INFLUENCEOF THE PLACEMENTOF TIBIA COMPONENTS OF KNEE REPLACEMENTSON THE PATELLA FORCES K.Weinmann Department of Mechanics (A!. Techn. Univ. Munich. Arcisstr.21. D-4000 Miinchen 2. Fed. Rep. Germany Experiments with cadaver knees in a knee kinemator and a study with a mathematical mode1 of the patello-femoral joint were carried out to investigate the influence of the placement of tibia1 components on the patella forces. Results show an obvious increase of the patello-femoral forces for anterior placements of rhe tibia1 component and an decrease for posterior placements in the whole range of flexion from 0 to 120 degrees. Forces in the lig. patellae were not changed by component displacement. Different proximaldistal positions of the component without correction by an adequate component height did not effect a change of the patello-femoral forces until 50 degrees ffexion. At further flexion. forces increased for distal component positions.
THE FRICTIONALBEHAVIOUR OF ARTICULARCARTILAGECONTAINING SURFACECRYSTALS B.Hartis*, P.A.Dieppe***, I.C.Turner*, A.J.Collins* A.Hayes*. S.E.Clift**, *Schools of Materials Science and Pharmacy and Pharmacology, University of Bath, Bath, U.K. **Faculty of Technology, The Open University, Milton Keynes, U.K. ***Department of Medicine, Bristol Royal Infirmary, Bristol, U.K. A characteristic feature of many degenerative joint diseases is the destruction of the articular cartilage. This is sometimes accompanied by crystal deposition within the joint. This study explores the possible mechanical contribution of these crystal deposits to the destruction of the articular cartilage. A technique has been developed to measure the frictional behaviour of small specimens of articular cartilage on a plug of subchondral bone. In an initial study the coefficient of friction of normal and diseased human articular cartilage was correlated with the fibrillation of the articular surface. A further study correlated the coefficient of friction with the crystal density on the surface of the articular cartilage. The results suggest that the coefficient of friction of articular cartilage is directly correlated with the incidence of crystal deposition and the fibrfllation of the articular cartilage.
A IkElHID OF NON-INVASIVEFRACTURESTIFFNESS hEG= K.M. Shah*, A.C. Nicol , J.B. Richardson (Glasgow) *University Department of Orthopaedic Surgery, Western Infirmary, Glasgow, Cl1 6NT. Scotland (U.K.) The potential contributions of fracture stiffness as a functional measure of patient and to provide healing are in two areas: to rronitor progress in an individual Stiffness characterizes the gradual change in tissue comparisons between patients. tissue to 2000 during healing from a Young’s modulus of .005 Kp/mn;! for granulation The clinician requires a 400.000 fold change. Kp/mnZ for mature bone. representing informstlon on healing to allow safe removal of splintage as early as possible to avoid canplications such as joint stiffness. Fracture stiffness can be measured using a strain gauge gonianoter by calculating deflection at the fracture site in response to a known load when the site of fracture Load is applied at the knee and measured is known from the point of load application. The goniometer is applied using Orthoplast bridges at the heel by a load transducer. ‘Ihis pilot study has found the strain gauge goniometer on either side of the fracture. capable of masuring fracture stiffness in patients under treatment with external fixators or splintage.