Stanmore stem long-term survivorship

Development of the Stanmore hip system Following its development at the Department for Biomedical Engineering, Royal National Orthopaedic Hospital Stanmore the Stanmore stem was first implanted in 1973. The original design was manufactured from cast CoCr alloy (AliviumTM) which was supplemented by a forged titanium alloy (TivaloyTM) version in 1979. At this time both the CoCr and titanium alloy versions were monobloc components with the femoral head integral with the stems. In the early 1990’s a modular version of the stem was introduced with Biomet Type 1 taper thus allowing the stem to be used with metallic and ceramic Biomet modular femoral heads. The stem manufactured from forged CoCr alloy has been supplemented in 2008 by a lateralised version to allow more lateral offset whilst minimising the effect on patients’ leg length. Since its launch in 1973, the Stanmore stem has an unchanged collared geometry and vapour blast surface finish for cement fixation. It has been employed in primary hip arthroplasty with differing cementing techniques varying from the less than optimum “thumbing method” to the vacuum mixing/ cement pressurisation systems afforded by the fourth generation cementing techniques. The Stanmore cup designed for cement fixation has been developed and refined over the same period of time. The external geometry has remained the same however the sizes have been subject to change to incorporate an increasing number of femoral head sizes. Initially made by machining from slab moulded RCH1000 polyethylene, the current version is made from ArCom material. In the late 1990’s a metal-on-metal version of the cup was introduced and used clinically. This utilised a CoCr bearing surface which was incorporated into a pre-form shape of moulded polyethylene, the external geometry of the cup being machined from this pre-form. Table 1. Survivorship, National Joint registries