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Does hard work prevent disc protrusion?
Clinical Biomechanics
1987; 2: 198-198
Printed in Great Britain
Does hard work prevent disc protrusion? Richard W Porter,
MD, FRCS
Doncaster Royal Infirmary, Doncaster, UK
Summary This study compares the prevalence of coal miners attending hospital with three defined back pain syndromes, with the number of miners in the working population. Of the men who attended hospital with back pain there were more miners than would be expected (2.78% of the miners compared with 1.99% of the non-miners). 0.32% of the miners had criteria of disc protrusion compared with 0.4% of non-miners; significantly more had syndromes associated with degenerative change. Relatively few men requiring disc excision were miners, whilst there were many who had decompressive surgery. This is compatible with the concept that heavy manual work strengthens the spine, restraining encroachment of a disc protrusion into the vertebral canal.
Relevance These findings suggest a need to identify and encourage activities in early life which may develop annular and ligamentous strength. Furthermore, unfit workers should not be deployed to areas of heavy work and we should re-examine advice about light work after the first disc protrusions. $?‘trds:
Disc prctrusicn, Work. Epidemiology, Surgery, Degenerative change, Spine, Backpain,
Introduction
There is conflicting evidence about the relationship between heavy manual work and the incidence of back pain. Most studies suggest that back pain is related to heavy load handling but Kelsey’ found a high incidence of disc herniation amongst sedentary workers. In an attempt to determine whether heavy manual work reduces the risk of symptoms from disc herniation, this paper examines the prevalence of coal miners presenting with various back pain syndromes, comparing this with the percentage of miners in the population.
Method
Men attending a back pain clinic over a 3-year period were asked if they had been underground coal miners from leaving school, or had worked underground for at least 5 years. The percentage of these miners fulfilling criteria for three defined back pain syndromes was then recorded.
Submitted: 24 April 1987. In revised form: 3 July 1987. Correspondence and reprint requests to: Mr R W Porter. Department of Orthopaedics, Doncaster Royal Infirmary, Doncaster DN2 SLT,
UK.
I. Lower lumbar disc lesion (PID). Three or more of the criteria described by McCulloch’: unilateral leg pain in a typical sciatic root distribution below the knee; specific neurological symptoms incriminating a single nerve; limited straight leg raising by at least 50% of normal; at least two neurological changes of muscle wasting, muscle weakness, sensory change or hyporeflexia; and radiculographic evidence of disc protrusion. 2. Root entrapment syndrome (RE)-lateral canal stenosis. Pain in the leg below the knee incriminating a single root, severe and constant, unrelieved by rest, spinal extension less than a third of normal range, straight leg raising better than 70 degrees, over 40 years of age and radiological evidence of degenerative change’.“‘. 3. Neurogenic ciaudication (NC). Discomfort in both legs above and below the knees when walking with less than 500 metres tolerance, relieved by rest, and a positive myelogram or CT scan showing central canal stenosis. The percentage of miners of the total men admitted for bed rest, whose symptomatic disc lesion had not settled at home was recorded, and also the percentage of miners of the men requiring surgical disc excision, and surgical decompression for central or root canal stenosis”-‘“.
Porter: Does hard work prevent disc protrusion?
197
Table 1. Number of miners and non-miners in the Doncaster population, attending the back pain clinic, with three defined back pain syndromes and ‘other causes’, expressed as a percentage of miners and non-miners in the population Doncaster workers Miners Non-miners
16,000 49,100
Back pain clinic
445 (2.78%) 977 (1.99%) x2=33*4 P
PID
R.E.
N. C.
Other
52 (0.32%) 198 (0.40%) x2=14.9 P
93 (0.58%) 152 (0.31%) x2=6-9 P
35 (0.22%) 21 (0.04%) x2=26.4 P-CO-001
265 (1.65%) 606 (1.23%) n.s.
