounding occupational exposure to noise , and suggest that it may extend to causes of blanching other than vibration induced white finger . Further investigations are warranted to confirm the association and explore possible mechanisms , such as sympathetic vasoconstriction in the cochlea Study Design This was a prospect i ve study of patients ( study group ) with symptomatic disc herniations and asymptomatic volunteers ( control group ) matched for age , sex , and work-related risk factors . Objective To determine the prevalence of disc herniation in a matched group of asymptomatic volunteers and to access the diagnostic accuracy of magnetic resonance imaging , work perception , and psychosocial factors in identifying symptomatic disc herniations . Summary of Background Data Disc herniations have been reported to occur in 20–36 % of asymptomatic volunteers . A valid comparison of asymptomatic individuals and patients with disc herniations has not been performed . Methods Forty-six patients with low back pain and sciatica severe enough to require a disceclomy were compared with 46 age- , sex- , and risk factor-matched ( heavy lifting , twisting and bending , vibration , and sedentary activity ) asymptomatic voluteers .  Both groups had a complete clinical and magnetic resonance imaging examination and completed a question naire to assess differences in the psychosocial and work perception profiles . The prevalence and the severity of morphologic alterations ( disc herniation , disc degeneration , and neural compromise ) was analyzed by two independent radiologists in a blinded fashion . Differences between both groups regarding MRI findings , work perception ( occupational mental stress , intensity of concentration , job satisfaction , and job-related resignation ) and psychosocial factors ( anxiety , depression , self-control , social support , and marital status ) were compared using multivariate techniques . Stepwise discriminate analysis was used to identify the best discriminating variables within the magnetic resonance image , work perception , and psychosocial categories in terms of the diagnostic accuracy to predict group membership ( study [ pain ] or control [ no pain ] group ) . Results Matched controls had significantly more risk factors than a group of normal individuals . The present study has presented evidence that an age- , gender- , and occupational risk factors-matched group of asymptomatic patients shows a high incidence rate of disc herniations ( 76 % ) . Although significantly less than the symptomatic group incidence of 96 % , this represents a much higher prevalence rate than generally expected and reported in other studies of unmatched asymptomatic volunteers . Patients had more severe disc herniations ( disc extrusions ) than asymptomatic volunteers ( 35 % vs. 13 % ) . There was no significant differences regarding disc degeneration between both groups ( 96 % vs. 85 % ) . The only substantial morphologic difference between both groups was the presence of a neural compromise ( 83 % vs. 22 % ) , which was highly significant ( P < 0.0001 ) . There were significant differences between both groups regarding work perception ( occupational  mental stress , intensity of concentration , job satisfaction , and resignation ; P<0.027 ) and psychosocial factors ( anxiety , depression , self-control , marital status ; P<0.0001 ) . The best single predictor of a group membership was the extent of neural compromise . A combination of this factor with occupational mental stress , depression , and marital status was the best predictive model . With this model , the false-negative rate ( potential overtreatment of disc morphology ) was reduced by more than half compared with morphologic factors ( nerve root compression ) alone ( 22 % vs. 11 % ) . Conclusions . In an age- , sex- , and risk factormatched group of asymptomatic individuals , disc herniation had a substatially higher prevalence ( 76 % ) than previously reported in an unmatched group . Individuals with minor disc herniations ( i.e. , protrusion , contained discs ) are at a very high risk that their magnetic resonance images are not a causal explanation of pain because a high rate of asymptomatic subjects ( 63 % ) had comparable morphologic findings . The only highly significant difference between the study group and control group regarding morphologic findings was the criteria of a nerve root compromise . Work perception and psychosocial factors were helpful in discriminating between symptomatic