Influence of size and CCD-angle of a short stem hip arthroplasty on strain patterns of the proximal femur : an experimental study

Purpose: The number of primary total hip arthroplasties (THA) is steadily increasing. Over the last decade numerous so-called short stem hip arthroplasties were introduced on the market. The aim of these implants with a predominantly metaphyseal anchorage is to reduce stress shielding and thereby the risk of aseptic loosening. One of the short stem arthroplasties with predominant metaphyseal fixation is the METHA® short stem (Aesculap, Tuttlingen, Germany). In order to reconstruct the biomechanics the METHA stem is available in different sizes with different centrum-collum-diaphysis-angles (CCD-angle). In this study, we want to address the research question of how the size of the implant and different CCD-angles influence the strain patterns of the proximal femur. Methods: Three different stem sizes (size 2, 3 and 4 – CCD-angle 130°) and three stems with different CCD-angles (size 3 – 120°, 130° and 135° CCD-angle) were successively implanted in a synthetic femur. Eight strain gauges monitored the corresponding strain patterns of the proximal femur. Results: Independent of stem size and CCD-angle only small changes in the strains were recorded around the distal part of the METHA stem when compared to the intact femur. However, all stems increased the strains in the region of the calcar. This was most pronounced by smaller CCD-angles and major sizes. Conclusion: The stem size and CCD-angle primarily influence the region of the calcar. Greater sizes and smaller CCD-angles lead to increased strains at the calcar. The other regions are hardly influenced by the stem size and CCDangle of the femoral component

αBSM failed as a carrier of rhBMP-2 to enhance bone consolidation in a sheep model of distraction osteogenesis

One of the problems associated with callus distraction is a long time period needed for consolidation of the newly formed bone. The goal of this study was to determine whether percutaneous injections of rhBMP 2 in BSM would enhance bone consolidation. Methods: A unilateral tibial osteotomy combined with external stabilization was performed in 20 adult sheep. After a latency of four days, distraction was conducted for 20 days. Sheep were divided into three groups: group 1 received rhBMP-2/αBSM injections at day 23 and 30, group 2 buffer/BSM injections at day 23 and 30 and group 3 did not receive any injection. The radiographs and in-vivo torsional stiffness measurements were obtained weekly during the following 50 days. Post-mortem bone densitometry (DXA) and mechanical testing were performed. Results: In-vivo stiffness assessments, DXA values and the maximum torsional moment of the sheep tibia treated with two rhBMP-2 injections were not significantly greater than those of both control groups. Conclusions: Presented application of rhBMP-2 in BSM failed to enhance bone consolidation in distraction osteogenesis

Development of an integration and application platform for diverse identification and positioning technologies

Diverse identification and positioning technologies like radio-frequency identification (RFID), real-time locating systems (RTLS), and wireless sensor networks (WSN) are among the enablers for the Internet of Things (IoT). Although the cost-effective integration of these enabling technologies into existing enterprise infrastructures is very important for companies, integration aspects are ignored by researches frequently. Even worse, the increasing diversity of identification and positioning technologies and corresponding applications leads to more expensive integration and application development processes. Up to now these technologies are used rather separately in different applications, but it is only a question of time before these technologies have to be used within the same application in parallel. Furthermore it could be observed, that existing commercial middleware products aiming at integration are focusing on passive RFID only. Hence there is a need to functionally extend existing solutions. This contribution introduces an integration and application platform for diverse enabling technologies for the Internet of Things that has been derived from the requirements of real world applications. An overview on applications of the Internet of Things is given and a selection of applications that have been successfully implemented in research and development projects is examined in detail. The functionalities provided by the platform and the corresponding abstract software architecture are derived from these applications

ASAP: A MAC Protocol for Dense and Time-Constrained RFID Systems

We introduce a novel medium access control (MAC) protocol for radio frequency identification (RFID) systems which exploits the statistical information collected at the reader. The protocol, termed adaptive slotted ALOHA protocol (ASAP), is motivated by the need to significantly improve the total read time performance of the currently suggested MAC protocols for RFID systems. In order to accomplish this task, ASAP estimates the dynamic tag population and adapts the frame size in the subsequent round via a simple policy that maximizes an appropriately defined efficiency function. We demonstrate that ASAP provides significant improvement in total read time performance over the current RFID MAC protocols. We next extend the design to accomplish reliable performance of ASAP in realistic scenarios such as the existence of constraints on frame size, and mobile RFID systems where tags move at constant velocity in the reader's field. We also consider the case where tags may fail to respond because of a physical breakdown or a temporary malfunction, and show the robustness in those scenarios as well