Assessing the contribution of occupational activities to knee osteoarthritis presents several methodological difficulties. Nevertheless, a strong body of evidence has accumulated that the disease is more common in people who have carried out heavy physical work, and particularly in those whose work has entailed prolonged or repeated kneeling or squatting. The precise definition of occupational kneeling and squatting has varied between studies, but relative risks have often been two or higher.
It seems likely that the hazard arises from unusual mechanical stresses on the joint, and it is notable that the same occupational activities have also been linked with degenerative tears of the menisci. In addition, some occupations such as professional footballers carry a risk of acute meniscal injury which may later lead to osteoarthritis.
The challenge now is to translate these epidemiological observations into effective policies for the prevention of disease. In most developed countries, the requirement for heavy physical work has declined over recent decades as a consequence of increasing mechanisation. However, there are still many jobs that involve kneeling or squatting. Often, as for example in the construction industry, the work work environment is difficult to control and the hazardous tasks cannot easily be eliminated or substituted. Knee pads may be used to reduce discomfort and protect against pre-patellar bursitis, but as yet we have no evidence that they reduce the risk of osteoarthritis.
Another approach might be to identify individuals who are at unusually high risk from kneeling because of the concomitant presence of other risk factors. For example, in a recent case-control study, the interaction of occupational kneeling with obesity was approximately multiplicative. It follows that the absolute reduction in risk from avoidance of obesity would be greater in workers who have to kneel in their jobs. Where the combination of occupational kneeling with other risk factors leads to exceptionally high risk, there may even be a case for selectively excluding such individuals from certain jobs.
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