Abstract
Orthopaedic surgeons are astounded with the strength of bone found in Polynesians. Furthermore the rate at which new Polynesian bone over-grows metal fixation of a recent fracture is impressive. Studies demonstrate that Polynesians have a higher Bone Mineral Density (BMD) than age and weight matched Europeans in NZ (1, 2). In addition, Polynesians have a lower incidence of hip fractures when compared to other ethnic groups (3). This suggests that the higher BMD or other inherent differences must account for the lower incidence of hip fractures in Polynesians.
The aim of this study was to identify (if any) a difference in osteoblast mitosis between European and Polynesian bone. Samples were collected from 13 patients that had joint replacements in accordance with the MCNZ ethics approval. The bone is processed and osteoblasts cultured in the lab to 50% confluence. The cells are then tagged with Propidium Iodide. Using Fluorescence-Activated Cell Sorting (or FACS) the number of osteoblasts in the different phases of the cell cycle are counted. The percentage of cells in G0/G1, S and G2/M phase can be determined by entering the FACS data into a program called mod-fit. This study shows that Polynesians have a greater proportion of cells undergoing replication (i.e S-phase) than their European counterparts.
Incidentally we have also shown that the proportion of cells undergoing mitosis lowers with age irrespective of ethnicity.
