Finite element analysis of four Kirschner wire fixation methods for treating patellar transverse fractures

Abstract

BACKGROUND: Kirschner wire and tension band internal fixation is the preferred surgical procedure for treating transverse patellar fractures, but it is often associated with postoperative instability, nonunion, and internal fixation failure. Therefore, optimizing the internal fixation method is of great clinical significance. OBJECTIVE: To investigate the effect of crossed Kirschner wire placement on the fixation of transverse patellar fractures. METHODS: A patellar model was constructed using normal lower limb CT scan data. A transverse patellar fracture and Kirschner wire model was further constructed. Parallel, 30°, 45°, and 60° crossed Kirschner wire placement models were designed. Finite element analysis was performed to analyze the fracture surface stress, fracture surface displacement, Kirschner wire stress, and wire stress under five different working conditions (neutral knee position, 5° flexion, 15° flexion, 45° flexion, and 60° flexion). RESULTS AND CONCLUSION: The fracture surface stresses in the four internal fixation models ranged from 2.06 to 40.00 MPa. The parallel Kirschner wire fixation group had the highest fracture surface stress among all five conditions. The crossed 30° Kirschner wire fixation group had lower fracture surface stress at 15° of knee flexion than the crossed 45° and crossed 60° Kirschner wire fixation groups. The fracture surface displacements in the four internal fixation models ranged from 0.03 to 0.61 mm. The crossed 60° Kirschner wire fixation group had the largest fracture surface displacement at 5° and 15° of knee flexion, while the parallel group had the smallest at 5° and the crossed 30° group had the smallest at 15°. The wire stresses ranged from 56.80 to 2511.00 MPa. The parallel group had the largest wire stress at 5° and 15° of knee flexion, while the crossed 30° group had the smallest. The Kirschner wire stresses ranged from 65.67 to 1018.00 MPa. The crossed 60° group had the largest Kirschner wire stress at 5° of knee flexion, the parallel group had the largest at 15°, and the crossed 30° group had the smallest at both 5° and 15°. The results indicate that 30° crossed Kirschner wire placement provides the best fracture stability and stress distribution, demonstrating superior biomechanical advantages.

1. Introduction

Patellar fractures are common intra-articular fractures, accounting for approximately 1% of all fractures, with transverse fractures being the most frequent type, comprising about 23% of patellar fractures. These injuries often severely impair knee extension function, affecting patients' mobility and quality of life, and leading to prolonged rehabilitation and functional disability.

According to clinical guidelines, surgical fixation is typically recommended for displaced transverse patellar fractures, especially when displacement exceeds 3 mm or articular step-off exceeds 2 mm. The primary goal of surgery is to achieve anatomical reduction and stable fixation to promote healing and restore knee function. Among various fixation methods, Kirschner wire tension band wiring is widely used due to its simplicity, cost-effectiveness, and efficacy. However, this technique is associated with complications such as postoperative instability, nonunion (2.4%-12.5%), and hardware-related issues like soft tissue irritation and wire breakage. Studies have shown that the placement depth and bending of Kirschner wires significantly affect clinical outcomes. The conventional parallel placement may have limited resistance to sagittal plane and torsional forces, potentially leading to fixation failure. Therefore, optimizing the placement angle of Kirschner wires is of great clinical importance.

Finite element analysis (FEA) has become a valuable tool in orthopedic biomechanics, allowing for detailed simulation of mechanical behavior under various loading conditions. FEA enables the evaluation of different fixation constructs without the need for physical specimens, saving costs and providing insights for surgical optimization. In this study, we employed FEA to compare four Kirschner wire fixation configurations (parallel, 30°, 45°, and 60° crossed) for treating transverse patellar fractures, aiming to identify the most biomechanically favorable approach.