A full body musculoskeletal model based on flexible multibody simulation approach utilised in bone strain analysis during human locomotion

Load-induced strains applied to bone can stimulate its development and adaptation. In order to quantify the incident strains within the skeleton, in vivo implementation of strain gauges on the surfaces of bone is typically used. However, in vivo strain measurements require invasive methodology that is challenging and limited to certain regions of superficial bones only such as the anterior surface of the tibia. Based on our previous study [Al Nazer et al. (2008) J Biomech. 41:1036&ndash;1043], an alternative numerical approach to analyse in vivo strains based on the flexible multibody simulation approach was proposed. The purpose of this study was to extend the idea of using the flexible multibody approach in the analysis of bone strains during physical activity through integrating the magnetic resonance imaging (MRI) technique within the framework. In order to investigate the reliability and validity of the proposed approach, a three-dimensional full body musculoskeletal model with a flexible tibia was used as a demonstration example. The model was used in a forward dynamics simulation in order to predict the tibial strains during walking on a level exercise. The flexible tibial model was developed using the actual geometry of human tibia, which was obtained from three-dimensional reconstruction of MRI. Motion capture data obtained from walking at constant velocity were used to drive the model during the inverse dynamics simulation in order to teach the muscles to reproduce the motion in the forward dynamics simulation. Based on the agreement between the literature-based in vivo strain measurements and the simulated strain results, it can be concluded that the flexible multibody approach enables reasonable predictions of bone strain in response to dynamic loading. The information obtained from the present approach can be useful in clinical applications including devising exercises to prevent bone fragility or to accelerate fracture healing.<br /

Analysis of dynamic strains in tibia during human locomotion based on flexible multibody approach integrated with magnetic resonance imaging technique

Bone is known to adapt to the prevalent strain environment while the variation in strains, e.g., due to mechanical loading, modulates bone remodeling, and modeling. Dynamic strains rather than static strains provide the primary stimulus of bone functional adaptation. The finite element method can be generally used for estimating bone strains, but it may be limited to the static analysis of bone strains since the dynamic analysis requires expensive computation. Direct in vivo strain measurement, in turn, is an invasive procedure, limited to certain superficial bone sites, and requires surgical implementation of strain gauges and thus involves risks (e.g., infection). Therefore, to overcome difficulties associated with the finite element method and the in vivo strain measurements, the flexible multibody simulation approach has been recently introduced as a feasible method to estimate dynamic bone strains during physical activity. The purpose of the present study is to further strengthen the idea of using the flexible multibody approach for the analysis of dynamic bone strains. Besides discussing the background theory, magnetic resonance imaging is integrated into the flexible multibody approach framework so that the actual bone geometry could be better accounted for and the accuracy of prediction improved.<br /

Time to Relapse after Epilepsy Surgery as a Predictor of Future Seizures

Epilepsy affects more than 50 million people worldwide. Refractory epilepsy, defined as failure to respond to two anti-epileptic medications, is often considered for surgery. 30-50% of those who undergo surgery experience seizures after their procedure. Those who experience a seizure following surgery may benefit from prognostic information to determine when subsequent seizures will occur. This knowledge may inform best practices with respect to further surgeries or pharmacologic intervention, thus improving tertiary prevention and public health. Current literature uses the length of time between surgery and the first post-surgery seizure (seizure latency) to predict the long-term outcome of the patient. This study uses seizure latency to examine short-term outcomes and identify the timing of the second and third seizure after surgery. Data was used from a retrospective database at Thomas Jefferson University Hospital’s Comprehensive Epilepsy Center that has been maintained since 1986. Records were initially stratified into temporal (N = 943) and extratemporal (N = 125) surgeries. Statistical analyses were done using SAS software and utilized a Cox proportional hazards model while controlling for demographics and clinical factors. Generally, as seizure latency increased, the time between the first seizure recurrence and subsequent seizures increased. These results were statistical meaningful in the temporal group (First-to-Second Analysis: Wald Chi Square: 39.85, df = 5,

Obtaining various shapes of machined surface using tool with a compound multi-insert cutting edge

A novel design of a universal form tool is presented for machining complex planar and axisymmetric surfaces. The geometric and kinematic flexibility (GKF) of this tool type means that it can machine a wide range of profiles using a single setup. The operating principle of this multi-insert tool is its combination of single cutting edges, each of which form the individual details of the machined surface. The structure and application of both turning and milling multi-insert tools with combinations of single edges are described in the paper. Complex shapes and forms can be machined by changing the cutting-edge positions. The number of combinations of a given tool set can be determined by using the relations detailed in this study. Both turning and milling tools are utilized in a unique tool holder that clamps the inserts into position and allows their adjustment that is facilitated by special prepared analytical software to the desired object profiles. It is possible to use these tools in machining both wood and aluminum alloys. Finally, the design of the multi-insert tools for turning and milling and its functional features were experimentally verified with positive results