Abstract
Introduction: The CPS-Plus stem (Endoplus UK) is a polished double-taper with a rectangular cross section maintained throughout for rotational stability. There are 5 stem sizes with proportionate offset, together with 5 neck length options, and a unique proximal stem centraliser which has been shown to increase proximal cement pressurisation during insertion in-vitro, assists with alignment of the stem and helps create an even cement mantle. RSA analysis has demonstrated linear subsidence in a vertical plane, without the posterior head migration and valgus tilt associated with other designs.
Data on the CPS-Plus stem has been obtained from a multi-centre prospective clinical trial. 231 hips in 223 patients have been entered into the study. 151 of these have reached 3 years follow-up.
Method: Patients were recruited by surgeons working at three centres in the UK and two in Norway. Merle d Aubigne and Postel, Harris, and Oxford hip scores were recorded pre-operatively and at follow-up (3, 6, 12, 24, 36, 60 months). Radiographic assessment included evaluation of subsidence and the presence of any radiolucencies.
Results: Objective and subjective scoring have indicated very satisfactory results. Radiological subsidence is less than 1.5mm in over 95% of cases and only one stem has subsided more than 3mm. There has been one revision for deep sepsis, 7 dislocations and one femoral fracture, but none of these complications were related to the choice of femoral component. There have been no revisions for aseptic loosening. Kaplan Meier survivorship analysis at 36 months for aseptic stem loosening is 0.997 (95% CI 0.977 – 1) and for all-cause revision is 0.981 (95% CI 0.958 – 1).
Discussion: The tradition of polished tapered stems arose from serendipity and most results have been excellent. The CPS-Plus stem represents an attempt to re-examine the issues relating to rotational stability, subsidence, cement pressurisation and offset. Earlier laboratory studies have now been supplemented by this clinical evaluation, performed in a number of different centres by several surgeons, and the evidence is encouraging.
In particular, the RSA subsidence characteristics, cement pressurisation and rotational stability already associated with this implant in-vitro have been supported by excellent survivorship analysis, and the authors believe that increasing familiarity with the concepts raised by this implant will result in clinical benefits in relation to polished taper cemented stem longevity.
Theses abstracts were prepared by Professor Roger Lemaire. Correspondence should be addressed to EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