Chi muare tests between miners and non-miners performed on contingency tables for each diagnosis v all other
patients)
Results The collieries in the catchment area of Doncaster Royal Infirmary employed 16,000 miners in the period under review. In the same catchment area there were 65,100 working men between 20 and 60 years of age, 24.6% of whom were miners. Four hundred and forty-five miners attended the back pain clinic over a 3-year period (2.78% of the miners in the population) compared with 977 nonminers (1.99% of the non-miners in the population). Only 0.32% of the miners in the population attended with criteria of symptomatic disc protrusion, compared with 0.40% of non-miners. The Chi-square (x2) test showed significant differences P < 0.001. Proportionately more miners however attended with root entrapment syndrome and neurogenic claudication than did other men in the population (Table 1). There were 869 men with ‘other causes’ of back pain, including some with more than one of the three defined syndromes, comprising 1.65% of the mining population, and 1.23% of the non-miners. One hundred and three men were admitted with symptomatic disc protrusion; 70 settled with bed rest, and 33 required surgery (Table 2). The proportion of the mining population having symptoms which settled with bed rest in hospital was 0*06%, compared with 0.12% of the non-mining population, whilst 0.02% of the mining population required discectomy compared with 0.06% of the non-miners. There were, however, many miners requiring decompressive surgery for central or root stenosis.
Discussion
Mechanisation of coal mines has largely relegated the pick and shovel to a previous era, but the fluid nature of underground strata and its effects on the roadways, the need to transport equipment to and from the coal face and the unpredictable failure of machinery in confined spaces, still subjects the miner’s spine to large mechanical forces (Figure 1). It is not surprising that musculoskeletal disorders are the largest cause of absenteeism in the coal mining industry. The most significant of these is low back pain14, which is responsible for up to 18% of sickness absence in some British coalfields”. Understandably, more miners attend the back pain
Table 2. Numbers of miners and non-miners in who required hospital bed rest and discectomy, expressed as a percentage of miners and non-miners in the population Admitted for bed rest and symptoms settled without surgery Miners Non-miners
IO (0.06%) 60 (0.12%) x2=0.55
Required surgery 3 (0.02%) 30 (0.06%) P=n.s.
Figure 1. A damaged underground roadway in a coal mine, caused by shifting strata. It will be repaired manually.
clinic than would be expected from their numbers in the population. Either it is more difficult to work underground with a painful back than in other environments, or heavy manual work increases the risk of acute or chronic back pain. The risk would appear to be selective, however, when considering the three defined back pain syndromes. The miner is at no greater risk of presenting with the symptoms of disc protrusion. He is, however, more likely to complain of those syndromes associated with degenerative change-lateral canal and central canal stenosis (RE and NC)-and to require decompressive surgery for these degenerative conditions, The incidence of miners attending hospital with disc symptoms was less than the percentage of miners in the
198
C/in. Biomech. 1987; 2: No 4
population, and the proportion of miners amongst those patients admitted with disc symptoms was significantly less (P < 0401). Few of these, however, failed to respond to conservative treatment. In fact, it was the dearth of miners requiring surgical disc excision that prompted this study. Although the miner subjects his spine to greater loads than many others in the population, he appears to be protected from the disabling effects of disc protrusion. There is no evidence that his genetic stock is different to other workers. It is possible that the low incidence of disabling disc symptoms is the result of self-selection; men with vulnerable discs having left the industry early. But then it is difficult to explain why the same self-selection did not reduce the incidence of other back pain syndromes. There are two alternative explanations. Either a miner has less annular damage because of strong muscles and efficient protective reflexes, or he is equally prone to disruption of a disc, but is able to contain it more effectively. Heavy manual work in early life may strengthen the spinal ligaments, and possibly the peripheral annulus, thus restraining the disc nucleus from encroaching into the vertebral canal. A similar protrusion in a sedentary worker could extrude into the vertebral canal unprotected by a weak peripheral annulus. If this concept is correct, we should identify and encourage activities which in early life develop annular and ligamentous strength. Unfit workers should not be deployed to areas of heavy load-handling. We may also need to modify advice about light work after the first disc symptoms and instead encourage a graduated return to work and recommend activities which strengthen the spine. References 1 Matthews J. J Agric Eng Res 1964; 9: 3
