Hand workload and the metacarpal cortical index. A study of middle-aged teachers and dentists

We studied load-related predictors (handedness, occupation and workload history) of cortical bone mass as estimated by the metacarpal cortical index (MCI). After being randomly selected from trade-union registers, 295 female dentists and 248 teachers, aged 45–63 years (mean 54 years), participated in the study. The MCI was defined from the second metacarpal of both hands by analogue radiographs. Data regarding anthropometric measures, handedness, occupational exposure, number of pregnancies, hormonal therapy and contraceptive use, the presence of chronic diseases, dietary factors, smoking and leisure time physical activity were collected by questionnaire. Weight was measured. The dentists’ workload was assessed in detail in 10-year periods. Multivariate methods were used in the statistical analysis. The metacarpal index averaged 0.62 in the right hand and 0.61 in the left hand (P=0.02) among the right-handed subjects, while no differences by hand were observed among the left-handed or mixed-handed. The MCI of the teachers and dentists did not differ from each other, when we controlled for potential confounders. The MCI decreased similarly by age in both occupational groups. Among the dentists, workload history was inversely associated with the MCI in multivariate analyses by age group. Computer use was a positive predictor for MCI among dentists aged 55–63 years. Occupational factors seem to have contradictory effects on the MCI. Too heavy or one-sided manual work may be deleterious for cortical bone mass.