BackgroundAchieving stability of the tibial implant is essential following cementless total knee arthroplasty with bone grafting. We investigated the effects of bone grafting on the relative micromotion of the tibial implant and stress between the tibial implant and adjacent bone in the immediate postoperative period.MethodsTibial implant models were developed using a nonlinear, three-dimensional, finite element method. On the basis of a preprepared template, several bone graft models of varying sizes and material properties were prepared.ResultsMicromotion was larger in the bone graft models than in the intact model. Maximum micromotion and excessive stress in the area adjacent to the bone graft were observed for the soft and large graft models. With hard bone grafting, increased load transfer and decreased micromotion were observed.ConclusionsAvoidance of large soft bone grafts and use of hard bone grafting effectively reduced micromotion and undue stress in the adjacent area.

BackgroundThe stability of acetabulum reconstructions using reinforcement rings and hooks is important for successful replacement surgery. The objective of this study was to biomechanically determine the effects of the hook on stress and the related micromotions of the acetabular reinforcement ring during the immediate postoperative period.MethodsAcetabular reinforcement ring models were developed using a nonlinear, three-dimensional, finite element method. Using a pre-prepared template, we constructed without-hook and bone graft models of varying volumes and material properties.ResultsThe stress on the inferior margin of the acetabulum was higher in the with-hook model than in the without-hook model, especially with increased bone graft volumes, and the stiffness of the bone graft material was decreased. Relative micromotions in the without-hook model were higher than in the with-hook models. The highest relative micromotion was observed in the model with increased bone graft volume and lower stiffness of bone graft material.ConclusionsIn biomechanical analyses, the hook effectively dispersed stress and improved the initial fixation strength of the acetabular reinforcement ring.

In this study, the evaluation of flowability of cohesive powder using the test of powder discharge from an orifice by air flow has been examined. The powder used was three kinds of Calcium hydroxide with different particle diameter. The mean particle diameter of an original powder, Ca(OH) 2-A, is 13.1 μm. Other particle diameters, i.e. Ca(OH) 2-B and Ca(OH) 2-C, are 14.1 μm and 2.5 μm respectively. The initial void fraction and the interstitial air pressure have been varied as the experimental conditions. As a result the powder flow of Ca(OH) 2-C indicated the lowest flowability which was judged from the relationship between the mass flow rate and the average interstitial air pressure. Furthermore, the cohesiveness of Ca(OH) 2-C which has the smallest particle diameter was the strongest because the ratio of separation force to gravity force was high. In addition, it is inferred that the main factor of the cohesive force was van der Waals force.

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