Paper 144: Effect of Opening-wedge High Tibial Osteotomy on Three-dimensional Knee Kinematics

Abstract

Medial opening-wedge high tibial osteotomy (HTO) is a treatment for medial tibiofemoral osteoarthritis caused by varus malalignment. This malalignment shifts the line of action of the ground reaction force relative to the centre of the knee, which increases load in the medial compartment. This increased load is widely believed to be the cause of medial tibiofemoral (TF) OA. HTO restores the line of action to a neutral or slightly lateral position. Consensus has emerged on an optimal range of varus/valgus angular correction, however achieving this correction does not guarantee good clinical results. A key limitation of current assessment that may explain this is that the current standard for assessing tibiofemoral alignment, a standing radiograph, provides a poor assessment of the mechanics of the joint. Three-dimensional measurements of tibiofemoral and patellofemoral kinematics in vivo have recently become available but the effect of opening-wedge high tibial osteotomy on knee kinematics is not clear. Our research question was: how does opening-wedge HTO affect 3D tibiofemoral and patellofemoral kinematics? Three-dimensional tibiofemoral and patellofemoral kinematics were assessed in four subjects before HTO surgery and at 6 months follow-up using a validated MR imaging method (1Fellows R.A. et al.J Biomech. Aug 2005; 38: 1643-1652Abstract Full Text Full Text PDF PubMed Scopus (57) Google Scholar, 2Fellows R.A. et al.J Magn Reson Imaging. 2005; 22: 145-153Crossref PubMed Scopus (34) Google Scholar). Ethics board approval was granted and informed consent was obtained from all subjects for this study. Titanium surgical hardware was used for minimum artifact in the images. For each assessment, the subject lay supine in the MR scanner. A high-resolution T1-weighted mulitslice scan of the knee was performed in a relaxed position. Low resolution images of the knee were then obtained at six flexion angles (10°–60°) while the subject loaded his/her knee using a specially designed loading rig. Bone was segmented from the MR images using Analyze. Surfaces (high-res) and contours (low-res) were then imported into MATLAB. The high-resolution models were shapematched to the low-resolution data sets using an iterative closest points algorithm. Anatomical axes were assigned to each bone using anatomical landmarks. Kinematic parameters (rotations and translations) with respect to femur for both tibia and patella were output. Linear best fits were calculated for each parameter with respect to tibial flexion. Slope and intercept were examined using a paired t-test. HTO significantly shifted the tibia anteriorly through the range of flexion (p<0.05). The average change at 30 degrees was 6.5 mm. Correlation coefficients for the linear fits were r^2 = 0.73-0.98. HTO significantly shifted the patella distally through the range of flexion (p<0.05). The average change at 30 degrees was 1.9 mm. Correlation coefficients for the linear fits were r^2 = 0.92-0.99. Other kinematic parameters were changed following surgery, but the changes were not statistically significant in this small group: tibial adduction, patellar spin, patellar tilt, tibial proximal translation, and patellar flexion. Changes were evident in the patellar parameters spin and tilt, however the r^2 values for the linear fits were low. If there is a consistent pattern in these kinematic parameters, it may be best represented by a higher-order polynomial fit. HTO decreased tibiofemoral adduction (up to 10 degrees) in three subjects, while it remained similar in one subject. Tibial anterior translation with surgery is clinically important because it suggests that the contact centers in the tibiofemoral joint may have shifted posteriorly, an outcome thought to be related to changes in tibial slope (3Rodner C.M. et al.52nd ORS. 2006; (Paper No. 0250)Google Scholar). Anterior translation in this case is not due to a major change in tibial slope: for three subjects direct confirmation was obtained showing tibial slope change was less than 3 degrees.