Abstract:Objective To propose some detailed methods for diagnosis of aseptic loosening failure in clinic by studying the mechanical mechanism and the specific causes of aseptic loosening failure after the total hip arthroplasty (THA). Methods The causes of aseptic loosening were investigated from the view of biomechanics, such as strength of the bone cement layer, interface fretting, stress shielding, wear and osteolysis; the relationships between aseptic loosening failure and products, clinical and patient factors were analyzed; the method to detect loosening before the revision surgery was also studied. Results The reasoning route for aseptic loosening failure analysis after THA was proposed, and detection of aseptic loosening with fluoroscopic analysis (FSA) technique before the revision surgery was conducted successfully. Conclusions The reasoning route for aseptic loosening failure analysis can help to discover reasons of failure occurrence. Loosening can be detected and confirmed in vivo by FSA method, which can also assist the clinician for diagnosis and treatment of aseptic loosening after the THA.

Abstract:Objective To investigate effects of aging on the fracture mechanical behavior of human dentin with finite element numerical method. Methods The finite element model was established according to the typical compact tension specimen in the experiment. The stable crack growth in human dentin was simulated with the cohesive zone model to compare the crack extensions of the young and aged dentin. Results The growth toughness and plateau toughness of the aged dentin were 0.51 and 1.19 MPa?m1/2, respectively, which were significantly lower than those of the young dentin (7.48, 1.71 MPa?m1/2). However, the initiation toughness of the young and aged dentin showed no significant difference with 0.51 and 0.38 MPa?m1/2, respectively. Conclusions The crack growth resistance of human dentin is decreased significantly with aging. Based on the cohesive zone model, the crack growth behavior of biological hard tissue, whose mechanical properties are related with age (such as the human dentin), can be well predicted by using numerical methods.

Abstract:Objective To investigate the influence of acetabular morphology on contact mechanics of the human hip joint. Methods One anatomical finite element (FE) model of natural hip joint and three simplified FE models with different acetabular geometry were established to study the contact mechanics of hip joint under gait loads. Results (1) Contact predicted by the anatomical model was mainly distributed in the acetabular medial-superior area, from anterior to posterior, with the peak contact pressure occurred in the anterior-superior area; (2) Compared with the anatomical model, the rotational ellipsoid produced similar contact behavior, while the sphere and the rotational conchoids predicted that contact was distributed in the medial-lateral direction; (3) The rotational ellipsoid predicted the largest contact area and the lowest peak contact pressure and Von-Mises stress; (4) The sphere and rotational conchoids had similar contact mechanical behavior. Conclusions Compared with the sphere and rotational conchoids, the rotational ellipsoid could be more preferable to represent the anatomical morphology of the acetabulum and its contact mechanics.

Abstract:ObjectiveTo develop a finite element computational model of the torso for the numerical simulation of mechanical responses of human torso to non-penetrating ballistic impact. MethodsBased on the CT data of a Chinese adult man, the finite element model of human torso was created by using the medical image processing software Mimics and the finite element pre-processing software HyperMesh. The pressure and acceleration response of the human torso outfitted with soft body armor to the ballistic impact from 9 mm ammunition at a velocity of 360 m/s was calculated numerically by the explicit finite element code LS-DYNA. ResultsThe finite element model of human torso including thoracic skeletal structure, organs, mediastinum and muscle/skin was established. The pressure response of heart, lung, liver and stomach, as well as the acceleration response of sternum were obtained by numerical calculation. It was found that the peak pressure and its time phase were dependent on the distance between the impact point and the measured p