Abstract
Carpal tunnel syndrome is regarded as a “simple” compression neuropathy but the present debate regarding its aetiology and pathogenesis is complex. Both environmental and individual risk factors have been the focus of research and debate. In the environmental research arena occupational factors have been under most scrutiny, probably because the economic benefits for insurance organizations are a major issue. In this issue of the Journal of Hand Surgery there are four articles challenging our concept of the aetiology of, and risk factors for, carpal tunnel syndrome. Kamolz et al.’s study suggests that hand anthropometry is a risk factor for carpal tunnel syndrome. This is consistent with the probable biomechanical mechanisms of compression and provides a possible explanation for the high incidence of bilateral carpal tunnel syndrome.
The impact of individual risk factors is convincing and is endorsed by the large case-control study of Geoghegan et al. which has a data set of almost 17,000 individuals. They were able to verify and measure important risk factors, including rheumatoid arthritis and obesity. However, they could not confirm the previous reports that smoking was a risk factor for carpal tunnel syndrome: the odds ratio of 1.03 for smoking as a risk factor for carpal tunnel syndrome in this large case-control study implies a negative relationship. A negative finding must be distinguished from a non-positive finding as it indicates that there is no relationship between a risk factor and an outcome. By contrast, a non-positive study (usually a small study) does not demonstrate that there is no relationship between a risk factor and an outcome. Non-positive relationships were found for work practices and histopathological changes in the tenosynovium in carpal tunnel syndrome among men in the study by Pickering et al. Innovative and promising objective exposure indicators such as callosities and ingrained dirt in the hands were used and related to the histopathological findings. Power problems (few patients) may explain why no significant relationship between manual exposure and fibrous thickening of the tenosynovium was found. Dias et al. found that the job title of women of working age was not a risk factor for either the incidence or aggravation of carpal tunnel syndrome. Although a non-positive study, it emphasises that there is probably no occupation for women that is a risk factor for carpal tunnel syndrome, but it does not exclude the possibility of occupational risk factors within an occupation (Rossignol et al., 1997). Thus the study demonstrates that it is important for the practising surgeon to obtain an occupational history, and not just record job title when investigating possible occupational causation/aggravation. Work tasks have to be specified and assessed by their intensity, duration and repetition (Hagberg, 2002). Such detailed exposure assessments to suggest that reducing the duration, frequency or intensity of exposure to forceful repetitive work, extreme wrist postures and vibration is likely to result in a reduction in the incidence or severity of carpal tunnel syndrome in working populations (Viikari-Juntura and Silverstein (1999)).
Attempts to balance the skewed publication of only positive findings (statistically significant) must be supported in order to improve science. The publication of non-positive findings in this issue shows the scientific excellence of the Journal of Hand Surgery.