2
3 4
5 6
7
8 9
10 1I
12
13 14
15
16
Troup JDG. The function of the lumbar spine. PhD Thesis. University of London, 1968 Cust G, Pearson JCG, Mair A. The prevalence of low back pain in nurses. Int Nursing Rev 1972; 19: 169-79 Chaffin DN. Parks KS. A longitudinal study of low back pain as associated with occupational weight lifting factors. Am Indust Hyg Assoc J 1973; 34: 513-23 Aliawi A. PhD Thesis, University of London, 1978 Frymoyer JW. Pope MH, Clements JH, Wilder DG, MacPhearson B. Ashikaga T. Risk factors in low back pain. J Bone Joint Surg 1983; 65-A: 213-8 Kelsey JL. An epidemiological study of acute herniated lumbar intervertebral discs. Rheumatol Rehabil1975; 14: 144-59 McCulloch JA. Chemonucleolysis. J Bone Joint Surg 1977; 59-B: 45-52 Getty CJM, Johnson JR, Kirwan EOG, Sullivan MF. Partial undercutting facetectomy for bony entrapment of the lumbar nerve root. J Bone Joint Surg 1981; 63-B: 33&5 Porter RW, Hibbert C, Evans C. The natural history of root entrapment syndrome. Spine 1984; 9: 418-22 Verbiest H. A radicular syndrome from developmental narrowing of the lumbar vertebral canal. J Bone Joint Surg 1954; 36-B: 230-7 Ehni G. Significance of the small lumbar spinal canal cauda equina compression syndromes due to spondylosis. J Neurosurg 1969; 31: 490-4 Blau JN, Logue V. The natural history of intermittent claudication of the cauda equina. Brain 1978; 101: 211-22 Lloyd MH, Gauld S, Soutar CA. Epidemiological study of back pain in miners and office workers. Spine 1986. 11: 13-o MacDonald EB, Porter R, Hibbert C, Hart J. The relationship between spinal canal diameter and back pain in coal miners: ultrasonic measurements a screening test? J Occup Med 1984; 26: 23-8 Nachemson A. Work for all. Clin Orthop Rel Res 1983; 179: 77-85
1987; 2: 198-198
Printed in Great Britain
Does hard work prevent disc protrusion? Richard W Porter,
MD, FRCS
Doncaster Royal Infirmary, Doncaster, UK
Summary This study compares the prevalence of coal miners attending hospital with three defined back pain syndromes, with the number of miners in the working population. Of the men who attended hospital with back pain there were more miners than would be expected (2.78% of the miners compared with 1.99% of the non-miners). 0.32% of the miners had criteria of disc protrusion compared with 0.4% of non-miners; significantly more had syndromes associated with degenerative change. Relatively few men requiring disc excision were miners, whilst there were many who had decompressive surgery. This is compatible with the concept that heavy manual work strengthens the spine, restraining encroachment of a disc protrusion into the vertebral canal.
Relevance These findings suggest a need to identify and encourage activities in early life which may develop annular and ligamentous strength. Furthermore, unfit workers should not be deployed to areas of heavy work and we should re-examine advice about light work after the first disc protrusions. $?‘trds:
Disc prctrusicn, Work. Epidemiology, Surgery, Degenerative change, Spine, Backpain,
Introduction
There is conflicting evidence about the relationship between heavy manual work and the incidence of back pain. Most studies suggest that back pain is related to heavy load handling but Kelsey’ found a high incidence of disc herniation amongst sedentary workers. In an attempt to determine whether heavy manual work reduces the risk of symptoms from disc herniation, this paper examines the prevalence of coal miners presenting with various back pain syndromes, comparing this with the percentage of miners in the population.
Method
Men attending a back pain clinic over a 3-year period were asked if they had been underground coal miners from leaving school, or had worked underground for at least 5 years. The percentage of these miners fulfilling criteria for three defined back pain syndromes was then recorded.
Submitted: 24 April 1987. In revised form: 3 July 1987. Correspondence and reprint requests to: Mr R W Porter. Department of Orthopaedics, Doncaster Royal Infirmary, Doncaster DN2 SLT,
UK.
