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.