The engineering and biology of femoral impaction grafting
Femoral impaction grafting is a technique where bone graft is impacted into the femur prior to cementing a stem in place. The technique is designed to compensate for bone stock loss in revision surgery, however it has associated problems of implant movement / subsidence and periprosthetic fractures. The hypothesis for this thesis was that the stability and remodelling of impaction grafting could be improved, either by changing the graft size or by adding a synthetic graft. To quantify the technique of impaction grafting the Exeter slap hammer was modified, enabling force readings to be measured in nine surgical cases with four different surgeons. The results found that the average force that travels through the impactor is 1.8 to 8.4 kN, which is equivalent to three to eleven times body weight. These readings were used in the subsequent studies to replicate the current technique. It was hypothesised that varying the graft size might alter the porosity, strength and remodelling of impacted graft. Three graft groups were studied Small, Large and a Graded mix. The results found that the impacted Large graft had higher porosity and lower axial stiffness than the Small and Graded Graft. A noted reduction in graft density was found after six weeks in-vivo compared with twelve, irrespective of graft type. Since density can be related to mechanical strength this led to the question: Could the inclusion of a synthetic bone graft improve the mechanical properties of remodelling graft A 50:50 mix of allograft and BoneSave was compared with allograft. No difference in stiffness was found between the groups after six and twelve weeks remodelling. These studies were carried out using small test samples either in the laboratory or in- vivo. In order to determine if synthetic graft extenders could be used clinically tests in more realistic models were undertaken. Mechanical analysis was conducted on the 50 % inclusion of two graft extenders with allograft, namely: BoneSave and Appapore-60. The results of both projects showed a positive result.