|Abstract / Summary
Bone grafting is important in the revision of failed total joint replacements. However the clinical results on revisions still do not match those of the primary inserted arthroplasties. Histological examinations of impacted bone in revision surgery often show incomplete incorporation and significant subsidence of the prosthesis is often seen. One aim of the thesis was to investigate if bone growth factor osteogenic protein-1 (OP-1) or platelet rich plasma (PRP) increases fixation and bone incorporation of bone allografted implants.
Bone allograft, especially fresh frozen, is associated with a number of potential disadvantages and risks however. Risks of viral transmission, bacterial contamination and insufficient supply might limit the use of bone allograft. Different processing techniques almost eliminate the risk of viral transmission or bacterial contamination. Substitutes such as granular ceramics might replace or expand the volume of bone allograft in the future.
The thesis is based on five experimental in vivo studies in canines. In all studies, we used nonloaded, stable, hydroxyapatite (HA) coated implants surrounded by a gap. Observation time was three weeks. Evaluation was based on histomorphometry and mechanical push-out tests.
In study I and II we examined the effect of recombinant human OP-1 in combination with bone allograft, HA granules or a composite of those. We showed, that OP-1 not only stimulates bone formation but also accelerated bone graft resorption dramatically. As a consequence, OP-1 did not increase fixation of bone allografted implants. Since ProOsteon is very slowly resorbed, OP-1 enhanced mechanical stability of implants grafted with HA granules.
In study III we investigated the influence of OP-1 on the mechanical properties of bone allograft and HA-granules after three weeks. OP-1 increased all mechanical parameters of bone allograft and HA-granules.
In study IV and V we focused on platelet rich plasma (PRP) as a source of growth factor. We found no effect of PRP alone or in combination with bone allograft. We found no influence of processing by defatting, irradiation and freeze drying on the incorporation of impacted bone allograft.