Pre-Coated Orthopedic Implants with Bone Cement

Abstract

A 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 sandblasted steel rod with pre-coating were implanted into canine femurs in vitro and in vivo to evaluate the interfacial shear strengths in addition to the bench test. After serial sectioning the samples in discs, push-out tests were made to evaluate the interfacial strengths of cement-bone-implant. 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 for in vitro (1.17 MPa) and in vivo (1.68 MPa). The shear strength of rod/cement interface increased substantially by sandblasting (6.84 MPa). The microscopic observation of the interface showed somewhat smaller gaps developed for the pre-coated rod than the uncoated rod due to the shrinkage effect. In addition to the overall increase in interfacial strength, the pre-coating 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 believed to be advantageous over conventional cement fixation method.