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We aim to demystify the development of neuro-biomechanical modeling in OpenSim with zero configuration, easy to share models while accessing to free GPUs on a web-based platform of Google Colaboratory. OpenSim is an open-source biomechanical package. OpenSim is used in a variety of applications and developed in C++; however, it is available for a wide range of users with bindings in MATLAB, Python, Jython and Java via OpenSim Application Programing Interface (API). OpenSim installation on a personal computer is well described by the developers but its implementation may still be time-consuming and challenging for the new users. Cloud-based computing is expanding in almost all engineering domains with zero configuration, though it is in its early stages within biomechanics community. In this study, we aim to access OpenSim functionality on the Google cloud platform. The methods can also be used in other cloud-based platforms. We installed OpenSim on the Google Colab via Anaconda cloud and named it OpenColab. To use OpenColab, one requires only a connection to the internet and a Gmail account. Moreover, such a platform enables the users to access vast libraries of machine learning available within free Google products e.g., TensorFlow. OpenColab takes advantage of zero configuration of cloud-based platforms even on a smart phone, provides access to free GPUs and enables users to share and reproduce modeling approaches for further validation. Finally, we performed inverse problem in biomechanics and compared OpenColab results with OpenSim GUI’s for validation. Step-by-step installation processes and examples can be found freely at: https://simtk.org/projects/opencolab.

Biomechanical strain is a major stimulus of subchondral bone (SCB) tissue adaptation in joints but may also lead to initiation and propagation of microcracks, highlighting the importance of quantifying the intratissue strain in subchondral bone. In the present study, we used micro computed tomography (μCT) imaging, mechanical testing, and digital image correlation (DIC) techniques to evaluate the biomechanical strains in equine SCB under impact compression applied through the articular surface. We aimed to investigate the effects of in vivo accumulated microdamage in equine SCB on the distribution of mechanical impact strain through the articular cartilage. Under the applied strain of 2.0 ± 0.1% (mean ± standard deviation, n=15) to the articular surface of cartilage-bone plugs, the overall thickness of the SCB developed e

Articular cartilage is a soft tissue that distributes the loads in joints and transfers the compressive load to the underlying bone. At high rate and magnitudes of mechanical loading, cartilage and subchondral bone together are susceptible to damage. In addition, any disruption to the cartilage's structure, caused by injury, trauma or disorder such as osteoarthritis (OA), can alter the mechanism of load transfer from the cartilage to the underlying bone. Changes in the cartilage structure can also alter the ability of cartilage-bone to absorb and dissipate the impact energy. To investigate the effects of cartilage degradation on cartilage-bone shock absorption ability, the top 50% of the cartilage thickness was removed (modified cartilage) to mimic the cartilage thickness reduction in Grade III cartilage lesion and the remaining cartilage-bone unit (modified cartilage-bone) was compressed at high-rate (4% strain at 5 Hz). High-speed camera and microscope were used to capture microscopic deformation, and digital image correlation technique (DIC) employed to quantify the deformation of cartilage and bone. The mechanical properties (i.e. stiffness, strain, absorbed and dissipated energies) of cartilage and bone were calculated before and after the removal of the top 50% of the cartilage thickness, consisting of both the superficial tangential zone (STZ) and part of the middle zone of the cartilage. The results showed a significant degradation in the mechanical properties of the cartilage-bone unit after the removal of the top 50% cartilage thickness. The stiffness of the modified cartilage reduced significantly (by ~39%) and energy absorption in underlying bone increased by 32%, which can make the bone more vulnerable to damage in the modified cartilage-bone unit. In addition, the energy dissipation in the modified cartilage-bone unit was also increased by approximately 14%. These changes in mechanical properties suggest a crucial role of the STZ and middle zone (within the top 50% cartilage thickness) in protecting the underlying bone from the severe compressive impact loading. Results also indicated that under physiological contact stress of 7 MPa, strain in damaged cartilage was increased by 3.22% without affecting the mechanical behaviour of the underlying bone.

