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Intra-operative local 3D vessel representations have the potential to significantly decrease the use of contrast agents and exposure to ionizing radiation during endovascular procedures, while overcoming the 2D visualization limitation of fluoroscopic guidance. By fusing intravascular ultrasound (IVUS) imaging and electromagnetic (EM) pose sensing in a robotic catheter tip, a real-time local 3D model of the vasculature could be constructed intra-operatively. This letter proposes the use of a cylinder model to approximate the vessel geometry near the catheter tip. An unscented Kalman filter is employed to robustly estimate the cylinder that best fits IVUS and EM data while navigating through the vessel. This forms a radiation-free alternative to conventional radiation-based guidance. Validation on one in silico and two in vitro models showed median estimation errors of cylinder radius of 0.14 mm, 0.42 mm and 0.70 mm; cylinder position of 0.45 mm, 1.07 mm and 0.96 mm; and cylinder orientation of $2.94^\circ$ , $4.60^\circ$ and $3.03^\circ$ showing great potential for helping interventionists preventing harmful interactions between the instrument tip and the vessel wall.

Objective: Cerebral contusions (CC) represent a frequent lesion in traumatic brain injury, with potential morbidity from mass effect and tissue loss. Better understanding of the mechanical etiology will help to improve head protection. The goal of this study is to investigate the threshold for mechanical impact parameters to induce CC in an in vivo porcine controlled cortical impact model. Methods: Thirty-four adult male pigs underwent craniotomy and controlled cortical impact with a hemispherical tip on intact dura under general anesthesia. Peak impact depth varied between 1.1 and 12.6 mm, and impact velocity between 0.4 and 2.2 m/s while the dwell time was kept at 200 ms. Two days following impact, the animals underwent magnetic resonance (MR) imaging of the brain, and were subsequently sacrificed for brain extraction. CC damage was investigated by magnetic resonance imaging and histology. Results: All animals recovered from the impact without overt neurological deficit. Provoked injuries were histologically confirmed to be CC. Decreasing probability of cortical damage and white matter edema volume was observed with decreasing impact depth and velocity. No CC could be demonstrated below a product of impact depth and velocity of 0.8 mm*m/s, whereas the probability for CC was one third below 15 mm*m/s. The threshold for CC development as estimated from the current series of experiments, was situated at an impact depth of 2.0 mm and impact velocity of 0.4 m/s Conclusion: Mechanical thresholds for CC development could be explored in the current porcine controlled cortical impact model. Findings will be used to further refine a cerebral contusion porcine model with volumetric histology data in light of future finite element cerebral contusion validation studies.

Postero-anterior (PA) mobilization is widely used to manage low back pain by physiotherapists. The PA load is applied through the spinous process of a vertebra. Low bone density is a counter-indication of PA mobilization, whether PA mobilization may cause fractures in fragile vertebrae is unclear. Therefore, the aim of this study was to quantify the role of bone density on a fracture risk in the first lumbar vertebra subjected to PA load. A finite element model of the first lumbar (L1) vertebra of an elderly female was created to predict the fracture risk of the PA mobilization. The von Mises stress and minimum principal strain were used as the assessment indicators. Three different bone density cases were evaluated to reflect healthy, osteoporotic, and severe osteoporotic conditions by assuming heterogeneous moduli based on local bone density converted from computed tomographic images. In the severe osteoporotic condition under PA load, the maximum von Mises stress and largest compressive strain occurred in the pedicles and spinous process. These stress and strain exceeded the yield stress and yield strain indicating a high risk for failure. The resulted stress and strain were also excessive in the pedicles for healthy and moderate osteoporotic conditions. PA mobilization can increase the risk of vertebra fracture in elderly with osteoporosis. The pedicles and spinous process of osteoporotic L1 vertebra are the critical regions prone to fracture. We recommend that it is crucial to be reduce force when applying the PA mobilization to elderly with osteoporosis.

OBJECTIVE: The level of primary implant fixation in cementless total hip arthroplasty is a key factor for the longevity of the implant. Vibration-based methods show promise for providing quantitative information to help surgeons monitor implant fixation intraoperatively. A thorough understanding of what is driving these changes in vibrational behavior is important for further development and improvement of these methods. Additionally, an instrument must be designed to enable surgeons to leverage these methods. This study addresses both of these issues. METHOD: An augmented system approach was used to develop an instrument that improves the sensitivity of the vibrational method and enables the implementation of the necessary excitation and measurement equipment. The augmented system approach took into account the dynamics of the existing bone-implant system and its interaction with the added instrument. RESULTS: Two instrument designs are proposed, accompanied by a convergence-based method to determine the insertion endpoint. The modal strain energy density distribution was shown to affect the vibrational sensitivity to contact changes in certain areas. CONCLUSION: The augmented system approach led to an instrument design that improved the sensitivity to changes in the proximal region of the combined bone-implant-instrument system. This fact was confirmed both in silico and in vitro. Clinical Impact: The presented method and instruments address practical intraoperative challenges and provide perspective to objectively support the surgeon's decision-making process, which will ensure optimal patient treatment. ispartof: Ieee Journal Of Translational Engineering In Health And Medicine-Jtehm vol:9 ispartof: location:United States status: Published online

Background Assessment of glenoid bone defects is important to select the optimal glenoid component design during shoulder arthroplasty planning and implantation. This study presents a fully automated method to describe glenoid bone loss using 3-dimensional measurements without the need for a healthy contralateral reference scapula. Methods The native shape of the glenoid is reconstructed by fitting a statistical shape model (SSM) of the scapula. The total vault loss percentage, local vault loss percentages, defect depth, defect area percentage, and subluxation distance and region are computed based on a comparison of the reconstructed and eroded glenoids. The method is evaluated by comparing its results with a contralateral bone–based reconstruction approach in a data set of 34 scapula and humerus pairs with unilateral glenoid bone defects. Results The SSM-based defect measurements deviated from the contralateral bone–based measurements with mean absolute differences of 5.5% in the total vault loss percentage, 4.5% to 8.0% in the local vault loss percentages, 1.9 mm in the defect depth, 14.8% in the defect area percentage, and 1.6 mm in the subluxation distance. The SSM-based method was statistically equivalent to the contralateral bone–based method for all parameters except the defect area percentage. Conclusion The presented method is able to automatically analyze glenoid bone defects using 3-dimensional measurements without the need for a healthy contralateral bone.

