Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine最新文献

The annuus fibrosus (AF) and nucleus pulposus (NP) of the intervertebral disc (IVD) work in conjunction to dissipate spinal loads. In this study we have isolated the contribution of the NP to the overall response of the disc and investigated the effect of extreme structural changes to the disc on the mechanical behaviour. Linear stiffness, overall load range, hysteresis area and total energy were used to evaluate the impact of these changes on the spine and surrounding structures. Six porcine lumbar isolated disc specimens were tested in 6 DOFs with a 400 N compressive axial preload at low strain rates in three conditions: intact (IN), after total nucleotomy (NN) and after the injection of bone cement into the nuclear void (SN). The latter two conditions, NN and SN, were chosen to emulate the effect of extreme changes to the NP on disc behaviour. When comparing with intact specimens, significant changes were noted primarily in axial compression-extension, mediolateral bending and flexion-extension. NN and SN cases demonstrated significant increases in linear stiffness, overall load range and total energy for mediolateral bending and flexion-extension compared to the intact (IN) state. SN also demonstrated a significant increase in total energy for axial compression-extension, and significant decreases in the elastic contribution to total energy in all axes except flexion-extension. These changes to total energy indicate that surrounding spinal structures would incur additional loading to produce the same motion in vivo after structural changes to the disc.

The selection of internal fixation as the primary fixation modality for the patient is one of the challenges for the surgeon treating the patient in question. A model of the lateral tibial plateau fracture was established. Three different configurations of internal fixators namely L bone plate, T bone plate, and screw-washer were analyzed. Three stages after surgery were simulated to assess the displacement of bone plates, screws, washers, and the stress shielding ratio in the fracture area.At three stages after surgery, the T bone plate showed better stability for patients during rehabilitation compared with the remaining two schemes, and the screw-washer scheme was the least stable due to the larger internal fixation displacement and stress shielding ratio in the fracture area. In contrast, the L bone plate scheme showed better stability in the early stages after surgery but was second only to the screw-washer scheme in the middle and late stages after surgery. The T bone plate showed better stability and became a new selection for surgeons to treat related patients. At three stages after surgery, the T bone plate has better biomechanical stability compared to the L bone plate and screw-washer schemes.

Bone microstructure governs microcrack propagation complexity. Current research, relying on linear elastic fracture mechanics, inadequately considers authentic multi-level structures, like cement lines and osteons, impacting stress intensity at cracks. This study, by constructing models encompassing single or multiple osteons, delves into the influence of factors like crack length, osteon radius, and modulus ratio on the stress intensity factor at the crack tip. Employing a fracture mechanics phase-field approach to simulate crack propagation paths, it particularly explores the role of cement lines as weak interfaces in crack extension. The aim is to comprehensively and systematically elucidate the critical factors of bone microstructure in the context of crack propagation.

Aseptic loosening is the primary cause of failure following posterior-stabilized total knee arthroplasty. It is unclear whether tibial post loading of posterior-stabilized prosthesis increases the risk of aseptic loosening of the tibial prosthesis. The purpose of this study is to investigate the biomechanical effects of tibial post loading on the tibial prosthesis fixation interface during level walking, squatting, stair descent, and standing up-sitting down activities. In this paper, finite element models with and without post were established to compare the effects of tibial post loading on the von Mises stress of the proximal tibia, shear stress of the cement, and the bone-prosthesis interface micromotion during four physiological activities. The tibial post loading had an insignificant influence on tibial biomechanics and bone-prosthesis interface micromotion during leveling walking activity. However, compared to the insert without post condition, tibial post loading significantly increased the maximum tibial von Mises stress, the maximum shear stress in the medial of cement, and the bone-prosthesis interface peak micromotion by 912.84%, 612.77%, and 921.09%, respectively, at the moment of the maximum flexion angle for the stair descent activity, and 637.92%, 351.43%, and 519.13%, respectively, at the moment of the maximum flexion angle for the standing up-sitting down activity. Tibial post loading increased the risk of postoperative aseptic loosening of tibial prosthesis in patients with posterior-stabilized total knee arthroplasty, and it was recommended that the post-cam contact mechanism of posterior-stabilized prosthesis should be optimized to reduce the biomechanical impact of tibial post loading on tibial prosthesis fixation.

The conical stem tibial design of total ankle replacement (TAR) has high implant-bone micromotion. This may lead to aseptic loosening which can be avoided by improving the tibial design. The objective was to propose the best stem design parameters to reduce implant-bone micromotion along with minimizing stress shielding using an integrated Finite Element-Multi Criteria Decision Making (FE-MCDM) approach. FE models of implanted tibia bones were prepared by changing the height of the stem, the diameter of the stem, and the slant of the stem. Weighted Aggregated Sum Product Assessment (WASPAS), Technique for Order of Preference by Similarities to Ideal Solution (TOPSIS), Evaluation based on Distance from Average Solution (EDAS), and VIseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR) MCDM techniques with equal weights for micromotion and stress shielding were considered. The micromotion and stress shielding were greater when the height of the stem was increased. Whereas, the increase in diameter and slant affected them marginally. The best-performing design was the Model with stem height 6 mm (diameter 6.4 mm and slant 4°) and after that was the Model with stem height 8 mm (diameter 6.4 mm and slant 4°), and then the Model with stem height 10 mm (diameter 6.4 mm and slant 4°). The height of the stem is the most important stem design parameter. Shorter height, moderate thickness, and moderate slanting stem designs are recommended.

A biologically-inspired actuation system, including muscles, spinal reflexes, and vestibular feedback, may be capable of achieving more natural gait mechanics in powered prostheses or exoskeletons. In this study, we developed a Virtual Muscle Reflex (VMR) system to control ankle torque and tuned it using data from human responses to anteroposterior mechanical perturbations at three walking speeds. The system consists of three Hill-Type muscles, simulated in real time, and uses feedback from ground reaction force and from stretch sensors on the virtual muscle fibers. Controller gains, muscle properties, and reflex/vestibular time delays were optimized using Covariance Matrix Adaptation (CMA) to minimize the difference between the VMR torque output and the torque measured from the experiment. We repeated the procedure using a conventional finite-state impedance controller. For both controllers, the coefficient of determination ($R^2$) and root-mean-square error (RMSE) was calculated as a function of time within the gait cycle. The VMR had lower RMSE than the impedance controller in 70%, and in 60% of the trials, the $R^2$ of the VMR controller was higher than for the impedance controller. We concluded that the VMR system can better reproduce the human responses to perturbations than the impedance controller.

The photoplethysmographic (PPG) signal of the finger is being used to create embedded devices that estimate physiological variables. This project outlines an innovative method for developing a synthetic PPG generator that produces both actual reference digital signals and their equivalent analog signals using open-source technology. A series of PPG profiles is synthesized using three variant Gaussian functions. A low-frequency trend induced by respiratory frequency and background noise are then added. To generate a diverse range of continuously variable PPG profiles within specified boundaries and customizable levels of interference, all parameters undergo random fluctuations on a cycle-by-cycle basis, as per user-defined constraints. The generated signal is then converted into its equivalent analog form through the use of an RC filter that low-frequency filters a Pulse-Width Modulation square wave that is modulated directly by the generated signal. The software returns different PPG profiles and allows the signal comparison before vs after the addition of different-intensity modulated respiratory trends and background noise. The digital signal is faithfully converted into an equivalent analog voltage signal capable of reproducing not only the waveform profile but also the respiratory trend and various levels of noise.