Mechanical Engineering

An Assessment of a novel approach for determining the player kinematics in elite rugby union players

Rugby is intrinsically an impact sport which results in concussions being a frequent injury within the game. Repeated concussion is linked to early-onset dementia and depression, and the rules for limiting repeated concussion are an ongoing controversy. Therefore a greater understanding of the dynamics of head impacts in rugby and the mechanism of concussion is required. Accordingly, this study focuses on assessing the use of Model Based Image Matching (MBIM) and multi-camera view video for measuring six degree of freedom head kinematics during an impact event in rugby union. The matching is performed on video evidence using 3-D animation software Poser 4. The surroundings are built in the virtual environment based on the real dimensions of the sport field. A skeleton model is then used to fit the player’s anthropometry for each video frame thus allowing player kinematics to be measured. The results from this initial study suggest that the MBIM method can be applied to head impact cases in rugby union. The head kinematics results from this case are similar to those reported in literature. The MBIM method should be applied to a number of head impact cases to establish thresholds for concussion injuries in rugby. The data gained from the MBIM method can allow for more reliable kinematic data to be inputted into finite element analysis and rigid body simulations of concussion impacts. This can allow multi-axis force measurements to be measured within the brain and neck. This can ultimately lead to an improvement in concussion injury prevention and management.
Listed In: Biomechanical Engineering, Biomechanics, Mechanical Engineering, Sports Science


Bilateral assessment of cartilage with UTE-T2* quantitative MRI and associations with knee center of rotation following anterior cruciate ligament reconstruction

Purpose: Anterior cruciate ligament (ACL) tear greatly increases the risk of knee osteoarthritis (OA), even when patients undergo ACL reconstruction surgery (ACLR). Changes to walking kinematics following ACLR have been suggested to play a role in this degenerative path to post-traumatic OA by shifting the location of repetitive joint contact loads that occur during walking to regions of cartilage not conditioned for altered loads. Recent work has shown that changes to the average knee center of rotation during walking (KCOR) between 2 and 4 years after ACLR are associated with long term changes in patient reported outcomes at 8 years. Changes to KCOR result in changes to contact patterns between the femur and the tibial plateau. However, it is unknown if changes to this kinematic measure are reflected by changes to cartilage as early as 2 years after surgery. Ultrashort TE-enhanced T2* (UTE-T2*) mapping has been shown to be sensitive to subsurface changes occurring in deep articular cartilage early after ACL injury and over 2 years after ACLR that were not detectable by standard morphological MRI. Thus, the purpose of this study was to test the hypothesis that side to side differences in KCOR correlate with side to side differences in UTE-T2* quantitative MRI (qMRI) in the central weight bearing regions of the medial and lateral tibial plateaus at 2 years following ACLR. Methods: Thirty-five human participants (18F, Age: 33.8±10.5 yrs, BMI: 24.1±3.3) with a history of unilateral ACL reconstruction (2.19±0.22 yrs post-surgery) and no other history of serious lower limb injury received bilateral examinations on a 3T MRI scanner. UTE-T2* maps were calculated via mono-exponential fitting on a series of T2*-weighted MR images acquired at eight TEs (32μs -16 ms, non-uniform echo spacing) using a radial out 3D cones acquisition. All subjects completed bilateral gait analysis. Medial-lateral (ML) and anterior-posterior (AP) coordinates of average KCOR during stance of walking were calculated for both knees. Side to side differences in KCOR were tested for correlations with side to side differences in mean full thickness UTE-T2* quantitative values in the central weight bearing regions of the medial and lateral tibial plateau using Pearson correlation coefficients. Results: There was a distribution in UTE-T2* values, with some subjects having higher UTE-T2* and some lower in the ACLR knee relative to the contralateral knee. A significant correlation (R=0.407, p=0.015, Figure 1A) was observed between UTE-T2* and the ML KCOR with a more lateral KCOR corresponding to higher values of UTE-T2* for the medial tibia. Similarly, for the lateral tibia, a lower UTE-T2* was correlated with a more posterior KCOR (R=0.363, p=0.032, Figure 1B). Significant correlations were not observed for UTE-T2* in the lateral tibia with the ML position of KCOR or for UTE-T2* in the medial tibia with the AP position of KCOR. Conclusions: The results of this study support the hypothesis that side to side differences in mean full thickness UTE-T2* qMRI correlate with side to side differences in knee kinematics at 2 years after ACLR. The finding that a more lateral KCOR in the ACLR knee correlates with UTE T2* values in the medial tibia that were higher than the contralateral side suggests that this kinematic change, which has been previously shown to result in more relative motion between the femur and tibia in the medial compartment, could be affecting subsurface matrix integrity, inducing changes detectable by UTE-T2* mapping. Additionally, the finding that a more posterior KCOR in the ACLR knee correlated with UTE-T2* values in the lateral tibia that were lower than the contralateral knee further suggests that the UTE-T2* metric may reflect early changes in cartilage health. When interpreted within the context of prior work showing that a posterior shift in KCOR from 2 to 4 years post-surgery correlated with improved clinical outcomes at 8 years, the observed lower UTE-T2* with a more posterior KCOR, which is reflective of improved quadriceps recruitment, suggests positive cartilage matrix properties. In spite of the limitations of this cross-sectional and exploratory study, and the difficulty accounting for changes in the contralateral knee, these results support future studies of the relationship between UTE-T2* and KCOR to provide new insight into predicting the risk for OA after ACLR.
Listed In: Biomechanical Engineering, Biomechanics, Gait, Mechanical Engineering, Orthopedic Research, Sports Science