OBJECTIVE: This study proposes a computationally efficient method to quantify the effect of surgical inaccuracies on ligament strain in total knee arthroplasty (TKA). More specifically, this study describes a framework to determine the implant position and required surgical accuracy that results in a ligament balanced post-operative outcome with a probability of 90%. METHODS: The response surface method is used to translate uncertainty in the implant position parameters to uncertainty in the ligament strain. The designed uncertainty quantification technique allows for an optimization with feasible computational cost towards the planned implant position and the tolerated surgical error for each of the twelve degrees of freedom of the implant position. RESULTS: It is shown that the error does not allow for a ligament balanced TKA with a probability of 90% using preoperative planning. Six critical implant position parameters can be identified, namely AP translation, PD translation, VV rotation, IE rotation for the femoral component and PD translation, VV rotation for the tibial component. CONCLUSION: We introduced an optimization process that allows for the computation of the required surgical accuracy for a ligament balanced postoperative outcome using preoperative planning with feasible computational cost. SIGNIFICANCE: Towards the research society, the proposed method allows for a computationally efficient uncertainty quantification on a complex model. Towards surgical technique developers, six critical implant position parameters were identified, which should be the focus when refining surgical accuracy of TKA, leveraging better patient satisfaction. ispartof: IEEE Transactions On Biomedical Engineering vol:68 issue:11 pages:3273-3280 ispartof: location:United States status: published

Current fixation plates used to operatively stabilize clavicular fractures are suboptimal, leading to reoperation rates up to 53%. Plate irritation, which can be caused by a poor geometric fit and plate thickness, has been found to be an important factor for reoperation. Moreover, muscle attachment sites (MAS) have to be detached occasionally. To improve current surgical clavicle fracture treatment with plate osteosynthesis, a change in plate design is required. The goal of this study was to design a patient-specific clavicle fracture fixation plate that includes geometrical optimization and stiffness determination. Its biomechanical performance has been compared with a commercial plate by examining the geometric fit, anatomical outline, stresses and interfragmentary motion using a finite element analysis with physiological loading and boundary conditions. Evaluation showed a better geometrical fit of the patient-specific plate as well as an improved fracture reduction. Displacements between fracture fragments were lower in case of the patient-specific plate, both when a fracture gap and no fracture gap were present. Results indicate a superior mechanical performance in terms of all investigated outcomes of the patient-specific plate compared to the commercial plate, while better aligning with the patient-specific geometry and without the need for MAS release. Due to the patient-specific geometry and reduced thickness, these fixation plates are expected to decrease the operation time, as intraoperative contouring will become irrelevant, and to decrease reoperation rates as implant irritation will be minimized. ispartof: JOURNAL OF ORTHOPAEDIC RESEARCH vol:40 issue:7 pages:1695-1706 ispartof: location:United States status: published

Controlled cortical impact (CCI) on porcine brain is often utilized to investigate the pathophysiology and functional outcome of focal traumatic brain injury (TBI), such as cerebral contusion (CC). Using a finite element (FE) model of the porcine brain, the localized brain strain and strain rate resulting from CCI can be computed and compared to the experimentally assessed cortical lesion. This way, tissue-level injury metrics and corresponding thresholds specific for CC can be established. However, the variability and uncertainty associated with the CCI experimental parameters contribute to the uncertainty of the provoked cortical lesion and, in turn, of the predicted injury metrics. Uncertainty quantification via probabilistic methods (Monte Carlo simulation, MCS) requires a large number of FE simulations, which results in a time-consuming process. Following the recent success of machine learning (ML) in TBI biomechanical modeling, we developed an artificial neural network as surrogate of the FE porcine brain model to predict the brain strain and the strain rate in a computationally efficient way. We assessed the effect of several experimental and modeling parameters on four FE-derived CC injury metrics (maximum principal strain, maximum principal strain rate, product of maximum principal strain and strain rate, and maximum shear strain). Next, we compared the in silico brain mechanical response with cortical damage data from in vivo CCI experiments on pig brains to evaluate the predictive performance of the CC injury metrics. Our ML surrogate was capable of rapidly predicting the outcome of the FE porcine brain undergoing CCI. The now computationally efficient MCS showed that depth and velocity of indentation were the most influential parameters for the strain and the strain rate-based injury metrics, respectively. The sensitivity analysis and comparison with the cortical damage experimental data indicate a better performance of maximum principal strain and maximum shear strain as tissue-level injury metrics for CC. These results provide guidelines to optimize the design of CCI tests and bring new insights to the understanding of the mechanical response of brain tissue to focal traumatic brain injury. Our findings also highlight the potential of using ML for computationally efficient TBI biomechanics investigations. Frontiers ispartof: Frontiers In Bioengineering And Biotechnology vol:9 ispartof: location:Switzerland status: published

© 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group. Surface registration, in which a mapping between surfaces is calculated, is a powerful tool to create patient-specific musculoskeletal and statistical shape models. However, to create these models, surface registration must assure a one-to-one correspondence between both surfaces. To enhance this process, a surface registration framework that uses a combination of manual and automatic landmark detection is presented in this study. In addition, an extensive parameter study of the framework for a femur and a clavicle is conducted. The average correspondence quality of nine femur landmarks decreased from 15.6 mm using automatic point detection to 6.1 mm by combining manually and automatically indicated landmarks. For the clavicle, the average distance of five landmarks decreased from 2.8 to 0.9 mm. Combining manual and automatic landmark detection clearly improved correspondence quality. Results confirmed the applicability of the proposed registration framework for femur and clavicle, although with different parameter settings. ispartof: Computer Methods in Biomechanics and Biomedical Engineering: Imaging and Visualization vol:8 issue:1 pages:94-102 status: published

BACKGROUND: Adequate deltoid and rotator cuff elongation in reverse shoulder arthroplasty is crucial to maximize postoperative functional outcomes and to avoid complications. Measurements of deltoid and rotator cuff elongation during preoperative planning can support surgeons in selecting a suitable implant design and position. Therefore, this study presented and evaluated a fully automated method for measuring deltoid and rotator cuff elongation. METHODS: Complete scapular and humeral models were extracted from computed tomography scans of 40 subjects. First, a statistical shape model of the complete humerus was created and evaluated to identify the muscle attachment points. Next, a muscle wrapping algorithm was developed to identify the muscle paths and to compute muscle lengths and elongations after reverse shoulder arthroplasty implantation. The accuracy of the muscle attachment points and the muscle elongation measurements was evaluated for the 40 subjects by use of both complete and artificially created partial humeral models. Additionally, the muscle elongation measurements were evaluated for a set of 50 arthritic shoulder joints. Finally, a sensitivity analysis was performed to evaluate the impact of implant positioning on deltoid and rotator cuff elongation. RESULTS: For the complete humeral models, all muscle attachment points were identified with a median error < 3.5 mm. For the partial humeral models, the errors on the deltoid attachment point largely increased. Furthermore, all muscle elongation measurements showed an error < 1 mm for 75% of the subjects for both the complete and partial humeral models. For the arthritic shoulder joints, the errors on the muscle elongation measurements were

Background Various studies have investigated the load-bearing capacity of patient-specific cranial implants. However, little attention has been given to the evaluation of the design of ceramic-titanium (CeTi) implants. Methods A biomechanical evaluation of 3 patient-specific cranial implants was performed using finite element analysis. Results The results of the analyses allowed the identification of the implant regions as well as the magnitudes of the maximum stresses on, and displacements along, these regions after traumatic impact. The analyses also showed that polyether ether ketone cranial implants offer inferior brain and neurocranial protection due to their high flexibility and local peak stresses at the bone-screw interface. In contrast, CeTi implants were able to evenly distribute the stresses along the interface and thus reduced the risk of neurocranial fracture. The scaffold structure at the border of these implants reduced stress shielding and enhanced bone ingrowth. Moreover, brain injuries were less likely to occur, as the CeTi implant exhibits limited deflection. Conclusions From the finite element analyses, CeTi cranial implants appear less likely to induce calvarial fractures with a better potential to protect the brain under impact loads.