Skeletal fragility is a major complication of type 2 diabetes mellitus (T2D), but there is a poor understanding of mechanisms underlying T2D skeletal fragility. The increased fracture risk has been suggested to result from deteriorated bone microarchitecture or poor bone quality due to accumulation of advanced glycation end-products (AGEs). We conducted a clinical study to determine whether: 1) bone microarchitecture, AGEs, and bone biomechanical properties are altered in T2D bone, 2) bone AGEs are related to bone biomechanical properties, and 3) serum AGE levels reflect those in bone. To do so, we collected serum and proximal femur specimens from T2D (n = 20) and non-diabetic (n = 33) subjects undergoing total hip replacement surgery. A section from the femoral neck was imaged by microcomputed tomography (microCT), tested by cyclic reference point indentation, and quantified for AGE content. A trabecular core taken from the femoral head was imaged by microCT and subjected to uniaxial unconfined compression tests. T2D subjects had greater HbA(1)c (+23%, p ≤ 0.0001), but no difference in cortical tissue mineral density, cortical porosity, or trabecular microarchitecture compared to non-diabetics. Cyclic reference point indentation revealed that creep indentation distance (+18%, p ≤ 0.05) and indentation distance increase (+20%, p ≤ 0.05) were greater in cortical bone from T2D than in non-diabetics, but no other indentation variables differed. Trabecular bone mechanical properties were similar in both groups, except for yield stress, which tended to be lower in T2D than in non-diabetics. Neither serum pentosidine nor serum total AGEs were different between groups. Cortical, but not trabecular, bone AGEs tended to be higher in T2D subjects (21%, p = 0.09). Serum AGEs and pentosidine were positively correlated with cortical and trabecular bone AGEs. Our study presents new data on biomechanical properties and AGEs in adults with T2D, which are needed to better understand mechanisms contributing to diabetic skeletal fragility.

Subchondral bone injury due to high magnitude and repetition of compressive loading is common in humans and athletic animals such as Thoroughbred racehorses. Repeated loading of the joint surface may alter the subchondral bone microstructure and initiate microdamage in the bone adjacent to the articular cartilage. Understanding the relationship between microdamage, microstructure and mechanical properties of the subchondral bone adjacent to the articular cartilage is, therefore, essential in understanding the mechanism of subchondral bone injury. In this study, we used high-resolution µCT scanning, a digital image-based strain measurement technique, and mechanical testing to evaluate the three-dimensional pre-existing microcracks, bone volume fraction (BVF) and bone mineral density (BMD), and mechanical properties (stiffness and hysteresis) of subchondral bone (n = 10) from the distopalmar aspect of the third metacarpal (MC3) condyles of Thoroughbred racehorses under high-rate compression. We specifically compared the properties of two regions of interest in the subchondral bone: the 2 mm superficial subchondral bone (SSB) and its underlying 2 mm deep subchondral bone (DSB). The DSB region was 3.0 ± 1.2 times stiffer than its overlying SSB, yet it dissipated much less energy compared to the SSB. There was no correlation between structural properties (BVF and BMD) and mechanical properties (stiffness and energy loss), except for BMD and energy loss in SSB. The lower stiffness of the most superficial subchondral bone in the distal metacarpal condyles may protect the overlying cartilage and the underlying subchondral bone from damage under the high-rate compression experienced during galloping. However, repeated high-rate loading over time has the potential to inhibit bone turnover and induce bone fatigue, consistent with the high prevalence of subchondral bone injury and fractures in athletic humans and racehorses.

In Thoroughbred racehorses, fractures of the distal limb are commonly catastrophic. Most of these fractures occur due to the accumulation of fatigue damage from repetitive loading, as evidenced by microdamage at the predilection sites for fracture. Adaptation of the bone in response to training loads is important for fatigue resistance. In order to better understand the mechanism of subchondral bone adaptation to its loading environment, we utilised a square root function defining the relationship between bone volume fraction [Formula: see text] and specific surface [Formula: see text] of the subchondral bone of the lateral condyles of the third metacarpal bone (MCIII) of the racehorse, and using this equation, developed a mathematical model of subchondral bone that adapts to loading conditions observed in vivo. The model is expressed as an ordinary differential equation incorporating a formation rate that is dependent on strain energy density. The loading conditions applied to a selected subchondral region, i.e. volume of interest, were estimated based on joint contact forces sustained by racehorses in training. For each of the initial conditions of [Formula: see text] we found no difference between subsequent homoeostatic [Formula: see text] at any given loading condition, but the time to reach equilibrium differed by initial [Formula: see text] and loading condition. We found that the observed values for [Formula: see text] from the mathematical model output were a good approximation to the existing data for racehorses in training or at rest. This model provides the basis for understanding the effect of changes to training strategies that may reduce the risk of racehorse injury.

