Hip implant simulator for virtual surgery training

With an ageing population the number of hip replacements is increasing – as is the demand for well-trained orthopaedic surgeons. The surgical procedure requires precision and physical strength and currently the training depends on donor bodies and animals before the junior surgeon can perform the intervention in the OR supervised by an experienced colleague.

“The use of virtual reality (VR) combined with haptic simulation would enable future surgeons to practice the intervention as often as necessary without having to rely on donor bodies or animals and without having to put real patients at risk,” says Dr Mario Lorenz, research associate at the Institute for Machine Tools and Production Processes (IWP) at the Technical University (TU) Chemnitz. The simulator is designed to complement current training methods and to save scarce training resources.

Dynamic HIPS is the successor project of HIPS (HüftImplantatPfannenfräsSimulator) which was completed in 2019. “At the end of HIPS we had developed a technically fully functioning system that was able to simulate milling the acetabulum and implanting the replacement hip with haptic feedback in virtual reality,” Lorenz explains. But something was amiss, he adds: “The hard contact when placing the mill on the bone has to be generated by the robot within milliseconds in order to make the situation real for the surgeon.” However, in the first clinical tests this haptic feedback was outside the time range envisaged by the scientists.

Project aims

This is how Dynamic HIPS was born, says Lorenz: “We want to develop a haptic simulator which offers the surgeon the same sensory experience as real surgery. Above all we want to map the forces at play when sawing or milling a bone.”

With the exception of opening the body and closing the wound the researchers want to include all steps of hip replacement surgery in their expanded simulator – removing the femoral head with a bone saw, shaping the socket and placing the implant in the reshaped socket.

In the real OR the surgeon works on the femur and the acetabulum to fit the implant. In the virtual OR the surgeon see the virtual body and “feels” it since the tools give mechanical feedback. The scientists want to identify the forces, torques and speeds that occur during each step of the procedure. On the basis of this data they plan to develop a robotic arm and to further optimize current haptic tools. First, the project partners create a mathematical model that more precisely simulates the resistance and the bone tissues removal.

Furthermore, the team aims to develop a virtual OR where the surgeon in training is supervised by an experienced senior physician. Such a remote training session could be performed across long distances and would facilitate knowledge transfer to newly developed and developing countries. “We want a collaborative multi-user system,“ says Lorenz. To this end, the project partners are developing a mathematical model that simulates the resistance and material removal on the bone even more precisely.

Current results

Due to travel restrictions caused by the Corona pandemic material tests had to be postponed to autumn 2021. Nevertheless, the project partners were able to finish all individual components as Lorenz explains: “We expect to be able to join all components that is to completely finish our extended prototype by spring 2022.”

The project partners

In addition to TU Chemnitz the University of Bremen and several companies are involved in the project. FAKT Software GmbH will integrate the components and build the training system as well as the multi-user system. CAT Production GmbH developed the 3D models of patient anatomy and of the OR. Haption GmbH will contribute an enhanced haptic systems and a module for user safety.

YOUSE GmbH will ensure the user-centred approach of the project and monitor ELSI, i.e. the ethical, legal and social implications of Dynamic HIPS.

The medical experts on the project are the Department of Orthopaedic, Trauma and Plastic Surgery at the University Hospital Leipzig, the Centre for the Study of the Musculoskeletal System (ZESBO), the Division of Macroscopic and Clinical Anatomy at the Medical University Graz (Austria) and the med-tech department of the Fraunhofer Institute for Machine Tools and Forming Technology (IWU).

Profile:
After having completed his computer science study program at Westsächsische Hochschule Zwickau in 2010, Mario Lorenz received his PhD at the University Leipzig in 2020. He has been research associate for VR and AR at the chair for production systems and processes at TU Chemnitz since 2011. Moreover, he is research fellow at the Department of Orthopaedic, Trauma and Plastic Surgery at the University Hospital Leipzig (since 2016) and at the Division of Macroscopic and Clinical Anatomy of the Medical University Graz (since 2020).

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