The regional dynamic mechanical properties of mouse, rat, pig, and human brain tissue were compared directly in this first-of-its-kind study. Our results suggest the use of pig or mouse brain tissue as suitable surrogates to characterise human brain tissue. The importance of this work is highlighted by the extensive use of constitutive data from animal brain tissue in traumatic brain injury research in the absence of human brain tissue data without any direct evidence supporting their use. Indentation force-relaxation experiments were performed on mouse, rat, pig, and human brains at 10/s strain rate up to 35% strain to determine the dynamic mechanical properties of brain tissue. Finite element models have become useful tools to investigate the biomechanics of traumatic brain injury - a global leading cause of death and disability and a risk factor for developing neurodegenerative diseases. However, these models require accurate constitutive data for brain tissue to produce reliable results. The results presented here provide validation for the use of pig and mouse brain tissue data in such models. Statement of Significance The significance of this work is underscored by the extensive use of animal brain tissue as a surrogate for human brain tissue without any direct evidence supporting the validity of their use. For the first time ever, we demonstrate that porcine and murine brain tissue can be used as surrogates for human brain tissue under dynamic loading conditions. These findings will allow researchers to select appropriate animal surrogates for human brain tissue under dynamic loading conditions. Furthermore, our findings support the use of animal surrogate data to improve the fidelity of computational models of the human brain, and provide experimental data to develop constitutive models of brain tissue.

The initial stability of cementless total hip arthroplasty (THA) implants is obtained by an interference fit that allows osseointegration for a long term secondary stability of the implant. Yet, finding the insertion endpoint that corresponds to an appropriate initial stability is currently often based on a number of subjective experiences of the orthopedic surgeon, which can be challenging. In order to assist the orthopedic surgeons in their pursuit to find this optimal initial stability, this study aims to determine whether the analysis of sound that results from the implant insertion hammer blows can be used to objectively monitor the insertion process of cementless THA implants. An in vivo study was conducted. The experimental results revealed vibro-acoustic behavior sensitive to implant seating, related to the low frequency content of the response spectra. This sensitive low-frequency behavior was quantified by a set of specific vibro-acoustic features and metrics that reflected the power and similarity of the low-frequency response. These features and metrics allowed monitoring the implant seating and their convergence agreed well with the endpoint of insertion as determined by the orthopedic surgeon. Intraoperative fractures caused an abrupt and opposite change of the vibro-acoustic behavior prior to the notification of the fracture by the orthopedic surgeon. The observation of such an abrupt change in the vibro-acoustic behavior can be an important early warning for loss of implant stability. The presented vibro-acoustic measurement method shows potential to serve as a decision supporting source of information as it showed to reflect the implant seating. ispartof: JOURNAL OF ORTHOPAEDIC RESEARCH vol:39 issue:6 pages:1164-1173 ispartof: location:United States status: published

Total knee arthroplasty (TKA) is a common procedure that has become the standard of treatment for severe cases of knee osteoarthritis. Biomechanics and quality of movement similar to healthy were found to improve patient-reported outcomes.In this study, an evaluated musculoskeletal model predicted ligament, contact and muscle forces together with secondary tibiofemoral kinematics. An artificial neural network applied to the musculoskeletal model searched for the optimal implant position in a given range that will minimize the root-mean-square-error (RMSE) between post- TKA and native experimental tibiofemoral kinematics during a squat.We found that, using a cruciate-retaining implant, native kinematics could be accurately reproduced (average RMSE 1.47 mm (± 0.89 mm) for translations and 2.89° (± 2.83°) for rotations between native and optimal TKA alignment). The required implant positions changes maximally 2.96 mm and 2.40o. This suggests that when using pre- operative planning, off-the-shelf CR implants allow for reproducing native knee kinematics post-operatively.

Modal parameters are often investigated in order to assess the initial fixation of an implant. Most of studies are focused on the natural frequencies and frequency response function. Usually the femoral stem is tested although the acetabular cup fixation is important as well. The results of implant stability assessment are inconsistent and seem to suggest that frequency as a stability indicator is not sufficiently sensitive. In this study the sensitivity of the modal properties to changes in the bone-implant interface was investigated with the help of the finite element method (FEM). A novel fixation index based on modal shape curvature was investigated as a potential measure of the implant fixation. Modal frequencies are sensitive to interface changes in some manner, but suffer from insensitivity to local changes at bone-implant interface. The sensitivity up to 44% of natural frequencies to stiffness change due insertion steps was observed. The tested damage indicators are able to detect localized small changes in peripheral stiffness (5% stiffness reduction) with 95% confidence under the noise up to 1%. The modal shapes and their curvatures have a great potential to be a robust fixation indicator. ispartof: MEDICAL ENGINEERING & PHYSICS vol:60 pages:30-38 ispartof: location:England status: published

A reliable computational model of the human head is necessary for better understanding of the physical mechanisms of traumatic brain injury (TBI), car-crash investigation, development of protective head gear and advancement of dural replacement materials. The performance and biofidelity of these models depend largely on the material description of the different structures present in the head. One of these structures is the dura mater, the protective layer around the brain. We tested five human dura mater specimens, with samples at different locations, using planar biaxial tests. We describe the resulting stress-strain curves using both the anisotropic Gasser-Ogden-Holzapfel (GOH) model and the isotropic one-term Ogden model. The low-strain section of the curves is also described using a Neo-Hookean formulation. The obtained stress-strain curves reveal highly nonlinear but isotropic behaviour. A significant amount of inter- and intra-specimen variability is noticed, whereby the latter does not seem to be influenced by location. The GOH model achieves the best fit of the individual test data. A simple Neo-Hookean model can only be used with extreme caution, as it does not manage to capture the nonlinear effects present even at low strains.

