The Journal of Bone and Joint Surgery, Vol 70, Issue 2 160-172, Copyright © 1988 by Journal of Bone and Joint Surgery, Inc
Comparison of replacement prostheses for segmental defects of bone. Different porous coatings for extracortical fixation
Y Okada, T Suka, FH Sim, JP Gorski and EY Chao
Department of Orthopedics, Mayo Clinic, Rochester, Minnesota 55905.
The extent of extracortical bone-bridging and ingrowth into porous-coated
prostheses for the stabilization of segmental defects was studied in a
canine model. Initial fixation of the implant was achieved using bone
cement. Autogenous bone grafts were applied over the porous-coated
segmental portion of the prosthesis to stimulate the ingrowth and formation
of bone. At twelve weeks, bone-bridging and ingrowth occurred uniformly in
both the titanium fibermesh and the cobalt-chromium-molybdenum beaded
prostheses. Maximum formation of osseous tissue over the implants occurred
at two to four weeks. More bone formed in the posterior aspect of the
prosthesis. At twelve weeks, 26 per cent of the porous space of the
titanium fibermesh prosthesis and 47 per cent of the porous space of the
cobalt-chromium-molybdenum beaded prosthesis were filled with bone. The
torsional strength and stiffness of the prosthetic midsection that
contained a conical coupling joint were increased significantly due to
bone-bridging and ingrowth. The cortical bone that was apposed to the
segmental prosthesis showed an increase in porosity. The use of bone cement
did not appear to impede new-bone formation extracortically. The initial
stability of the implant and the application of sufficient autogenous bone
grafts are two important factors that contribute to the ultimate stable
fixation of an implant by extracortical bone formation.