[Spontaneous formation of angiogenic woven bone within cancellous bones. Some observations on microfractures of...

Femoral heads removed for subcapital fracture of the femur were embedded in methacrylate. Contact roentgen films of slabs of 1--2 mm thickness were screened for aggregates of woven bone. A variety of form exceeding that seen by other methods was found, not only in association with isolated trabecula. The distribution was found to confirm earlier findings by Todd et al. (1972), Freeman et al. (1974) and Watson (1975). The aggregates were seen more frequently in porotic areas than in the trajectorial groups of trabecula in the femoral heads. Aggregates of typical shapes were also found in one hemipelvis and in a humeral head. In embedded specimens discontinuities were seen in some trabecula with aggregates and not in other elements. There was no evidence of cracks where aggregates were attached to the edges of bone plates. Some trabecula with aggregates were ground down to 100 micrometer for microradiography. Cracks of the underlying trabecula could be shown, but neither signs of resorption nor of formation or osteocyte activation could be found. Aggregates of woven bone within cancellous bone have been found in subchondral bone of experimental animals being impact loaded and in connection with discontinuities. They are found near areas bypassed by the transmission of loads, too, in osteoporosis beside the groups of pricipal trabecula, and without association with discontinuities. It is concluded, that aggregates of woven bone are the product of mesenchymal activation or some defect in the regulation of mesenchymal activity and associated with causes of bone atrophy rather than with specific mechanical conditions.