Rigid Bones Research Articles

3D Printing of Double Network Granular Elastomers with Locally Varying Mechanical Properties.

Fast advances in the design of soft actuators and robots demand for new soft materials whose mechanical properties can be changed over short length scales. Elastomers can be formulated as highly stretchable or rather stiff materials and hence, are attractive for these applications. They are most frequently cast such that their composition cannot be changed over short length scales. A method that allows to locally change the composition of elastomers on hundreds of micrometer lengths scales is direct ink writing (DIW). Unfortunately, in the absence of rheomodifiers, most elastomer precursors cannot be printed through DIW. Here, 3D printable double network granular elastomers (DNGEs) whose ultimate tensile strain and stiffness can be varied over an unprecedented range are introduced. The 3D printability of these materials is leveraged to produce an elastomer finger containing rigid bones that are surrounded by a soft skin. Similarly, the rheological properties of the microparticle-based precursors are leveraged to cast elastomer slabs with locally varying stiffnesses that deform and twist in a predefined fashion. These DNGEs are foreseen to open up new avenues in the design of the next generation of smart wearables, strain sensors, prosthesis, soft actuators, and robots.

An upright life, the postural stability of birds: a tensegrity system.

Birds are so stable that they can rest and even sleep standing up. We propose that stable static balance is achieved by tensegrity. The rigid bones can be held together by tension in the tendons, allowing the system to stabilize under the action of gravity. We used the proportions of the bird's osteomuscular system to create a mathematical model. First, the extensor muscles and tendons of the leg are replaced by a single cable that follows the leg and is guided by joint pulleys. Analysis of the model shows that it can achieve balance. However, it does not match the biomechanical characteristics of the bird's body and is not stable. We then replaced the single cable with four cables, roughly corresponding to the extensor groups, and added a ligament loop at the knee. The model is then able to reach a stable equilibrium and the biomechanical characteristics are satisfied. Some of the anatomical features used in our model correspond to innovations unique to the avian lineage. We propose that tensegrity, which allows light and stable mechanical systems, is fundamental to the evolution of the avian body plan. It can also be used as an alternative model for bipedal robots.

One-pot ternary sequential reactions for photopatterned gradient multimaterials

One-pot ternary sequential reactions for photopatterned gradient multimaterials

Robot programming by demonstration with a monocular RGB camera

PurposeThis paper aims to present a new approach for robot programming by demonstration, which generates robot programs by tracking 6 dimensional (6D) pose of the demonstrator’s hand using a single red green blue (RGB) camera without requiring any additional sensors.Design/methodology/approachThe proposed method learns robot grasps and trajectories directly from a single human demonstration by tracking the movements of both human hands and objects. To recover the 6D pose of an object from a single RGB image, a deep learning–based method is used to detect the keypoints of the object first and then solve a perspective-n-point problem. This method is first extended to estimate the 6D pose of the nonrigid hand by separating fingers into multiple rigid bones linked with hand joints. The accurate robot grasp can be generated according to the relative positions between hands and objects in the 2 dimensional space. Robot end-effector trajectories are generated from hand movements and then refined by objects’ start and end positions.FindingsExperiments are conducted on a FANUC LR Mate 200iD robot to verify the proposed approach. The results show the feasibility of generating robot programs by observing human demonstration once using a single RGB camera.Originality/valueThe proposed approach provides an efficient and low-cost robot programming method with a single RGB camera. A new 6D hand pose estimation approach, which is used to generate robot grasps and trajectories, is developed.

Non-linear finite element model established on pectoralis major muscle to investigate large breast motions of senior women for bra design

This paper presents a three-dimensional nonlinear biomechanical finite element model to simulate elderly breast deformation under arm abduction. The finite element model was constructed based on complex anatomical structures that consist of the soft tissues including torso, breast, pectoralis major muscle, and rigid bones including humerus, sternum, clavicle and ribs. The elderly breast was defined as material nonlinearity and geometric nonlinearity. The computational model can simulate and illustrate the deformation of soft tissues during arm abduction from 30° to 90°. The finite element model was validated by motion data. The Young’s modulus for the clavicular portion and the sternocostal portion of the pectoralis major muscle was characterized as 0.1 MPa and 0.08 MPa, respectively. Besides this, the finite element model presented here features the musculoskeletal system for breast deformation and reveals the synergistic relationship between the breast and the pectoralis major muscle. A questionnaire was conducted to analyze the importance of purchasing factors and the discomfort positions in a sports bra from the perspective of senior women. Combined with the finite element model results, this study provides a promising basis for the design of sports bras in an ergonomic way.

