The relationship between porosity and fatigue characteristics of bone cements.

In this study, the fatigue strengths of acrylic cement prepared by various commercially available reduced pressure mixing systems were compared with the fatigue strength of cement mixed by hand (control) under atmospheric conditions. The following observations were made from this investigation. The mean fatigue strength of reduced pressure mixed acrylic bone cement is double that of cement mixed by hand using an open bowl, 11,354+/-6,441 cycles to failure for reduced pressure mixing in comparison with 5,938+/-3,199 cycles for mixing under atmospheric conditions. However, the variability in mean fatigue strengths of reduced pressure mixed bone cement is greater for some mixing devices. The variation in fatigue strengths for the different mixing techniques is explained by the different porosity distributions. The design of the reduced pressure mixing system and the technique employed during mixing strongly contribute to the porosity distribution within the acrylic bone cement. The level of reduced pressure applied during cement mixing has an effect on the fatigue strength of bone cement, but the mixing mechanism is significantly more influential.

A review of biomechanical studies of intramedullary nails.

Fracture management is becoming less conservative, and more frequently surgical intervention is the treatment of choice. Intramedullary mailing is a modern surgical method of internal fracture used in long bones such as the femur, tibia and humerus. The nails' function is to stabilize the fracture fragments, allowing load transfer across the fracture site while maintaining anatomic alignment of the bone. There are a large number of different intramedullary nails available commercially but no universal guideline stating the conditions at which each nail will perform at its optimum. Numerous animal, biomechanical and clinical studies have documented the performance of the nails. Biomechanical studies have shown that in torsion, slotted nails have a considerably lower rigidity than non-slotted nails but that in bending, the slot makes little difference to the nails' behaviour and so the two nail types have similar stiffnesses. Studies also recommend that in unstable fractures an interlocked intramedullary nail is essential if limb shortening or malunion is to be avoided. It is the aim of this review to outline the work that has been published to date on the biomechanical testing of intramedullary nails and to highlight areas that require further investigation.