Radiologically detectable lumbar disc degeneration in concrete reinforcement workers.

WIIKERI, M., NUMMI, J., RIIHIMAKI, H. and WICKSTROM, G. Radiologically detectable lumbar disc degenera,uon in concrete 'reinforcement workers. Scand. j. work environ. & health 4 (1'978): supp!. 1, 47-53. Two hundred and ninety-Nve male Finnish cOincrete reinforcement workers, ag,ed 19 to 6,4 years and ·enga,ged in heavy physical work including pI1olonged stoopimg, were rndiologically examined by >antem-posterior ·aond lateral views of the lumbar spine wihi'le Ithey wer,e staJnding. The findings of ,lumbar di'sc degeneration were classified as none, slight, moderate or severe. The prevalence and degree of I1adiologically detectable lumba'r disc degeneration depended strongly on age and ,increased especially rapidly from 40 to 44 yea["s on. Lumbar disc degeneration sihowedan age-dndependeIllt assooia tion to both a history of lumbago (X 2 = 10.5, P < 0.01) and a hi,story of ~dJatica (X 2 = 11.8, P < 0.001). When disc degeneration was compaI1ed to I1eporis of stiffness, fatigue, ache, and sharp pain in the baok durmg an ordinary workday, no s.taiis tically significant associa.tions were found, wh1'ledi5C degenerattion was found to be sl<ightly more common (X 2 = 4.6, P < 0.05) in the men reporting back symptoms as they bent down than in the men who did not report such symptoms. No associa tion between leng,th of exposure to static and dynamic back loads in re1nforcemen,t work and the pI1evalence of lumbar disc deg,enem,tion could be established, but definite conclusions on the possible effect of reinforcement work on the lumbar spine could not be drawn from the Qa,ta.

In the general popula tion the prevalence of radiologically detectable lumbar disc degeneration increases 'almost linearly between 25 and 50 years of age, after which the increase slows down. By the age of 65 years the prevalence is over 90 0J0 (7).
Concrete reinforcement workers are skiHed construction workers. Their task is 1 Institute of Occupaluonal Heal~h, Helsinki, FinIand. 2 Labor Pension Fund, Helsinki, Finland. 3 Turku Regionai Ins.titute of OccupauOlllal Hea:lth, Turku, F.tnland. to build steel skeletons upon which concrete is later poured by other workers. Reinforcement work consists of pulling long steel rods from a stack, cutting and bending the rods (mostly by ma,chines), and tying the rods together according to sketches. An ergonomic study of back loads in reinforcement work showed gr·eat static loads from working iJn bent-double and forward-leaning postures during the tying tasks. Dynamic loads occurred mainiy in the preparation tasks and were considered of less importance than the static ones; ,even so, the substantial momentary load of lifting rods in a stooped posture when disengaging them from the stack and the dynamic load of pulling the rods to the cutting .and bending machines were also regarded as loads whioCh might contribute to ,a possible pr,emature degeneration of the lumbar intervertebral discs (11).
To evaluate the effect of~oncrete reinforcement work on the back, we made a cross-sectional epidemiologic study of the backs of 295 male Finnish concrete reinf.orcement workers ag.ed 19 to 64 years.
Additional characteristi'Cs of the populahon studi'ed ·and the experience of lowback pain syndromes and back symptoms in this gl"oup have heen I"eported :in an article by Wkkstr6m et al. (13).
In this article we have reported the prev-.alenee of lumbar disc deg,eneration ·tn r,einforoement workers by age and have compared the length of r,einforcement work to the pr,eval,ence of degenerative changes. We have also compared the radtological findings with the history of lowback pain syndwmes and with present back symptoms.