Effects of Total Knee Replacement Material Pairing on Implant Kinematics and Stability

Physical testing of TKR systems to assess stability is an important aspect in screening candidate TKR designs which can be expensive and time consuming. Costs can be reduced by utilizing 3D printed plastic components. The objective is to compare the kinematics and intrinsic constraint of metal-on-plastic (M-P) and plastic-on-plastic (P-P) implants under physiologically relevant loading, with and without simulated ligament contributions, in order to elucidate the effects of material pairings. A cruciate retaining TKR implant was created by combining a 3D printed ABS plastic tibial component with the standard cobalt chrome femoral component, as well as a 3D printed ABS plastic replica femoral component. This results in both M-P and P-P articulations that were mounted to a VIVO 6-DOF joint motion simulator (AMTI, Watertown, MA), which was used for in vitro constraint testing using functional laxity tests. Anterior-posterior (AP) and internal-external (IE) constraint was measured based on resulting deviations from the normal path when superimposed AP and IE loads were applied. Ligaments were simulated as tension-only point-to-point springs using the soft tissue modelling capabilities of the VIVO. Different kinematics were observed between the M-P and P-P implants which could be the result of different initial implant positioning on the joint motion simulator or due to “stiction” of the P-P implant. The functional laxity of the implant system tested appears to be relatively insensitive to the material pairing and ligament presence. These relationships are complex and hard to predict, which underscores the importance of pre-clinical in vitro testing.
Listed In: Biomechanical Engineering, Biomechanics, Gait, Mechanical Engineering, Orthopedic Research


Elasto-Plastic Computational Modelling of Damage Mechanisms in Total Elbow Replacements

As a treatment for end-stage elbow joint arthritis, total elbow replacement (TER) results in joint motions similar to the intact joint; however, bearing wear, excessive deformations and/or early fracture may necessitate early revision of failed implant components. A finite element model of a TER assembly was developed based on measurements from a Coonrad-Morrey implant (Zimmer, Inc., Warsaw, IN) using nonlinear elasto-plastic UHMWPE material properties and a frictional penalty contact formulation. The loading scenario applied to the model includes a flexion-extension motion, a joint force reaction with variable magnitude and direction and a time varying varus-valgus (VV) moment with a maximum magnitude of 13 N.m, simulating a chair-rise scenario as an extreme loading condition. Model results were compared directly with corresponding experimental data. Experimental wear tests were performed on the abovementioned implants using a VIVO (AMTI, Watertown, MA) six degree-of-freedom (6-DOF) joint motion simulator apparatus. The worn TER bushings were scanned after the test using micro computed tomography (μCT) imaging techniques, and reconstructed as 3D models. Contact pressure distributions on the humeral and ulnar bushings correlate with the sites of damage as represented by the μCT data and gross observation of clinical retrievals. The results demonstrate UHMWPE bushing damage due to different loading protocols. Numerical results demonstrate strong agreement with experimental data based on the location of deformation and creep on bushings and exhibit promising capabilities for predicting the damage and failure mechanisms of TER implants.
Listed In: Biomechanical Engineering, Biomechanics, Biotribology, Mechanical Engineering, Orthopedic Research


