Biomechanical finite element analysis of different ulnar shortening osteotomy techniques in treatment of ulnar impaction syndrome

Abstract

BACKGROUND: Ulnar impaction syndrome is a common wrist disorder, and ulnar shortening osteotomy is one of the definitive surgical interventions for its treatment. Although various ulnar shortening osteotomy techniques exist, numerous clinical comparative studies have focused on pairwise comparisons, while biomechanical simulations comparing the efficacy of different osteotomy methods via finite element analysis remain unreported. OBJECTIVE: To simulate and compare the biomechanical characteristics of ulnar impaction syndrome under different osteotomy treatment modalities employing finite element method so as to provide references and evidence for clinical decision-making. METHODS: CT data of the intact ulna and radius from a healthy adult male volunteer were utilized. Modeling and finite element software platforms — Mimics 19.0, Geomagic Studio 2013, SolidWorks 2019, and Ansys 17.0 — were sequentially applied to construct five ulnar osteotomy models: (1) distal ulnar V-shaped osteotomy; (2) distal ulnar transverse osteotomy; (3) ulnar metaphyseal transverse osteotomy; (4) distal ulnar trapezoidal osteotomy; (5) distal ulnar oblique osteotomy. According to the experimental design and internal fixation principles, plates and screws were assembled. Subsequently, three motion modes of wrist joint axial compression, pronation, and supination were simulated, and corresponding boundary conditions and loads were applied to each group to obtain stress distribution and displacement at the osteotomy site and internal fixation devices. Finally, the results were compared with established experimental data standards to draw relevant conclusions. RESULTS AND CONCLUSION: (1) Under three different motions and loads, the five different ulnar shortening osteotomy methods all maintained stable osteotomy ends without significant relative differences. (2) There were certain differences in the stress and deformation of internal fixation devices among the five methods under three simulated motion states: under simulated pronation, the internal fixation plate of ulnar metaphyseal transverse osteotomy was at risk of fracture; under simulated supination, the plate also exhibited deformation risk. (3) Regarding stress and displacement of internal fixation, the distal ulnar V-shaped osteotomy showed relative advantages in stability under all three simulated states.

1. Introduction

Ulnar impaction syndrome is a degenerative condition affecting the ulnocarpal joint, first described by Professor MILCH in 1941. It most commonly occurs in wrists with positive ulnar variance, where the ulnar head is more than 2 mm longer than the radius. The pathomechanism involves repetitive impaction of the elongated ulnar head against the triangular fibrocartilage complex, lunate, and proximal articular surface of the triquetrum [1-2]. This condition can be secondary to malunited distal radius fractures, radial head resection, congenital positive ulnar variance, premature closure of the radial epiphysis, or any wrist disorder leading to relative lengthening of the ulna [3]. When the ulnar head impacts the lunate or triquetrum, not only is ulnar variance visible on radiographs, but MRI may show edema signals in the ulnar aspect of the lunate, radial aspect of the triquetrum, and the ulnar head. As symptoms progress, osteolytic subchondral cysts or osteosclerosis may be observed on MRI of the lunate or triquetrum [4]. Based on this, ulnar shortening osteotomy, which shortens the excessively long ulna, has become one of the most definitive methods to correct positive ulnar variance [5-6]. Studies have shown that shortening the ulna by 2.5 mm reduces ulnocarpal load pressure to 4.3% [7-8]. In clinical practice, various ulnar shortening osteotomy techniques exist, with the most common being ulnar metaphyseal transverse osteotomy [9-11], distal ulnar oblique osteotomy [12-13], distal ulnar transverse osteotomy [8], distal ulnar trapezoidal osteotomy, and distal ulnar V-shaped osteotomy [4-5,14-15]. The choice among these techniques largely depends on the surgeon's preference and proficiency, and reliable clinical data supporting the superiority of one technique over another are lacking.

Finite element analysis is a numerical method first proposed by American engineer CLOUGH in 1960. Its core principle involves dividing a complex solution domain into smaller, interconnected subdomains called finite elements. For each element, a relatively simple approximate solution is assumed. Then, by deriving and solving the overall satisfaction conditions, such as structural equilibrium conditions, an approximate solution for the entire domain is obtained [16]. In 1972, BREKELMANS and RYBICKI first applied finite element analysis to biomechanical studies of the femur. Over more than 50 years of development and validation by numerous experts and scholars, finite element analysis has become a reliable tool for biomechanical research in medicine [17-18]. Finite element biomechanical analysis has been increasingly reported in studies of the radius, ulna, and wrist joint [19-21]. Regarding comparative studies of different ulnar shortening osteotomy techniques for ulnar impaction syndrome, most existing research consists of one-to-one clinical comparisons [22-25], while biomechanical simulation comparisons using finite element analysis have not been reported.