METHODS
The reinforcement workers wer·e radiologically examtoed by an antera-posterior and a lateral view of the lumbar spine; in the 'antero-posterior projection, the sa,croilia,c joints were toduded. The radiographs were taken with a Siemens Tridoros 4 apparatus on 20 X 40 em Agfa-Gaevert film. The subJect was standing straight with the X-ray tube at 'a distanoe of 1.5 m at the lev·el of the ,crista iHca. Large focus was used. Exposure values, about 75 kV and 100 mAs in theantero-posterior pr,oj'ection and about 90 kV 'and 200 mAs in the lateral projectton, were modified according to the body build of the subje,ct examined. The sedor of the X-Day beams was screened down to limi't the exposur,e of tissues to radiation.
The radiologioCal parameter determined in this study was lumbar disc degeneration. It was graded on four levels as "none," "slight," "moderate," 0·1" "severe" according to the following definitions: none = no signs of disc degeneration, slight = narrowing of intervertebral space without other signs of disc degenera lion, moderate = narr,owing of intervertebral spac·e and osteophytosis, 48 severe narrowing of intervertebral space, osteophytosis, and end-plate sclerosis.
The radiographs were interpreted separately by a radiologist and an orthopedic surgeon. Both physicians knew they were looking at films of c-oncrete reinforcement workers, but they had no knowledg.e of the age of the worker nor of any anamnestic or .clinical orthopedic data. If their interpreta tions differed as to whether disc degenerahon w,as present or if their cLassifioations of observed disc degeneration differed by more than one degree, the radiologist reviewed the films to consider the "suggestions" of the orthopedic surgeon. The radi;ologist's decision during this slElcond reading was reool"ded as the definite classification.
In the graphi,c presentation of the results the findings are smoothed by calculation of the prevalence estimates for 15-y,ear moving age ranges.

RESULTS
Radiologi,cally detectable lumbar disc degeneration was found in 44 % of the re-Inforcement workers. Be10w the age of 25 years no ease was f·ound, whHe the prevalence of disc degenera'bon increased swiftly from this age on, with an espedally sharp ri'se from age 40-44 years to age 45-49 years. In the age group 60-64 years only one man did not show any signs of lumbar degenerati'On (table 1).
The degree of lumbar disc degener,ation was classified as light in 12 % of the men, as moderate in 23 %, ,and as severe in 9 0/0. The relation between degre'e of disc degeneration and 'age is shown in fig. 1. The prevalence of moderate and severe changes increased rapj.dly from age 45 years on.
We analyzed the effect of reinforcement work on lumbar disc degeneration by eomparing the length of experienoe in concrete reinforcement work to radiologically detectable signs of lumbar disc degeneration. For the age groups 35-39, 40-44, 45-49 and 50-54 years no statistkally significant association was found with Mantel's test (9). Table 1. Radiologically detectable lumbar disc degenera~ion by the age of the subjects and their experience in rei.nforcement work.
As the prevalences of both a history of previous low-back pain syndromes and radiologically detectable lumbar disc de-generatIon accumulate as the age of the subject progresses, an associ'ation between these variables is to be expected. Hence aUowanoe w.as made for age in the analysis. The two paraa:nelers "lumbar disc degeneration" and "history of lumbago" were combined~nto one parameter Wi'th four classes (disc degeneration negative  and history of lumbago negative, disc degeneration positive 'and history of lumbago negative, disc degeneration negative and history of lumbago positive, and disc degeneratton pos~tive and history of lumbago positive). This combined variaJble is shown by age in fig. 2. When lumbar disc degeneration and experience of lumbago were ,compal'ed after age stratification, an association indkating a relatLonship independent of age (X 2 = 10.5, P < 0.01) was found between these variables. A similar four-dass variable was constructed from the variables of "disc degeneratton" and "history of sciatka," as shown in fig. 3. When the r'elation hetween lumbar disc degeneration and a history of sciatica was analyzed in 5-year age groups by the Mantel-Haenszel's test (9), there was an a,ssodati'on independent of age (X 2 = 11.8, P < 0.001).
When lumbar disc degeneration was compared to pr,esent back symptoms, degenerative changes were slightly more common in the men reporting a,cheand sharp pain than in those without these symptoms. For fatigue and stiffness the radiologkal signs were somewhat more commonaanong the symptom-free, but none of the differences wel'e statistically significant ( fig. 4).
Lumbar disc degeneration was more common in workers reporting back symptoms as they bent down than among the men without such symptoms (X 2 = 4.6,

