Christian Rotsch

Development of an optical measurement system for hip implant surgery to evaluate the leg length and the hip rotation center

The correct leg length and the position of the hip rotation center are the most important parameters for hip implant surgery. Until now there exist no suitable methods to measure it objectively. This paper describes an approach for determining leg length and hip rotation center with an optical measurement system for total hip replacement procedures. A software was programmed by the authors for this application implementing also commercial software solutions. The 3D models of the leg before and after the positioning of the hip implant were created with the Microsoft Kinect camera. Two scanned models of the leg were compared with each other. The difference between the point datasets on the screen is colored visualized and shall show the surgeon if the leg has the same length with the implant as before. During a feasibility study 30 leg models in different positions were compared to evaluate the accuracy, performance and usability of the software and the Kinect camera itself. The accuracy study shows that 96.4% of the 3D-model data points are within a range of 0-10mm. It can be recognized that the application of the Microsoft Kinect camera could be a suitable approach for determining leg length and hip rotation center in a cost-efficient and patient-friendly way.

Novel concept of a modular hip implant could contribute to less implant failure in THA: a hypothesis

BackgroundThe modularity in total hip arthroplasty (THA) allows orthopaedic surgeons for an exact reconstruction of hip biomechanical parameters especially in revision and tumor arthroplasty. Modular structured femoral stems using taper junctions showed increased implant breakage in the recent past.Presentation of the hypothesisWe hypothesize that a novel modular stem-neck-interface leads to less implant breakage compared to conventional femoral stems.Testing of the hypothesisFor this purpose, a novel modular femoral stem for THA was to design and manufacture. Therefore, three different variants of interface mechanisms were developed that enable a simple connection between the stem and the neck modules and allow for intra-operatively adjustment. Three prototypes A, B and C were manufactured and subsequently dynamic fatigue (ISO 7206–6) and body donor tested.Implication of the hypothesisModularity in THA is mainly applied in THA as well as in revision and tumor arthroplasty. Modular implants are barely used because of the high risk of breakage. Another risks in this context are taper fretting, corrosion and disconnection. With the novel design, it should be possible to detach the stem and neck module intra-operatively to adapt the anatomical situation. The novel coupling mechanism of the rotating interface seems to be the most suitable for a secure stem-neck connection and is characterized by good intraoperative handling.

Concept of patient-specific shape memory implants for the treatment of orbital floor fractures

PurposeWe will aim to develop implants made of a Ni-Ti shape memory alloy which can be applied for the treatment of midface fractures, such as isolated orbital floor fractures. These can then be implanted in a compressed form and unfold automatically in the body. With the help of newly developed application instruments, the implants can be applied along transnasal and transantral approaches into the maxillary sinus. Our objective is to evaluate the operation process and the functionality of these implants, already in a pre-investigation by an experienced surgeon on a phantom.MethodsThe functionality of the surgical procedure and an implant prototype were both evaluated with the help of a realistic phantom. The minimally invasive application was carried out using the transnasal and transantral approach. Instruments and implant were rated individually on a scale, from −2 (not at all) to +2 (very good) for vaious criteria, such as the implants functionality or the ergonomics of the entire procedure. For a geometric comparison between the manufactured implant and the planned target geometry, the implants were scanned by micro-computed tomography. CAD models were derived from the scans by using reverse engineering.ResultsBoth the implants and the application procedure were assessed as good; thus, the implant concept is suitable for further development.ConclusionsImplants made of shape memory alloys could allow in the future and allow less invasive access to treat orbital floor fractures. The implant design has to be modified that the implant can be stabilized and fixed with screws or a suture to avoid dislocation or implant loosening. The complication rates and risks of conventional orbital reconstructions should be lowered by this new method.

Topology-Optimized Implants: Medical Requirements and Partial Aspects of a Design Engineering Process Chain

Establishing a process chain for designing topology-optimized implants requires the inclusion of discipline-specific design paths that may vary significantly when considered from a medical or an engineering point of view. Creating a joint design platform is viewed as an innovative approach. The objectives include efficient communication and transfer of results between engineers and medical professionals based on software-implemented interfaces. These include aspects of modeling for design, translation to the medical environment and the surgeon’s planning of the surgical procedure. Selected partial aspects of the developed design engineering process chain are presented based on project examples from the fields of vascular surgery and hip arthroplasty.

Simulation of adaptive structures made of textile and shape memory alloy.

Medical textiles are widely used as bandages for diverse purposes. Usually textiles have a certain stiffness depending on the passive material and the manufacturing technique. To improve and extend the applications by making the stressstrain characteristic adaptive, hybrid structures made of textile with integrated shape memory alloys (SMA) are investigated and evaluated regarding its capability. This article focuses the benefits given by the numerical simulation of smart textiles using the finite element method (FEM).