Evaluation of an occipito-cervico fusion with a new implant design: a biomechanical study

BackgroundA novel implant for occipitocervical fusion consisting of a median plate with an additional hook inserting in the foramen magnum was tested. Aim of this study was to test the stability of a new implant for occipitocervical fusion against the already available and employed median plate implant without hook.Material and method36 rigid polyurethane foams occipital artificial bones were used. The two occipital implants, namely the occipital plate with hook (Group 1) and the one without hook (Group 2), were applied to the artificial occiput trough three occipital screws and ensured into the experimental setup trough a crossbar. The test parameters were set using the testing machine software as follows: (1) test speed: 10 mm/ min, with 25 mm/ min maximum; (2) preload: 5 N; (3) force switch-off threshold: 90% force drop from F_max. Failure force and path were recorded. Failure force is defined as the maximum reaction force under which failure occurs (F_max), while failure path is the travel path during which failure occurs (dL).ResultsGroup 1 (plate with hook) showed a mean failure force of 459.3 ± 35.9 N and a mean failure path of 5.8 ± 0.3 mm Group 2 (plate without hook) showed a mean failure force of 323.9 ± 20.2 N and a mean failure path of 7.2 ± 0.4 mm. The Shapiro-Wilk test score was not significant (P > 0.1), assuming that data were normally distributed. Group 1 had a statistically significant greater F_max (+ 135.37; P > 0.0001) and less dL (− 1.52; P > 0.0001) compared to group 2.ConclusionsMedial plates with foramen magnum hooks showed to be more stable that plates without a hook. These new implants may represent a new tool in OCJ fixation, but further studies are required to investigate their behavior in an anatomical setting.

3D-printed, partially passive piano player

Robotic Manipulation Our bodies are capable of a wide range of complex behaviors, but these abilities are limited by the specific anatomic and environmental conditions. Hughes et al. used this “conditional model” concept to test three-dimensionally (3D)–printed skeletal robot hands with ligaments of varied elasticity connecting rigid finger bones. Moving the base of the hand made the fingers play a piece of piano music. Varying ligament stiffness and hand movement enabled or restricted subsequent actions, such as a finger and thumb simultaneously pressing keys far apart. By changing these parameters, one hand could play three pieces of music that each required a different playing style. Sci. Robot. 3 , eaau3098 (2018).

Projective Skinning

We present a novel approach for physics-based character skinning. While maintaining real-time performance it overcomes the well-known artifacts of commonly used geometric skinning approaches, it enables dynamic effects, and it resolves local self-collisions. Our method is based on a two-layer model consisting of rigid bones and an elastic soft tissue layer. This volumetric model is easily and efficiently computed from an input surface mesh of the character and its underlying skeleton. In particular, our method neither requires skinning weights, which are often expensive to compute or tedious to hand-tune, nor a complex volumetric tessellation, which fails for many real-world input meshes due to self-intersections.

Deformable image registration for adaptive radiotherapy with guaranteed local rigidity constraints.

