title: Implementation, accuracy evaluation, and preliminary clinical trial of a CT-free navigation system for high tibial opening wedge osteotomy.
abstract: OBJECTIVE
  The objectives of this study are to design and evaluate a CT-free intra-operative planning and navigation system for high tibial opening wedge osteotomy. This is a widely accepted treatment for medial compartment osteoarthritis and other lower extremity deformities, particularly in young and active patients for whom total knee replacement is not advised. However, it is a technically demanding procedure. Conventional preoperative planning and surgical techniques have so far been inaccurate, and often resulting in postoperative malalignment representing either under- or over-correction, which is the main reason for poor long-term results. In addition, conventional techniques have the potential to damage the lateral hinge cortex and tibial neurovascular structures, which may cause fixation failure, loss of correction, or peroneal nerve paralysis. All these common problems can be addressed by the use of a surgical navigation system.
  
  
  METHODS
  Surgical instruments are tracked optically with the SurgiGATE((R)) navigation system (PRAXIM MediVision, La Tronche, France). Following exposure, dynamical reference bases are attached to the femur, tibia, and proximal fragment of the tibia. A patient-specific coordinate system is then established, on the basis of registered anatomical landmarks. After intra-operative deformity measurement and correction planning, the osteotomy is performed under navigational guidance. The deformities are corrected by realigning the mechanical axis of the affected limb from the diseased medial compartment to the healthy lateral side. The wedge size, joint line orientation, and tibial plateau slope are monitored during correction. Besides correcting uni-planar varus deformities, the system provides the functionality to correct complex multi-planar deformities with a single cut. Furthermore, with on-the-fly visualization of surgical instruments on multiple fluoroscopic images, penetration of the hinge cortex and damage to the neurovascular structures due to an inappropriate osteotomy can be avoided.
  
  
  RESULTS
  The laboratory evaluation with a plastic bone model (Synbone AG, Davos, Switzerland) shows that the error of deformity correction is <1.7 degrees (95% confidence interval) in the frontal plane and <2.3 degrees (95% confidence interval) in the sagittal plane. The preliminary clinical trial confirms these results.
  
  
  CONCLUSIONS
  A novel CT-free navigation system for high tibial osteotomy has been developed and evaluated, which holds the promise of improved accuracy, reliability, and safety of this procedure.
authors.affiliation: Maurice E. Mueller Research Center for Orthopaedic Surgery, University of Bern, Bern, Switzerland.
authors.forename: Gongli
authors.initials: G
authors.lastname: Wang
authors.forename: Guoyan
authors.initials: G
authors.lastname: Zheng
authors.forename: Peter
authors.initials: P
authors.lastname: Keppler
authors.forename: Florian
authors.initials: F
authors.lastname: Gebhard
authors.forename: Alex
authors.initials: A
authors.lastname: Staubli
authors.forename: Urs
authors.initials: U
authors.lastname: Mueller
authors.forename: Daniel
authors.initials: D
authors.lastname: Schmucki
authors.forename: Simon
authors.initials: S
authors.lastname: Fluetsch
authors.forename: Lutz-Peter
authors.initials: LP
authors.lastname: Nolte
mesh_terms: D001182:Arthroscopy / Q000379:methods*; D005471:Fluoroscopy; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000601:surgery; D019060:Minimally Invasive Surgical Procedures / Q000295:instrumentation / Q000379:methods; D016343:Monitoring, Intraoperative / Q000295:instrumentation*; D015588:Observer Variation; D010027:Osteotomy / Q000295:instrumentation* / Q000379:methods; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D025321:Surgery, Computer-Assisted / Q000379:methods*; D013673:Technology Assessment, Biomedical; D013977:Tibia / Q000601:surgery*; D014057:Tomography, X-Ray Computed