[Micro-callus formation of spongiosa. An up to now underestimated repair mechanism of the skeletal system].

Microcallus formations are demonstrable in nearly all cancellous bones by means of suitable preparation techniques. Histologically, these structures are immature fibrous bone formed in local overloaded parts of the trabeculae. Using a preparation technique that allows combined two- and three-dimensional analysis, 26 normal human spines and 11 osteoporotic spines were investigated for microcallus. Microcallus formations occur frequently in people over 45 years of age. They are mainly localized in the lower thoracic and lumbar spine and occur significantly more frequent in females than in males. The number of microcallus formations depends more on the microarchitecture of the cancellous bone than on individual trabecular parameters. In about 33% of cases microfractures are demonstrable in the centre of the microcallus formation. In non-invasive studies the bone mass could be misinterpreted due to microcallus. Although it indicates instability of the bone structure, microcallus formation is not a purely negative mechanism. It stabilizes and regenerates the bone tissue. Furthermore, complete new trabeculae can be formed due to bridges of microcallus between residual trabeculae. Osteoporosis is not the result of an inability to form microcallus.