A new method for preoperative planning before knee TEP Coregistration of 3D DVT with 2D X-ray whole leg images.
Schlüter-Brust K.1 , Tobolski O. 2 , Steinseifer A. 1 , Königsfeld S. 1 , Glanz M. 1 1St Franziskus Hospital Cologne, Orthopedics, Cologne, Germany 2Sporthomedic, Cologne, Germany
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Introduction
Digital volume tomography (DVT) is an X-ray procedure that is increasingly being used in orthopedics. To date, this three-dimensional tomography technique has been used primarily in dentistry, ear, nose and throat medicine, and oral and maxillofacial surgery. In orthopedics, it currently has use for imaging the upper extremity and also the lower extremity with emphasis on the knee and ankle joints. A possible advantage compared to 3D CT images is on the one hand the reduction of the radiation dose and on the other hand the possibility to generate 3D volume images in the knee and foot area under load. Two- and three-dimensional planning with the software mediCAD (company mediCAD Hectec) has been possible for years and has been used in our clinic for a long time. In this paper, we present a method that makes it possible to plan 3-dimensionally on DVT volume data of the knee joint.
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Methodology
For this purpose, a DVT scan of the knee joint under load is coregistered with the whole-leg stance image of the same patient.
In the first step, a point cloud is defined at the proximal end of the tibia and at the distal portion of the femur.
These multiple points are marked on the DVT image of the knee joint and analogously on the whole leg stance image. Both images have been taken under load of the respective extremity.
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Suitable point areas are the areas around the medial and lateral epicondyles on the femur, as well as the most distal areas on the epicondyles medially and laterally. Correspondingly on the tibia, points on the bony joint line and the furthest medial and lateral bony points one centimeter below the joint line.
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These coordinates are co-registered from the X-ray image of the whole leg with those of the DVT image using a special software add-on from the company mediCAD Hectec 3 D) This process is also called matching The more and the more characteristic the points are defined in both systems, the more accurate this matching can be.
This process now generates a 3 D knee Dicom cloud with 2 D data from the femoral head and ankle joint, without having to collect 3 D data e.g. via a radiation-intensive CT in the hip and ankle area. In the 3 D knee module of the mediCAD software, the femoral head center and the center of the ankle joint can now be defined. It is now possible to complete the entire 3 D knee TEP planning. Planning is now possible with images under load.
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Diskussion
This procedure enables patient-specific three-dimensional planning of a knee prosthesis without CT, with a higher resolution and a significant reduction in radiation dose. It also provides volume data of the knee joint under load. Analyses on the accuracy of the matching process are still pending and need to be performed before a release of this procedure. Another point of criticism is certainly still the currently increased time required and the technically demanding procedure of planning. However, in the authors’ opinion, the educational added value is clearly in the foreground when planning for primary knee TEPS, revisions, and in the future for osteotomies.
