Development of a reinforced PMMA-based hip spacer adapted to patients' needs

Two-stage reimplantation using an interval hip prosthesis (spacer) of antibiotic-impregnated bone cement has become a well-accepted method to eradicate infection and prevent limb shortening. However, custom made as well as prefabricated spacers share a weakness of limited strength and hence several fractures of spacers have been observed, even for partial weight bearing. The purpose of this study was therefore to improve the strength of the custom made spacer, used at the Orthopaedic Department of the Saarland University Hospital (Germany). As the material strength of bone cement is limited, several reinforced spacers with a metal core consisting of titanium grade two have been developed and investigated. Loading procedure was close to the ISO 7206/4, though small adaptation was made. An inserted rod of titanium grade two increased the collapse load up to 1000-1300 N, but considering a maximum expected load of about three times the body weight, still below the required value. A "full-stem" reinforced spacer, i.e. spacer with a titanium endoskeleton and a minimum of 2-3mm PMMA-coating in order to assure drug release, provides a mobile and functional joint through the treatment course. Those with 8mm thickness of titanium endoskeleton endured up to one million load cycles in a load range of 300-2300 N. To give further support for individual cases a meaningful S-N curve for this device was determined.