Prof Lars Lidgren

Lars Lidgren, Professor, MD PhD,
Department of Orthopedics,
Lund University Hospital
Lund
Sweden

Mixing and delivery / Reproducible high quality bone cement
The development of cement mixing and delivery systems has been governed by three key objectives: to standardize the cementing technique, to improve cement quality and to minimize monomer exposure.

Porosity and fatigue
A hip joint is subjected to forces as great as ten times body weight and runs for up to two million times each year. Thus fatigue properties of cement are critical. Porosity has been found to decrease mechanical strength of bone cement. Pores or other inclusions concentrate stress in the material and initiate fatigue cracks, which may lead to failure. Other factors contributing to poor bone cement behaviour are molecular weight, viscosity, type of cement and implant.

Mixing and collection under vacuum
Vacuum mixing reduces microporosity. Reports show that fatigue fractures occur at the largest macropores. Macroporosity is greatly effected by choice of vacuum mixing system. Studies have shown that the Optivac system, with its patented design for vacuum collection, produces a cement of much lower macroporosity than cement mixed in other vacuum mixing systems.

Reproducible, homogeneous cement mix
A non-homogeneous cement mix with unbonded particles may also compromise cement quality. Hand mixing with a spatula and bowl and transferral to a delivery system makes it difficult to achieve a homogeneous cement mix. Modern mixing systems produce reproducible, homogeneous cement of consistently high quality.

Closed delivery systems
A system with a cement delivery gun produces better pressurization of cement into bone bed than does a system with manual delivery. Closed, pre-packed systems, which offer enhanced ease-of-use and reduced exposure are the future of cement mixing and delivery. Systems pre-filled with polymer powder are the first step in this direction.