• Ming Ling, Shi Zhan, Dajun Jiang, Hai Hu, and Changqing Zhang.
• 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.
• J Orthop Surg Res. 2019 Jan 11; 14 (1): 14.

BackgroundThe 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.MethodsThe 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.ResultsThe 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.ConclusionsThe 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.

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