A cybernetic approach to osteoporosis in anorexia nervosa

A group of 25 female individuals, who had been admitted to the University Hospital with the diagnosis of anorexia nervosa (AN) 3 to 10 years before, was seen for a follow-up visit in the hospital. These women got a psychiatric exploration to detect a present eating disorder. Moreover, parameters of the muskuloskeletal interaction were determined on the non-dominant forearm. Bone mineral content (BMC) of the radius was measured by pQCT and maximal grip force was evaluated by the use of a dynamometer. Eating disorders were present in 12 females. The mean of BMC standard deviation (SD) score was significantly reduced in comparison with reference values. Furthermore, the mean of BMC SD score was also significantly lower than the mean of grip force in SD score. These results gave the suggestion that the adaptation of bone mass to biomechanical forces is disturbed in AN. The linear regression analyses between the parameters grip force and BMC were compared between the study and the reference group. The comparison delivered a significantly lower constant in the regression equation of the study group. This result can be interpreted on the background of the mechanostat theory. The affection with an eating disorder decreases the set point in the feedback loop of bone modeling. The results offer for the first time the possibility to analyse osteoporosis in anorexic females under the paradigm of muskuloskeletal interaction.