A CT-free Intraoperative Planning and Navigation System for High Tibial Dome Osteotomy G. Wang 1, G. Zheng 1, P.A. Grützner 2, J. von Recum 2, L.P. Nolte 1 1 2

MEM Research Center – ISTB, University of Bern, Bern, Switzerland BG Truma Center Ludwigshafen, University of Heidelberg, Germany

Intraoperative Deformity Measurement

Introduction •

High tibial dome osteotomy is a widely used treatment for osteoarthritis of the knee and other lower extremity deformities. With this technique, a sequence of parallel pinholes equidistant from a central rotational axis are drilled to create a cylindrical shaped osteotomy surface. The deformity is corrected when proximal and distal bone fragments slide on each other under manual stress

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It is a technically demanding procedure. The most common complication is the postoperative malalignment, which is one of the main reasons for poor long-term results. Moreover, Inaccurate osteotomies, such as damage to the neurovascular structure or pin penetration of the tibial plateau, can be observed

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This work represents the first report of an intraoperative planning and navigation system for high tibial dome osteotomy. It is developed based on our previous introduced concept of a CT-free computer assisted navigation system for opening wedge osteotomy

3D measurement of the deformity. No reliance on conventional error-prone full-leg X-ray radiographs Possibility to check soft tissue balance and dynamical behaviors Accurate measurement of functional parameters is the prerequisite of a subsequent successful surgical procedure

Joint line convergence angle (JLCA) is measured for differentiating primary osseous varus with secondary deformities resulting from soft tissue deficiencies

Goals • Development of a navigation system aiming to reduce the risk of intraoperative complications and postoperative malalignments • Reliability assessment with laboratory setup and preliminary clinical trials

Materials and Methods System Components

Osteotomy Planning and Navigation Interactively planning of the osteotomy plane with the aid of fluoroscopy images Automatic calculation of necessitated correction angle according to measured deformities and surgeon-defined postoperative alignments Continually monitoring of the incision of surgical instruments on multiple fluoroscopic images

The system is developed based on SurgiGATE® system (PraximMediVision, La Tronche, France). A software module and a set of navigated instruments were developed. The surgical procedure for using the system consists of (1) image acquisition and landmarks registration, (2) deformity measurement, (3) planning of the osteotomy plane, and (4) navigational guidance of the planned surgical procedure The 3D cylindrical osteotomy surface is decomposed into frontal and sagittal key features. They are then superimposed on 2D fluoroscopic images for planning and navigational guidance

Deformity Correction Real time feedback of correctional angle and other functional parameters Intraoperative accurate control of the weigh-bearing axis of the operated limb

System components consists of (a) optoelectric localizer and computer system, (b) registered fluoroscopy C-arm, (c) three dynamical reference bases affixed to the patient’s anatomy, and (d) other navigated instruments, including navigated chisel, pointing device, gravity direction measurement tool, and accuracy checker, shown from top left to bottom right, respectively

Hybrid Landmark Registration (1) Biplanar 3D point reconstruction with multiple registered fluoroscopic images, (2) kinematic pivoting movement, and (3) percutaneous digitization using a pointing device Patient specific coordinate system established with registered landmarks A previously introduced image-based biplanar three dimensional (3D) point reconstruction concept (Hofstetter et al, 1999) is the primary method of landmark registration. The necessitated landmarks include hip center, defined as the spherical center of the femoral head, ankle center, defined as the center of the talus, femoral posterior condylar axis, defined as the connecting line of the most posterior aspects of the femoral condyles, and tibial plateau contour, defined with four points situated at the most lateral, medial, anterior and posterior edges of the tibial plateau

Conclusion A CT-free navigation system for high tibial dome osteotomy has been developed A laboratory evaluation and preliminary clinical trial suggests that the proposed system is safe and accurate

Deformity correction is the most critical and difficult step. Until now, no conventional tools were capable of accurately measuring 3D correctional angle and other functional parameters during the actual procedure. Only with navigational guidance, surgeons can continually monitor these variables, thus perform the planned surgical procedure precisely

System Validation In-laboratory Plastic Bone Evaluation Inter-observer difference evaluated with an entire leg model (RR0119, Synbone AG, Davos, Switzerland) was found to be 0.3° for varus/valgus, 0.6° for flexion/extension, and 1.0° for tibial slope, respectively Intra-observer reproducibility evaluated with 25 pairs fluoroscopic images (acquired within 10° deviation from the well-aligned position) was 0.4° for varus/valgus, 0.4° for flexion/extension, and 1.0° for tibial slope, with a standard deviation (95% confidence interval) of 0.6°, 0.8°, and 1.2°, respectively

Preliminary Clinical Trial The proposed system has been successfully introduced into the clinical practice of the surgery. Postoperative X-ray radiographs confirmed that the system is safe and accurate. No complications were found with the use of navigation system

7th International conference on medical image computing and computer assisted intervention Saint-Malo, France. 26-30 September, 2004

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