Effects of plate contouring quality on the biomechanical performance of high tibial osteotomy fixation: A parametric finite element study

Abstract

Locking plates have threaded holes, in which threaded-head screws are affixed. Hence, they do not need to be in intimate contact with underlying bone to provide fixation. There are, however, reports that a large distance between the plate and the bone might cause clinical complications such as delayed union or nonunion, screw pull out, and screw and plate breakage. Considering the diversity in the capabilities and costs of different plate customization techniques, the purpose of this study was to investigate the effect of the plate contouring quality on the biomechanical performance of high tibial osteotomy (HTO) fixation. A finite element model of proximal tibia was developed in Abaqus, using the QCT data of a cadaver. The model was then subjected to open-wedge HTO (correction angle 12°) with TomoFix plate fixation. The sagittal curvature of the plate was changed parametrically to provide certain levels of geometrical fit, and the biomechanical performance parameters of fixation were assessed. Results indicated 5%, 9% and 38% increase in the stiffness of the construct, and the von Mises stress in the plate and locking screw just above the osteotomy site, respectively, when the level of fit of plate changed from 0% (initial non-contoured initial shape) to 100% (fully adapted shape). The same change decreased the pressure at the lateral hinge of the osteotomy by 61%, and the mean of the tensile stress on the screw shaft by 12%. It was concluded that the level of fit has conflicting effects on the biomechanical parameters of the HTO fixation system, that is, the structural stiffness, the pressure at the lateral hinge, the stresses in the plate and screws, and the pull out resistance of the screws. In particular, for HTO patients with high quality bone, the optimal level of fit should provide a tradeoff between these parameters.

Geometrical analysis of the opening gap after tibial condylar valgus osteotomy for proper hinge point selection

“…With the gradual opening of the osteotomy gap, the horizontal distance between the proximal fragments, distal fragments, and the bone-plate clearance increase correspondingly (11,12,15). A bone-plate mismatch may increase the risk of implant failure from, for example, locking pin backout or screw breakage after tibial osteotomy (18)(19)(20).…”

“…The proper fitting of the plate to the bony surface is essential for the appropriate and effective delivery of physiological stress, which prevents a loss of fixation stability and plate fracture (13)(14)(15)26). Previous biomechanical studies have also revealed that a large clearance between the locking plate and the bone beneath the plate is associated with a greater concentration of stress at the construct, increased pressure at the lateral hinge, and weakened axial stiffness (27)(28)(29).…”

“…To address this issue, intraoperative plate contouring at both ends of the opening gap may help to fit the surface geometry. However, the accuracy of this technique is rather low and requires the surgeon to be proficient (15). The application of the circular external fixator or additional fixation on the more medial aspect of the tibia would be necessary but would increase the surgical difficulty and costs (11,30).…”

“…The application of the circular external fixator or additional fixation on the more medial aspect of the tibia would be necessary but would increase the surgical difficulty and costs (11,30). Customized and patient-specific implants fabricated by a 3D-printing technique might ensure satisfactory contouring, but this method is often criticized for its high costs and low fatigue strength (15,31). Unlike the incomplete osteotomy of OWHTO, which has an intact lateral cortex for supporting the construct after surgery, TCVO can be regarded as a complete osteotomy with a proximal tibial fracture.…”

“…In such circumstances, a larger degree of mismatch between the patient-specific bony surface and the factory-made locking plate can impose a higher stress on the construct and weaken the structural stiffness of the implant, leading to an increased risk of technical complications, such as hinge fracture, screw pullout, and plate breakage (12)(13)(14)(15). In addition, the significant prominence of the implant beneath the medial subcutaneous border and the small contact area between the plate and the bone at the distal end can cause postoperative pain (11,15). Thus, the hinge position that leads to the smallest gap opening angle should be favored by surgeons during TCVO.…”