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.