Cannulated Screws and Braided Polyester Tension Band as an Alternative for Fixation of Transverse Patella Fracture: A Finite Element Analysis Study

Abstract

BACKGROUND: Modified tension band wiring is a common surgical technique forfixation of patella fractures; however, various complications have been associated withmetal implants in this configuration. Modification of techniques and non-metallicimplants have been proposed in order to reduce hardware associated complications whileoptimizing fixation strength. Our study investigated the biomechanical strengthprovided by various modifications of figure-of-eight tension band constructs.MATERIALS AND METHODS: A finite element (FE) model of normal patella wasreconstructed based on CT images of a 46-year old man. Mathematical variations fromconversion of actual DICOM images into 3D geometric mesh were recorded. Simpletransverse fracture at the midpole was established with a 0.5 mm fracture gap. Twointerfragmentary fixations were made by using: 1) 2.0 mm K-Wires or 2) 4.0 mm. cannulatedcancellous screws. Figure-of-eight loop with 1.25 mm stainless-steel wire or FiberWireno.5 were allocated to each group. Figure of-eight loops in the K-wire group were invertical orientation while figure-of-eight loops in the cannulated screw group were inhorizontal orientation. These combinations constituted four different FE models. Analysiswas done on each model under the same environment, which was a 400N load on eachfragment at 45o flexion. Implant stress/strain and material deformation were determined.RESULTS: The models with cannulated screws have von Mises stress on implant thatis three times less than those with K-wires. The least von Mises stress occurred on thecombined cannulated screws and horizontal FiberWire loop model (471.2 MPa). Thiscombination also provided least deformation to loading condition (0.1267 mm).Traditional construct with K-wires and metal wire loop was found to have maximalstress (1422.9 MPa) and maximal deformation (0.3856 mm).CONCLUSION: Cannulated screws combined with FiberWire figure-of-eight loopoffers favorably low implant stress. Our findings demonstrate superior stability andresistance to implant failure of the construct. This low-profile tension band fixation couldbe a good alternative for transverse patella fracture.