Effect of cortical bone decollagenisation on fracture biomechanics at low strain rate

Introduction The ability of bone to resist failure is directly dependant on the intrinsic properties, namely the inorganic (hydroxyapetite) and organic (collagen) contents. Traditionally, inorganic content has been associated with stiffness of bone, whereas organic content has been associate with toughness. The aim of this research is to study the biomechanical effects of staged demineralisation and decollagenisation of femoral cortical segments. The staged protocol for decollagenisation should be considered a novel component of this study. A clinical correlation study to complement the biomechanical work was also undertaken. Femoral shaft fracture patterns in all ages were clinically and radiologically assessed to delineate if any correlation exists with the biomechanical findings of manipulated bone. Methods Ovine femoral cortical bone specimens were demineralised in 10% EDTA under ultrasonic assistance. Decollagenisation was achieved using 5M and 10M NaOH solution at 44 degrees celsius. Bone processing was undertaken at time points 0, 6, 12, 24 and 48 hours. Samples were mechanically tested under low strain four-point bending. ANOVA testing was undertaken to compare groups with p<0.05 significant. This biomechanical data was correlated with clinical data analysing femoral shaft fractures in three age groups; (paediatric (0-16), adult (17-54) and older age (>55)) to reflect immature, peak bone age and osteoporotic bone respectively. Binary logistic analysis was used to assess significance of bone age with respect to fracture pattern (pvalue <0.05 was significant). Results Demineralised bone demonstrated a reduction of ultimate strength, yield strength and elastic modulus at 48 hours (p<0.05). There was significant increase in toughness at 48 hours. Decollagenised bone showed a reduction in ultimate and yield strength at 12 hours. There was an initial increase in elastic modulus at 6 hours after immersion in both NaOH solutions (p<0.05), followed by progressive reduction. There was over 70% decrease in toughness in decollagenised samples at 48 hours (p