Abstract
Abstract To increase learning success in surgical training, physical simulators are supplemented by measurement technology to generate and record objective feedback and error detection. An opportunity to detect fractures following hip stem implantation early can be measurement of occurring strains on bone surface. These strains can be determined while using strain gauges, digital image correlation (DIC) or photoelasticity. In this research strain gauges and DIC were compared regarding their suitability as strain measurement tools for use in physical simulators. Therefore a testing method was described to replicate the implantation of a hip stem. Testing devices modelled on a realistic prosthesis were pressed into prepared porcine femora in a two-step procedure with a material testing machine. The local strains occurring on bone surface were determined using an optical measurement system for DIC and strain gauges. The initial fractures in the tested femora are located medial-anterior in most cases (73,6%). With increasing indentation depth of the test device, the strains on bone surface increase. Comparing the local strains determined by DIC and strain gauges consistencies in curves are noticeable. Maximal determined strains before fracturing amount to 0,69% with strain gauges and 0,75% with DIC. In the range of the fracture gap, strain gradients are determined by using DIC. However the detected surfaces are of low quality caused by gaps and motion artefacts. The results show strains on bone surfaces for early fracture detection are measurable with strain gauges and DIC. DIC is assessed as less suitable compared to strain gauges. Furthermore strain gauges have greater level of integration and economic efficiency, so they are preferred the use in surgical training simulators.
Highlights
The treatment of a hip joint with an endoprosthesis is a main area of surgical orthopaedics and requires extensive anatomical knowledge and experience to ensure the treatment of patients without complications
In literature no methods are described with regard to early error detection of intraoperative fractures following hip stem implantation
Thereby strains, that lead to fractures and occur when a prosthesis is impacted, can be measured with strain gauges and optical measurements. [1, 7]
Summary
The treatment of a hip joint with an endoprosthesis is a main area of surgical orthopaedics and requires extensive anatomical knowledge and experience to ensure the treatment of patients without complications. For these purposes physical simulators are used in surgical training. Strain gauges are accurate measuring tools for determining local strains. Due to their size, strain gauges have a high degree of integration and are cost-effective compared to alternative methods e.g. optical measurements. For determining strain distributions on surfaces, several strain gauges are applied in an array Thereby the mechanical behavior of the test specimen is not affected. [4]
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