Abstract
Background
Bioresorbable materials offer the potential of developing fracture fixation plates with similar mechanical properties to bone thereby minimizing stress shielding and obviating the need for implant removal.
Aim
To determine the in vivo degradation profile of a novel phosphate glass fibre composite bioresorbable plate and effects on the underlying bone.
Methods
Twenty five NZW rabbits underwent application of the plate to the intact right tibia. They were divided into 5 groups corresponding to the time points from surgery to sacrifice −2, 6, 12, 26 and 52 weeks. Outcomes included radiographs, nanoCT imaging, scanning electron microscopy (SEM) and mechanical testing of the plated bone and the opposite unplated tibia at each time point.
Results
At sacrifice, plate integrity was retained up to 12 weeks with no evidence of macroscopic inflammation. The mean load to failure of the plated bones expressed as a percentage of the opposite unplated bones was 179, 174, 172 and 115% after implantation for 2, 6, 12 and 26 weeks respectively. The flexural stiffness of the plated bones expressed as a percentage of the opposite bones revealed a mean increase of 245, 317, 205 and 110% at 2, 6, 12 and 26 weeks respectively. Although radiographs did not reveal any evidence of structural changes in the bones, NanoCT and SEM analysis revealed early porosity and progressive thinning of the cortex beneath the implant. However, bone formation around the plate progressed up to 26 weeks with improved cross sectional area characteristics of the plated bone compared to the control bone.
Discussion
Cortical changes beneath the plate would indicate that stress shielding may occur even in plates with similar mechanical characteristics to bone. However, this is only one part of the adaptive response of the bone which overall maintains the mechanical properties of the plated bone.
