Finite element analysis of the performance of additively manufactured scaffolds for scapholunate ligament reconstruction

Abstract

Rupture of the scapholunate interosseous ligament can cause the dissociation of scaphoid and lunate bones, resulting in impaired wrist function. Current treatments (e.g., tendon-based surgical reconstruction, screw-based fixation, fusion, or carpectomy) may restore wrist stability, but do not address regeneration of the ruptured ligament, and may result in wrist functional limitations and osteoarthritis. Recently a novel multiphasic bone-ligament-bone scaffold was proposed, which aims to reconstruct the ruptured ligament, and which can be 3D-printed using medical-grade polycaprolactone. This scaffold is composed of a central ligament-scaffold section and features a bone attachment terminal at either end. Since the ligament-scaffold is the primary load bearing structure during physiological wrist motion, its geometry, mechanical properties, and the surgical placement of the scaffold are critical for performance optimisation. This study presents a patient-specific computational biomechanical evaluation of the effect of scaffold length, and positioning of the bone attachment sites. Through segmentation and image processing of medical image data for natural wrist motion, detailed 3D geometries as well as patient-specific physiological wrist motion could be derived. This data formed the input for detailed finite element analysis, enabling computational of scaffold stress and strain distributions, which are key predictors of scaffold structural integrity. The computational analysis demonstrated that longer scaffolds present reduced peak scaffold stresses and a more homogeneous stress state compared to shorter scaffolds. Furthermore, it was found that scaffolds attached at proximal sites experience lower stresses than those attached at distal sites. However, scaffold length, rather than bone terminal location, most strongly influences peak stress. For each scaffold terminal placement configuration, a basic metric was computed indicative of bone fracture risk. This metric was the minimum distance from the bone surface to the internal scaffold bone terminal. Analysis of this minimum bone thickness data confirmed further optimisation of terminal locations is warranted.

Mechanical and Computational Fluid Dynamic Models for Magnesium-Based Implants

“…To compute Young's modulus, estimate the mechanical stress, and measure the displacement, the two designed CAD models were placed between two rigid bodies with thicknesses of 0.2 mm and areas equal to the base area of the implants. The applied mechanical test was compression in accordance with many literature studies [47,[51][52][53][54][55][56]. To model the real behavior of a universal testing machine, we applied a surface-distributed force on the Z axis on the superior rigid body.…”

Finite Element Modeling of the Fingers and Wrist Flexion/Extension Effect on Median Nerve Compression

“…The carpal bones move during flexion and extension of the wrist, which changes the geometry of the carpal canal and consequently affects the movement of tendons and the median nerve; this was not taken into account in this study. However, consideration of the carpal bone interaction is a separate complex task considered in many other studies [11][12][13][14][15]. Adding the effect of carpal bone motion would greatly complicate calculations and increase calculation time to an unacceptable level.…”

“…Only bones and ligaments were included in the study. Perevoshchikova et al 2021 [12] studied von Mises stress distribution in a novel multiphase bone-ligament-bone scaffold during physiological wrist movements. The study presented a patient-specific computational biomechanical evaluation of the effect of scaffold length, and positioning of the bone attachment sites.…”

Finite Element Modeling of the Human Wrist: A Review

“…Since smaller wrist sections are simulated, authors can choose more complex constitutive laws to represent features such as anisotropy in soft tissues. However, as each published model studies a distinct problem, 15,[17][18][19] comparing partial-wrist models may not be possible as opposed to comparing whole-wrist models.…”