Background: Navigation allows for determination of the mechanical axis of the lower extremity during high tibial osteotomy (HTO) procedures. The objectives of this study were to (1) evaluate the reliability of noninvasive registration with an image-free navigation system for HTO and (2) determine the accuracy of the navigation system to monitor changes in lower limb alignment as compared with alignment measured with a novel 3-dimensional computed tomography method.
Hypothesis: Navigated limb alignment demonstrates good reliability and accuracy in all 3 planes.
Study design: Descriptive laboratory study.
Methods: Thirteen cadaver legs were used to examine the intra- and interobserver registration reliability of 3 observers. Initial coronal, sagittal, and axial alignment was measured on 6 legs, 3 times each, at intervals >36 hours. Navigated HTOs were then performed on all 13 legs, pre- and postoperative alignment was recorded, and data were compared with equivalent measures obtained by 3-dimensional computed tomography. Reliability and accuracy data were both analyzed using intraclass correlation coefficients with the following established thresholds: good, >0.75; fair, 0.4 to 0.75; and poor, <0.4.
Results: Intraclass correlation coefficients for intraobserver reliability were categorized as follows: varus-valgus, good; flexion-extension, fair; and femoral-tibial rotation, poor. For interobserver reliability, results were varus-valgus, fair; flexion-extension, fair; and femoral-tibial rotation, poor. Intraclass correlation coefficients for navigation accuracy were varus-valgus, good; tibial slope, good; and tibial torsion, poor. Maximum differences in navigation-computed tomography measurements were Delta varus-valgus angle, 4.5 degrees; Delta tibial slope, 8.8 degrees; and Delta tibial torsion, 16.5 degrees.
Conclusion and clinical relevance: Navigation may be reliable and clinically useful for dynamic monitoring of coronal leg alignment but has limits in determination of sagittal and axial plane alignment.