BACKGROUND: Component malalignment remains a major concern in total knee arthroplasty (TKA). Patient-specific guides (PSG) were developed to increase accuracy of bone resections and component placement, but available evidence is contradictory. We assessed the accuracy of 3D component placement in TKA with PSG compared to conventional surgery using virtual 3D bone models. METHODS: Fifty patients were randomly assigned to the PSG or conventional instrumentation group, 44 were finally analyzed. Preoperatively, MRI and CT scans were converted into virtual 3D models and a surgical plan was developed. Surgery was performed and changes in component sizing were recorded. Postoperative CT images were converted to 3D models and aligned to the planned, preoperative models and implant orientation. Differences between planned and postoperative implant orientations were calculated in 3D. RESULTS: PSG allowed significantly more accurate varus/valgus placement for the femoral component (PSG: 0.14±1.47; control: 1.40±1.99; p

Replicate composite bones are used extensively for in vitro testing of new orthopedic devices. Contrary to tests with cadaveric bone material, which inherently exhibits large variability, they offer a standardized alternative with limited variability. Accurate knowledge of the composite’s material properties is important when interpreting in vitro test results and when using them in FE models of biomechanical constructs. The cortical bone analogue material properties of three different fourth-generation composite bone models were determined by updating FE bone models using experimental and numerical modal analyses results. The influence of the cortical bone analogue material model (isotropic or transversely isotropic) and the inter- and intra-specimen variability were assessed. Isotropic cortical bone analogue material models failed to represent the experimental behavior in a satisfactory way even after updating the elastic material constants. When transversely isotropic material models were used, the updating procedure resulted in a reduction of the longitudinal Young’s modulus from 16.00 GPa before updating to an average of 13.96 GPa after updating. The shear modulus was increased from 3.30 GPa to an average value of 3.92 GPa. The transverse Young’s modulus was lowered from an initial value of 10.00 GPa to 9.89 GPa. Low inter- and intra-specimen variability was found.

Background: Altered kinematics and persisting ankle instability have been associated with degenerative changes and osteochondral lesions. Purpose: To study the effect of ligament reconstruction surgery with suture tape augmentation (isolated anterior talofibular ligament [ATFL] vs combined ATFL and calcaneofibular ligament [CFL]) after lateral ligament ruptures (combined ATFL and CFL) on foot-ankle kinematics during simulated gait. Study Design: Controlled laboratory study. Methods: Five fresh-frozen cadaveric specimens were tested in a custom-built gait simulator in 5 different conditions: intact, ATFL rupture, ATFL-CFL rupture, ATFL-CFL reconstruction, and ATFL reconstruction. For each condition, range of motion (ROM) and the average angle (AA) in the hindfoot and midfoot joints were calculated during the stance phase of normal and inverted gait. Results: Ligament ruptures mainly changed ROM in the hindfoot and the AA in the hindfoot and midfoot and influenced the kinematics in all 3 movement directions. Combined ligament reconstruction was able to restore ROM in inversion-eversion in 4 of the 5 joints and ROM in internal-external rotation and dorsiflexion-plantarflexion in 3 of the 5 joints. It was also able to restore the AA in inversion-eversion in 2 of the 5 joints, the AA in internal-external rotation in all joints, and the AA in dorsiflexion-plantarflexion in 1 of the joints. Isolated ATFL reconstruction was able to restore ROM in inversion-eversion and internal-external rotation in 3 of the 5 joints and ROM in dorsiflexion-plantarflexion in 2 of the 5 joints. Isolated reconstruction was also able to restore the AA in inversion-eversion and dorsiflexion-plantarflexion in 2 of the joints and the AA in internal-external rotation in 3 of the joints. Both isolated reconstruction and combined reconstruction were most successful in restoring motion in the tibiocalcaneal and talonavicular joints and least successful in restoring motion in the talocalcaneal joint. However, combined reconstruction was still better at restoring motion in the talocalcaneal joint than isolated reconstruction (1/3 for ROM and 1/3 for the AA with isolated reconstruction compared to 1/3 for ROM and 2/3 for the AA with combined reconstruction). Conclusion: Combined ATFL-CFL reconstruction showed better restored motion immediately after surgery than isolated ATFL reconstruction after a combined ATFL-CFL rupture. Clinical Relevance: This study shows that ligament reconstruction with suture tape augmentation is able to partially restore kinematics in the hindfoot and midfoot at the time of surgery. In clinical applications, where the classic Broström-Gould technique is followed by augmentation with suture tape, this procedure may protect the repaired ligament during healing by limiting excessive ROM after a ligament rupture.

Conventional anatomically contoured plates do not adequately fit most tibiae. This emphasizes the need for a more thorough morphological study. Statistical shape models are promising tools to display anatomical variations within a population. Herein, we aim to provide a better insight into the anatomical variations of the tibia and tibia plateau. Seventy-nine CT scans of tibiae were segmented, and a principal component analysis was performed. Five morphologically important parameters were measured on the 3D models of the mean tibial shapes as well as the -3SD and +3 SD tibial shapes of the first five components. Longer, wider tibiae are related to a more rounded course of the posterior column, a less prominent tip of the medial malleolus, and a more posteriorly directed fibular notch. Varus/valgus deformations and the angulation of the posterior tibia plateau represent only a small percentage of the total variation. Right and left tibiae are not always perfectly symmetrical, especially not at the level of the tibia plateau. The largest degree of anatomical variation of the tibia is found in its length and around the tibia plateau. Because of the large variation in the anatomy, a more patient-specific approach could improve implant fit, anatomical reduction, biomechanical stability and hardware-related complications. ispartof: Scientific Reports vol:9 issue:1 ispartof: location:England status: published

BACKGROUND: The clavicle presents a large variability in its characterizing sigmoid shape. Prominent and nonproperly fitting fixation plates (FP) cause soft tissue irritation and lead to hardware removal. It is therefore key in FP design to account for shape variations. Statistical shape models (SSMs) have been built to analyze a cluster of complex shapes. The goal of this study was to describe the anatomic variation of the clavicle using SSMs. METHODS: Two different SSMs of the clavicle were created, and their modes of variation were described. One model contained 120 left male and female clavicles. The other model consisted of 76 left and corresponding right clavicles, 41 originating from men and 35 from women. RESULTS: The model of 120 left clavicles showed that 10 modes of variation are necessary to explain 95% of the variation. The most important modes of variation are the clavicle length, inferior-superior bow, and medial and lateral curvature. Statistically significant differences between male and female clavicles were seen in length, sigmoid shape, and medial curvature. Comparison in men between left and right revealed significant differences in length and medial curvature. For women, a statistically significant difference between left and right was only seen in the length. CONCLUSIONS: Although the operative treatment of displaced midshaft clavicular fractures has clear benefits, the variable anatomy of the clavicle often makes it challenging for the surgeon to make the plate fit adequately. Based on the identified variability in the clavicle's anatomy, it seems unlikely that a clavicle plating system can fit the entire population. ispartof: JOURNAL OF SHOULDER AND ELBOW SURGERY vol:28 issue:4 pages:631-638 ispartof: location:United States status: published

To account for proximal femoral deformities in children with cerebral palsy (CP), subject-specific musculoskeletal models are needed. Non-rigid deformation (NRD) deforms generic onto personalized bone geometry and thereby transforms the muscle points. The goal of this study was to determine to what extent the models and simulation outcomes in CP patients differ when including subject-specific detail using NRD or Magnetic Resonance Imaging (MRI)-based models. The NRD models slightly overestimated hip contact forces compared to MRI models and differences in muscle point positions and moment arm lengths (MALs) remained, although differences were smaller than for the generic model. ispartof: Computer Methods In Biomechanics And Biomedical Engineering vol:22 issue:4 pages:376-385 ispartof: location:England status: published