Subchondral bone (SCB) microdamage is commonly observed in traumatic joint injuries and has been strongly associated with post-traumatic osteoarthritis (PTOA). Knowledge of the three-dimensional stress and strain distribution within the SCB tissue helps to understand the mechanism of SCB failure, and may lead to an improved understanding of mechanisms of PTOA initiation, prevention and treatment. In this study, we used high-resolution micro-computed tomography (µCT)-based finite element (FE) modelling of cartilage-bone to evaluate the failure mechanism and the locations of SCB tissue at high-risk of initial failure under compression. The µCT images of five cartilage-bone specimens with an average SCB thickness of 1.23±0.20mm were used to develop five µCT-based FE models. The FE models were analysed under axial compressions of approximately 30MPa applied to the cartilage surface while the bone edges were constrained. Strain and stress-based failure criteria were then applied to evaluate the failure mechanism of the SCB tissue under excessive compression through articular cartilage. µCT-based FE models predicted two locations in the SCB at high-risk of initial failure: (1) the interface of the calcified-uncalcified cartilage due to excessive tension, and (2) the trabecular bone beneath the subchondral plate due to excessive compression. µCT-based FE models of cartilage-bone enabled us to quantify the distribution of the applied compression which was transferred through the articular cartilage to its underlying SCB, and to investigate the mechanism and the mode of SCB tissue failure. Ultimately, the results will help to understand the mechanism of injury formation in relation to PTOA.

Subchondral bone (SCB) microdamage is prevalent in the joints of human athletes and animals subjected to high rate and magnitude cyclic loading of the articular surface. Quantifying the effect of such focal in vivo fatigue-induced microdamage on the mechanical response of the tissue is critical for the understanding of joint surface injury and the development of osteoarthritis. Thus, we aimed to quantify the mechanical properties of cartilage-bone from equine third metacarpal (MC3) condyles, which is a common area of accumulated microdamage due to repetitive impact loading. We chose a non-destructive technique, i.e. high-resolution microcomputed tomography (µCT) imaging, to identify various degrees of in vivo microdamage in SCB prior to mechanical testing; because µCT imaging can only identify a proportion of accumulated microdamage, we aimed to identify racing and training history variables that provide additional information on the prior loading history of the samples. We then performed unconfined high-rate compression of approximately 2% strain at 45%/s strain rate to simulate a cycle of gallop and used real-time strain measurements using digital image correlation (DIC) techniques to find the stiffness and shock absorbing ability (relative energy loss) of the cartilage-bone unit, and those associated with cartilage and SCB. Results indicated that stiffness of cartilage-bone and those associated with the SCB decreased with increasing grade of damage. Whole specimen stiffness also increased, and relative energy loss decreased with higher TMD, whereas bone volume fraction of the SCB was only associated negatively with the stiffness of the bone. Overall, the degree of subchondral bone damage observed with µCT was the main predictor of stiffness and relative energy loss of the articular surface of the third metacarpal bone of Thoroughbred racehorses under impact loading.

BACKGROUND: Standard fatigue testing of bone uses a single load and frequency applied until failure. However, in situ, the subchondral bone of Thoroughbred racehorses is subjected to a combination (or a spectrum) of loads and frequencies during training and racing. OBJECTIVE: To investigate the use of a fatigue testing method for equine third metacarpal (McIII) subchondral bone under a spectrum of loading conditions which a racehorse is likely to experience during a fast workout. STUDY DESIGN: In vitro biomechanical experimental study. METHODS: McIII subchondral bone specimens (n = 12) of racehorses were harvested from left and right medial condyles. A novel fatigue loading protocol was developed based upon a standard sequence of gaits during a typical fast workout protocol. This loading pattern, or loading loop, was repeated until the failure of the specimen. RESULTS: The mean ± standard deviation for all specimens for total time‐to‐failure was 76,393 ± 64,243 s (equivalent to 18.3 ± 15.7 fast workouts). Ten of twelve specimens withstood at least one complete loop equivalent to a fast workout. All specimens failed during simulated gallop loading. MAIN LIMITATIONS: The resting time between loops was much shorter than in vivo resting time and specimens were unconfined during compressive testing. CONCLUSIONS: This novel fatigue loading protocol more closely mimics in vivo fatigue loading of McIII subchondral bone and demonstrates the importance of the highest speeds in the development of subchondral bone injury.

