Radiolucencies beneath the tibial component are well recognized in knee arthroplasty; the aetiology and significance are poorly understood. Non-progressive narrow radiolucencies with a sclerotic margin are thought not to be indicative of loosening. Factors which decrease the incidence of radiolucencies include cementless fixation and the use of pulse lavage. Leg/component alignment or BMI do not influence radiolucency. We are not aware of any studies that have looked at the effect of load type on radiolucency. The Oxford domed lateral tibial component was introduced to decrease the bearing dislocation rate that was unacceptably high with the flat tibial tray. However, the introduction of the domed tibial component alters the forces transmitted through the implant-cement-bone interface. As the Oxford UKR uses a fully congruent mobile bearing, the forces transmitted through the interface with a flat tray are compressive, except for the effect of friction. However, with the domed tibial component shear forces are introduced. The aim of this study was to assess the prevalence of radiolucency beneath the previous flat design and the new domed tibial tray. A consecutive series of 248 cemented lateral UKRs (1999–2009) at a single institution were assessed. The first 55 were with a flat tibia and the subsequent 193 with a domed component. One year post-op radiographs were assessed, by two observers, for the presence (full or partial) and distribution of radiolucency. The distribution and thickness of each radiolucency. Cases were excluded for missing or poorly aligned radiographs.Introduction
Patients and methods
Quality of cementation in the early postoperative period has been proven to be an indicator of long-term survival of the total hip arthroplasty. Cementation grading described by Barrack et al is widely used but has certain limitations. It is based upon second-generation cementation technique and has unacceptably high inter- and intra-observer variability due to its subjective evaluation method. We are introducing a new grading system of quality of femoral cementation. It is based upon the ratio of the length of radiological lucency to the total length of cement-bone interface on both antero-posterior and lateral views. Because of its objective nature, it is likely to show reproducible results. We recruited five observers of various grades of surgical experience (trainees to consultant). Each observer graded the quality of femoral cementation on immediate postop xrays twice (gap of atleast two weeks) of 30 primary hip arthroplasties, using Barrack's grading and a new cementation index measured by dividing the ength of
