No abstract

Knee osteoarthritis (OA) is believed to result from high levels of contact stresses on the articular cartilage and meniscus after meniscal damage. This study investigated the effect of meniscal tears and partial meniscectomies on the peak compressive and shear stresses in the human knee joint. An elaborate three-dimensional finite element model of knee joint including bones, articular cartilages, menisci and main ligaments was developed from computed tomography and magnetic resonance imaging images. This model was used to model four types of meniscal tears and their resultant partial meniscectomies and analysed under an axial 1150 N load at 0° flexion. Three different conditions were compared: a healthy knee joint, a knee joint with medial meniscal tears and a knee joint following partial meniscectomies. The numerical results showed that each meniscal tear and its resultant partial meniscectomy led to an increase in the peak compressive and shear stresses on the articular cartilages and meniscus in the medial knee compartment, especially for partial meniscectomy. Among the four types of meniscal tears, the oblique tear resulted in the highest values of the peak compressive and shear stresses. For the four partial meniscectomies, longitudinal meniscectomy led to the largest increase in these two stresses. The lateral compartment was minimally affected by all the simulations. The results of this study demonstrate meniscal tear and its resultant partial meniscectomy has a positive impact on the maintenance of high levels of contact stresses, which may improve the progression of knee OA, especially for partial meniscectomy. Surgeons should adopt a prudent strategy to preserve the greatest amount of meniscus possible.

No abstract

During virtual three-dimensional orthognathic surgery in cases where an overlap or penetrability occurs between the 2 jaws due to the repositioning of the maxillary segment, it is necessary to establish a vertical opening of the mandible to obtain a relatively good relationship with the maxillary segment for the fabrication of an intermediate occlusal splint. However, there are few reports that address the precise definition of the rotational axis of the mandible during virtual surgery. Here, we present the idea that the mandible's movement during virtual three-dimensional orthognathic surgery is similar to hinge movement in vivo and developed a method for locating the geometric center of the three-dimensional condyle using Hypermesh software combined with Mimics software. Subsequently, we defined the rotational axis of the mandible based on the located geometric centers of the bilateral condyles, and the mandible was then rotated around the defined axis from the retruded contact position to mimic the hinge movement. Preliminary results indicated that the presented method could approximately mimic the hinge movement of the mandible with a relatively high accuracy in a three-dimensional environment, which may improve the accuracy of virtual intermediate occlusal splint.

BackgroundIndividualized and accurate implantation of a femoral component during total knee arthroplasty (TKA) is essential in achieving equal distribution of intra-articular stress and long-term survival of the prosthesis. However, individualized component implantation remains challenging. This study aimed to optimize and individualize the positioning parameters of a femoral component in order to facilitate its accurate implantation.MethodsUsing computer-simulated TKA, the positioning parameters of a femoral component were optimized individually by finite element analysis in combination with orthogonal array testing. Flexion angle, valgus angle, and external rotation angle were optimized in order to reduce the peak value of the pressure on the polyethylene liner of the prosthesis.ResultsThe optimal implantation parameters of the femoral component were as follows: 1° flexion, 5° valgus angle, and 4° external rotation. Under these conditions, the peak value of the pressure on the polyethylene liner surface was minimized to 16.46 MPa. Among the three parameters, the external rotation angle had the greatest effect on the pressure, followed by the valgus angle and the flexion angle.ConclusionFinite element analysis in combination with orthogonal array testing can optimize the implantation parameters of a femoral component for TKA. This approach would possibly reduce the wear of the polyethylene liner and prolong the survival of the TKA prosthesis, due to its capacity to minimize stress. This technique represents a new method for preoperative optimization of the implantation parameters that can achieve the best possible TKA outcome.

The biomechanical relationship between the articular cartilage defect and knee osteoarthritis (OA) has not been clearly defined. This study presents a 3D knee finite element model (FEM) to determine the effect of cartilage defects on the stress distribution around the defect rim. The complete knee FEM, which includes bones, articular cartilages, menisci and ligaments, is developed from computed tomography and magnetic resonance images. This FEM then is validated and used to simulate femoral cartilage defects. Based on the obtained results, it is confirmed that the 3D knee FEM is reconstructed with high-fidelity level and can faithfully predict the knee contact behavior. Cartilage defects drastically affect the stress distribution on articular cartilages. When the defect size was smaller than 1.00 cm 2 , the stress elevation and redistribution were found undistinguishable. However, significant stress elevation and redistribution were detected due to the large defect sizes ( 1.00 cm 2 ). This alteration of stress distribution has important implications relating to the progression of cartilage defect to OA in the human knee joint.

The optimisation process of the orthogonal experiment was designed by Taguchi experiment. Nanopores structure was prepared on the surface of stainless steel by anodic oxidation in the nitric acid solution containing sodium chloride and thiourea, and the nanopores were expanded in the solution containing sodium chloride, hydrochloric acid and sulfuric acid. The range and variance analysis results demonstrated that when the anodising process parameters were nitric acid concentration 90 mL L −1 , thiourea concentration 3.5 g L −1 , sodium chloride concentration 20 g L −1 , oxidation time 120 s, oxidation voltage 5.0 V, and expanding time 50 s, a nanopore structure with an average porosity of 36.75% was prepared stably on the surface of stainless steel. Using the bonding strength of polymer-metal assembly as a testing index, the stably and repeatability of the optimal process parameters were verified by injection moulding and tensile tests.

A mandibular finite element model with heterogeneous material properties is built. By analyzing the EM value of this model, it is concluded that the actual EM in anterior-posterior direction in mandibular ramus and EM in superior-inferior direction in mandibular body match the empirical EM better than the other directions.