Abstract
The use of prostheses with porous surfaces in cementless total hip arthroplasty now predominates. Beads are popular for use as a porous coating, but their mechanical strength may be insufficient because of displacement of some of the beads from the coating. In this study, we propose a new porous surface, created by making direct holes in the metal surface using a YAG laser. A titanium-alloy (Ti-6Al-4V) rod was used. A Bead-type prosthesis was made by diffusion bonding pure titanium beads to the rod; it was 5 mm in diameter and 35% in porosity. A Laser type was made by directly creating holes in the same rod surface using a YAG laser; it was 5 mm in diameter and 33.7% in porosity. Both implants were evaluated in vivo using the hemitranscortical cylindrical model in two beagle dogs. Four prostheses were implanted into each femur through the lateral cortex, for a total of eight of each type, and remained in place for 12 weeks. Except for the proximal implant, push-out tests were performed to measure the shear strength of fixation of the implants to the cortical bone. For observations of the implant-bone interface, decalcified specimens of the proximal femur were stained with toluidine blue and observed with an optical microscope. The mean push-out strength of the Laser type was approximately 10.2 MPa and that of the Beads type was approximately 10.7 MPa. There was no significant difference in interface push-out strength between the groups. Bone ingrowth into both types was sufficient, however, some specimens of the Beads type demonstrated displacement of some of the beads from the rod surface. This study indicates that a porous surface created with a YAG laser might be useful not only for its shear strength, but also for the strength of the surface itself.
The abstracts were prepared by Nico Verdonschot. Correspondence should be addressed to him at Orthopaedic Research Laboratory, University Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