BackgroundDeformable image registration (DIR) is a key component in many radiotherapy applications. However, often resulting deformations are not satisfying, since varying deformation properties of different anatomical regions are not considered. To improve the plausibility of DIR in adaptive radiotherapy in the male pelvic area, this work integrates a local rigidity deformation model into a DIR algorithm.MethodsA DIR framework is extended by constraints, enforcing locally rigid deformation behavior for arbitrary delineated structures. The approach restricts those structures to rigid deformations, while surrounding tissue is still allowed to deform elastically. The algorithm is tested on ten CT/CBCT male pelvis datasets with active rigidity constraints on bones and prostate and compared to the Varian SmartAdapt deformable registration (VSA) on delineations of bladder, prostate and bones.ResultsThe approach with no rigid structures (REG0) obtains an average dice similarity coefficient (DSC) of 0.87 ± 0.06 and a Hausdorff-Distance (HD) of 8.74 ± 5.95 mm. The new approach with rigid bones (REG1) yields a DSC of 0.87 ± 0.07, HD 8.91 ± 5.89 mm. Rigid deformation of bones and prostate (REG2) obtains 0.87 ± 0.06, HD 8.73 ± 6.01 mm, while VSA yields a DSC of 0.86 ± 0.07, HD 10.22 ± 6.62 mm. No deformation grid foldings are observed for REG0 and REG1 in 7 of 10 cases; for REG2 in 8 of 10 cases, with no grid foldings in prostate, an average of 0.08 % in bladder (REG2: no foldings) and 0.01 % inside the body contour. VSA exhibits grid foldings in each case, with an average percentage of 1.81 % for prostate, 1.74 % for bladder and 0.12 % for the body contour. While REG1 and REG2 keep bones rigid, elastic bone deformations are observed with REG0 and VSA. An average runtime of 26.2 s was achieved with REG1; 31.1 s with REG2, compared to 10.5 s with REG0 and 10.7 s with VMS.ConclusionsWith accuracy in the range of VSA, the new approach with constraints delivers physically more plausible deformations in the pelvic area with guaranteed rigidity of arbitrary structures. Although the algorithm uses an advanced deformation model, clinically feasible runtimes are achieved.Electronic supplementary materialThe online version of this article (doi:10.1186/s13014-016-0697-4) contains supplementary material, which is available to authorized users.

Loss of ephrinB1 in osteogenic progenitor cells impedes endochondral ossification and compromises bone strength integrity during skeletal development

The EphB receptor tyrosine kinase family and their ephrinB ligands have been implicated as mediators of skeletal development and bone homeostasis in humans, where mutations in ephrinB1 contribute to frontonasal dysplasia and coronal craniosynostosis. In mouse models, ephrinB1 has been shown to be a critical factor mediating osteoblast function. The present study examined the functional importance of ephrinB1 during endochondral ossification using the Cre recombination system with targeted deletion of ephrinB1 (EfnB1fl/fl) in osteogenic progenitor cells, under the control of the osterix (Osx:Cre) promoter. The Osx:EfnB1−/− mice displayed aberrant bone growth during embryonic and postnatal skeletal development up to 4weeks of age, when compared to the Osx:Cre controls. Furthermore, compared to the Osx:Cre control mice, the Osx:EfnB1−/− mice exhibited significantly weaker and less rigid bones, with a reduction in trabecular/ cortical bone formation, reduced trabecular architecture and a reduction in the size of the growth plates at the distal end of the femora from newborn through to 4weeks of age. The aberrant bone formation correlated with increased numbers of tartrate resistant acid phosphatase positive osteoclasts and decreased numbers of bone lining osteoblasts in 4week old Osx:EfnB1−/− mice, compared to Osx:Cre control mice. Taken together, these observations demonstrate the importance of ephrinB1 signalling between cells of the skeleton required for endochondral ossification.

Fast garment simulation with aid of hybrid bones

A data-driven method was proposed to realistically animate garments on human poses in reduced space. Firstly, a gradient based method was extended to generate motion sequences and garments were simulated on the sequences as our training data. Based on the examples, the proposed method can fast output realistic garments on new poses. Our framework can be mainly divided into offline phase and online phase. During the offline phase, based on linear blend skinning (LBS), rigid bones and flex bones were estimated for human bodies and garments, respectively. Then, rigid bone weight maps on garment vertices were learned from examples. In the online phase, new human poses were treated as input to estimate rigid bone transformations. Then, both rigid bones and flex bones were used to drive garments to fit the new poses. Finally, a novel formulation was also proposed to efficiently deal with garment-body penetration. Experiments manifest that our method is fast and accurate. The intersection artifacts are fast removed and final garment results are quite realistic.

Importance of material properties and porosity of bone on mechanical response of articular cartilage in human knee joint--a two-dimensional finite element study.

