MICROCALLUS FORMATION IN CANCELLOUS BONE - AN IMPORTANT REPAIR MECHANISM

Microcallus formations are demonstrable in nearly all cancellous bones by means of suitable preparation techniques. Histologically, these st ructures are immature fibrous bone formed in local overloaded parts of the trabeculae. Using a preparation that allows combined two- and thr eedimensional analysis, 26 normal human spines and 11 osteoporotic spi nes were investigated for microcallus. Microcallus formations occur fr equently in people over 45 years of age. They are mainly localized in the lower thoracic and lumbar spine and occur significantly more frequ ent in females than in males. The number of microcallus formations dep ends more on the microarchitecture of the cancellous bone than on indi vidual trabecular parameters. In about 33% of cases microfractures are demonstrable in the centre of the microcallus formation. In noninvasi ve studies the bone mass could be misinterpreted due to microcallus. A lthough it indicates instability of the bone structure, microcallus fo rmation is not a purely negative mechanism. It stabilizes and regenera tes the bone tissue. Furthermore, complete new trabeculae can be forme d due to bridges of microcallus between residual trabeculae. Osteoporo sis is not the result of an inability to form microcallus.