Abstract
Modern cementation techniques in hip arthroplasty are enhanced by the use of a cement restrictor. Failure of cemented hip replacements is commonly caused by aseptic loosening. Cement plugs which occlude the medullary canal are widely used to increase cementation pressures. Many plug types with variable performance exist. Ideally, plug performance should be sufficient regardless of other factors. All plug designs are circular in cross section, yet the vast majority of human femora are of oval section, the average ellipticity for human femora being 1.3. This study aims to determine (I) the effect of cement viscosity, canal shape and canal size on plug performance and (II) which designs of cement restrictor are able to withstand cementation pressures, regardless of values of other potentially influential factors.
Methods: Artificial femoral canals were drilled in oak blocks. Canals had diameters of 12 or 17.5 mm and oval or circular cross section. Four synthetic plug types (Hardinge, Exeter, Summit and OptiPlug.) and a bone plug (human allograft, Sulzer instrumentation) were tested. The effect of canal diameter, canal shape and low or regular cement viscosity was assessed.
Results: Maximal pressures achieved varied significantly between plugs. (OptiPlug 448±66 kPa, Hardinge 142±66, Exeter 705±66, Amber Flex 475±72, Bone plug 502±97 kPa; p=0.002, all mean±SEM). Al plugs performed worse in canals of increased size and of elliptical canal cross section (12 mm 529±49, 18 mm 356±47; p=0.03), canal shapes (Round 631±45, Oval 254±51; p=0.004). Cement viscosity had no statistical effect.
Discussion: Elliptical canal cross section and increased canal diameter adversely affects performance of all plug designs. Of the five tested, the Exeter and bone plugs performed best in all adverse circumstances. The Opti-Plug and AmberFlex, which are both resorbable, had an intermediate performance. The Hardinge plug performed worse. These factors should be considered when selecting plug design.
The abstracts were prepared by Mr Peter Kay, Editorial Secretary. Correspondence should be addressed to British Hip Society, The Hip Centre, Wrightington Hospital, Appley Bridge, Wigan, Lancashire WN6 9EP.