Subchondral bone microdamage due to high-impact loading is a key factor leading to post-traumatic knee osteoarthritis. A quantified assessment of the mechanical characteristics of subchondral bone at the tissue-level is essential to study the mechanism of impact-induced microdamage. We combined mechanical impact testing of equine cartilage-bone with µCT image-based finite element models (μFEM) of each specimen to determine subchondral bone (including calcified cartilage: CCSB) elastic tissue modulus and local stresses and strains associated with micro-fractures within the CCSB tissue. The material properties of each specimen-specific μFEM were iteratively adjusted to match the FE-predicted stress-strain curves with experimental results. Isotropic homogeneous material properties for both uncalcified cartilage (UC) and CCSB were assumed. UC large-deformation was simulated using hyperelastic material properties. Final UC shear and CCSB tissue elastic modulus of G=38±20MPa and E(t)=3.3±0.7GPa were achieved after fit procedure. The results suggested that initial failure in CCSB occurred at local tensile and compressive stresses of 29.47±5.34 MPa and 64.3±21.3MPa, and tensile and compressive strains of 1.12±0.06% and 1.99±0.41%, respectively. Tissue-level material properties can be used in finite element modeling of diarthrodial joints under impact loading, and also in designing artificial cartilage-bone to replace the damaged tissue in the joint. Results can provide an estimate for the threshold of initial failure in subchondral bone tissue due to an impact compression transmitted through the overlying articular cartilage.

Fatigue-induced subchondral bone (SCB) injuries are prevalent among athletes due to the repetitive application of high magnitude loads on joints during intense physical training. Existing fatigue studies on bone utilize a standard fatigue test approach by applying loads of a constant magnitude and frequency even though physiological/realistic loading is a combination of various load magnitudes and frequencies. Metal materials in implant and aerospace applications have been studied for fatigue behavior under physiological or realistic loading, however, no such study has been conducted on biological materials like bones. In this study, we investigated fatigue behavior of SCB under the range of loads likely to occur during a fast-workout of an equine athlete in training. A loading protocol was developed by simulating physiological loads occurring during a fast-workout of a racehorse in training, which consisted of a sequence of compression-compression load cycles, including a warm-up (32, 54, 61 MPa) and cool-down (61, 54, 32 MPa) before and after the slow/fast/slow gallop phase of training, also referred to as a training loop. This loading protocol/training loop was applied at room temperature in load-control mode to cylindrical SCB specimens (n = 12) harvested from third metacarpal medial condyles (MCIII) of twelve thoroughbred racehorses and repeated until fatigue failure. The mean ± standard deviation for total time-to-failure (TTF) was 76,393 ± 64,243 s (equivalent to 18.3 ± 15.7 training workouts) for n = 12 specimens. We observed the highest relative energy loss (REL, hysteresis loss normalized to energy absorbed in a load cycle) under loads equivalent to gallop speeds and all specimens failed under these gallop loads. This demonstrates the importance of the gallop speeds in the development of SCB injury, consistent with observations made in live racehorses. Moreover, specimens with higher mean REL and lower mean stiffness during the first loop had a shorter fatigue life which further confirms the detrimental effect of high energy loss in SCB. Further studies are required to reconcile our results with fatigue injuries among equine athletes and understand the influence of different training programs on the fatigue behavior of subchondral bone.