I. Lower lumbar disc lesion (PID). Three or more of the criteria described by McCulloch’: unilateral leg pain in a typical sciatic root distribution below the knee; specific neurological symptoms incriminating a single nerve; limited straight leg raising by at least 50% of normal; at least two neurological changes of muscle wasting, muscle weakness, sensory change or hyporeflexia; and radiculographic evidence of disc protrusion. 2. Root entrapment syndrome (RE)-lateral canal stenosis. Pain in the leg below the knee incriminating a single root, severe and constant, unrelieved by rest, spinal extension less than a third of normal range, straight leg raising better than 70 degrees, over 40 years of age and radiological evidence of degenerative change’.“‘. 3. Neurogenic ciaudication (NC). Discomfort in both legs above and below the knees when walking with less than 500 metres tolerance, relieved by rest, and a positive myelogram or CT scan showing central canal stenosis. The percentage of miners of the total men admitted for bed rest, whose symptomatic disc lesion had not settled at home was recorded, and also the percentage of miners of the men requiring surgical disc excision, and surgical decompression for central or root canal stenosis”-‘“.
Porter: Does hard work prevent disc protrusion?
197
Table 1. Number of miners and non-miners in the Doncaster population, attending the back pain clinic, with three defined back pain syndromes and ‘other causes’, expressed as a percentage of miners and non-miners in the population Doncaster workers Miners Non-miners
16,000 49,100
Back pain clinic
445 (2.78%) 977 (1.99%) x2=33*4 P
PID
R.E.
N. C.
Other
52 (0.32%) 198 (0.40%) x2=14.9 P
93 (0.58%) 152 (0.31%) x2=6-9 P
35 (0.22%) 21 (0.04%) x2=26.4 P-CO-001
265 (1.65%) 606 (1.23%) n.s.
Chi muare tests between miners and non-miners performed on contingency tables for each diagnosis v all other
patients)
Results The collieries in the catchment area of Doncaster Royal Infirmary employed 16,000 miners in the period under review. In the same catchment area there were 65,100 working men between 20 and 60 years of age, 24.6% of whom were miners. Four hundred and forty-five miners attended the back pain clinic over a 3-year period (2.78% of the miners in the population) compared with 977 nonminers (1.99% of the non-miners in the population). Only 0.32% of the miners in the population attended with criteria of symptomatic disc protrusion, compared with 0.40% of non-miners. The Chi-square (x2) test showed significant differences P < 0.001. Proportionately more miners however attended with root entrapment syndrome and neurogenic claudication than did other men in the population (Table 1). There were 869 men with ‘other causes’ of back pain, including some with more than one of the three defined syndromes, comprising 1.65% of the mining population, and 1.23% of the non-miners. One hundred and three men were admitted with symptomatic disc protrusion; 70 settled with bed rest, and 33 required surgery (Table 2). The proportion of the mining population having symptoms which settled with bed rest in hospital was 0*06%, compared with 0.12% of the non-mining population, whilst 0.02% of the mining population required discectomy compared with 0.06% of the non-miners. There were, however, many miners requiring decompressive surgery for central or root stenosis.
Discussion
Mechanisation of coal mines has largely relegated the pick and shovel to a previous era, but the fluid nature of underground strata and its effects on the roadways, the need to transport equipment to and from the coal face and the unpredictable failure of machinery in confined spaces, still subjects the miner’s spine to large mechanical forces (Figure 1). It is not surprising that musculoskeletal disorders are the largest cause of absenteeism in the coal mining industry. The most significant of these is low back pain14, which is responsible for up to 18% of sickness absence in some British coalfields”. Understandably, more miners attend the back pain
Table 2. Numbers of miners and non-miners in who required hospital bed rest and discectomy, expressed as a percentage of miners and non-miners in the population Admitted for bed rest and symptoms settled without surgery Miners Non-miners
IO (0.06%) 60 (0.12%) x2=0.55
Required surgery 3 (0.02%) 30 (0.06%) P=n.s.
