Changes in calcium and hydroxyproline content of cortical bone after compression and neutral plate fixation

Calcium and hydroxyproline content of intact rabbit tibio-fibular bone was assay chemically 1 day to 36 weeks after compression and neutral plate fixation with a 4-hole stainless steel ASIF/DCP plate. During the first three postoperative weeks calcium content of the cortical bone decreased by an almost significant amount (P less than 0.05); thereafter, calcium values remained subnormal but did not differ significantly from initial postoperative values. Hydroxyproline content increased steadily throughout the experiment (P less than 0.001). The changes in chemical composition of the bone were of the same magnitude after compression and neutral plate fixation. The results suggest that the cancellous transformation of cortical bone, known to take place under rigid plates, reflects an active remodelling process of the bone in which the calcium and hydroxyproline content changes only slightly.