Microdamage accumulation and adaptation of subchondral bone subjected to intensive cyclic loading are important processes associated with catastrophic bone failure, and joint degeneration in athletic humans and racehorses. At the tissue-level, they lead to a spatial variation in bone tissue mineral density (TMD) which affects the response of the bone to mechanical load. Quantifying the spatial distribution of mechanical load within the subchondral bone is critical for understanding the mechanism of the joint failure. Previously, a gradient of TMD and mechanical properties has been reported under unconfined compression in osteochondral plugs. In the present study, we used micro computed tomography (μCT)-based finite element (FE) models of cartilage-bone to investigate the gradient of strain in the subchondral bone (SCB) from the third metacarpal (MC3) condyle of racehorses under simulated in situ compression. Non-destructive mechanical testing of specimens under high-rate compression provided the apparent-level modulus of SCB. FE models were analysed using unconfined and confined boundary conditions. Unconfined FE-predicted apparent-level gradient of modulus across the SCB thickness correlated well with the experimental results (R2 ​= ​0.72, p ​

Despite the important role of subchondral bone in maintaining the integrity of the overlying articular cartilage, little research has focused on measuring its mechanical behavior, particularly under injurious load conditions such as impact compression. In this study, the stiffness and the absorbed energy of subchondral bone were compared to that of its overlying cartilage by applying impact compression to equine cartilage-bone specimens. Deformations of the cartilage and subchondral bone were examined independently within the cartilage-bone unit by analyzing real-time images of cartilage-bone explants. Peak subchondral bone and cartilage stiffness (mean ± SD) were 800.7 ± 250.0 MPa and 119.9 ± 50.8 MPa respectively. The maximum absorbed energy per unit volume of subchondral bone was approximately 4 times lower than that of cartilage. Micro-computed tomography (μCT) images at 9 μm resolution revealed oblique fissures at the cartilage articular surface. At the cartilage-bone interface, micro-cracks as thin as 30 μm in width and micro-fractures of width 200 μm could be seen in the μCT images. The relative energy loss in bone was 76.5 ± 6.8% in specimens with bone fracture and 23.0 ± 20.4% in specimens without bone fracture. Our results indicate that both articular cartilage and subchondral bone absorb shock under impact compression, but the energy absorption of bone is much higher in specimens that fracture. This may spare the overlying cartilage from immediate injury, but is a potential risk for subsequent post-traumatic osteoarthritis (PTOA).

The aim of this study was to identify the contribution of the Soleus and Gastrocnemius (Gastroc) muscles' forces to anterior cruciate ligament (ACL) loading during single-leg landing. Although Quadriceps (Quads) and Hamstrings (Hams) muscles were recognized as the main contributors to the ACL loading, less is known regarding the role of ankle joint plantarflexors during landing. Eight healthy subjects performed single-landing tasks from 30 and 60cm heights. Scaled generic musculoskeletal models were developed in OpenSim to calculate lower limb muscle forces. The model consisted of 10 segments with 23 degrees of freedom and 92 lower body muscle-tendon units. Knee joint reaction forces were calculated based on the estimated muscle forces and used to predict ACL forces. We hypothesized that Soleus and Gastrocs muscle forces have opposite effects on tibial loading in the anterior/posterior directions. In situations where greater landing height would lead to an increase in GRF and risk of ACL injury, we further hypothesized that posterior forces of the Soleus and Hams would increase correspondingly to help protect the ACL during a safe landing maneuver. Our results demonstrated the antagonistic and agonistic roles of Gastrocs and Soleus respectively in ACL loading. The posterior force of Soleus reached 28-32% of Ham's posterior force for both landing heights at peak GRF while the posterior force of Gastrocs on femur was negligible. ACL injury risk during single-leg landing is not only dependent on knee musculature but also influenced by muscles that do not span the knee joint, such as the Soleus. In conclusion, the role of the ankle plantarflexors should be considered when developing training strategies for ACL injury prevention.

