[The structural changes of cortical bone beneath plate after rigid platefixation and removal]

We investigated the structural changes of bone under the plate after plate fixation and removal. Twenty-four New Zealand white rabbits were plated on their intact left tibiae with stainless steel plates and 4 animals served as controls. The plates were removed 2 months after implantation in 20 plated animals, of which, 4 were sacrificed immediately after plate removal and the other were killed in successive groups of 4 each at 1, 2, 3 and 4 months after plate removal respectively. The remaining 4 plated animals were killed at 6 months after implantation. Bone samples were harvested and prepared for scanning microscopic observation. Internal fixation with a rigid plate may lead not only to osteopenia of the cortex under the plate, but also to disorganization of the cortex, in which the mineral column and collagen fibers were oriented in a randomized pattern. The regional osteoporosis could recover gradually after removal of the rigid plate. However, the restoration of normal bone structure occurred later than that of the bone mass. Delayed restoration of bone structure might be one of the potential causes of refracture of the plated bone.