Institute for
Robotics and Process Control

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High Tibia Osteotomy

Project Description

Problem

In cooperation with the trauma department of the Medizinische Hochschule Hannover(External) and the Institut für Werkstoffkunde of the Leibniz Universität Hannover(External) novel methods for robot-assisted surgery for correction of deformities of the lower limbs are explored in this project.

Congenital, from fractures or by tumors acquired deformities of the lower extremities of the human skeleton under stress usually lead to an uneven distribution of pressure in the adjacent joints (knee / hip). If these malalignments are left untreated, the result is often wear of the articular cartilage which in an advanced stage often requires a joint replacement. An early performed corrective surgery may help to prevent the implantation of a prostheses or at least delay this intervention significantly. Establishing an optimal pressure distribution in the knee is a crucial factor for a successful operation with the desired positive long-term result for the patient. However, there are currently no intraoperative tools available which allow measuring the pressure distribution within the loaded knee reliably and non-invasively. Moreover, the optimal type of osteotomy (bone cutting technique) according to biomechanical aspects is the focal-dome osteotomy. But this technique is due to the difficult technical implementation not clinically established. So in practice surgeons fall back to suboptimal types of osteotomy.
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Types of osteotomy

Project Goals

This project aims to develop and test new methods of operation with an increased quality of the above-mentioned surgical procedures based on precise surgical planning and implementation. Using a robotized sensory analysis of force and pressure conditions in the knee joint, a surgical plan that includes both an optimally located osteotomy (cutting plane or curve) and an optimal correction angle is automatically generated. For the cutting process new technologies are used that exceed the conventional methods in terms of quality (surface smoothness) of the cut surfaces and thermal effects during the cutting process. The water jet cutting is a technology that meets both these conditions and will be further developed and tested for this clinical application. Guiding the water jet cutting instrument is performed with high precision by a robot that eventually performs the motion correction using a force-torque sensor, X-ray imaging and surgical navigation.


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Osteotomy performed with a waterjet

In a first step, we developed a method for pressure prediction within the knee. From CT scans of the knee we create a detailed surface model of the knee. This model serves as the basis for a pressure analysis using the Rigid Body Spring Model Method (RBSMM). Femur and tibia are modeled as rigid bodies. The cartilage within the knee is modeled as a series of springs, which are uniformly distributed on the tibia plateau. Using the method of virtual displacement, for a global input force F it is possible to determine the local spring force for each spring. All local spring forces together build a surface pressure distribution, which is visualized in the following figure.
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Pressure distribution on the tibia plateau

Further Information


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