Patellar kinematics after knee arthroplasty: experimental validation of a numerical model

Subject-specific modelling of Total Knee Arthroplasty could be an efficient method to preoperatively evaluate surgical options. In particular, the question of the necessity of patellar resurfacing is still a debatable issue. The aim of this work was to validate a numerical model of Total Knee Arthroplasty using an instrumented robotic knee simulator equipped with kinematic sensors. The patellar kinematics during a loaded knee flexion were measured with the knee simulator and compared with the values predicted by the model. The mean absolute difference between measured and predicted patellar translations and rotations was respectively 1.4 mm and 2.4 deg. This numerical model will be later used for subject-specific predictions of patellar kinematics and strain state after Total Knee Arthroplasty

A patient-specific model of total knee arthroplasty to estimate patellar strain: A case study

Inappropriate patellar cut during total knee arthroplasty can lead to patellar complications due to increased bone strain. In this study, we evaluated patellar bone strain of a patient who had a deeper patellar cut than the recommended. A patient-specific model based on patient preoperative data was created. The model was decoupled into two levels: knee and patella. The knee model predicted kinematics and forces on the patella during squat movement. The patella model used these values to predict bone strain after total knee arthroplasty. Mechanical properties of the patellar bone were identified with micro-finite element modeling testing of cadaveric samples. The model was validated with a robotic knee simulator and postoperative X-rays. For this patient, we compared the deeper patellar cut depth to the recommended one, and evaluated patellar bone volume with octahedral shear strain above 1%. Model predictions were consistent with experimental measurements of the robotic knee simulator and postoperative X-rays. Compared to the recommended cut, the deeper cut increased the critical strain bone volume, but by less than 3% of total patellar volume. We thus conclude that the predicted increase in patellar strain should be within an acceptable range, since this patient had no complaints 8 months after surgery. This validated patient-specific model will later be used to address other questions on groups of patients, to eventually improve surgical planning and outcome of total knee arthroplasty

Constructing 'homeland' and 'target' cities in the 'war on terror'.

No abstract available for this item

Unexpected wear of unicompartimental knee arthroplasty in oxidized zirconium.

Unicompartimental knee arthroplasty is a successful procedure for the treatment of localized osteoarthritis to one compartment of the knee with good long-term results. However, several modes of failure of unicompartimental knee arthroplasty have been described, namely aseptic or septic loosening, progression of disease, wear, and instability. Metallosis after unicompartimental knee arthroplasty is rarely reported and is most often related with polyethylene wear or break. We report on a case of rapid failure of unicompartimental knee arthroplasty in oxidized zirconium associated with metallosis secondary to the dislocation of the polyethylene