Modeling 3D Ground Reaction Forces During Walking Using Nanocomposite Piezo-Responsive Foam Sensors

This study presents a new technique for acquiring ground reaction forces from novel, nanocomposite piezo-responsive foam (NCPF) sensors. A shoe was fitted with four NCPF sensors located at the heel, arch, ball, and toe positions. Running data was collected simultaneously from both the shoe sensors and from a force-sensing treadmill. A portion (30 randomly selected stance phases) of the treadmill data was used to develop a predictive stochastic model of GRF based on the sensor inputs. The stochastic model was then used to predict GRF for the remaining shoe sensor data, which was then benchmarked against the treadmill data. The results indicated that this model was able to predict forces in the x-axis (anterior-posterior) with 2.38% error, forces in the y-axis (medial-lateral) with 6.01% error, and forces in the z-axis (vertical) with 2.43% error. These novel sensors hold potential to dramatically improve both the ease and expense associated with GRF data, as well as allow unprecedented ability to measure GRF during real world applications outside of the laboratory.
Listed In: Biomechanical Engineering, Gait, Mechanical Engineering, Sports Science


Human cadaveric bi-Segment impact experiments at different postures

Victims of improvised explosive devices (IEDs) that have presented spinal injury in recent conflicts have been shown to have a high incidence of lumbar spine fractures. Previous studies have shown that the initial positioning of spinal bone-disc-bone complexes affects their biomechanical response when loaded quasi-statically; such a correlation, however, has not been explored at appropriate high loading rate scenarios that simulate injury. This study aims to investigate the response of lumbar spine cadaveric segments in different postures under axial impact conditions. Three T11-L1 bi-segments were dissected and tested destructively in a drop tower under flexed/neutral/extended postures. Strains were measured on the vertebral body and the spinous process of T12. Forces were measured cranially using a 6-axis load cell, and a high-speed camera was used to capture displacements and fracture. The impacted specimens were CT-scanned to identify the fracture pattern. Whilst axial force to failure was similar for flexed and extended postures, the non-axial forces and the bending moments, however, were dissimilar between postures. Although all specimens showed a burst fracture pattern, the extended posture failed more posteriorly. This suggests that axial force alone is not adequate to predict injury severity in the lumbar spine. This insight would not have been possible without the use of the 6-axis load cell. As metrics for spinal injury in surrogates take into account only the axial force, this programme of work may provide data for a better injury criterion and allow for a mechanistic understanding of the effects of posture on injury risk.
Listed In: Biomechanical Engineering, Biomechanics, Mechanical Engineering, Orthopedic Research


One Hundred Data-Driven Haptic Texture Models and Open-Source Methods for Rendering on 3D Objects

This work introduces the Penn Haptic Texture Toolkit (HaTT), a publicly available repository of haptic texture models for use by the research community. HaTT includes 100 haptic texture and friction models, the recorded data from which the models were made, images of the textures, and the code and methods necessary to render these textures using an impedance-type haptic interface such as a SensAble Phantom Omni. This work reviews our previously developed methods for modeling haptic virtual textures, describes our technique for modeling Coulomb friction between a tooltip and a surface, discusses the adaptation of our rendering methods for display using an impedance-type haptic device, and provides an overview of the information included in the toolkit. Each texture and friction model was based on a ten-second recording of the force, speed, and high-frequency acceleration experienced by a handheld tool moved by an experimenter against the surface in a natural manner. We modeled each texture’s recorded acceleration signal as a piecewise autoregressive (AR) process and stored the individual AR models in a Delaunay triangulation as a function of the force and speed used when recording the data. Measurements of the user’s instantaneous normal force and tangential speed are used to synthesize texture vibrations in real time. These vibrations are transformed into a texture force vector that is added to the friction and normal force vectors for display to the user.
Listed In: Mechanical Engineering, Other


