Introduction: Wear particle induced osteolysis is one of the main reasons for revision total hip replacements (THRs). Loss in bone stock as a result of aseptic loosening is responsible for inferior results in revision THRs. Results from impaction grafting to fill osteolytic defects are frequently inconsistent. Our hypothesis is that the combination of autologous mesenchymal stem cells (MSCs) and allograft will enhance bone regeneration. This study asks whether: MSCs with allograft scaffolds survive at a normal impaction force during revision THRs.

Method: MSCs were isolated from a sheep iliac crest aspirate, expanded in culture and seeded onto irradiated sheep allografts (n=9). Viability of MSCs was assayed with alamar blue with absorbance measured on day 4 (before impaction). The constructs were then impacted using forces 3, 6, and 9 kN extrapolated in surgery then assayed daily for 6 days. The control was 0 kN. Samples were resin embedded after 10 days for histology and pieces of graft were taken for scanning electron microscopy (SEM).

Results: The 0KN control shows an MSC growth curve with a lag period and log phase. Compared with the control, the 3 and 6 kN showed initial reduction in cell proliferation measured by alamar blue (^p=0.015, ^p=0.002) but recovered by day 8, while 9kN showed a significant reduction (^p=0.011) over the time (Figure 1).

For cell proliferation over time, 3 and 6 kN showed no differences, but 9 kN showed a significant difference between day 4 and day 8 (^p=0.031). SEM and histological analysis showed a network of cuboidal cells on the allograft surface.

Conclusions: The results showed that MSCs recovered from impaction of 3 and 6 kN after an initial reduction in metabolism and exceeded original cell seeding densities with no significant difference in proliferation. Viability of MSCs were not effected by impaction forces up to 6 kN. This study shows that stem cells mixed with allograft are a potential method for repairing bone defects in revision total hip replacements.

Introduction: To investigate the head/neck interface of total hip replacements and to see whether the use of small spigots (minispigots) results in enhanced wear and corrosion of tapers compared to standard spigots and the influence of the surface finish on this.

Methods: In the total hip replacement combinations the heads were made of cobalt-chrome (CoCr) and the stems of titanium alloy (Ti). Firstly wear and corrosion of minisigots were compared with standard spigots (Test 1) and secondly, these minispigots were compared with another minispigot with a smoother taper surface finish (Test 2). The samples were immersed in aerated Ringers solution (37°C) and loaded for 10 million cycles. The specimens surface parameters and profiles were measured before & after the test. Electrochemical static corrosion tests were carried out on the rough & smooth minispigots from Test 2 where the current was measured with constant potential under loaded and non-loaded conditions. A cyclical sinusoidal load of 1500-200 Newtons for 1000 cycles at ~1 Hz was used. Pitting tests measured the current while increasing and then decreasing the potential of non-loaded and loaded specimens. Two newly manufactured rough and smooth minispigots were subjected to the same electrochemical corrosion tests.

Results: In Test 1 the results demonstrated that pre-test the surfaces of the female tapers were similar for all heads. Post-testing the Ra values on the female tapers had become greater for the minispigots compared with standard spigots. An abrupt change was noted on the surface profile of the female taper where it was in contact with the male Ti taper, indicating the the CoCr head had corroded. The Ti male tapers were unchanged. Scanning electron microscopy showed that the coarser profile in the corroded region of the CoCr was similar to the profile on the Ti male taper. Pitting corrosion was evident in the grooves on the CoCr. In Test 2 the smooth spigots were not affected, but in the rough minispigots, Ra values had increased in the female tapers. Static corrosion tests showed evidence of fretting in the rough but not the smooth minispigots. When comparing new rough & smooth minispigots, static corrosion testing with clyclical loading showed that for minispigots with a rough finish the current fluctuated with each cycle. Pitting scans showed a greater hysteresis with the rough minispigot compared with the smooth minispigot indicating potentially greater corrosion in the former.

Conclusion: The cobalt-chrome/titanium alloy combinations where the surface finish on the male taper was coarse, corrosion was increased in minispigots compared with standard spigots. This was due to the smaller area of contact of the minispigot at the interface. This corrosion appears to be mediated through the mechanism of fretting corrosion. Surface finish was crucial and corrosion of the minispigot was reduced if the surface finish was smooth. Manufacturers should investigate the effect of surface finish on the corrosion of their tapers particularly where cobalt-chrome/titanium alloy combinations are used.

Aims: To investigate whether the use of mini-spigots result in enhanced wear and corrosion of tapers compared to standard spigots and the influence of the surface finish on this. Methods: The heads were cobalt chrome and the stems titanium alloy. Firstly wear and corrosion of standard spigots were compared with mini-spigots and secondly, these mini-spigots with another mini-spigot with a smoother surface finish. The samples were immersed in aerated Ringers solution (37°C) and loaded for 10 million cycles. Then samples were sectioned and the surface parameters measured and interfaces investigated using scanning electron microscopy. Static corrosion tests were used under loaded and non-loaded conditions and pitting tests for non-loaded samples. Results: Pre-experimentation the surfaces of the female tapers were similar for all heads. At the end of the first test the surface parameters on the female tapers had become significantly greater (p=0.034) for the mini-spigots compared with standard spigots and an abrupt change noted on the surface profile of the female taper where it contacted the male taper, indicating that the cobalt chrome head had corroded. Scanning electron microscopy showed that the coarser profile in the corroded region of the cobalt chrome head was similar to the profile on the titanium stem taper. Pitting corrosion was evident in the grooves on the cobalt chrome. The smooth mini-spigots were less affected. Conclusions: In cobalt chrome- titanium alloy combinations where the surface finish on the taper is coarse, corrosion is increased on a mini spigot compared with standard spigot. Surface finish is crucial and corrosion of the mini spigot is reduced if the surface finish is smooth.