Total knee arthroplasty (TKA) is a reliable surgical procedure, yet up to a fifth of primary implant patients remains unsatisfied. Musculoskeletal modeling (MSM) has the potential to explore the relationship between implant alignment and functional outcome [3]. Consequently, implant alignment can be quantitatively optimized to restore the pre- TKA joint behavior and, therefore, achieve the most favorable functional outcome for the specific patient. For this reason, we developed a method to optimize the implant alignment, with the aim of restoring the native kinematics and ligament elongations of the patient before undergoing TKA. Subject-specific optimization towards ligament elongations demonstrated to accurately emulate the pre-TKA ligament behavior, in contrast to the mechanically aligned approach. However, the values of the optimized implant positions resulting from the pre-TKA kinematic optimization were extreme in some cases. The presented modelling approach is a promising starting point for allowing surgeons to evaluate the patient-specific implant alignment and restore the patient- specific biomechanics.

During a transcatheter aortic valve implantation, an axisymmetric implant is placed in an irregularly shaped aortic root. Implanting an incorrect size can cause complications such as leakage of blood alongside or through the implant. The aim of this study was to construct a method that determines the optimal size of the implant based on the three-dimensional shape of the aortic root. Based on the pre-interventional computed tomography scan of 89 patients, a statistical shape model of their aortic root was constructed. The weights associated with the principal components and the volume of calcification in the aortic valve were used as parameters in a classification algorithm. The classification algorithm was trained using the patients with no or mild leakage after their intervention. Subsequently, the algorithms were applied to the patients with moderate to severe leakage. Cross validation showed that a random forest classifier assigned the same size in 65 ± 7% of the training cases, while 57 ± 8% of the patients with moderate to severe leakage were assigned a different size. This initial study showed that this semi-automatic method has the potential to correctly assign an implant size. Further research is required to assess whether the different size implants would improve the outcome of those patients. ispartof: MEDICAL & BIOLOGICAL ENGINEERING & COMPUTING vol:57 issue:10 pages:2081-2092 ispartof: location:United States status: published

The performance of implant placement technologies are often evaluated based on their achieved post-operative implant alignment. Therefore accurate assessment techniques are necessary to compare pre-operatively planned implant positions with the corresponding post-operatively placed implant positions in total knee arthroplasty. This paper describes a CT based 3D measurement method for evaluation of implant positioning accuracy comparing post-operative implant position to the corresponding pre-operative planned implant position using 3D virtual models. TKAs were carried out on three phantoms and processed three times to investigate the accuracy of the method. The measurements were then assessed against measurements taken through an optical scan. The results indicate that an average measurement error less than 1 ° and 0.5 mm can be obtained except in the proximal–distal direction where the error was up to 1.34 mm. The accuracy of this 3D measurement technique is sufficiently reliable to enable reporting on implant position and orientation in the same coordinate system as pre-operatively defined independently of the planning system or the surgical implant placement technology (patient-specific guides, robotics, and navigation).

Multibody simulations of human motion require representative models of the anatomical structures. A model that captures the complexity of the foot is still lacking. In the present work, two detailed 3D multibody foot-ankle models generated based on CT scans using a semi-automatic tool are described. The proposed models consists of five rigid segments (talus, calcaneus, midfoot, forefoot and toes), connected by five joints (ankle, subtalar, midtarsal, tarsometatarsal and metatarsophalangeal), one with 15DOF and the other with 8DOF. The calculated kinematics of both models were evaluated using gait trials and compared against literature, both presenting realistic results. An inverse dynamic analysis was performed for the 8DOF model, again presenting feasible dynamic results. peerreview_statement: The publishing and review policy for this title is described in its Aims & Scope. aims_and_scope_url: http://www.tandfonline.com/action/journalInformation?show=aimsScope&journalCode=gcmb20 ispartof: Computer Methods in Biomechanics and Biomedical Engineering vol:20 issue:2 pages:153-159 ispartof: location:England status: published

Objectives To evaluate clinical, radiographic, microbiologic, and biomechanical parameters related to bone remodeling around implants with external hexagon (EH) and Morse-taper (MT) connections. Materials and Methods Twelve totally edentulous patients received four custom-made implants in the interforaminal region of the mandible. Two of those implants had the same macroscopic design, but different prosthetic connections. All patients received an immediate implant-supported prosthesis. Clinical parameters (periimplant probing pocket depth (PPD), modified gingival index (mGI), and mucosal thickness (MTh)) were evaluated at 12 months follow-up. The distance between the top of the implant and the first bone-to-implant contact (IT-FBIC) was evaluated on standardized digital peri-apical radiographs acquired at 1, 3, 6, and 12 months follow-up. Samples of the subgingival microbiota were collected 1, 3, and 6 months after implant loading and used for the quantification of Tanerella forsythia, Porphyromonas gingivalis, Aggragatibacter actinomycetemcomitans, Prevotella intermedia, and Fusobacterium nucleatum. Further, 36 computerized-tomography based finite element (FE) models were accomplished, simulating each patient under three loading conditions. Results The evaluated clinical parameters were equal for EH and MT implants. Mean IT-FBIC was significantly different between the tested connections (1.17 ± 0.44 mm for EH, and 0.17 ± 0.54 mm for MT, considering all evaluated time periods). No significant microbiological differences could be observed between tested connections. FE analysis showed a significantly higher peak of equivalent (EQV) strain (p = 0.005) for EH (mean 3,438.65 µe) compared to MT (mean 840.98 µe) connection. Conclusions Radiographic periimplant bone loss depends on the implant connection type. MT connections showed less periimplant bone loss, compared to EH connections.

Background Glenoid dissociation is a rare postoperative complication in reverse shoulder arthroplasty that has severe consequences for the patient and requires revision in most cases. A mechanically compromised Morse taper is hypothesized to be the main cause of this complication, with bony impingements and soft tissue interpositioning being cited as the most important problems. Intraoperative assessment of the taper assembly is challenging. Current methods require applying considerable torque to the glenosphere or relying on radiographs. Materials and methods This in vitro study demonstrates how the assembly quality can be accurately determined in a nondestructive way by exploiting the implant-specific relation between screw and Morse taper characteristics by measuring the angular rotation–torque curve. Results The feasibility of the method is demonstrated on 2 reverse implant models. Several data features that can statistically discriminate between optimal and suboptimal assemblies are proposed. Conclusion Suboptimal assemblies can be detected using the method presented, which could easily be integrated in the current surgical workflow. Clinical recommendations based on the method's rationale are also presented, allowing detection of the most severe defect cases with surgical instruments currently in use.

