Pin-on-plate and pin-on-disk wear tests are typically used for assessing the wear behavior of a given material coupling and estimating its wear coefficient using the Archard wear law. This study investigates differences in the Archard law for pin-on-plate and pin-on-disk cases, particularly for flat-ended pins. Both analytical and finite element models of the two tests were developed, assuming a 21 N normal load and a 50π mm sliding distance. In pin-on-disk simulations three different distances between pin and disk axes were considered, i.e., 1.25–2.5–5 times the pin radius (5 mm). For the results, wear volumes, pressure and wear depth maps were compared. Some interesting aspects arose: (i) the rotational effect in pin-on-disk tests causes higher wear volumes (up to 13%) with respect to pin-on-plate tests: the nearer the pin to the disk axis, the higher the wear volume; (ii) a simple quadratic formula is defined to correct the wear volume estimation for pin-on-disk tests; (iii) pressure redistribution occurs with higher values closer to disk axis, opposite to the wear depth trend. Due to the high computational costs, only the running-in phase of wear tests was considered. Numerical strategies are currently under investigation to extend this study to the steady state phase.

The paper introduces a tool called Automatic Scaling Tool (AST) designed for improving and expediting musculoskeletal (MSK) simulations based on generic models in OpenSim. Scaling is a crucial initial step in MSK analyses, involving the correction of virtual marker locations on a model to align with actual experimental markers. The AST automates this process by iteratively adjusting virtual markers using scaling and inverse kinematics on a static trial. It evaluates the root mean square error (RMSE) and maximum marker error, implementing corrective actions until achieving the desired accuracy level. The tool determines whether to scale a segment with a marker-based or constant scaling factor based on checks on RMSE and segment scaling factors. Testing on three generic MSK models demonstrated that the AST significantly outperformed manual scaling by an expert operator. The RMSE for static trials was one order of magnitude lower, and for gait tasks, it was five times lower (8.5 ± 0.76 mm vs. 44.5 ± 7.5 mm). The AST consistently achieved the desired level of accuracy in less than 100 iterations, providing reliable scaled MSK models within a relatively brief timeframe, ranging from minutes to hours depending on model complexity. The paper concludes that AST can greatly benefit the biomechanical community by quickly and accurately scaling generic models, a critical first step in MSK analyses. Further validation through additional experimental datasets and generic models is proposed for future tests.

Acetabular fractures have a high impact on patient’s quality of life, and because acetabular fractures are high energy injuries, they often co-occur with other pathologies such as damage to cartilage that could increase related morbidity; thus, it appears of primary importance developing reliable treatments for this disease. This work aims at the evaluation of the biomechanical performances of non-conservative treatments of acetabular fractures through a finite element approach. Two pelvic plates models (the standard suprapectineal plate—SPP, and a suprapectineal quadrilateral surface buttressing plate—SQBP) were analyzed when implanted on transverse or T-shaped fractures. The plates geometries were adapted to the specific hemipelvis, mimicking the bending action that the surgeon performs on the plate intraoperatively. Implemented models were tested in a single leg stance condition. The obtained results show that using the SQBP plate in transverse and T-shaped acetabular fractures generates lower bone stress if compared to the SPP plate. Interfragmentary movement analysis shows that the SQBP plate guarantees greater stability in transverse fractures. In conclusion, the SQBP plate seems worthy of further clinical analysis, having resulted as a promising option in the treatment of transverse and T-shaped acetabular fractures, able to reduce bone stress values and to get performances comparable, and in some cases superior, to traditional fixation.

Pin-on-plate and pin-on-disk wear tests are typically used for assessing the wear behavior of a given material coupling. Such a behavior is frequently described by a wear coefficient k, which is estimated, according to the Archard’s law, as the ratio between the measured wear volume V and the product of the applied normal force F and the sliding distance s, i.e. k=V/(F s). This study demonstrates that such a relationship is correct for pin-on-plate but not for pin-on-disk, particularly for flat-ended pins. Both analytical and finite element models of the two tests were developed, considering three different distances pin-disk axis. As results, wear volumes, pressure and wear depth maps were examined and compared for the same sliding distance. Though this study is focused only on the initial transient part of the wear tests, some interesting aspects arose: i) rotational effect in pin-on-disk tests affects k estimation, especially when the pin is near to the disk axis; ii) a simple analytical function is defined to correct the wear volume estimation for pin-on-disk tests; iii) due to the different sliding distances of contact points in pin-on-disk tests, pressure redistribution occurs with higher values on the inner side (closer to disk axis); the opposite trend is observed in wear depth maps. From a computational point of view, the pin-on-disk problem, only apparently simple, required very small time increments to correctly describe the circular trajectories of points, with high computational costs. Numerical strategies are currently under investigation to extend the study to the steady state phase of both tests.

Posterior fossa syndrome (PFS) is a rare manifestation of ponto-mesencephalic lesions frequently reported in post-surgical pediatric tumors, rarely described as a consequence of vascular, infective or inflammatory lesions. The aim of this article is to report the clinical and neuroradiological characteristics of a patient with an acute PFS presentation as a relapse in relapsing-remitting MS, significantly responsive to Alemtuzumab treatment. 24-year-old patient affected by multiple sclerosis developed motor-cognitive and behavioral syndrome related to an extensive ponto-mesencephalic lesion under Fingolimod treatment. Our case highlights the significant and rapid effect of Alemtuzumab therapy on both cognitive and motor symptoms occurring during a MS relapse with atypical neuroradiological localization.

Purpose: “Cuban Motion” (CM) is a term often used to label a basic movement of many Latin-American dances, such as salsa and bachata. It is characterized by a cyclical and rhythmic flexion and rotation of the pelvis, accompanied by ample movements of the spine and lower limbs. Since Latin dances are considered both a recreational activity and a kind of healthy gymnastics for young and older subjects, a biomechanical analysis of the CM was performed to quantitatively assess the main features of this movement, from joint kinematics to muscle activations. Method: The study combined experimental acquisitions with a Vicon Motion Capture system and musculoskeletal analyses in OpenSim. Only one subject was considered, an instructor of Latin dances, who was equipped with 55 retro-reflective markers, according to the Full Body CGM2.5 marker set. Data were processed in OpenSim, using the ThoracoLumbar model (111 DoFs and 620 musculo-tendon actuators). Results: The cycle of the CM and its main events were defined. Results showed a wide RoM of many joints, with correlations between hip and knee flexion angles and among list, between hip adduction and shoulder flexion. The main role of the iliopsoas and the ileus costalis muscles was observed. Conclusions: The current study quantified the CM as a physical exercise using a biomechanical approach similar to a gait analysis. The main kinematic and kinetic features were described, also providing an estimation of the muscle activations and joint reactions, derived from simulation activity in OpenSim. The main limitation of this study is the focus on a single subject, but this step was necessary to define a context and guidelines for future investigations, where we are going to compare èlite vs. novices and male vs. female dancers.