Mechanical behavior of bone is determined by the structure and intrinsic, local material properties of the tissue. However, previously presented knee joint models for evaluation of stresses and strains in joints generally consider bones as rigid bodies or linearly elastic solid materials. The aim of this study was to estimate how different structural and mechanical properties of bone affect the mechanical response of articular cartilage within a knee joint. Based on a cadaver knee joint, a two-dimensional (2D) finite element (FE) model of a knee joint including bone, cartilage, and meniscus geometries was constructed. Six different computational models with varying properties for cortical, trabecular, and subchondral bone were created, while the biphasic fibril-reinforced properties of cartilage and menisci were kept unaltered. The simplest model included rigid bones, while the most complex model included specific mechanical properties for different bone structures and anatomically accurate trabecular structure. Models with different porosities of trabecular bone were also constructed. All models were exposed to axial loading of 1.9 times body weight within 0.2 s (mimicking typical maximum knee joint forces during gait) while free varus-valgus rotation was allowed and all other rotations and translations were fixed. As compared to results obtained with the rigid bone model, stresses, strains, and pore pressures observed in cartilage decreased depending on the implemented properties of trabecular bone. Greatest changes in these parameters (up to -51% in maximum principal stresses) were observed when the lowest modulus for trabecular bone (measured at the structural level) was used. By increasing the trabecular bone porosity, stresses and strains were reduced substantially in the lateral tibial cartilage, while they remained relatively constant in the medial tibial plateau. The present results highlight the importance of long bones, in particular, their mechanical properties and porosity, in altering and redistributing forces transmitted through the knee joint.

Smooth skinning decomposition with rigid bones

This paper introduces the Smooth Skinning Decomposition with Rigid Bones (SSDR), an automated algorithm to extract the linear blend skinning (LBS) from a set of example poses. The SSDR model can effectively approximate the skin deformation of nearly articulated models as well as highly deformable models by a low number of rigid bones and a sparse, convex bone-vertex weight map. Formulated as a constrained optimization problem where the least squared error of the reconstructed vertices by LBS is minimized, the SSDR model can be solved by a block coordinate descent-based algorithm to iteratively update the weight map and the bone transformations. By employing the sparseness and convex constraints on the weight map, the SSDR model can be used for traditional skinning decomposition tasks such as animation compression and hardware-accelerated rendering. Moreover, by imposing the orthogonal constraints on the bone rotation matrices (rigid bones), the SSDR model can also be applied in motion editing, skeleton extraction, and collision detection tasks. Through qualitative and quantitative evaluations, we show the SSDR model can measurably outperform the state-of-the-art skinning decomposition schemes in terms of accuracy and applicability.

Repositioning the Knee Joint in Human Body FE Models Using a Graphics-Based Technique

Objective: Human body finite element models (FE-HBMs) are available in standard occupant or pedestrian postures. There is a need to have FE-HBMs in the same posture as a crash victim or to be configured in varying postures. Developing FE models for all possible positions is not practically viable. The current work aims at obtaining a posture-specific human lower extremity model by reconfiguring an existing one. Methodology: A graphics-based technique was developed to reposition the lower extremity of an FE-HBM by specifying the flexion–extension angle. Elements of the model were segregated into rigid (bones) and deformable components (soft tissues). The bones were rotated about the flexion–extension axis followed by rotation about the longitudinal axis to capture the twisting of the tibia. The desired knee joint movement was thus achieved. Geometric heuristics were then used to reposition the skin. A mapping defined over the space between bones and the skin was used to regenerate the soft tissues. Mesh smoothing was then done to augment mesh quality. Results: The developed method permits control over the kinematics of the joint and maintains the initial mesh quality of the model. For some critical areas (in the joint vicinity) where element distortion is large, mesh smoothing is done to improve mesh quality. Conclusions: A method to reposition the knee joint of a human body FE model was developed. Repositions of a model from 9 degrees of flexion to 90 degrees of flexion in just a few seconds without subjective interventions was demonstrated. Because the mesh quality of the repositioned model was maintained to a predefined level (typically to the level of a well-made model in the initial configuration), the model was suitable for subsequent simulations.

Analysis of carotid artery deformation in different head and neck positions for maxillofacial catheter navigation in advanced oral cancer treatment