In vitro gait simulations have been available to researchers for more than two decades and have become an invaluable tool for understanding fundamental foot-ankle biomechanics. This has been realised through several incremental technological and methodological developments, such as the actuation of muscle tendons, the increase in controlled degrees of freedom and the use of advanced control schemes. Furthermore, in vitro experimentation enabled performing highly repeatable and controllable simulations of gait during simultaneous measurement of several biomechanical signals (e.g. bone kinematics, intra-articular pressure distribution, bone strain). Such signals cannot always be captured in detail using in vivo techniques, and the importance of in vitro experimentation is therefore highlighted. The information provided by in vitro gait simulations enabled researchers to answer numerous clinical questions related to pathology, injury and surgery. In this article, first an overview of the developments in design and methodology of the various foot-ankle simulators is presented. Furthermore, an overview of the conducted studies is outlined and an example of a study aiming at understanding the differences in kinematics of the hindfoot, ankle and subtalar joints after total ankle arthroplasty is presented. Finally, the limitations and future perspectives of in vitro experimentation and in particular of foot-ankle gait simulators are discussed. It is expected that the biofidelic nature of the controllers will be improved in order to make them more subject-specific and to link foot motion to the simulated behaviour of the entire missing body, providing additional information for understanding the complex anatomical structure of the foot. ispartof: Proceedings of the Institution of Mechanical Engineers H, Journal of Engineering in Medicine vol:230 issue:5 pages:440-9 ispartof: location:England status: published

Glenoid component and screw malpositioning in cases of severe glenoid defects might result in complications. We examined the efficacy of a surgical method to treat severe glenoid defects, including a custom-made glenoid component and accurate screw positioning, using a patient-specific positioning guide.Glenoid defects were created in 10 cadaveric shoulders. Computed tomography images were used to plan reversed shoulder arthroplasty and design patient-specific glenoid components. A patient-specific positioning guide was designed for 5 specimens. The remaining 5 specimens were implanted without the guide. Computed tomography images were used to determine the postoperative glenoid component and screw positions. Differences from the preoperatively planned implant and screw positions were calculated.The patient-specific positioning guide significantly reduced the angular deviations from the planned glenoid implant positioning (P .05) and also significantly improved the positioning of the screws (P .001). In the group without the guide, the average total intraosseous screw length was 52% of the ideal preoperatively planned length compared with 89% for the group with the guide. A strong correlation (r = -0.85) was found between the orientation of the implant and the postoperative total intraosseous screw length.A patient-specific positioning guide significantly improves the position and fixation of a custom-made glenoid component in cases of severe glenoid defects.

Purpose: To compensate for the lack of haptic feedback by surgical robots, limitation of exerted forces could be implemented. The limits should be based on the observed relationship between tissue load and induced damage. This study examines whether age-related changes influence this relationship. Methods: Descending thoracic aortas of male C57BL/6J mice of 10, 25 and 40 weeks were clamped in vivo (no clamp, 0.5N or 2.0N) for 2 min. Functional integrity was tested in vitro by studying endothelium-dependent and -independent vasoreactivity. Results: Endothelium-dependent relaxation deteriorated with increased clamping force at all ages. Clamping did not influence endothelium-independent vasodilation. Age (10, 25 and 40 weeks) did not significantly impact on the effect of clamping on endothelium-dependent and independent vasoreactivity. Conclusions: Within the tested conditions, mechanical clamping induces damage to the vascular endothelium, but not to the smooth muscle cells. Age has no effect on the obtained results in mice from 10 to 40 weeks old.

Traumatic brain injury (TBI) is an important cause of mortality and morbidity worldwide. Finite element models of the human head are used widely to simulate TBI loading scenar- ios, to improve the understanding of the mechanical pathogenesis of head trauma. The re- liability of such computational models depends strongly on the accuracy of the mechanical properties of the different components of the brain. Here, we address the shortage of high- quality data on the region-specific properties of human brain tissue at dynamic rates and under large deformation. We mechanically characterized 12 different regions of the human brain including cerebrum, cerebellum and brainstem through n = 595 force-relaxation ex- periments with a custom-built micro-indentation apparatus. We imposed up to 35% strain at 10/s strain rate, i.e. values representative for TBI. Pronounced differences in mechani- cal response were observed across the brain. This work both highlights and addresses the need to assign accurate, region-specific viscoelastic properties to different brain regions in finite element head models. ispartof: International Journal Of Engineering Science vol:155 status: Published online

Replicate bones are widely used as an alternative for cadaveric bones for in vitro testing. These composite bone models are more easily available and show low inter-specimen variability compared to cadaveric bone models. The combination of in vitro testing with in silico models can provide further insights in the evaluation of the mechanical behavior of orthopedic implants. An accurate numerical representation of the experimental model is important to draw meaningful conclusions from the numerical predictions. This study aims to determine the elastic material constants of a commonly used composite clavicle model by combining acoustic experimental and numerical modal analysis. The difference between the experimental and finite element (FE) predicted natural frequencies was minimized by updating the elastic material constants of the transversely isotropic cortical bone analogue that are provided by the manufacturer. The longitudinal Young's modulus was reduced from 16.00 GPa to 12.88 GPa and the shear modulus was increased from 3.30 GPa to 4.53 GPa. These updated material properties resulted in an average natural frequency difference of 0.49% and a maximum difference of 1.73% between the FE predictions and the experimental results. The presented updated model aims to improve future research that focuses on mechanical simulations with clavicle composite bone models. ispartof: JOURNAL OF FUNCTIONAL BIOMATERIALS vol:11 issue:4 ispartof: location:Switzerland status: published

Computed tomography is used more routinely to design patient-specific instrumentation for knee replacement surgery. Its moderate imaging cost and simplified segmentation reduce design costs compared with magnetic resonance (MR) imaging, but it cannot provide the necessary cartilage information. Our method based on statistical shape modelling proved to be successful in predicting tibiofemoral cartilage in leave-one-out experiments. The obtained accuracy of 0.54 mm for femur and 0.49 mm for tibia outperforms the average cartilage thickness distribution and reported inter-observer MR segmentation variability. These results suggest that shape modelling is able to predict tibiofemoral cartilage with sufficient accuracy to design patient-specific instrumentation. ispartof: COMPUTER METHODS IN BIOMECHANICS AND BIOMEDICAL ENGINEERING vol:21 issue:9 pages:568-578 ispartof: location:England status: published

Glenoid implant position and scapula shape affect the impingement-free range-of-motion (ROM) of a patient's glenohumeral joint. Currently, methods to evaluate the impingement-free ROM during preoperative planning do not result in one overall score, which is required for an objective optimization of the implant position. Therefore, our study aims to quantify the impingement-free ROM so that surgeons can easily compare the result for various implant positions.250 virtual shapes from a healthy scapula statistical shape model (SSM) were virtually implanted with a reverse glenoid implant in diverse positions. The impingement-free ROM was visualised on a 2D polar plot and quantified based on healthy kinematic motion data.ROM scores for a neutral implant position resulted in a mean value of 0.84 +/- 0.06. A lateral, inferior and posterior implant position and a negative shape coefficient in the first SSM mode improved the mean ROM score. The impact of implant position and scapula shape was also visible in the 2D polar plots.Hence, the defined ROM score was sensitive to implant position and scapula shape. A lateral, inferior and posterior implant position resulted in a better ROM, which agrees with many studies in literature. We conclude that the ROM score proposed in this study agrees well with what has been published in literature and is therefore considered as a suitable candidate to objectively evaluate and improve an implant plan during preoperative planning.

