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Radiolucent lines frequently appear on radiographs around unicompartmental knee arthroplasties. It is unknown why this occurs, although the lines usually appear during the first year following the procedure. Knee arthroplasty implants are also known to migrate during the first year. Considering the similarity in the timing of appearance of radiolucency and implant migration, it seems that they could be related. The aim of this study was to determine whether there is a correlation between presence of radiolucency and the migration of Oxford unicompartmental knee arthroplasty implants.

Finite element (FE) analysis is widely used to calculate stresses and strains within human bone in order to improve implant designs. Although validated FE models of the human femur have been created (Lengsfeld et al., 1998), no equivalent yet exists for the tibia. The aim of this study was to create such an FE model, both with and without the tibial component of a knee replacement, and to validate it against experimental Results: A set of reference axes was marked on a cleaned, fresh frozen cadaveric human tibia. Seventeen triaxial stacked strain rosettes were attached along the bone, which was then subjected to nine axial loading conditions, two four-point bending loading conditions, and a torsional loading condition using a materials testing machine (MTS 858). Deflections and strain readings were recorded. Axial loading was repeated after implantation of a knee replacement (medial tibial component, Biomet Oxford Unicompartmental Phase 3). The intact tibia was CT scanned (GE HiSpeed CT/i) and the images used to create a 3D FE mesh. The CT data was also used to map 600 transversely isotropic material properties (Rho, 1996) to individual elements. All experiments were simulated on the FE model. Measured principal strains and displacements were compared to their corresponding FE values using regression analysis. Experimental results were repeatable (mean coefficients of variation for intact and implanted tibia, 5.3% and 3.9%). They correlated well with those of the FE analysis (R squared = 0.98, 0.97, 0.97, and 0.99 for axial (intact), axial (implanted), bending, torsional loading). For each of the load cases the intersects of the regression lines were small in comparison to the maximum measured strains (

This paper describes a motion analysis ultrasound system (MAUS) designed for the in-vivo study of the kinematics of patellofemoral joints (PFJ) in both normal and replaced knees. This system utilises non-iodising radiation to effectively acquirekinematic data during weight-bearing activities. Validation studies on a phantom established that the measurement accuracy of the system was 1.43 mm. A clinical validation trial is included.

Objective: Conventional knee-endoprostheses show modified kinematics in comparison with the human knee. There is high percentage of sliding during the movement, which causes higher stress on the material compared to the physiological rolling. Despite of good clinical results the durability and patient[for full text, please go to the a.m. URL], Deutscher Kongress für Orthopädie und Unfallchirurgie; 74. Jahrestagung der Deutschen Gesellschaft für Unfallchirurgie, 96. Tagung der Deutschen Gesellschaft für Orthopädie und Orthopädische Chirurgie, 51. Tagung des Berufsverbandes der Fachärzte für Orthopädie