Evaluation of Haversian Bone Fracture Healing in Simulated Microgravity

The inherent reduction in mechanical loading associated with microgravity has been shown to result in dramatic decreases in the bone mineral density (BMD) and mechanical strength of skeletal tissue. Importantly, there is a concomitant increase in fracture risk during long-duration spaceflight missions. Thus, the objective of this study was to investigate the effects of microgravity loading on long-bone fracture healing in a previously-developed Haversian bone model of simulated microgravity over a 4-week period. For in vivo mechanical evaluation, strains of an implanted orthopaedic fixation plate were quantified for known hindlimb ground reaction forces with a six degree-of-freedom load cell (AMTI, Watertown, MA). In vivo strain measurements demonstrated significantly higher orthopaedic plate strains in the Microgravity Group as compared to the Control Group following the 28-day healing period due to inhibited healing in the microgravity environment. DEXA BMD in the treated metatarsus of the Microgravity Group decreased 17.6% at the time of the ostectomy surgery and decreased an additional 5.4% during the 28-day healing period. Four-point bending stiffness of the Microgravity Group was 4.4 times lower than that of the Control Group (p<0.01), while µCT and histomorphometry demonstrated reduced periosteal callus area, mineralizing surface, mineral apposition rate (p<0.001), bone formation rate, and periosteal/endosteal osteoblast numbers as well as increased periosteal osteoclast number. These data provide strong evidence that the mechanical loading environment dramatically affects the fracture healing cascade and resultant mineralized tissue strength, and that the microgravity loading environment has negative effects on fracture healing in Haversian systems.
Listed In: Biomechanical Engineering, Biomechanics, Mechanical Engineering, Orthopedic Research


Optimization and design modeling for continuous roll compaction granulation

In granulation processes, the mechanical properties of the powder being processed are very influential on the characteristics of the end product. For this reason the modified Drucker-Prager/Cap model parameters of Micro-crystalline cellulose (MCC), a commonly used pharmaceutical excipient was determined. In particular, the influence of particle size of MCC on the DPC parameters was studied. In this study three grades of MCC (MCC 101, MCC102 & MCC200) were studied. It was found that the compaction properties were insensitive the particle size of MCC.


Listed In: Mechanical Engineering


Load Rating and Evaluation of Railroad Bridges Based on Non-Destructive Testing and Finite Element Modeling

The Federal Rail Association (FRA) mandated an increase in freight railcar weight limits from 1170 kN (263,000 lb) to 1272 kN (286,000 lb). However, most of the railway bridges were built prior to World War II and are not designed to handle this increased railcar weight. Thus, there is a need for accurate and efficient methods to evaluate and load rate existing bridges that will reveal their actual capacities. In this study, the research approach adopted is aimed at providing an efficient method to load rate railway bridges. Three load rating methods were utilized and compared: (1) traditional method based on American Railway Engineering and Maintenance-of-Way Association (AREMA) specifications, (2) refined traditional method using data from field tests, and (3) load rating using testing data and finite element (FE) modeling. Various types of bridges were field tested and evaluated. Results from a typical railway bridge will be used to demonstrate and compare each one of the three load rating methods. For this bridge, non-destructive testing was performed. The collected responses were used to improve the traditional method and calibrate a 3-D FE model. The rating results indicated that method (1) can be relatively conservative and does not reflect the actual behavior of the structure while method (3) provided accurate results it was more tedious. It is suggested that the refined traditional method (2) be used since it provided similar accurate rating results without developing a detailed FE model.
Listed In: Mechanical Engineering, Other