A commonly heard concern in the Ross procedure, where a diseased aortic valve is replaced by the patient's own pulmonary valve, is the possibility of pulmonary autograft dilatation. We performed a biomechanical investigation of the use of a personalized external aortic root support or exostent as a possibility for supporting the autograft. In ten sheep a short length of pulmonary artery was interposed in the descending aorta, serving as a simplified version of the Ross procedure. In seven of these cases, the autograft was supported by an external mesh or so-called exostent. Three sheep served as control, of which one was excluded from the mechanical testing. The sheep were sacrificed six months after the procedure. Samples of the relevant tissues were obtained for subsequent mechanical testing: normal aorta, normal pulmonary artery, aorta with exostent, pulmonary artery with exostent, and pulmonary artery in aortic position for six months. After mechanical testing, the material parameters of the Gasser-Ogden-Holzapfel model were determined for the different tissue types. Stress-strain curves of the different tissue types show significantly different mechanical behavior. At baseline, stress-strain curves of the pulmonary artery are lower than aortic stress-strain curves, but at the strain levels at which the collagen fibers are recruited, the pulmonary artery behaves stiffer than the aorta. After being in aortic position for six months, the pulmonary artery tends towards aorta-like behavior, indicating that growth and remodeling processes have taken place. When adding an exostent around the pulmonary autograft, the mechanical behavior of the composite artery (exostent + artery) differs from the artery alone, the non-linearity being more evident in the former. ispartof: Journal of the Mechanical Behavior of Biomedical Materials vol:78 pages:164-174 ispartof: location:Netherlands status: published

Objectives The current study quantified the influence of cartilage defect location on the tibiofemoral load distribution during gait. Furthermore, changes in local mechanical stiffness representative for matrix damage or bone ingrowth were investigated. This may provide insights in the mechanical factors contributing to cartilage degeneration in the presence of an articular cartilage defect. Methods The load distribution following cartilage defects was calculated using a musculoskeletal model that included tibiofemoral and patellofemoral joints with 6 degrees-of-freedom. Circular cartilage defects of 100 mm2 were created at different locations in the tibiofemoral contact geometry. By assigning different mechanical properties to these defect locations, softening and hardening of the tissue were evaluated. Results Results indicate that cartilage defects located at the load-bearing area only affect the load distribution of the involved compartment. Cartilage defects in the central part of the tibia plateau and anterior-central part of the medial femoral condyle present the largest influence on load distribution. Softening at the defect location results in overloading, i.e., increased contact pressure and compressive strains, of the surrounding tissue. In contrast, inside the defect, the contact pressure decreases and the compressive strain increases. Hardening at the defect location presents the opposite results in load distribution compared to softening. Sensitivity analysis reveals that the surrounding contact pressure, contact force and compressive strain alter significantly when the elastic modulus is below 7 MPa or above 18 MPa. Conclusion Alterations in local mechanical behavior within the high load bearing area resulted in aberrant loading conditions, thereby potentially affecting the homeostatic balance not only at the defect but also at the tissue surrounding and opposing the defect. Especially, cartilage softening predisposes the tissue to loads that may contribute to accelerated risk of cartilage degeneration and the initiation or progression towards osteoarthritis of the whole compartment., PLoS ONE, 13 (10), ISSN:1932-6203

At present, Finite Element (FE) analyses are often used as a tool to better understand the mechanisms of head injury. Previously, these models have been compared to cadaver experiments, with the next step under development being accident reconstructions. Thus far, the main focus has been on deriving an injury threshold and little effort has been put into correlating the documented injury location with the response displayed by the FE model. Therefore, the purpose of this study was to introduce a novel image correlation method that compares the response of the FE model with medical images. The injuries shown on the medical images were compared to the strain pattern in the FE model and evaluated by two indices; the Overlap Index (OI) and the Location Index (LI). As the name suggests, OI measures the area which indicates both injury in the medical images and high strain values in the FE images. LI evaluates the difference in center of mass in the medical and FE images. A perfect match would give an OI and LI equal to 1. This method was applied to three bicycle accident reconstructions. The reconstructions gave an average OI between 0.01 and 0.19 for the three cases and between 0.39 and 0.88 for LI. Performing injury reconstructions are a challenge as the information from the accidents often is uncertain. The suggested method evaluates the response in an objective way which can be used in future injury reconstruction studies.

Patient-specific biomechanical modelling can improve preoperative surgical planning. This requires patient-specific geometry as well as patient-specific material properties as input. The latter are, however, still quite challenging to estimate in vivo. This study focuses on the estimation of the mechanical properties of the arterial wall. Firstly, in vivo pressure, diameter and thickness of the arterial wall were acquired for sheep common carotid arteries. Next, the animals were sacrificed and the tissue was stored for mechanical testing. Planar biaxial tests were performed to obtain experimental stress-stretch curves. Finally, parameters for the hyperelastic Mooney-Rivlin and Gasser-Ogden-Holzapfel (GOH) material model were estimated based on the in vivo obtained pressure-diameter data as well as on the ex situ experimental stress-stretch curves. Both material models were able to capture the in vivo behaviour of the tissue. However, in the ex situ case only the GOH model provided satisfactory results. When comparing different fitting approaches, in vivo vs. ex situ, each of them showed its own advantages and disadvantages. The in vivo approach estimates the properties of the tissue in its physiological state while the ex situ approach allows to apply different loadings to properly capture the anisotropy of the tissue. Both of them could be further enhanced by improving the estimation of the stress-free state, i.e. by adding residual circumferential stresses in vivo and by accounting for the flattening effect of the tested samples ex vivo. • Competing interests: none declared • Word count: 4716. ispartof: Medical Engineering & Physics vol:55 pages:16-24 ispartof: location:England status: published

Background Description of the native shape of a glenoid helps surgeons to preoperatively plan the position of a shoulder implant. A statistical shape model (SSM) can be used to virtually reconstruct a glenoid bone defect and to predict the inclination, version, and center position of the native glenoid. An SSM-based reconstruction method has already been developed for acetabular bone reconstruction. The goal of this study was to evaluate the SSM-based method for the reconstruction of glenoid bone defects and the prediction of native anatomic parameters. Methods First, an SSM was created on the basis of 66 healthy scapulae. Then, artificial bone defects were created in all scapulae and reconstructed using the SSM-based reconstruction method. For each bone defect, the reconstructed surface was compared with the original surface. Furthermore, the inclination, version, and glenoid center point of the reconstructed surface were compared with the original parameters of each scapula. Results For small glenoid bone defects, the healthy surface of the glenoid was reconstructed with a root mean square error of 1.2 ± 0.4 mm. Inclination, version, and glenoid center point were predicted with an accuracy of 2.4° ± 2.1°, 2.9° ± 2.2°, and 1.8 ± 0.8 mm, respectively. Discussion and conclusion The SSM-based reconstruction method is able to accurately reconstruct the native glenoid surface and to predict the native anatomic parameters. Based on this outcome, statistical shape modeling can be considered a successful technique for use in the preoperative planning of shoulder arthroplasty.