and asymptomatic disc herniations Study Design A double-blind prospect i ve study was used to measure interobserver and intraobserver variability when interpreting lumbar spine magnetic resonance imaging studies of disc abnormalities . Objectives To evaluate reader consistercy when interpreting disc extension beyond the interspace , and assess the effect of two distinct nomenclatures on reader consistency . Summary of Background Data Interobserver and intraobserver variability in interpretation of lumbar disc abnormalities is an important consideration in analyzing the technical efficacy of an imaging modality . However , this has not been well measured ( particularly for st and ardized nomenclature ) . Methods  Magnetic resonance imaging studies of the lumbar spine performed prospect ively in 98 asymptomatic volunteers , and an additional 27 selected studies from symptomatic patients , were read blindly by two experienced neuroradiologists , using two separate nomenclatures . Only the discs were evaluated ( 625 interspaces ) . Nomenclature I was normal , bulge , herniation . Nomenclature II was normal , bulge , protrusion , extrusion . Intraobserver and interobserver variation were measured with Kappa statistic analysis . Results Interobserver agreement was 80 % for both nomenclatures with a Kappa statistic of 0.58 . Intraobserver agreement was 86 % for each reader , with a Kappa statistic of 0.71 and 0.69 , respectively . The most common disagreement was for normal versus bulge . The next most common disagreement ( 5–6 % ) was for bulge versus herniation ( or protrusion in Nomenclature II ) . Herniation was read in 23 % of the asymptomatic subjects . Using Nomenclature II . protrusion was seen in 27 % of these subjects . Extrusion was read in only two asymptomatic subjects . Conclusions Experienced readers using st and ardized nomenclature showed moderate to substantia agreement when interpreting disc extension beyond the interspace on magnetic resonance imaging BACKGROUND Magnetic resonance ( MR ) imaging is frequently used to evaluate first-time episodes of serious low back pain ( LBP ) . Common degenerative findings are often interpreted as recent developments and the probable anatomic cause of the new symptoms . To date no prospect i ve study has established a baseline MR status of the lumbar spine in subjects without significant LBP problems and prospect ively surveyed these subjects for acute changes shortly after new and serious LBP episodes . This method can identify new versus old MR findings possibly associated with the acute symptomatic episode . PURPOSE To determine if new and serious episodes of LBP are associated with new and relevant findings on MRI . STUDY DESIGN Prospect i ve observational study with baseline and post-LBP MRI monitoring of 200 subjects over 5 years . OUTCOME MEASURES Clinical outcomes : LBP intensity ( visual analogue scale ) , Oswestry Disability Index , and work loss . MRI outcomes : disc degeneration , herniation , annular fissures , end plate changes , facet arthrosis , canal stenosis , spondylolisthesis , and root impingement . METHODS 200 subjects with a lifetime history of no significant LBP problems , and a high risk for new LBP episodes were studied at baseline with physical examination , plain radiographs , and MR imaging . Subjects were followed every 6 months for 5 years with a detailed telephone interview . Subjects with a new severe  LBP episode ( LBP > or=6/10,>1 week ) were assessed for new diagnostic tests . New MR imaging , taken within 6 to 12 weeks of the start of a new LBP episode , was compared with baseline ( asymptomatic ) images . Two independent and blinded readers evaluated each baseline and follow-up study . RESULTS During the 5-year observation period of 200 subjects , 51 ( 25 % ) subjects were evaluated with a lumbar MRI for clinical ly serious LBP episodes , and 3/51 ( 6 % ) had a primary radicular complaint . These 51 subjects had 67 MR scans . Of 51 subjects , 43 ( 84 % ) had either unchanged MR or showed regression of baseline changes . The most common progressive findings were disc signal loss ( 10 % ) , progressive facet arthrosis ( 10 % ) , or increased end plate changes ( 4 % ) . Only two subjects , both with primary radicular complaints , had new findings of probable clinical significance ( 4 % ) . Subjects having another MR were more likely to have had chronic pain at baseline ( odds ratio [OR]=3.19 ; 95 % confidence interval [ CI ] 1.61 - 6.32 ) , to smoke ( OR=5.81 ; 95 % CI 1.99 - 16.45 ) , have baseline psychological distress ( OR 2.27 ; 95 % CI 1.15 - 4.49 ) , and have previous disputed compensation cl aims ( OR=2.35 ; 95 % CI 0.97 - 5.69 ) . Subjects involved in current compensation cl aims were also more likely to have an MR scan to evaluate the LBP episode ( risk ratio=4.75 , p<.001 ) , but were unlikely to have significant new findings . New findings were not more frequent in subjects with LBP episodes developing after minor trauma than when LBP developed spontaneously . CONCLUSION Findings on MR imaging within 12 weeks of serious LBP inception are highly unlikely to represent any new structural change . Most new changes ( loss of disc signal , facet arthrosis , and end plate signal changes ) represent progressive age changes not associated with acute events . Primary radicular syndromes may have new root compression findings associated with root irritation BACKGROUND The relation between abnormalities in the lumbar spine and low back pain is controversial . We examined the prevalence of abnormal findings on magnetic resonance imaging ( MRI ) scans of the lumbar spine in people without back pain . METHODS We performed MRI examinations on 98 asymptomatic people . The scans were read independently by two neuroradiologists who did not know the clinical status of the subjects . To reduce the possibility of bias in interpreting the studies , abnormal  MRI scans from 27 people with back pain were mixed r and omly with the scans from the asymptomatic people . We used the following st and ardized terms to classify the five intervertebral disks in the lumbosacral spine : normal , bulge ( circumferential symmetric extension of the disk beyond the interspace ) , protrusion ( focal or asymmetric extension of the disk beyond the interspace ) , and extrusion ( more extreme extension of the disk beyond the interspace ) . Nonintervertebral disk abnormalities , such as facet arthropathy , were also documented . RESULTS Thirty-six percent of the 98 asymptomatic subjects had normal disks at all levels . With the results of the two readings averaged , 52 percent of the subjects had a bulge at at least one level , 27 percent had a protrusion , and 1 percent had an extrusion . Thirty-eight percent had an abnormality of more than one intervertebral disk . The prevalence of bulges , but not of protrusions , increased with age . The most common nonintervertebral disk abnormalities were Schmorl 's nodes ( herniation of the disk into the vertebral-body end plate ) , found in 19 percent of the subjects ; annular defects ( disruption of the outer fibrous ring of the disk ) , in 14 percent ; and facet arthropathy ( degenerative disease of the posterior articular processes of the vertebrae ) , in 8 percent . The findings were similar in men and women . CONCLUSIONS On MRI examination of the lumbar spine , many people without back pain have disk bulges or protrusions but not extrusions . Given the high prevalence of these findings and of back pain , the discovery by MRI of bulges or protrusions in people with low back pain may frequently be coincidental BACKGROUND CONTEXT Assessment of patients with complaints of low back or leg pain varies with the subspecialty of the treating physician . The evaluation of the spine patient may include magnetic resonance imaging ( MRI ) , bone scan , or single-photon emission computed tomography ( SPECT ) imaging . The interpretation of these tests and the examiner 's biases will impact the outcome of patient treatment and the cost to the health-care system . PURPOSE To evaluate interobserver reliability of MRI and nuclear imaging studies and determine the predictability of nuclear medicine results based upon MRI findings . STUDY DESIGN / SETTING Retrospective radiographic review for patients with low back pain .  MRI , planar bone scan imaging , and SPECT imaging techniques were evaluated . PATIENT SAMPLE Seventeen patients ( 80 lumbar levels ) who presented to an orthopedic spine specialist with a complaint of mechanical low back or leg pain were r and omly selected . Inclusion criteria were age greater than 21 years and a workup that included MRI , bone scan , and SPECT scan images .  