BackgroundTo improve the accuracy of catheter navigation, it is important to develop a method to predict shifts of carotid artery (CA) bifurcations caused by intraoperative deformation. An important factor affecting the accuracy of electromagnetic maxillofacial catheter navigation systems is CA deformations. We aimed to assess CA deformation in different head and neck positions.MethodsUsing two sets of computed tomography angiography (CTA) images of six patients, displacements of the skull (maxillofacial segments), C1–C4 cervical vertebrae, mandible (mandibular segment), and CA along with its branches were analyzed. Segmented rigid bones around CA were considered the main causes of CA deformation. After superimposition of maxillofacial segments, C1–C4 and mandible segments were superimposed separately for displacement measurements. Five bifurcation points (vA–vE) were assessed after extracting the CA centerline. A new standardized coordinate system, regardless of patient-specific scanning positions, was employed. It was created using the principal axes of inertia of the maxillofacial bone segments of patients. Position and orientation parameters were transferred to this coordinate system. CA deformation in different head and neck positions was assessed.ResultsAbsolute shifts in the center of gravity in the bone models for different segments were C1, 1.02 ± 0.9; C2, 2.18 ± 1.81; C3, 4.25 ± 3.85; C4, 5.90 ± 5.14; and mandible, 1.75 ± 2.76 mm. Shifts of CA bifurcations were vA, 5.52 ± 4.12; vB, 4.02 ± 3.27; vC, 4.39 ± 2.42; vD, 4.48 ± 1.88; and vE, 2.47 ± 1.32. Displacements, position changes, and orientation changes of C1–C4 segments as well as the displacements of all CA bifurcation points were similar in individual patients.ConclusionsCA deformation was objectively proven as an important factor contributing to errors in maxillofacial navigation. Our study results suggest that small movements of the bones around CA can result in small CA deformations. Although patients’ faces were not fixed properly during CT scanning, C1–C4 and vA–vE displacements were similar in individual patients. We proposed a novel method for accumulation of the displacement data, and this study indicated the importance of surrounding bone displacements in predicting CA bifurcation.

The Physical and Laying Characteristics of Golden Sex-Linked Hens under the Humid Tropical Environment

A total of fifty-two Golden-sex link (brown) hens in their 65th week of lay were used in a study conducted to determine the oviposition time and interval, total egg production, clutch length and number of pause days of the birds under the humid tropical environment. The hens were also divided into four classes on the basis of their laying performances as follows: good layers, intermediate layers, poor layers and non layers and their physical conditions appraised. The birds were supplied water ad libitum and fed layers mash containing 16.5% crude protein and 9.62 MJ/kg ME for 5 weeks. Results showed that the peak of lay was between 7.30-8.30 am and declined gradually until only one egg was laid between 3.30-4.30 pm. About 66.36% and 33.64% of the eggs were laid in the morning hours and in the afternoon hours, respectively. The mean oviposition interval was 26.61 h, while the average laying intensity was 48.90%. About 98% of the clutch lengths were of 5 cycle lengths and below, with the highest frequency of occurrence being 1 cycle length. The total number of pause days over all birds was 558 days. Hens with the longest clutches and shortest number of pause days produced the greatest number of eggs. Observation made on the physical characteristics revealed that good layers had smooth and waxy comb and wattles. The vents were moist and enlarged with flexible pubic bone, soft abdomen and worn out feathers. Intermediate layers had similar features with the good layers except that eye rings, beaks and shanks were slightly bleached. Poor layers had dry combs and wattles; tight and hard abdomen and closed pubic bones. Non layers had scaly, dry and rough comb and wattles; dull eyes and rigid pubic bones which were relatively close together.

Identification of the material parameters of soft tissues in the compressed leg

Elastic compression is recommended in prophylaxis and the treatment of venous disorder of the human leg. However, the mechanisms of compression are not completely understood and the response of internal tissues to the external pressure is partially unknown. To address this later issue, a 3D FE model of a human leg is developed. The geometry is derived from 3D CT scans. The FE model is made up of soft tissues and rigid bones. An inverse method is applied to identify the properties of soft tissues which are modelled as hyperelastic, near-incompressible, homogeneous and isotropic materials. The principle is to calibrate the constitutive properties using CT scans carried out with and without the presence of a compression sock. The deformed geometry computed by the calibrated FE model is in agreement with the geometry deduced from the CT scans. The model also provides the internal pressure distribution, which may lead to medical exploitation in the future.

Explicit and implicit animation with fuzzy constraints of a versatile multi‐body system for virtual hand surgery

