THE REACTION TO NAILING OR CEMENTING OF THE FEMUR IN RATS - A MICROANGIOGRAPHIC AND FLUORESCENCE STUDY

Bone reaction to cement and to a cementless stem was studied in the ra t femur with histological fluorescence and microangiographic technique s. Periosteal and endosteal apposition, and consequent remodelling, ap peared as a reaction to reaming rather than caused by cement or a ceme ntless stem. Every change in bone began with proliferation, progressio n and orientation of the vessels. Endosteal apposition was absent in c emented femurs because the entire medulla was occupied by the acrylic cement, but remodelling of the subendosteal cortex followed medullary revascularisation which was far advanced after 90 days. In cementless stems, endosteal apposition of primary woven bone and remodelling was the basis for bony ingrowth and anchorage through bony bridges. Our re sults suggest that the pattern of blood supply is relevant to the stru ctural organisation of mature lamellar bone around the implant. Cement ed stems have maximum anchorage and stability as soon as they are inse rted, bur this decreases with rime as revascularisation occurs. Cement less stems can reach maximum integration later after insertion, and re vascularisation is less critical because they usually do not fill the canal completely.