Figure 1. A damaged underground roadway in a coal mine, caused by shifting strata. It will be repaired manually.
clinic than would be expected from their numbers in the population. Either it is more difficult to work underground with a painful back than in other environments, or heavy manual work increases the risk of acute or chronic back pain. The risk would appear to be selective, however, when considering the three defined back pain syndromes. The miner is at no greater risk of presenting with the symptoms of disc protrusion. He is, however, more likely to complain of those syndromes associated with degenerative change-lateral canal and central canal stenosis (RE and NC)-and to require decompressive surgery for these degenerative conditions, The incidence of miners attending hospital with disc symptoms was less than the percentage of miners in the
198
C/in. Biomech. 1987; 2: No 4
population, and the proportion of miners amongst those patients admitted with disc symptoms was significantly less (P < 0401). Few of these, however, failed to respond to conservative treatment. In fact, it was the dearth of miners requiring surgical disc excision that prompted this study. Although the miner subjects his spine to greater loads than many others in the population, he appears to be protected from the disabling effects of disc protrusion. There is no evidence that his genetic stock is different to other workers. It is possible that the low incidence of disabling disc symptoms is the result of self-selection; men with vulnerable discs having left the industry early. But then it is difficult to explain why the same self-selection did not reduce the incidence of other back pain syndromes. There are two alternative explanations. Either a miner has less annular damage because of strong muscles and efficient protective reflexes, or he is equally prone to disruption of a disc, but is able to contain it more effectively. Heavy manual work in early life may strengthen the spinal ligaments, and possibly the peripheral annulus, thus restraining the disc nucleus from encroaching into the vertebral canal. A similar protrusion in a sedentary worker could extrude into the vertebral canal unprotected by a weak peripheral annulus. If this concept is correct, we should identify and encourage activities which in early life develop annular and ligamentous strength. Unfit workers should not be deployed to areas of heavy load-handling. We may also need to modify advice about light work after the first disc symptoms and instead encourage a graduated return to work and recommend activities which strengthen the spine. References 1 Matthews J. J Agric Eng Res 1964; 9: 3
2
3 4
5 6
7
8 9
10 1I
12
13 14
15
16
Troup JDG. The function of the lumbar spine. PhD Thesis. University of London, 1968 Cust G, Pearson JCG, Mair A. The prevalence of low back pain in nurses. Int Nursing Rev 1972; 19: 169-79 Chaffin DN. Parks KS. A longitudinal study of low back pain as associated with occupational weight lifting factors. Am Indust Hyg Assoc J 1973; 34: 513-23 Aliawi A. PhD Thesis, University of London, 1978 Frymoyer JW. Pope MH, Clements JH, Wilder DG, MacPhearson B. Ashikaga T. Risk factors in low back pain. J Bone Joint Surg 1983; 65-A: 213-8 Kelsey JL. An epidemiological study of acute herniated lumbar intervertebral discs. Rheumatol Rehabil1975; 14: 144-59 McCulloch JA. Chemonucleolysis. J Bone Joint Surg 1977; 59-B: 45-52 Getty CJM, Johnson JR, Kirwan EOG, Sullivan MF. Partial undercutting facetectomy for bony entrapment of the lumbar nerve root. J Bone Joint Surg 1981; 63-B: 33&5 Porter RW, Hibbert C, Evans C. The natural history of root entrapment syndrome. Spine 1984; 9: 418-22 Verbiest H. A radicular syndrome from developmental narrowing of the lumbar vertebral canal. J Bone Joint Surg 1954; 36-B: 230-7 Ehni G. Significance of the small lumbar spinal canal cauda equina compression syndromes due to spondylosis. J Neurosurg 1969; 31: 490-4 Blau JN, Logue V. The natural history of intermittent claudication of the cauda equina. Brain 1978; 101: 211-22 Lloyd MH, Gauld S, Soutar CA. Epidemiological study of back pain in miners and office workers. Spine 1986. 11: 13-o MacDonald EB, Porter R, Hibbert C, Hart J. The relationship between spinal canal diameter and back pain in coal miners: ultrasonic measurements a screening test? J Occup Med 1984; 26: 23-8 Nachemson A. Work for all. Clin Orthop Rel Res 1983; 179: 77-85