An extendable modular endoprosthetic system for bone tumour management in the leg

A modular endoprosthetic system has been developed at the Groningen University Hospital and the University of Twente. The system can bridge a defect resulting from the resection of a malignant bone tumour which has developed around the knee joint of a child. Since the other healthy leg continues to grow, the system includes an element whose length can be adjusted non-invasively by using an external magnetic field. In addition to this lengthening element, there are one hip and two knee components, connectors of various lengths, and fixation elements. The paper describes the elements of the modular endoprosthetic system. Tables are created by means of which the elemental composition of such an endoprosthesis can be determined for each individual patient

The BLLAST field experiment: Boundary-Layer late afternoon and sunset turbulence

Due to the major role of the sun in heating the earth's surface, the atmospheric planetary boundary layer over land is inherently marked by a diurnal cycle. The afternoon transition, the period of the day that connects the daytime dry convective boundary layer to the night-time stable boundary layer, still has a number of unanswered scientific questions. This phase of the diurnal cycle is challenging from both modelling and observational perspectives: it is transitory, most of the forcings are small or null and the turbulence regime changes from fully convective, close to homogeneous and isotropic, toward a more heterogeneous and intermittent state. These issues motivated the BLLAST (Boundary-Layer Late Afternoon and Sunset Turbulence) field campaign that was conducted from 14 June to 8 July 2011 in southern France, in an area of complex and heterogeneous terrain. A wide range of instrumented platforms including full-size aircraft, remotely piloted aircraft systems, remote-sensing instruments, radiosoundings, tethered balloons, surface flux stations and various meteorological towers were deployed over different surface types. The boundary layer, from the earth's surface to the free troposphere, was probed during the entire day, with a focus and intense observation periods that were conducted from midday until sunset. The BLLAST field campaign also provided an opportunity to test innovative measurement systems, such as new miniaturized sensors, and a new technique for frequent radiosoundings of the low troposphere. Twelve fair weather days displaying various meteorological conditions were extensively documented during the field experiment. The boundary-layer growth varied from one day to another depending on many contributions including stability, advection, subsidence, the state of the previous day's residual layer, as well as local, meso- or synoptic scale conditions. Ground-based measurements combined with tethered-balloon and airborne observations captured the turbulence decay from the surface throughout the whole boundary layer and documented the evolution of the turbulence characteristic length scales during the transition period. Closely integrated with the field experiment, numerical studies are now underway with a complete hierarchy of models to support the data interpretation and improve the model representations.publishedVersio

A multiscale model to predict current absolute risk of femoral fracture in a postmenopausal population

Osteoporotic hip fractures are a major healthcare problem. Fall severity and bone strength are important risk factors of hip fracture. This study aims to obtain a mechanistic explanation for fracture risk in dependence of these risk factors. A novel modelling approach is developed that combines models at different scales to overcome the challenge of a large space–time domain of interest and considers the variability of impact forces between potential falls in a subject. The multiscale model and its component models are verified with respect to numerical approximations made therein, the propagation of measurement uncertainties of model inputs is quantified, and model predictions are validated against experimental and clinical data. The main results are model predicted absolute risk of current fracture (ARF0) that ranged from 1.93 to 81.6% (median 36.1%) for subjects in a retrospective cohort of 98 postmenopausal British women (49 fracture cases and 49 controls); ARF0 was computed up to a precision of 1.92 percentage points (pp) due to numerical approximations made in the model; ARF0 possessed an uncertainty of 4.00 pp due to uncertainties in measuring model inputs; ARF0 classified observed fracture status in the above cohort with AUC = 0.852 (95% CI 0.753–0.918), 77.6% specificity (95% CI 63.4–86.5%) and 81.6% sensitivity (95% CI 68.3–91.1%). These results demonstrate that ARF0 can be computed using the model with sufficient precision to distinguish between subjects and that the novel mechanism of fracture risk determination based on fall dynamics, hip impact and bone strength can be considered validated

A human model for low-severity rear-impacts

Neck injuries resulting from rear-end collisions rank among the top safety problems and have serious implications for society. In an attempt to minimize the severity of neck injuries in such accidents, an increasing number of studies to evaluate the effectiveness of head restraints has been performed. In these studies, volunteers, crash test dummies, and mathematical dummy models were used. In addition, a limited number of mathematical models of the human body was used. However, to the best of our knowledge, these models were not validated in an environment comparable with a rear-end collision. The objective of this study is to develop a mathematical model of a seated occupant and to better understand the biomechanical response of the spine and the occupant's interaction with the seat during rear-end collisions. For this purpose, a 3D mathematical model of a 50th percentile sitting adult male is developed for use in simulations of rear impacts. Special attention is paid to the modelling of the spine, including the neck, and the occupant's interaction with the seat. To obtain insight into its biofidelity, the model's response is compared with rear-end sled tests with volunteers and human cadavers at a ¿V of up to 30 km/hr. The model is then used to study and quantify the motion of the spine in low and medium severity rear-end collisions. This study revealed that, during the ''torso loading phase'', the pelvis was lifted from the seat while the vertical motion of the T1 vertebral body relative to the vehicle was slight. Spinal compression occurred during this phase, but it remained slight. Although a thorough validation of the model developed was not possible due to lack of experimental data, it can be concluded that this model has the potential to become a powerful tool for parametric studies to aid in a seat design process

A human model for low-severity rear-impacts

Neck injuries resulting from rear-end collisions rank among the top safety problems and have serious implications for society. In an attempt to minimize the severity of neck injuries in such accidents, an increasing number of studies to evaluate the effectiveness of head restraints has been performed. In these studies, volunteers, crash test dummies, and mathematical dummy models were used. In addition, a limited number of mathematical models of the human body was used. However, to the best of our knowledge, these models were not validated in an environment comparable with a rear-end collision. The objective of this study is to develop a mathematical model of a seated occupant and to better understand the biomechanical response of the spine and the occupant's interaction with the seat during rear-end collisions. For this purpose, a 3D mathematical model of a 50th percentile sitting adult male is developed for use in simulations of rear impacts. Special attention is paid to the modelling of the spine, including the neck, and the occupant's interaction with the seat. To obtain insight into its biofidelity, the model's response is compared with rear-end sled tests with volunteers and human cadavers at a ¿V of up to 30 km/hr. The model is then used to study and quantify the motion of the spine in low and medium severity rear-end collisions. This study revealed that, during the ''torso loading phase'', the pelvis was lifted from the seat while the vertical motion of the T1 vertebral body relative to the vehicle was slight. Spinal compression occurred during this phase, but it remained slight. Although a thorough validation of the model developed was not possible due to lack of experimental data, it can be concluded that this model has the potential to become a powerful tool for parametric studies to aid in a seat design process