Densification of cancellous bone with autologous particles can enhance the primary stability of uncemented implants by increasing the interface friction coefficient.

Sufficient primary stability is one of the most important prerequisites for successful osseointegration of cementless implants. Bone grafts, densification and compaction methods have proven clinically successful, but the related effects and causes have not been systematically investigated. Postoperatively, the frictional properties of the bone-implant interface determine the amount of tolerable shear stress. Frictional properties of different implant surfaces have been widely studied. Less attention has been paid to the influence of host bone modifications. The purpose of this study was to investigate the influence of densification of cancellous bone with bone particles on the interface friction coefficient. Cancellous bone samples from femoral heads were densified with bone particles obtained during sample preparation. The densification was quantified using micro-Ct. Friction coefficients of the densified and paired native samples were determined. Densification increased the BV/TV in the first two millimeters of the bone samples by 10.5 ± 2.7% to 30.5 ± 2.7% (p < 0.001). The static friction coefficient was increased by 10.5 ± 6.1% to 0.43 ± 0.03. The static friction coefficient increased with higher BV/TV of the bone interface, which is represented by the top 2 mm of the bone. The increase in contact area, intertrabecular anchorage and particle bracing could be responsible for the increase in friction. Optimization of particle shape and size based on the patient's individual bone microstructure could further increase frictional resistance. Bone densification has the potential to improve the primary stability of uncemented implants.

Fatigue strength reduction of Ti-6Al-4V titanium alloy after contact with high-frequency cauterising instruments.

Contact of implants with high-frequency cauterising instruments has serious implications for patient safety. Studies have reported a possible direct connection of fatigue failure of Ti-6Al-4V implants with electrocautery contact. Such contacts were observed at the polished neck of titanium hip stems, which are subjected to high-tension loads. Evidence of electrocautery contact has also been found on a retrieved spinal fixator with a rough surface; however, no fatigue failure related to electrocautery contact has been reported thus far. The influence of the heat-affected zone caused by flashover on the mechanical behaviour of the Ti-6Al-4V titanium alloy is not yet fully understood. Then, the aim of this study was to investigate whether the polished areas of Ti-6Al-4V implants are especially susceptible to fatigue failure after electrocautery contact. Flashovers caused by electrocautery contact were induced on titanium specimens with different surface roughnesses. These specimens were subjected to cyclic loading in a four-point-bending test setup, which represented the stress resulting from physiological loading activities (~861 MPa). In this test setup, electrocautery contact was found to reduce the fatigue strength of the titanium alloy significantly-by up to 96%-as revealed from the median value of the cycles to failure. Cycles to failure showed a dependence on the flashover duration, with a flashover for 40 ms leading to fatigue fracture. Despite the lower fatigue strength of a rough polished surface in the undamaged state, it is less prone to the damaging effect of flashover than a smooth polished surface.