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. 2019 Jan 11;14(1):14.
doi: 10.1186/s13018-019-1060-x.

Where should Kirschner wires be placed when fixing patella fracture with modified tension-band wiring? A finite element analysis

Ming Ling  1 , Shi Zhan  1 , Dajun Jiang  1 , Hai Hu  2 , Changqing Zhang  3
Affiliations

Where should Kirschner wires be placed when fixing patella fracture with modified tension-band wiring? A finite element analysis

Ming Ling et al. J Orthop Surg Res. .

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: Biomechanics; Finite element analysis; Kirschner wire; Modified tension-band wiring; Patella fracture.

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Conflict of interest statement

Ethics approval and consent to participate

CT image acquisition was approved by Ethics Committee of Shanghai Sixth People’s Hospital (Approval No. 2016-143) and a written consent was obtained from the participant.

Consent for publication

The participant enrolled into the study agreed the use of data for research.

Competing interests

The authors declare that they have no competing interests.

Publisher’s Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Figures

Fig. 1
Fig. 1
a The coordinate system of the patella. K-wires were placed in the direction of the y-axis (SP 3 for example). b Projection of all SPs on the median transverse section of the patella. SP 1–5 (red dots) were included in this study, and the most anterior and most posterior SPs (black dots) were excluded
Fig. 2
Fig. 2
Patella fracture models with different SPs of K-wires and different fashions of wiring
Fig. 3
Fig. 3
The model settings. The articular surface of the patella was in contact with the cartilage of the femur. The tendon attachments on the proximal and distal patella were coupled to the simulate origin of quadriceps (dot) and the insertion of patella tendon (circle) respectively. The origin of quadriceps was subjected to 200 N force along the direction of the muscle, and the movement of the femur was restricted, as well as the insertion of patella tendon. The model was open chained
Fig. 4
Fig. 4
a The separation of the fractures at different SP. b The location of the maximal and minimal separation on the fracture surfaces. c The average pressure of the proximal and distal fracture surfaces. Linear with SP (R = 0.99, P = 0.001). d The IPSA% of the fracture surfaces. Linear with SP (R = − 0.96, P = 0.01). e The improper stress area of the fracture surfaces. Each figure was superimposed by four fracture surfaces (two fashions of wiring, two fracture surfaces of a model)
Fig. 5
Fig. 5
a The average von Mises stress of K-wires. Linear with SP (R = − 0.93, P = 0.02). The ends of the whiskers represent the boundaries of outliers, and it is the same in Fig. 5b. b The average von Mises stress of SS-wires. c The stress distribution on the internal fixations. The internal fixations were semi-transparent, including the stress on both anterior and posterior sides
See this image and copyright information in PMC

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