Internal tibial rotation is a risk factor for anterior cruciate ligament (ACL) injury. The effect of restraining tibial rotation (RTR) to prevent ACL injury during single-leg landing is not well understood. We aimed to investigate the effect of impact load and RTR on ACL injury with respect to flexion angle. We hypothesized that RTR could protect the knee from ACL injury compared to free tibial rotation (FTR) regardless of flexion angle and create a safety zone to protect the ACL.Thirty porcine specimens were potted in a rig manufactured to replicate single-leg landing maneuvers. A mechanical testing machine was used to apply external forces in the direction of the tibial long axis. A 3D displacement sensor measured anterior tibial translation (ATT). The specimens were divided into 3 groups of 10 specimens and tested at flexion angles of 22 ± 1°, 37 ± 1° and 52 ± 1° (five RTR and five FTR) through a consecutive range of actuator displacements until ACL failure. After dissection, damage to the joint was visually recorded. Two-way ANOVA were utilized in order to compare compressive forces, torques and A/P displacements with respect to flexion angle.The largest difference between peak axial compressive forces (~3.4 kN) causing ACL injury between RTR and FTR was reported at a flexion angle of 22°. Tibial torques with RTR was in the same range and20 Nm at the instance and just before ACL failure, compared to a significant reduction when cartilage/bone damage (no ACL failure) was reported. Isolated ACL injuries were observed in ten of the 15 FTR specimens. Injuries to bone and cartilage were more common with RTR.RTR increases the threshold for ACL injury by elevating the compressive impact load required at lower flexion angles. These findings may contribute to neuromuscular training programs or brace designs used to avoid excessive internal/external tibial rotation. Caution must be exercised as bone/cartilage damage may result.

In spite of earlier experimental and modeling studies, the relative role of the intra-abdominal pressure (IAP) in spine mechanics has remained controversial. This study employs simple analytical and finite element (FE) models of the spine and its surrounding structures to investigate the contribution of IAP to spinal loading and stability. The analytical model includes the abdominal cavity surrounded by muscles, lumbar spine, rib cage and pelvic ring. The intra-abdominal cavity and its surrounding muscles are represented by a thin deformable cylindrical membrane. Muscle activation levels are simulated by changing the Young's modulus of the membrane in the direction of muscle fibers, yielding IAP values recorded under the partial Valsalva maneuver. In the FE model, the abdominal cavity is cylindrical and filled with a nearly incompressible fluid. The surrounding muscles are modeled as membrane elements with transverse isotropic material properties simulating their fiber orientation. Results indicate a good qualitative agreement between the analytical and FE models. Larger external force and/or higher levels of muscle activation generate higher IAP thereby increasing spinal stiffness. These effects are more pronounced for activation of muscles with more horizontally directed fibers, e.g., transverse abdominis (TA). The capacity of the abdominal muscles to indirectly unload and stabilize the spine by generating IAP depends mostly on their fiber orientation, and secondarily on their cross-section area.

In spite of the several experimental and modeling studies on the biomechanical characteristics of the human spine, the role and significance of the intra-abdominal pressure (IAP) in spine mechanics has remained controversial. This study represents a simple analytical and a 3-D finite element model of spine and its surrounding structures to investigate the contribution of IAP to spinal stability. The mathematical model included the lumbar spine column, the abdominal cavity and a muscular layer around it, the rib cage and the pelvic ring. The lumbar spine column was modeled as a beam and the rib cage and pelvis as rigid bodies. The intra-abdominal cavity and the surrounding muscular layer were represented by a thin-wall cylindrical vessel with deformable shell wall. The free body diagram and equilibrium equations of each body of the model were derived while an external load to the rib cage was applied. The equations were then combined with the force-deflection relationships for the beam bending, the IAP fluid volume variation, and the muscle shell traction. Muscle activation levels were simulated by changing the Young’s modulus of the shell in the direction of fibers, up to an upper-limit value which was obtained based on the Valsalva maneuver. In the Finite Element (FE) model, the abdominal cavity was assumed to be cylindrical and filled by fluid with a bulk modulus of IMPa. The surrounding muscular layer was modeled as membrane with transverse isotropic material properties considering their fibers orientation. The spine, rib cage and pelvic ring were modeled by beam elements. The top plate simulated the active and/or passive role of diaphragm through its vertical displacement. The bottom membrane and distal spine were fully constrained. Good agreement between the analytical and FE model results was obtained. A larger external force and/or higher level of muscle activation caused a higher IAP, improving spinal unloading and stability. This effect was more significant for muscles with more horizontally directed fibers, e.g., Transverse Abdominis (TA).Copyright © 2006 by ASME