Biomechanical application of finite elements in the orthopedics of stiff clubfoot

The effect of early weight-bearing on bone fusion after triple arthrodesis

Triple arthrodesis is an effective method for treating stiff horseshoe feet and severe osteoarthritis. However, it is still a challenge to improve postoperative bone fusion by changing early weight-bearing. This study improved the classical bone remodeling algorithm, established a mathematical relationship between density change rate and mechanical stimulation, and combined it with finite element theory. The proposed algorithm can not only predict the effect of early weight-bearing on triple arthrodesis but also visually demonstrate the change of bone mineral density with time. The analysis results indicated that 2.5% of the initial load was a potential factor leading to bone nonunion, and 50% of the initial load would result in bone resorption. Meanwhile, it was found that 25% of the external load was more conducive to postoperative rehabilitation. The study results have theoretical significance for enhancing the effect of postoperative bone fusion and formulating a more scientific rehabilitation program, thereby supporting patients' postoperative rehabilitation exercise.

Prediction of prognosis in supramalleolar osteotomy with or without additional fibula osteotomy by approaching a biomechanical study: a finite element analysis

Supramalleolar osteotomy (SMO) is a representative procedure to restore a malalignment in the varus ankle deformity by shifting the concentrated pressure on the medial ankle joint to the lateral area. Additionally, fibula osteotomy (FO) is selectively selected and performed according to the surgeon's preference. However, it is controversial whether FO is effective in shifting the abnormal pressure from the medial to the lateral area on the ankle joint. Some cadaveric studies have been performed to prove this. However, it is difficult to consistently reconstruct amount of the varus ankle deformities angle in cadavers and to guarantee reliable contact pressure between the ankle joint. Thus, the aim of this study was predicted and quantitatively compared a peak pressure between single SMO and SMO with FO procedure by using a finite element analysis as a powerful biomechanical tool to those limitations of cadaveric study. This study reconstructed total 4 3D foot and ankle models including a normal and pre-op model and 2 post-op models. The pre-op model was modified by assigning 10° varus tilting corresponding to stage 3b in the classification of varus ankle osteoarthritis based on the validated normal model. Also, the post-op models were reconstructed by applying single SMO and SMO with FO, respectively. All of the models were assumed as one-leg standing position and to mimic smooth ankle joint motion. Peak contact pressure change was predicted at the medial ankle joint by using computational simulation. As a result, 2 post-op models showed a remarkably peak pressure reduction by up to 5.5 times on the medial tibiotalar joint. However, a comparison between single SMO and SMO with FO model showed no appreciable differences. In conclusion, this study predicted that single SMO may be as effective as SMO with FO in reducing peak contact pressure on the medial tibiotalar joint in varus ankle osteoarthritis.

Comparative analysis of internal fixation modalities for PER type IV ankle fractures: a finite element study

BACKGROUND

There are many options for the surgical treatment of pronation external rotation (PER) type IV ankle fractures, including the use of fibular plates and screws, the aim of this study was to investigate the biomechanical stability and safety of different internal fixation methods for PER type IV ankle fractures via finite element analysis.

METHODS

A three-dimensional finite element model of the ankle joint and the whole foot of a healthy 26-years-old adult male was established and validated based on computed tomography images of his lower limb, and a computer-aided design was used to produce a PER type IV ankle fracture and plate and screw model. Four different internal fixation modes were simulated, including a (all ankle fixation-utilizing a fibular plate and screws for comprehensive stabilization of the ankle), b (inferior tibiofibular joint fixation + all ankle fixation), c (inferior tibiofibular joint fixation + unfixed anterior ankle), and d (inferior tibiofibular joint fixation + unfixed anterior and posterior ankles). The results of the four different fixation methods were compared via finite element analysis, and the von Mises stresses. The displacements of the four different fixation methods were analyzed as the output indices.

RESULTS

There were no significant differences between the results of using fibular plates and screws and the displacement of fracture breaks among the four internal fixation modalities. The von Mises stress in the tibiotalar joint, median ankle, posterior ankle, and anterior ankle was minimized in the working condition of d, d, b, and d respectively. The von Mises stress in the fibular plate and screws was minimized in the working condition of a. The von Mises stress in the distal fibula was minimized in the working condition of a. However, the stress was mainly concentrated at the attachment point of the inferior tibiofibular anterior ligament, and in the working condition with inferior tibiofibular joint fixation, the stress was significantly concentrated in the inferior tibiofibular joint screw in all the fibular plates and screws.

CONCLUSIONS

The results of this study demonstrate the feasibility of using finite element analysis to compare the biomechanical stability and safety of four configurations of fibular plates and screws for treating PER type IV ankle fractures. All four modalities provided comparable biomechanical stability and safety, showing no significant differences. However, the current limitations of the finite element analysis methodology preclude specific clinical inferences. Further refinement of the methodology in future studies is necessary to enable reliable clinical applications.

Cushioning mechanism of the metatarsals during landing for the skateboarding ollie maneuver

Skateboarding is an Olympic event with frequent jumping and landing, where the cushioning effect by the foot structure (from the arch, metatarsals, etc.) and damping performance by sports equipment (shoes, insoles, etc.) can greatly affect an athlete's sports performance and lower the risk of limb injury. Skateboarding is characterized by the formation of a "man-shoe-skateboard system," which makes its foot cushioning mechanism different from those of other sports maneuvers, such as basketball vertical jump and gymnastics broad jump. Therefore, it is necessary to clarify the cushioning mechanism of the foot structure upon landing on a skateboard. To achieve this, a multibody finite element model of the right foot, shoe, and skateboard was created using Mimics, Geomagic, and ANSYS. Kinetic data from the ollie maneuver were used to determine the plantar pressure and Achilles tendon force at three characteristics (T1, T2, and T3). The stress and strain on the foot and metatarsals (MT1-5) were then simulated. The simulation results had an error of 6.98% compared to actual measurements. During landing, the force exerted on the internal soft tissues tends to increase. The stress and strain variations were highest on MT2, MT3, and MT4. Moreover, the torsion angle of MT1 was greater than those of the other metatarsals. Additionally, the displacements of MT2, MT3, and MT4 were higher than those of the other parts. This research shows that skateboarders need to absorb the ground reaction force through the movements of the MTs for ollie landing. The soft tissues, bones, and ligaments in the front foot may have high risks of injury. The developed model serves as a valuable tool for analyzing the foot mechanisms in skateboarding; furthermore, it is crucial to enhance cushioning for the front foot during the design of skateboard shoes to reduce potential injuries.

Effects of Midsole Hardness on the Mechanical Response Characteristics of the Plantar Fascia during Running

High long-term stress on the plantar fascia (PF) is the main cause of plantar fasciitis. Changes in the midsole hardness (MH) of running shoes are an important factor leading to the alteration of the PF. This study aims to establish a finite-element (FE) model of the foot-shoe, and investigates the effects of midsole hardness on PF stress and strain. The FE foot-shoe model was built in ANSYS using computed-tomography imaging data. Static structural analysis was used to simulate the moment of running push and stretch. Plantar stress and strain under different MH levels were quantitatively analyzed. A complete and valid 3D FE model was established. With an increase in MH from 10 to 50 Shore A, the overall stress and strain of the PF were decreased by approximately 1.62%, and the metatarsophalangeal (MTP) joint flexion angle was decreased by approximately 26.2%. The height of the arch descent decreased by approximately 24.7%, but the peak pressure of the outsole increased by approximately 26.6%. The established model in this study was effective. For running shoes, increasing the MH reduces the stress and strain of PF, but also imposes a higher load on the foot.