EPIDEMIOLOGY

Epidemiology

A number of environmental and inherent factors thought to influence the development of sciatica have been studied, including gender, body habitus, parity, age, genetic factors, occupation, and environmental factors (Table 1).

A cross-sectional study of 2946 women and 2727 men showed neither gender nor body mass had an influence on the development of sciatica, although body mass may have been associated with low back pain.46 Body height may be a risk factor for sciatica, although this appears to be significant only in males in the 50–64 yr age group. Parity of up to six also has been identified as having no association with sciatica.46 – 48 The incidence of sciatica is related to age. Rarely seen before the age of 20, incidence peaks in the fifth decade and declines thereafter.35 This age distribution was also observed in those presenting for lumbar disc herniation surgery.98 The odds ratio (OR) of an episode of sciatica increased by 1.4 for every additional 10 yr of age, up to the age of 64.46 Interestingly, the site of disc herniation appears to change with age. Although the majority of disc herniations occur at the L4/5 or L5/S1 level, with advancing age, there appears to be a relatively increased incidence of herniation at the L3/4 or even L2/3 level.36

A genetic link with sciatica was first reported in a juvenile population.108 This has also been observed in the

adult population, where both retro- and prospective observational studies identified a higher incidence of sciatica or prolapsed disc among first-degree relatives than controls in a population of patients presenting for surgery on herniated lumbar discs.69 96 A study of 9365 pairs of adult twins identified the lifetime incidence of sciatica inmonozygotic and dizygotic twins as 17.7% and 12%, respectively. The estimated heritability was 20.8% for those reporting sciatica and 10.6% for those admitted to hospital with sciatica.45

Recreational activities, such as walking and jogging, may influence incidence of sciatica. Regular walking was

shown to almost double the incidence of sciatica in a group of 2077 workers who were pain free at baseline.

This study also showed that jogging had a dual effect on the incidence of sciatica. Although joggers who were pain free at baseline had a decreased incidence of sciatica, those with a previous history of sciatica were more likely to experience more episodes.73

Physical activity associated with occupation has also been shown to influence incidence of sciatica. Carpenters

(OR 1.7) and machine operators (OR 1.6) were shown to be more likely to develop sciatica than sedentary office

workers.88 89 Retired (OR 0.15) or part-time (OR 0.16) farmers were less likely to develop sciatica than full-time

ones.68 Risk factors identified for sciatica associated with occupation included awkward working position, working in a flexed or twisted trunk position (OR 2.6),73 or with the hand above the shoulder. Driving is also positively associated with sciatica or lumbar disc herniation.47 60 It is possible that driving causes exposure to vibration at around 4–5 Hz which may coincide with resonant frequency of the spine in the seated position and so leading to a direct mechanical effect on the lumbar disc.35 Smoking has been linked with sciatica35 and several hypotheses, such as tobacco disturbing the metabolic balance of intervertebral discs, coughing causing marked elevations of intra-disc pressures, or a possible fibrinolytic effect of tobacco, have been proposed. An analysis of eight studies of smoking and sciatica revealed a positive correlation in only four of eight studies in men and one of five studies in women. Although there was a weak association between smoking and sciatica, these studies were cross-sectional and it was impossible to say that smoking preceded the sciatica.39

CAUSES OF SCIATICA:

Disc herniation or degree of nerve root impingement

Impingement of the intervertebral disc on lumbar nerve

Roots Malignancy causing compression along the extra-spinal course of the sciatic nerve was noted in 32 cases of sciatica, which was constant, progressive, and

unresponsive to bed rest.

Eighteen of the cases were due to malignant tumours (six, metastatic; five, primary bone sarcoma; and seven, soft tissue sarcoma).

Two were tumours of the sciatic nerve itself.

Other rare malignant causes of sciatica include haemangioblastoma on a sacral root50 and lung adenocarcinoma metastasis in the pelvis

REFERENCE:

1)Hermier M, Cotton F, Saint-Pierre G, et al. Myelopathy and sciatica induced by an extradural S1 root haemangioblastoma. Neuroradiology 2002; 44: 494–8

2)Thomas E, Abiad L, Cyteval C, et al. Metastatic pudendal nerve compression presenting as atypical sciatica. J Spinal Disord Tech 2002; 15: 324–5

A 10 yr observational study of 280 patients, hospitalized with sciatica and confirmed disc herniation, showed that most patients with sciatica could recall an episode of low back pain in their 20s, usually provoked by trauma.

Radicular symptoms usually appeared approximately 10 yr later, after an episode of low back pain lasting days

to weeks, usually without a definite precipitating factor. This led to a peak onset of sciatica occurring around the age of 40.112

REFERENCE: Weber H. Lumbar disc herniation: a controlled, prospective study with ten years of observation. Spine 1983; 8: 131–40 113

Conclusion

Sciatica is a common condition that is a major cause of work absenteeism and a major financial burden to both

industry and health service provision. Although the intervertebral disc has been firmly implicated in the pathophysiology of this condition, the exact nature of the relationship to disc, nerve, and pain is not yet certain.

Current evidence suggests that the nucleus pulposus provokes a strong inflammatory response in sciatic nerve

roots and this is a likely source of pain. Evidence also exists which suggests that inflammation, abnormal

immune factors, and mechanical deformation of the nerve is required to produce pain, and this seems a likely combination. However, herniation of the nucleus pulposus is not the only cause of sciatica and other causes should not be forgotten. Fortunately, most cases of sciatica are self-limiting and pain tends to resolve within a matter of months. However, some cases progress to become chronic,and unfortunately, these can be difficult to treat.

Reference: Sciatica: a review of history, epidemiology, pathogenesis, and the

role of epidural steroid injection in management British Journal of Anaesthesia 99 (4): 461–73 (2007)

The physical demands of the work tasks were defined as follows: general physical strenuousness of work involved tasks

such as lifting or carrying heavy objects, excavating, digging, and pushing. Handling of heavy objects meant lifting, manually

carrying or pushing objects heavier than 20 kg on average at least 10 times per work day.