DISCUSSION
Degenerahon of the intervertebral discs is the first degenerative change in the lumbar spine. The observed prevalences of disc degeneration vary with the methods of investigation. Histological examination of the disc tissue is the most sensitive method, but also macroscopic autopsy studies yield higher prevalence figures than do radiological examinations of the lumbar spine in liIving subjects. Even relatively advanced disc degeneration may not be revealed by o,rdinary radiological methods (3). The radiolDgically detectable signs of dilSC degeneration are diminished height of the intervertebral disc space, sclerosis of the adjacent vertebral pl'ates, and growth of osteophytes.
The interobserver error in 'the evaluahoon of degenerative lumbar changes has been fDund to he great even among experienced interpreters; it mainly concerns differentiation hetween slight and moderate changes (5,6). In our study the radi,ologist first dassified :the findings of lumbar disc degeneration as negative in 187 men, slight in 24, moderate in 61, and severe in 23 men. For the orthopedist the oorresponding figures were 184, 40, 51 and 20, respectively. The radiologist thus classified fewer findings as slight and more findings as moderate than the orthopedist. Otherwise no consistent difference was discerned. After the reevaluation of the differently classified radiographs, the ra-diQlogist revised his classificatiQn in 30 cases. Twenty-eight findings were classifioed as repr,esenting a higher degree of disc degeneration than on the first interpretation, while two findings were l'eclassified ,to a lower i1.evel.
The possible effect of reinforcement work on lumbar disc degeneration was found difficult 'to interpret from the results of the present cross-sectional study. The age of the workers was quite closely related to the length of their experience in reinf,oroement work and most reinforcement workers had been employed in other physically strenuous occupations before entering reinforcement work (13).
When the data were evaluated by Mantel's method (9), there was no statis-  . Difference between those reporting and those not reporting back symptoms at a certain phase of stooping was statistically significant only for symptoms during bending down; radiologically detectable lumber disc degeneration was more common in men reporting back symptoms during bending down than in those not reporting such symptoms (X 2 = 4.6, P < 0.05). tically significant increase in the prevalenoe of deg,enerative changes because of {)ccupati,onal factors. No reference group was investigated explicitly to serve for comparison with the reinf.orcement workers. As the method for interpretation of radi1ologically detectable lumbar disc degeneration used in the present study is not iden tical to the methods employed in other studies made at the Institute of Occupational Health and 'as interobserver errors are known to be c()nsiderable, it is n()t possible to make a reliable comparison between the prev,alence {)f lumbar disc degeneration in roncrete reinforcement workers and other occupational groups alre'ady studied. Clear evidence supporting the assumptionthat the occupational load ,on Ithe back in concrete reinfor,cement work ,causes premature lumbar disc degeneration was not obtained in this study. Due t() the design of the present inv,estigation the results do not, 'however, rule out the possible existence of an occupati'Oual effect. The 5-y;ear .follow-up examination 'Of the reinforcement workers and the simultaneous investig.ation of a l'eference group, b()th of which ·are beimg carried out at pr·esent, should help answer this queshon.
The relation between radiologically detectable lumbar disc degenerati'On and lowback pain syndromes has been investigated in several previous studies. Hult (4) emphasized that disc degeneration should be looked upon as a more or less physiological change ooming wi'th age. It need not give rise to symptoms, but ,it presumably lays the foundation for chang,e.g that cause back symptoms. Nachemson (10) considered that most of the low-back disorders ultimately turn out to be discogenic, though others disagree.
Lumbar disc degeneration, especially pronounced ,changes, has been found to be more common in persons with a history of back symptoms than in persons without, but comparison of disc deg'eneration to different types of back trouble {insufficiency symptoms, lumbag'O ·and sciatica) pl'ovided no additional information (4). When radi'ologkally detectable lumbar disc degeneration is related to reported experience of back-hip sciatic pain, both sensitivity, 59 0/0, and specificity, 55 0/0, 52 are low. However, the correlation rises when incapacitating ratlher than trivial pain is oonsidered, past episodes rather than present manif.estations, pronounced radiological changes rather than all degenerative signs, and young age groups rather than older ones (7,14).
In the present study on concrete reinforcement workers slight, mooerate, and severe lumbar disc degeneration was related ,to a history of scia'tica, while only slight and moderate disc degenera'tion was more common in men wi,th a history of lumbago ,alone as c-ompared to men without a history of low-back pain syndromes. When the radiologi,cal findings of lumbar disc deg,eneration were oompared to r,eports of pr,esent ba.ck symptoms, almost no assodation was ·found; only the relahon to back symptoms during forwa,rd bending showed some statistical significance.
Radiological observations are of diagnostic value clinically, but they cannot show degenerative changes in the early stages. Nor do ,they demonstrate painonly a gr,eater probability {)f pain for some of the observed changes. Radiological examination of the lumbar spine is an attradive method for evaluatimg low-back morphology in epidemiologic studies, as radiologically detectable signs of lumbar disc degeneration accumulate with age and exposure to physical loads. It may be looked upon asa biological "dosimeter," although defectiv·e, for occupational expo-SUl'e to back loads. The primary drawbacks of the method are the health risks of the subjeds fl'om exposure to X rays and the 'heavy ag,e dependence of the findings. Even in occupations which put substantialload on the back tissues of workers, a possible acceleration of the degenerative process in the lumbar spine is difficult to prove because the close relation between age and exposure often makes ,analysis difficult. A continuous selective process acc·ording to level of health leaves only the healthier in the group of active workers.