Abstract: BACKGROUND: For the treatment of double fractures of the radioulnar shaft with percutaneous elastic intramedullary nails, the main entry points on the radius are the Lister tubercle and the radial styloid process. However, no reports have been found on the comparison between these two entry points.
OBJECTIVE: To establish three-dimensional finite element models of double fractures of the radioulnar shaft with entry points at the Lister tubercle and the radial styloid process respectively through three-dimensional finite element technology, simulate the normal movement of the human forearm, and analyze their biomechanical stability and safety.
METHODS: The geometric shapes of the radius and ulna were reconstructed based on the CT images of the radioulnar bones of a 24-year-old healthy adult male. The finite-element analysis software Mimics was used to establish two models with different entry points for double fractures of the radioulnar shaft, namely, the Lister tubercle entry-point model and the radial styloid process entry-point model. Four types of stresses, including rotation, flexion, tension, and compression, were applied to the models in Ansys software, and their biomechanical changes were analyzed.
RESULTS AND CONCLUSION: (1) Through three-dimensional finite element biomechanical analysis, by comparing the maximum displacement, stress peaks, and stress distributions of the two models with different entry points for double fractures of the radioulnar shaft under different stresses, it was found that both Lister tubercle and radial styloid process entry points could effectively control the displacement of the fracture ends, especially showing remarkable effects in resisting flexion stress. (2) The fixation stabilities of the two groups were similar. The maximum displacement value of the radial styloid process entry-point group was slightly smaller when resisting the four types of stresses, but the internal fixation stress was more concentrated. (3) Both models could effectively disperse the pressure, making the bone stress evenly distributed. The peak stresses of the bone and the internal fixation were concentrated at the entry point of the olecranon of the ulna. When resisting flexion stress, the internal fixation stress peak of the radial styloid process entry-point group was the largest, with a risk of nail breakage or stress fractures.

Key words: elastic intramedullary nail, double fractures of the radioulnar shaft, three-dimensional finite element, Lister's tubercle, styloid process of radius, biomechanics