The aim of this study was to quantify the effects of understuffing and overstuffing UKA on bone stresses, load distribution and ligament strains. For that purpose, a numerical knee model of a cadaveric knee was developed and was validated against experimental measurements on that same knee. Good agreement was found among the numerical and experimental results. This study showed that, even if a medial UKA is well-aligned with normal soft tissue tension and with correct thickness of the tibia component, it induces a stiffness modification in the joint that alters the load distribution between the medial and lateral compartments, the bone stress and the ligament strain potentially leading to an osteoarthritic progression. publisher: Elsevier articletitle: Load Sharing and Ligament Strains in Balanced, Overstuffed and Understuffed UKA. A Validated Finite Element Analysis journaltitle: The Journal of Arthroplasty articlelink: http://dx.doi.org/10.1016/j.arth.2014.01.020 content_type: article copyright: Copyright © 2014 Elsevier Inc. All rights reserved. ispartof: Journal of Arthroplasty vol:29 issue:7 pages:1491-8 ispartof: location:United States status: published

The determination of an optimal pivot point ( $${ OPP}$$ ) is important for instrument manipulation in minimally invasive surgery. Such knowledge is of particular importance for robotic-assisted surgery where robots need to rotate precisely around a specific point in space in order to minimize trauma to the body wall while maintaining position control. Remote center of motion (RCM) mechanisms are commonly used, where the RCM point is manually and visually aligned. If not positioned appropriately, this misalignment might lead to intolerably high forces on the body wall with increased risk of postoperative complications or instrument damage. An automated method to align the RCM with the $${ OPP}$$ was developed and tested. Computer vision and a lightweight calibration procedure are used to estimate the optimal pivot point. One or two pre-calibrated cameras viewing the surgical scene are employed. The surgeon is asked to make short pivoting movements, applying as little torque as possible, with an instrument of choice passing through the insertion point while camera images are being recorded. The physical properties of an instrument rotating around a pivot point are exploited in a random sample consensus scheme to robustly estimate the ideal position of the RCM in the image planes. Triangulation is used to estimate the RCM position in 3D. Experiments were performed on a specially designed mockup to test the method. The position of the pivot point is estimated with an average error less than 1.85 mm using two webcams placed from approximately 30 cm to 1 m away from the scene. The entire procedure was completed in a few seconds. An automated method to estimate the ideal position of the RCM was shown to be reliable. The method can be implemented within a visual servoing approach to automatically place the RCM point, or the results can be displayed on a screen to provide guidance to the surgeon. Further work includes the development of an image-guided alignment method and validation with in vivo experiments.

Currently, controversy exists whether restoration of neutral mechanical alignment should be attempted in all patients undergoing TKA. Our hypothesis was that restoration of constitutional rather than neutral mechanical alignment may in theory lead to a more physiological strain pattern in the collateral ligaments; therefore, it could potentially be beneficial to patients. Thus, the aim of this study was to measure collateral ligament strains during three motor tasks in the native knee and compare them with the strains noted after TKA in different post-operative alignment conditions.Six cadaver specimens (approval number ML4190 from the Research Ethics Committee of University of Leuven, Belgium) were examined using a validated knee kinematics rig under physiological loading conditions. The effect of coronal malalignment was evaluated by using custom-made tibial implant inserts that induced different alignment conditions. The study of six specimens allows us to show that a difference in the mean strains in MCL and LCL of 3.6 and 5.8 %, respectively, was statistically significant with a probability (power) of 0.8.The results indicated that after TKA insertion, the strains in the collateral ligaments closely resembled the pre-operative pattern of the native knee specimens when constitutional alignment was restored. Restoration to neutral mechanical alignment was associated with greater collateral strain deviations from the native knee.Based upon this study, it was concluded that restoration of constitutional alignment within a "safe zone" of ±2° during TKA leads to more physiological peri-articular soft tissue strains during loaded as well as unloaded motor tasks.

Background Traumatic brain injury is expected to become the major cause of death and disability for children and young adults by the year 2020. One of the most frequent and most morbid pathologies resulted from a head trauma is acute subdural haematoma (ASDH). For nearly one third of the ASDH cases the etiopathology directly relates to a bridging vein (BV) rupture. Methods In the current study the bridging vein–superior sagittal sinus (BV–SSS) units were axially stretched until failure for strain rates ranging from 2.66 s−1 to 185.61 s−1, in order to investigate any strain rate dependency in their mechanical behaviour. Findings Results showed that up to 200 s−1, the effect of the strain rate on veins' mechanical behaviour is outweighed by the large morphological intra- and inter-individual variations. Gender had a strong influence on the BVs geometrical description, but exerted no direct influence on the BV biomechanical parameters. Veins' dimensions had the strongest influence on the BV mechanical behaviour and on the failure mechanism. Interpretation The present study brings important contribution to the ASDH research, emphasising the importance of considering the BV–SSS complex as a whole when trying to describe the ASDH mechanopathology.

Reliable computer models are needed for a better understanding of the physical mechanisms of skull fracture in accidental hits, falls, bicycle - motor vehicle & car accidents and assaults. The performance and biofidelity of these models depend on the correct anatomical representation and material description of these structures. In literature, a strain energy criterion has been proposed to predict skull fractures. However, a broad range of values for this criterion has been reported. This study investigates if the impactor orientation, scalp thickness and material model of the skull could provide us with insight in the influencing factors of this criterion. 18 skull fracture experiments previously performed in our research group were reproduced in finite element simulations. Subject-specific skull geometries were derived from medical images and used to create high-quality finite element meshes. Based on local Hounsfield units, a subject-specific isotropic material model was assigned. The subject-specific models were able to predict fractures who matched visually with the corresponding experimental fracture patterns and provided detailed fracture patterns. The sensitivity study showed that small variations in impactor positioning as well as variations of the local geometry (frontal-temporal-occipital) strongly influenced the skull strain energy. Subject-specific modelling leads to a more accurate prediction of the force-displacement curve. The average error of the peak fracture force for all the 18 cases is 0.4190 for the subject-specific and 0.4538 for the homogeneous material model, for the displacement; 0.3368 versus 0.3844. But it should be carefully interpreted as small variations in the computational model significantly influence the outcome. ispartof: JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS vol:100 ispartof: location:Netherlands status: published