OUTCOME MEASURES Interobserver reliability was determined using kappa values ( 0.6 to < 0.8=substantial ; 0.8 - 1=perfect ) . Interobserver reliability was evaluated for all studies and compared with a " group consensus . " METHODS A team of orthopedists and radiologists of varying experience levels were assembled to interpret the imaging studies . All readings were performed independently followed by group interpretation and discussion . The review ers were asked to assess each lumbar level ( L1-L2 through L5-S1 ) . Phase one : Is the level degenerative ? Is there a spondylolisthesis present ? Does the level have Modic changes on MRI ? Phase two : Based on the MRI , will the planar bone scan be positive ? After this prediction , was the planar scan positive ? Identify the lesion location ( anterior column vs. posterior column ) . Phase three : Based on their assessment and predicted results on planar bone scan , was the SPECT scan able to improve this assessment ? RESULTS High kappa values were demonstrated in the identification of a degenerative disc , spondylolisthesis , and Modic change ( 0.773 , 0.728 , and 0.669 , respectively ) . Bone scan and SPECT scan yielded poorer kappa results ( 0.539 and 0.460 , respectively ) . Review er-predicted bone scan results demonstrated a positive predictive value of 68 % and a negative predictive value of 84 % . Predicated SPECT results were similar ( positive predictive value 66 % and negative predictive value 84 % ) . SPECT identified 24 % more lesions in the lumbar spine when compared with bone scan . CONCLUSIONS MRI interpretation of the lumbar spine is comparable between specialties . Nuclear imaging studies ( bone scan/SPECT ) demonstrated a poorer correlation between examiners . The presence of MRI changes enables an accurate prediction of bone scan or SPECT scan findings . SPECT scan demonstrates an increased sensitivity in the detection of spinal abnormalities and the ability to localize a lesion when compared with planar bone scan Abstract The authors present a prospect i ve study of quality of life ( SF-36 ) and MRI findings in patients with low back pain ( LBP ) . Disc herniation and nerve root compression contribute to LBP and poor quality of life . However , significant proportions of asymptomatic subjects have disc herniation and neural compromise . Little is known about the influence of disc abnormalities and neural compression on quality of life in symptomatic patients . The purpose of this study was to assess the relationship between the extent of disc abnormality , neural impingement and quality of life . A total of 317 consecutive patients with LBP referred for MRI completed an SF-36 health status question naire immediately before imaging and again 6 months later . Patients were grouped according to the most extensive disc abnormality and any neural compromise reported at MRI . The relationship between symptoms , radiological signs and SF-36 scores was assessed . Eighty percent ( 255/317 ) and 65 % ( 205/317 ) of patients completed the initial and 6-month SF-36 , respectively . Thirty-six percent of patients ( 115/317 ) had one or more herniated discs and 44 % ( 140/317 ) had neural impingement . There was little relationship between the extent of disc abnormality and quality of life . Patients with radiological evidence of neural impingement reported better general health ( P < 0.01 ) . SF-36 scores improved at 6 months in four dimensions , but general health deteriorated ( P < 0.01 ) . Patients with neural impingement had improved pain scores at 6 months ( P < 0.05 ) . The study results showed that the pain and dysfunction caused by disc herniation and neural compromise are not sufficiently distinct from other causes of back pain to be distinguished by the SF-36 . Whilst neural compromise may be the best radiological feature distinguishing patients who may benefit from intervention , it can not predict quality of life deficits in the diffuse group of patients with LBP
target: MRI findings of disc protrusion , nerve root displacement or compression , disc degeneration , and high intensity zone are all associated with LBP , but individually , none of these abnormalities provides a strong indication that LBP is attributable to underlying pathology .
  This limits their value in refining epidemiological case definitions for LBP
background: OBJECTIVE to assess how confidently  low back pain ( LBP ) can be attributed to abnormalities on magnetic resonance imaging ( MRI ) , and thereby explore the potential value of MRI abnormalities in refining case definition for mechanical LBP in epidemiological research .
  SUMMARY OF BACKGROUND DATA most epidemiological studies of mechanical LBP have defined cases only by reported symptoms , but it is possible that the potency of causes differs depending on whether there is demonstrable underlying spinal pathology .