Where should Kirschner wires be placed when fixing patella fracture with modified tension-band wiring? A finite element
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(2019) 14:14
RESEARCH ARTICLE
Open Access
Where should Kirschner wires be placed when fixing patella fracture with modified tension-band wiring? A finite element analysis Ming Ling†, Shi Zhan†, Dajun Jiang, Hai Hu*
and Changqing Zhang*
Abstract Background: The position of Kirschner wires (K-wires) has an influence on the outcome of modified tension-band wiring (MTBW) in fixing patella fractures. However, the instruction for K-wires positioning is not clear enough. This study tried to clarify the effect of K-wires positioning and provide evidence for a more definite instruction. Methods: The sagittal position (SP) suitable for placing K-wires was evenly divided into SP 1–5 from anterior to posterior, and the finite element models of midpatella transverse fractures fixed by the figure-of-eight or figure-of-zero MTBW were built up at each SP. Separating displacement of the fracture, stress of the fracture, and stress of the internal fixations were measured at 45° knee flexion by using finite element analysis. Results: The separating displacement of the fracture was smaller at SP 3–5 (23% smaller than SP 1–2). From SP 1 to 5, the compression of the fracture surfaces increased (R = 0.99, P = 0.001); the improper stress area of the fracture surfaces decreased (R = − 0.96, P = 0.01), and so was the stress of K-wires (R = − 0.93, P = 0.02). However, the stress of stainless steel wires showed a stable trend. Conclusions: The SP of K-wires plays a role in the function of MTBW in the surgical management of transverse patella fracture. At 45° knee flexion, posteriorly placed (close to the articular surface) K-wires enable optimal stability and stress for the fracture, which provides basis for the positioning of K-wires in clinical practice. Keywords: Patella fracture, Modified tension-band wiring, Kirschner wire, Finite element analysis, Biomechanics
Background The loosening of internal fixation is not rare among patients suffering from patella osteosynthesis. The interfragmental displacement was reported to be as high as 10– 20% [1–3]. Furthermore, 2.4–12.5% of patients suffered from bone nonunion [4], and about 5% of patients underwent a second surgery [2]. As modified tension-band wiring (MTBW) is the recommended surgical technique for patella fractures [5, 6], especially the transverse type, the loosening related to it should be taken seriously.
* Correspondence: [email protected]; [email protected] † Ming Ling and Shi Zhan contributed equally to this work. Department of Orthopedic Surgery and Orthopedic Biomechanical Laboratory, Shanghai Jiao Tong University Affiliated Sixth People’s Hospital, No. 600 Yishan Road, Shanghai 200233, People’s Republic of China
MTBW is performed by drilling two Kirschner wires (K-wires) in a parallel fashion into the patella longitudinally and placing a stainless steel wire (SS-wire) anteriorly in the form of a figure-of-eight or figure-of-zero, which is a dynamic fixation system and supposed to convert the anterior tensile force into posterior compression force [5, 7]. The sagitt
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