Atrophy of cortical bone caused by rigid internal fixation plates. An experimental study in the dog.

The cortical atrophy induced by a rigid internal fixation plate on diaphyseal bone was studied on the femora of seven dogs. When the plate, which had been in position for 7 months without previous osteotomy, was removed, a pronounced reduction of the cortical bone was observed in the previously plated section of the diaphyseal bone. The atrophy took the form of loss of cortical bone mainly caused by endosteal resorption with enlargement of the medullary cavity. Neither periosteal resorption nor formation of woven bone under the site of the plate were observed. The process of adaption to the changed stress and strain conditions, caused by the mechanical joint, i.e., implants and bone, was studied by means of a histological technique, and was still in progress after a period of seven months.