An important measure for the diagnosis and monitoring of knee osteoarthritis is the minimum joint space width (mJSW). This requires accurate alignment of the x-ray beam with the tibial plateau, which may not be accomplished in practice. We investigate the feasibility of a new mJSW measurement method from stereo radiographs using 3D statistical shape models (SSM) and evaluate its sensitivity to changes in the mJSW and its robustness to variations in patient positioning and bone geometry. A validation study was performed using five cadaver specimens. The actual mJSW was varied and images were acquired with variation in the cadaver positioning. For comparison purposes, the mJSW was also assessed from plain radiographs. To study the influence of SSM model accuracy, the 3D mJSW measurement was repeated with models from the actual bones, obtained from CT scans.Objectives
Materials and Methods
Wear of polyethylene inserts plays an important role in failure
of total knee replacement and can be monitored Before revision, the minimum joint space width values and their
locations on the insert were measured in 15 fully weight-bearing
radiographs. These measurements were compared with the actual minimum
thickness values and locations of the retrieved tibial inserts after
revision. Introduction
Method
The incidence of loosening of a cemented glenoid component in total shoulder arthroplasty, detected by means of radiolucent lines or positional shift of the component on true antero-posterior radiographs, has been reported to be between 0% to 44%. These numbers depend on the criteria used for loosening and on the length of follow-up. Radiolucent lines are however difficult to detect and to interpret, because of the mobility of the shoulder girdle and the obliquity of the glenoid, which hinder standardisation of radiographs. After review of radiolucencies around cemented glenoid components with a mean follow-up of 5. 3 years in 48 patients we found progressive changes to be present predominantly at the inferior pole of the component. This may hold a clue for the mechanism behind loosening of this implant. Since loosening is generally defined as a complete radiolucent line around the glenoid component and is difficult to assess as a result of the oblique orientation of the glenoid, an underestimation of the loosening rate using radiological data was suspected. Therefore a pilot study using Roentgen Stereophotogrammatric Analysis (RSA) was performed. In five patients an additional analysis of glenoid component loosening using digital Roentgen Stereophotogrammetric Analysis (RSA) was performed. The relative motion of the glenoid component with respect to the scapula was assessed and the length of this translation vector was used to represent migration. Loosening was defined as a migration of the component, exceeding the pessimistic estimate of the accuracy of RSA 0. 3 mm for this study. After three years of follow-up, three out of five glenoid components had loosened (1. 2 – 5. 5 mm migration). In only one patient with a gross loosened glenoid, the radiological signs were consistent with the RSA findings. It was concluded that when traditional radiographs are used for assessment of early loosening, the loosening rate is underestimated. We recommend that RSA be used for this.
The aim of this study was on the one hand to compare the fixation of a posterior stabilised prosthesis (PS) and a PCL retaining mobile bearing design (Interax, How-medica Osteonics, Rutherfort, USA) and on the other hand to measure the mobility of the mobile bearing. All measurements were carried out by means of Roentgen Stereophotogrammetric Analysis (RSA-CMS, Medis, Netherlands). Thirty-three patients with a total of forty-two consecutive primary cemented TKA were included in a prospective, randomised study at Leiden University Medical Centre. There were no significant differences among the two groups with regard to age (66. 5 ± 12. 1 years). The pre-operative Knee Society Score did not differ significantly between the two groups. At the one-year follow-up the PS group showed a significantly lower function score (p=0. 04) compared to the mobile bearing group. At the one-year follow-up evaluation, the micromotion of the PS-components and the mobile bearing components were not significantly different. The PS-tibial components subsided −0. 003 ± 0. 192 mm and the mobile bearing knee tibial components subsided 0. 057 ± 0. 082 mm. The PS tibial component showed a higher variability in the migration results indicating a number of PS with rather large micromotion. For three patients, the The wide range of kinematic patterns of mobile bearings during flexion that is observed in fluoroscopic studies is also observed in this study. A possible positive effect of mobile bearing movement may be found in the smaller variability of the micromotion of the mobile-bearing knees compared to the PS knees. The assumption was that shear forces in tibial bones implanted with a mobile bearing prosthesis would be better dissipated from the prosthesis-bone interface resulting in less micromotion. The kinematics of an additional number of mobile bearing knees -already included in the micro-motion study- will have to be assessed in order to determine the relation between mobility and micromotion. Mobile bearing, Posterior Stabilised, RSA, Kinematics
