Abstract
Background
Open-wedge high tibial osteotomy (OWHTO) is an operation involving proper load re-distribution in the treatment for medial uni-compartmental arthritis of the knee joint. Therefore, stable fixation is mandatory for safe healing of this additive type of osteotomy to minimize the risk of non-union and loss of correction. For stability, screws provide optimal support and anchorage of the fixator in the condylar area without risking penetration of either the articulating surface. The purpose of the study was to evaluate the screw insertion angle and orientation with an anatomical plate that is post-contoured to the surface geometry of the proximal tibia after OWHTO.
Methods
From March 2012 to June 2014, 31 uni-planar and 38 bi-planar osteotomies were evaluated. Postoperative computed tomography data obtained after open wedge high tibial osteotomy using a locking plate were used for reconstruction of the 3 dimensional model with Mimics v.16.0 of the proximal tibia and locking plate. Measurement data were compared between 2 groups (gap lesser than or equal to 10 mm (Group 1) and gap greater than 10 mm(Group 2)). These data were also compared between the uniplanar (Group 3) and bi-planar (Group 4) osteotomy groups.
Result
The dimensions of ‘L1’, ‘L2’, and ‘a’ were not statistically different, regardless of the correction degree and operative technique. Also, X1 and X3 were not statistically different, regardless of the correction degree and operative technique. In the axial plane, the angles ‘A_θ1, A_θ2, A_θ3, and A_θ4’ of screw insertion to the lateral hinge point were not statistically different, regardless of the correction degree and surgical technique(Figure 1). Also, the angles ‘C_θ1, C_θ2, C_θ3, and C_θ4’ of screw insertion to the lateral hinge point were not statistically different in the coronal plane, regardless of the correction degree and surgical technique in the coronal plane(Figure 1). Angles of screw insertion, based on quantitative assessment of the tibial bony surface to the lateral hinge point were larger at the A_θ1 and A_θ4 than A_θ2 and A_θ3 in the axial plane. Angle of the C_θ1 was smallest in the coronal plane and it was less than 90°. Angles of C_θ2, C_θ3, and C_θ4 were larger than 90°(Table 1).
Discussion & Conclusion
Dimensions of the medial proximal tibia of the sagittal plane, positions of the screw hole in the sagittal plane, and angles of screw insertion of all planes were not statistically different, regardless of the correction degree and operative technique. Additionally, angles of screw insertion were larger at the most anterior and posterior screw in the axial plane and most inferior screw showed smallest angle in the coronal plane. Using a post-contoured plate, the position and angle of the screw insertion were not different in the direction of the lateral hinge, regardless of the correction degree and operative technique. In our study, we evaluated the coronal insertion angle with targeting the lowest portion of the safe zone. Therefore, most screws of the proximal fragment could be inserted in the superior oblique direction if they are targeted to the ‘Safe Zone’.
For any figures or tables, please contact authors directly (see Info & Metrics tab above).
