Novel, Biplanar, Medial Opening Wedge, Posterior Tibial Slope-reducing High Tibial Osteotomy Aided by Patient-specific Instruments, With Tibial Tuberosity Serving as Hinge Axis: Cadaveric Study Assessing Accuracy of Biplanar Correction With Various Coronal and Sagittal Amounts of Correction

Introduction:

High tibial osteotomy (HTO) is a widely performed procedure in case of varus knee with medial compartment osteoarthritis (OA), with medial-opening wedge version performed more often than lateral-closing wedge one. While in most cases the goal of medial-opening wedge HTO (MOWHTO) is isolated correction of coronal limb alignment, unintentional increase of posterior tibial slope (PTS) after MOWHTO can occur, however its extent is usually limited. Meta-analysis by Nha et al. published in 2016 and summarizing 27 studies including 1260 MOWHTO procedures, reported mean increase of PTS by 2.02° (95% CI, 2.66° to 1.38°; P = .005). One of factors limiting the extent of PTS change both in above described unintentional circumstances and in desired biplanar corrections, can be the fact that in most cases lateral cortex of the tibia is not transected. Therefore, increase of PTS after MOWHTO was proposed to be caused by the unique anatomical characteristics of the proximal tibia such as non-perpendicular angle between anteromedial and lateral cortex. However, this phenomenon has its limitations and in cases when greater correction of PTS is required, transection of lateral tibial cortex may be necessary, as is routinely performed in osteotomies targeted at isolated PTS correction. In such cases, posterior cortex is remained intact to serve as hinge axis.

On the other hand, in some cases significant biplanar correction of both coronal and sagittal knee alignment is desired. However, transecting all three tibial cortexes increases technical difficulty of the procedure and may increase time to union and the risk of non-union. Therefore, optimal placement of hinge axis to achieve higher accuracy of desired biplanar correction is intensively studied and discussed. In general, anterolateral placement of hinge axis is established to be necessary in order to achieve both valgus correction and PTS decrease. Such biplanar correction may be desired i.e. in anterior cruciate ligament (ACL) revision cases with varus alignment, especially in cases with associated posterolateral corner (PLC) injury, as varus alignment was shown to increase stress both in ACL and PLC grafts. What is more, Won et al. have shown that as much as 19% of ACL revision cases presented with radiographic OA of Kellgren-Lawrence 2 or higher at the medial tibiofemoral joint, highlighting the potential indication for biplanar MOWHTO. Another issue faced during MOWHTO is its influence on patellar height. Multiple studies suggested the possibility of iatrogenic lowering of the patella or the patella baja after MOWHTO. However, as early as in 1979 Goutallier et al. reported that more anterior placement of hinge axis may diminish the impact of HTO on patellar height, which remains in agreement with the proposed anterolateral placement of hinge axis. Up to date, most of the studies assessing impact of hinge axis localization on biplanar correction are based on 3D models and simulations instead of cadavers of real-life procedures, with inherent limitations of that. What is more, accurate and reproducible placement of hinge axis remains technically challenging. One of the ideas developed to improve accuracy of hinge axis placement and accuracy of biplanar correction are Patient-Specific Instruments (PSI), with good results reported by multiple authors.

Therefore, the aim of this cadaveric study was to assess accuracy of biplanar correction with precisely planned increasing various coronal and sagittal amounts of correction utilizing novel, biplanar, medial-opening wedge, posterior tibial slope-reducing high tibial osteotomy aided by PSI, with tibial tuberosity serving as hinge axis. The primary hypothesis of this study was that: 1) There will be no significant differences between planned and achieved biplanar corrections neither in coronal nor sagittal planes. Secondary hypotheses were as follows: 2) Arhtrex PEEKPower HTO plates a) provide good intraoperative stabilization, b) regardless of the change of plate location there will be enough space to preserve soft tissues and no need for new plate design. c) Material used for plates construction will allow for precise evaluation in Computed tomography (CT); 3) No intraoperative fractures will occur; 4) No significant change of patellar height will occur.

Material and Methods: