Roles of the screw types, proximity and anterior band wiring in the surgical fixation of transverse patellar fractures: a finite element investigation

Chih-Hsien Chen,Chih-Han Chang,Chun-Ting Li,Yen-Nien Chen,Yao-Te Peng,Chih-Wei Chang

doi:10.1186/s12891-019-2474-7

Abstract

BackgroundCannulated screws with an anterior wire are currently used for managing transverse patellar fracture. However, the addition of anterior wiring with various types of screws via open surgery to increase the mechanical stability is yet to be determined. Hence, this study aimed to compare the mechanical behaviors of a fractured patella fixed with various screws types and at various screw locations with and without the anterior wire. The present study hypothesized that using the anterior wire reduces the fracture gap formation.MethodsA finite element (FE) model containing a fractured patella fixed with various types of cannulated screws and anterior wiring was created in this study. Three types of screws, namely partial thread, full thread, and headless compression screws, and two screw depths, namely 5 and 10 mm away from the anterior surface of the patella, were included. The effect of the anterior wire was clarified by comparing the results of surgical fixation with and without the wire. Two magnitudes and two loading directions were used to simulate and examine the mechanical responses of the fractured patella with various fixation conditions during knee flexion/extension.ResultsCompared with partial thread and headless compression screws, the full thread screw increased the stability of the fractured patella by reducing fragment displacement, fracture gap formation, and contact pressure while increasing the contact area at the fracture site. Under 400-N in the direction 45°, the full thread screw with 5-mm placement reduced the gap formation by 86.7% (from 2.71 to 0.36 mm) and 55.6% (from 0. 81 to 0. 36 mm) compared with the partial thread screw with 10-mm placement, respectively without and with the anterior wire.ConclusionThe anterior wire along with the full thread screw is preferentially recommended for maintaining the surgical fixation of the fractured patella. Without the use of anterior wiring, the full thread screw with 5-mm placement may be considered as a less invasive alternative; however, simple screw fixation at a deeper placement (10 mm) is least recommended for the fixation of transverse patellar fracture.

Highlights

Cannulated screws with an anterior wire are currently used for managing transverse patellar fracture
By using the finite element (FE) method, this study aimed to investigate the mechanical behaviors, including fracture gap formation, fragment displacement, and contact pressure and area at the fracture site, of a fractured patella fixed with various screw types, proximity and the use of anterior wire or not
Under the load of 400-N in the direction of 45°, the full thread screw with 5-mm placement reduced the gap formation by 86.7% and 55.6% compared with the partial thread screw with 10-mm placement, respectively without and with the anterior wire (Table 2)

Summary

Introduction

Cannulated screws with an anterior wire are currently used for managing transverse patellar fracture. Surgeons preferred the use of cannulated screws along with an anterior wire in a figure of eight for fracture fixation based on a higher mechanical stability obtained by this modification [14, 16, 17]. In this technique, two cannulated screws are used rather than the two conventional Kirschner wires to increase the structural stiffness and subsequently the stability of the fractured patella [18]

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