ABSTRACTThis work is designed to control the movement of hand structural agents under external action, using the implicit animation driven by explicit animation technique (AI‐CAE technique). Starting from the configuration of a hand at rest obtained by a 3D scanner and after meshing of the structural agents, we seek the configuration of the rigid agents under orthopaedic surgeon external action and interacting reliance of deformable and rigid agents. We have developed a model and software tools to answer this interactive application with adaptive execution. The first contribution comes from notations and definition of a versatile multi‐body system dedicated to the explicit and implicit animation. The second contribution comes from the implicit animation driven by explicit animation itself, and from its ability to mimic the role of cartilages and ligaments. The resulting technique is applied to the bone structure consistency of a specific human hand in the context of virtual hand orthopaedic surgery. The versatile specific multi‐body is made up of hierarchical interacting agents conceivable as a construction set of rigid bones with cartilages–ligaments and underlying links. The explicit animation produces a desired configuration from geometric command parameters of torsion, flexion, pivot and axis shifting, given in a scenario subdivided into temporal sequences. The implicit animation controls the movement by implementing a physics‐based model and fuzzy constraints of position and orientation. It gives better configuration than the explicit animation because it takes into account the interactions between agents, and it gives a neat solution without the problems of complexity due to geometric modelling. A methodology based on the AI‐CAE technique is discussed, medical expertise and validation tests are presented. Copyright © 2011 John Wiley & Sons, Ltd.

SU‐GG‐J‐109: A Study on Image Guided Radiotherapy Using Cone‐Beam Computed Tomography (CBCT) for Head and Neck Cancer IMRT Patient Setup

Purpose: To use our CBCT shift results to determine how much of the CTV to PTV margin is necessary to compensate for the daily setup uncertainty inherent in the treatment of head and neck cancer patients. Method and Materials: To accommodate the daily setup uncertainly, a 3–6 mm uniform margin is used for head and neck IMRT patients to expand CTV to PTV. In order to verify patient setup accuracy, CBCT is taken prior to the treatment. Our protocol calls for CBCT for the first five consecutive fractions, followed by two CBCT every week. Each CBCT is registered to the planning CT to determine the corresponding translational shift. The registration is based on the region‐of‐interest—the rigid bones near the tumor. On the days no CBCT is taken, the average of the previous three calculated translational shifts is used instead. No rotational correction is considered. Results: A total of 22 head and neck IMRT patients were studied with a Siemens Artiste linear accelerator using an MVision CBCT scanner. Each patient had approximately 14 sets of CBCT images taken over the entire course of treatment. The average interfraction shift was 0.6±1.6, 1.4±1.5, 0.1±1.6 mm in the anterior‐posterior, left‐right, and superior‐inferior dimensions, respectively. These data indicate that in the absence of CBCT image guided radiotherapy, a CTV to PTV margin of 2.5, 4.7 and 1.3 mm is needed in the anterior‐posterior, left‐right, and superior‐inferior dimensions, respectively. Conclusion: Our results have shown that asymmetric margins of 2.5, 4.7 and 1.3 mm can be used for CTV to PTV expansion for head and neck cancer radiotherapy if no IGRT presented. Our CBCT protocol will allow a reduction in the CTV to PTV margin. Further investigation needs to be done to find out the specific CTV to PTV margin with different CBCT frequency.

Effects of idealized joint geometry on finite element predictions of cartilage contact stresses in the hip

Computational models may have the ability to quantify the relationship between hip morphology, cartilage mechanics and osteoarthritis. Most models have assumed the hip joint to be a perfect ball and socket joint and have neglected deformation at the bone-cartilage interface. The objective of this study was to analyze finite element (FE) models of hip cartilage mechanics with varying degrees of simplified geometry and a model with a rigid bone material assumption to elucidate the effects on predictions of cartilage stress. A previously validated subject-specific FE model of a cadaveric hip joint was used as the basis for the models. Geometry for the bone-cartilage interface was either: (1) subject-specific (i.e. irregular), (2) spherical, or (3) a rotational conchoid. Cartilage was assigned either a varying (irregular) or constant thickness (smoothed). Loading conditions simulated walking, stair-climbing and descending stairs. FE predictions of contact stress for the simplified models were compared with predictions from the subject-specific model. Both spheres and conchoids provided a good approximation of native hip joint geometry (average fitting error ∼0.5 mm). However, models with spherical/conchoid bone geometry and smoothed articulating cartilage surfaces grossly underestimated peak and average contact pressures (50% and 25% lower, respectively) and overestimated contact area when compared to the subject-specific FE model. Models incorporating subject-specific bone geometry with smoothed articulating cartilage also underestimated pressures and predicted evenly distributed patterns of contact. The model with rigid bones predicted much higher pressures than the subject-specific model with deformable bones. The results demonstrate that simplifications to the geometry of the bone-cartilage interface, cartilage surface and bone material properties can have a dramatic effect on the predicted magnitude and distribution of cartilage contact pressures in the hip joint.