The aim of this study is to evaluate a new system for CT-based 3D planning, navigation and subsequent postoperative migration analysis in patients with total hip arthroplasty (THA). Patients (age 40-75 years) with osteoarthritis, eligible for surgery, are asked to participate, and the investigators plan to follow all patients for 2 years after surgery.

In THA surgery, the goal is to recreate the natural motion-center of the hip, adjust for possible leg length differences and to optimize prosthetic placement to reduce the risk of future dislocation or loosening. Today, usually a plain X-ray is taken before the operation to plan size and position. This has its limitations since the surgeon can not assess the 3D position on a 2D image. In this study, the investigators are using a new system for planning in 3D, based on a low-dose CT scan and with the help of AI. Moreover, the surgeon get real-time information of the prosthetic position during surgery (called navigation), after matching the physical patient to a virtual patient. The hypothesis is that prosthetic placement and patient satisfaction will improve with 3D planning and navigation, resulting in a more anatomical restoration, and that postoperative complications, such as dislocation and ultimately loosening will reduce.

Entering this study entails taking a CT scan before surgery (instead of a plain X-ray), and for validation, a postoperative CT scan. This enables the investigators to find out whether the planning and navigation are confirmed by the postoperative position. In addition to planning and navigation, the investigators wish to implement a way of measuring prosthetic migration after surgery. Today, this is done by implanting small metal (tantalum) markers in the bone during surgery, and then measuring the distance between prosthesis and markers over time in a special software on multiple X-rays (This method is called RSA, Radiostereometric Analysis). However, few hospitals have the expertise or equipment to do these analyses and it is a somewhat laborious process. This study will evaluate a new tool for making equivalent migration analysis, based on CT scans. By matching the postoperative CT image to subsequent CT scans at 3 months, 1 and 2 years after surgery, the investigators can see how much the prosthesis has moved in relation to the bone and hopefully being able to foresee future loosening. The hypotheses is that CT migration analysis will be as accurate and precise as the current gold standard (RSA). A subset of the patients will have RSA performed as well for direct comparison between the systems regarding migration.

A transition from plain X-ray images to low-dose CT will result in a marginal increase in the radiation dose. At the same time, it means that a much more accurate imaging of the skeleton is performed, and thus improved preoperative planning and a per-operative navigation can be done with much more predictable results. This study has been approved by the Swedish Ethical Review Authority, as well as the local radiation committee. The company, Ortoma, supplying the measurement system for planning and navigation (Ortoma Treatment Solution (OTS™)) has received ISO13485 certification and CE-certificate on all parts.