Abstract
Introduction: The current practice of impaction allograft to fill large defects in revision total hip replacements is sometimes useful but clinical results are inconsistent. Other studies have shown that addition of mesenchymal stem cells (MSC) in blocks of hydroxyapatite (HA) scaffold can enhance new bone formation in a critical sized defect. However, no study has been conducted on combined MSCs with morselised allograft and HA granules. It is hypothesized that impaction of allograft or HA granules seeded with MSCs or osteoprogenitors will enhance new bone formation compared with the groups without MSCs.
Materials and Methods: Six sheep were used for the study. Each sheep received 8 scaffolds which were embedded in both paraspinal muscles. Groups were: 1) 3.5g allograft, 2) 3.5g allograft with MSCs, 3) 3.5g allograft with osteoblasts; 4) 3.5g of 50:50 allograft/ HA, 5) 3.5g of 50:50 allograft/HA with MSCs, 6) 3.5g of 50:50 allograft/HA with osteoblasts; 7) a block of HA, 8) a block of HA with MSCs. The experimental scaffolds were seeded with either 10x106 MSCs/ml or 10x106 MSC-derived osteoprogenitors/ml, in 3ml autologous plasma. Grafts were impacted twenty times at 3KN. At eight weeks, samples were sectioned for histology analysis. Areas of new bone formation were measured as percentage to total available spaces. ANOVA was used for statistical analysis.
Results: Addition of MSCs increased new bone formation in allograft (4.98%), allograft/HA (5.15%) and HA block (7.09%) compared with their controls at 2.24%, 1.96% and 1.96% respectively. Statistical study showed significant increase in 50:50 allograft/HA with MSCs compared with 50:50 allograft/HA only (p=0.046) and 50:50 allograft/HA with osteoprogenitors (p=0.028). No difference was found in allograft groups. For the HA block groups, addition of MSCs showed a significant new bone increase compared to the control (p=0.028).
Conclusion: Addition of MSCs to the allograft and HA granules will enhance new bone formation after impaction which can be used for revision total hip replacements, especially when allograft and HA is mixed. However, addition of osteoprogenitors has not achieved the similar results. This study encourages a further clinical investigation of impaction tissue-engineered graft to repair bone defects in revision total joint replacements.
Correspondence should be addressed to Mr Carlos Wigderowitz, Senior Lecturer, University Department of Orthopaedic and Trauma Surgery, Ninewells Hospital and Medical School, Dundee DD1 9SY.
