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Inadequate bone stock is often found in revision surgery of femoral components of total knee replacements. Our aim was to test the hypothesis that these remodelling patterns can be explained by stress shielding, and that prosthetic bonding characteristics affect maintenance of bone mass. We made a three-dimensional finite-element model of an average male femur with a cemented femoral knee component. This model was integrated with iterative remodelling procedures. Two extreme prosthetic bonding conditions were analysed and gradual changes in bone density were calculated. The long-term bone loss under the femoral knee component resembled clinical findings which confirms the hypothesis that stress shielding can cause distal femoral bone loss. Our study predicts, contrary to clinical findings, that an equilibrium situation is not reached after two years, but that bone resorption may continue. This hidden bone loss may be so drastic that large reconstructions are needed at the time of revision.

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Contains fulltext : 21303___.PDF (Publisher’s version ) (Open Access)

Recently developed in vivo animal high-resolution micro-CT scanners offer the possibility to monitor longitudinal changes in bone microstructure of small rodents, but may impose high radiation doses that could damage bone tissue. The goal of this study was to determine the effects on the bone of 8 weeks of in vivo scanning of the proximal tibia in female Wistar rats. Eight weekly CT scans were made of the right proximal tibia of nine female, 30-week-old, retired-breeder, Wistar rats. Two weeks after the last weekly scan, a final scan was made. The left leg was only scanned during first and final measurements and served as a control. A two-way ANOVA with repeated measures was performed on the first and last measurements of left and right tibiae for six bone structural parameters. Bone marrow cells were flushed out and tested for cell viability. No significant difference was found between left and right for any of the bone structural parameters (p > 0.05). Structure model index and trabecular separation significantly changed as a result of aging, while none of the other parameters did. No significant difference was found between left and right in absolute and percentage number of cell viability. We did not find any indication that the applied scanning regime, in combination with the particular settings used, would affect the results of in vivo bone structural measurements in long-term studies using aged, female Wistar rats. However, careful consideration should be made when determining the number of scans, particularly when a different experimental design is used

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Contains fulltext : 26123___.PDF (Publisher’s version ) (Open Access)

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OBJECTIVE: To investigate the correlation between initial ligament damage and development of subsequent osteoarthritic changes. METHODS: Collagenase was injected intraarticularly into the knee joint of mice of strain C57B16 or C57B110. After 3 days, ligament damage was evaluated by measurements of knee laxity in the anterior-posterior direction as a measure of cruciate ligament function, and in the varus-valgus direction as a measure of collateral ligament function. The amount and location of cartilage loss and osteophyte formation were determined at Day 42. RESULTS: Significant correlations between the amount of laxity changes and the severity of cartilage loss (r = 0.78), the amount of laxity changes and the size of osteophytes (r = 0.87), and between the severity of cartilage loss and osteophyte size (r = 0.94) were demonstrated. The amount of cartilage loss and the degree of osteophyte formation at the medial side of the joint depended mainly on the severity of cruciate ligament damage. This is contrast to changes at the lateral side of the joint, which appeared not to be associated with the severity of ligament damage. CONCLUSION: A strong relationship exists between the severity of cruciate ligament damage and the severity of osteoarthritic changes on the medial side of the joint. In the lateral joint compartment, prone to spontaneous osteoarthritis in the mouse strain studied, this relation is absent

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Contains fulltext : 223625.pdf (Publisher’s version ) (Open Access) Chicago

—In many biomechanical motion studies, kinematic parameters are estimated from position measurements on a number of landmarks. In the present investigation, dummy motion experiments are performed in order to study the error dependence of kinematic parameters on geometric factors (number of markers, isotropic vs anisotropic landmark distributions, landmark distribution size), on kinematic factors (rotation step magnitude, the presence of translational displacements, the distance of the landmarks' mean position to the rotation axis), and on anisotropically distributed measurement errors. The experimental results are compared with theoretical predictions of a previous error analysis assuming isotropic conditions for the measurement errors and for the spatial landmark distribution. In general, the experimental findings agree with the predictions of the error model. The kinematic parameters such as translations and rotations are well-determined by the model. In the helical motion description, the same applies for the finite rotation angle about and the finite shift along the helical axis. However, the direction and position of the helical axis are ill-determined. An anisotropic landmark distribution with relatively few markers located in the direction of the rotation axis will even aggravate the ill-posed nature of the finite helical axis estimation.

In biomechanical joint-motion analyses, the continuous motion to be studied is often approximated by a sequence of finite displacements, and the Finite Helical Axis(FHA) or "screw axis" for each displacement is estimated from position measurements on a number of anatomical or artificial landmarks. When FHA parameters are directly determined from raw (noisy) displacement data, both the position and the direction of the FHA are ill-determined, in particular when the sequential displacement steps are small. This implies, that under certain conditions, the continuous pathways of joint motions cannot be adequately described. The purpose of the present experimental study is to investigate the applicability of smoothing (or filtering)techniques, in those cases where FHA parameters are ill-determined. Two different quintic-spline smoothing methods were used to analyze the motion data obtained with Roentgenstereophotogrammetry in two experiments. One concerning carpal motions in a wrist-joint specimen, and one relative to a kinematic laboratory model, in which the axis positions are a priori known. The smoothed and nonsmoothed FHA parameter errors were compared. The influences of the number of samples and the size of the sampling interval (displacement step) were investigated, as were the effects of equidistant and nonequidistant sampling conditions and noise invariance

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Contains fulltext : 144673.pdf (Publisher’s version ) (Open Access) KUN, 11 juni 2001 Promotores : Huiskes, R., Burger, E.H.

Contains fulltext : 146800.pdf (Publisher’s version ) (Open Access) 135 p.

Item does not contain fulltext KUN, 22 mei 2001 Promotores : Hermus, A.R.M.M., Huiskes, R.

Item does not contain fulltext KUN, 16 mei 2001 Promotores : Veth, R.P.H., Huiskes, R.

Item does not contain fulltext Katholieke Universiteit Nijmegen, 08 september 1998 Promotores : Huiskes, R., Lohman, A.H.M. Co-promotor : Blankevoort, L. 125 p.

Item does not contain fulltext Katholieke Universiteit Nijmegen, 11 juni 1998 Promotores : Slooff, T.J.J.H., Huiskes, R. Co-promotor : Buma, P. 96 p.

Contains fulltext : mmubn000001_253495539.pdf (Publisher’s version ) (Open Access) Promotor : R. Huiskes 131 p.

Contains fulltext : mmubn000001_234349484.pdf (Publisher’s version ) (Open Access) Promotores : R. Huiskes en H. Weinans cum laude 143 p.

Contains fulltext : mmubn000001_211170313.pdf (Publisher’s version ) (Open Access) KU Nijmegen, 28 november 1995 Promotor : Huiskes, R. 159 p.

Contains fulltext : mmubn000001_210341459.pdf (Publisher’s version ) (Open Access) Promotores : T. Slooff, R. Huiskes en P. Buma IX, 134 p.