Intramedullary fixation of implants pre-coated with bone cement: a preliminary study

A preliminary study on the feasibility of implants pre-coated with an acrylic bone cement has been performed. Four types of implants, an actual canine femoral prosthesis, a polished steel rod (0.49 cm dia. x 13 cm long) with and without pre-coating, and a sand-blasted steel rod with pre-coating were implanted into canine femurs in vitro to evaluate the interfacial shear strengths. After serial sectioning the samples in discs, push-out tests were made. The weakest interfacial shear strength was exhibited by the polished rod/cement interface (0.5 MPa) while the strongest was the "old" and "new" cement interface (23.4 MPa). The bone/cement interfacial strength was in between (1.17 MPa). The shear strength of rod/cement interface increased substantially by sand-blasting (6.84 MPa or 585% increase). The proposed method increases the modified implant's interfacial shear strength by 337% (from 1.17 to 3.84 MPa) over the conventional implants. It may furthermore reduce the setting temperature, the shrinkage, and the amount of monomer released during operation due to the reduced amount of cement at the time of implantation. The more gradual transmission of load from implant to bone and "auto-centering" of implants during operation by pre-coating, are thought to be advantageous over conventional cement fixation method.