Biomechanics of Cannulated Screw with Anterior Wire in Fixing Transverse Patellar Fracture

Abstract

Cannulated screws with an anterior wire are currently used for managing transverse patellar fracture However the addition of the anterior wire is often applied via an open approach which may increase the surgical trauma and compromise the following biological healing of the fracture Although fixation using the anterior wire increases the stability of the fractured patella more substantially than that without the anterior wire a less invasive fixation alternative using screws without the anterior wire was thus proposed based on the supporting strength from screws Without the anterior tension wiring these minimally invasive surgeries (MIS) were expected to reduce early postoperative pain results in higher mobility angles of the injured knee and decreases the incidence of complications Hence this study aimed to compare the mechanical behaviors of a fractured patella fixed with various screws types and at various screw proximities with and without the anterior wire Clarifying the effect of the anterior wire with various screw types and proximities on the stability helps the surgeon to make decisions in the management of patellar fractures An FE knee model contained a fractured patella which was fixed with various types of cannulated screws and an anterior wire was created in the present study Three types of screws namely partial thread full thread and headless compression screws and two screw proximities namely 5 and 10 mm away from the leading edge of the patella were used The effect of the anterior wire was clarified by comparing the results of fracture fixation with and without the wire Two different knee flexion degrees were considered namely knee full extension and flexion 45? furthermore two different loading magnitudes namely 400 N and 800 N were used to examine the mechanical responses of the fractured patella with various fixation conditions The maximum gap opening distance and fragment displacement under loading represent the “stability” of the fractured patella with various fixation conditions The ratio of the applied load and the gap opening distance obtained by linear regression was regarded as the stiffness of the structure The stiffness is also an index to access the stability Compared with partial thread screw the full thread screw increased the stability of the fractured patella with reducing fragment displacement and fracture gap opening distance Using the anterior wire and placing the screws at 5-mm proximity were also helpful to increase the stability The effect of the anterior wire was obvious with 10-mm screw proximity but nonobvious with 5-mm screw proximity In knee full extension the stiffness of the full thread and headless compression screws at 5-mm proximity without the anterior wire was 1924 6 and 1531 N/mm respectively By contrast the stiffness of the partial thread screw with the anterior wire was 1054 and 727 37 N/mm respectively at 5-mm and 10-mm proximities In knee flexion 45° the linear stiffness of the full thread and headless compression screws at 5-mm proximity without the anterior wire was 1652 1 and 1445 4 N/mm respectively while the linear stiffness of the partial thread screw with the anterior wire was 937 68 and 694 54 N/mm respectively at 5-mm and 10-mm proximities The 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 or headless compression screws 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

Date of Award	2020
Original language	English
Supervisor	Chih-Han Chang (Supervisor)