Abstract
AIM
Avascular necrosis (AVN) of the femoral head is a potentially debilitating disease of the hip in young adults. Impaction bone grafting (IBG) of morcellised fresh frozen allograft is used in a number of orthopaedic conditions. This study has examined the potential of skeletal stem cells (SSC) to augment the mechanical properties of impacted bone graft and we translate these findings into clinical practice.
STUDY DESIGN
We have examined the effect of SSC density on augmentation of bone formation. An in vitro model was developed to replicate the surgical IBG process. Plain allograft was used as the control, and the SSC's seeded at a density of 5×103, 5×104 and 2×105 cells per cc of allograft for the experimental groups. All samples were cultured for 2 weeks and mechanically tested to determine shear strength using the Mohr Coulomb failure curve. The approach was translated to 3 patients with early avascular necrosis (AVN) of the femoral head. The patient's bone marrow was concentrated in theatre using a centrifugation device and the concentrated fraction of SSC's were seeded onto milled allograft. The patient's necrotic bone was drilled, curetted and replaced with impacted allograft seeded with SSC's. Osteogenic potential of concentrated and unconcentrated marrow was simultaneously compared in vitro by colony forming unit assays.
RESULTS
The mechanical properties of the impacted allograft was significantly improved as a function of increasing SSC density. The difference compared to the control plain allograft was highly significant at the 2×105 level (p=0.001). Autologous SCC's on impacted bone allograft was subsequently applied in 3 patient cases and up to two year follow up demonstrates no deleterious effect. Critically the analysis of concentrated marrow demonstrated a higher SSC count in vitro than plain marrow aspirate.
DISCUSSION
We have demonstrated the potential of skeletal stem cells to augment the mechanical properties of impacted bone allograft in a laboratory model and subsequently translated these findings into a new technique for the treatment of AVN of the femoral head. Such an approach provides not only improved mechanical support to the overlying cartilage but critically improved biology for new bone formation. The early clinical results are encouraging and indicate potential use also in fracture non-unions and void filling of bone defects.
