On the kinematic modeling and the parameter estimation of the human knee joint.

This paper presents some results on the modeling and the parameter estimation of the human knee joint. Based on the geometric characteristics of the femur condyle and the tibia plateau, a part of femoro-tibial joint model includes an involute-on-plane submodel. Data recorded by camera type device are used to analyze the kinematic characteristics of the knee joint and to estimate the corresponding submodel parameters. Experimental results are presented and the model is further validated.     

The transmission of load through the human hip joint

This paper describes the results of loading experiments carried out on human hip joints. The unloaded surfaces of the femoral head and the acetabulum are slightly incongruous. The location and magnitude of the contact areas between the surfaces therefore depend on the magnitude and direction of the applied load. The contact areas were determined experimentally for a variety of loads typical of normal walking. Two distinct contact areas were found on the anterior and posterior aspects of the acetabulum at light loads, gradually merging with increasing load until, at a certain transition load, the dome of the acetabulum comes into contact and contact is then complete. The value of the transition load depends on the rate of loading, due to creep of the cartilage, and was found to vary from 50 per cent of body weight in young specimens to 25 per cent of body weight for elderly specimens for rates of loading typical of normal walking. Thus, the dome of the acetabulum is out of contact for a substantial portion of the swing phase of normal walking.

The analysis of a much simplified model of the hip joint is presented. The dependence of contact area on load is demonstrated, but also a method of determining the transition load for complete contact from the load/deflection relation for the hip is suggested. The values of the transition load quoted above were obtained by this method. The analysis further indicates that the distribution of pressure between the articular surfaces depends critically on the distribution of cartilage thickness throughout the joint. It is suggested that the distribution of cartilage thickness is such as to lead to a state of uniform pressure at the upper end of the physiological load range. Some experimental evidence is presented in support of this suggestion.

It is concluded that the function of joint incongruity is to allow the articular surfaces to come out of contact at light loads so that the cartilage may be exposed to synovial fluid for the purposes of nutrition and lubrication. At large loads, the distribution of cartilage thickness ensures that a state of hydrostatic pressure is achieved in order that cartilage, with a large fluid content, may transmit large pressures without flow and consequent loss of its integrity.     

In vivo hip joint loads and pedal forces during ergometer cycling

The rising prevalence of osteoarthritis and an increase in total hip replacements calls for attention to potential therapeutic activities. Cycling is considered as a low impact exercise for the hip joint and hence recommended. However, there are limited data about hip joint loading to support this claim. The aim of this study was to measure synchronously the in vivo hip joint loads and pedal forces during cycling. The in vivo hip joint loads were measured in 5 patients with instrumented hip implants. Data were collected at several combinations of power and cadence, at two saddle heights.Joint loads and pedal forces showed strong linear correlation with power. So the relationship between the external pedal forces and internal joint forces was shown. While cycling at different cadences the minimum joint loads were acquired at 60 RPM. The lower saddle height configuration results in an approximately 15% increase compared to normal saddle height.The results offered new insights into the actual effects of cycling on the hip joint and can serve as useful tools while developing an optimum cycling regimen for individuals with coxarthrosis or following total hip arthroplasty. Due to the relatively low contact forces, cycling at a moderate power level of 90 W at a normal saddle height is suitable for patients.     

Subject-specific biomechanics of trunk: musculoskeletal scaling,internal loads and intradiscal pressure estimation

Biomechanics and Modeling in Mechanobiology - Development of a subject-specific computational musculoskeletal trunk model (accounting for age, sex, body weight and body height), estimation of...     

Three-dimensional temporomandibular joint muscle attachment morphometry and its impacts on musculoskeletal modeling

In musculoskeletal models of the human temporomandibular joint (TMJ), muscles are typically represented by force vectors that connect approximate muscle origin and insertion centroids (centroid-to-centroid force vectors). This simplification assumes equivalent moment arms and muscle lengths for all fibers within a muscle even with complex geometry and may result in inaccurate estimations of muscle force and joint loading. The objectives of this study were to quantify the three-dimensional (3D) human TMJ muscle attachment morphometry and examine its impact on TMJ mechanics. 3D muscle attachment surfaces of temporalis, masseter, lateral pterygoid, and medial pterygoid muscles of human cadaveric heads were generated by co-registering measured attachment boundaries with underlying skull models created from cone-beam computerized tomography (CBCT) images. A bounding box technique was used to quantify 3D muscle attachment size, shape, location, and orientation. Musculoskeletal models of the mandible were then developed and validated to assess the impact of 3D muscle attachment morphometry on joint loading during jaw maximal open-close. The 3D morphometry revealed that muscle lengths and moment arms of temporalis and masseter muscles varied substantially among muscle fibers. The values calculated from the centroid-to-centroid model were significantly different from those calculated using the ‘Distributed model’, which considered crucial 3D muscle attachment morphometry. Consequently, joint loading was underestimated by more than 50% in the centroid-to-centroid model. Therefore, it is necessary to consider 3D muscle attachment morphometry, especially for muscles with broad attachments, in TMJ musculoskeletal models to precisely quantify the joint mechanical environment critical for understanding TMJ function and mechanobiology.     

Validation of hamstrings musculoskeletal modeling by calculating peak hamstrings length at different hip angles

Accurate estimates of hamstrings lengths are useful, for example, to facilitate planning for surgical lengthening of the hamstrings in patients with cerebral palsy. In this study, three models used to estimate hamstrings length (M1: Delp, M2: Klein Horsman, M3: Hawkins and Hull) were evaluated. This was done by determining whether the estimated peak semitendinosus, semimembranosus and biceps femoris long head lengths, as measured in eight healthy subjects, were constant over a range of hip and knee angles. The estimated peak hamstrings length depended on the model that was used, even with length normalized to length in anatomical position. M3 estimated shorter peak lengths than M1 and M2, showing that more advanced models (M1 and M2) are more similar. Peak hamstrings length showed a systematic dependence on hip angle for biceps femoris in M2 and for semitendinosus in M3, indicating that either the length was not correctly estimated, or that the specific muscle did not limit the movement. Considerable differences were found between subjects. Large inter-individual differences indicate that modeling results for individual subjects should be interpreted with caution. Testing the accuracy of modeling techniques using in vivo data, as performed in this study, can provide important insights into the value and limitations of musculoskeletal models.     

Validation of a functional method for the estimation of hip joint centre location

The present study assesses the accuracy with which the subject specific coordinates of the hip joint centre (HJC) in a pelvic anatomical frame can be estimated using different methods. The functional method was applied by calculating the centre of the best sphere described by the trajectory of markers placed on the thigh during several trials of hip rotations. Different prediction methods, proposed in the literature and in the present investigation, which estimate the HJC of adult subjects using regression equations and anthropometric measurements, were also assessed. The accuracy of each of the above-mentioned methods was investigated by comparing their predictions with measurements obtained on a sample of 11 male adult able-bodied volunteers using roentgen stereophotogrammetric analysis (RSA), assumed to provide the true HJC locations. Prediction methods estimated the HJC location at an average rms distance of 25-30 mm. The functional method performed significantly better and estimated HJCs within a rms distance of 13 mm on average. This result may be confidently generalised if the photogrammetric experiment is carefully conducted and an optimal analytical approach used. The method is therefore suggested for use in motion analysis when the subject's hip range of motion is not limited. In addition, the facts that it is not an invasive technique and that it has relatively small and un-biased errors, make it suitable for regression equations identification with no limit to sample size and population typology.     

Experimentally reduced hip abductor function during walking: Implications for knee joint loads

Hip and knee functions are intimately connected and reduced hip abductor function might play a role in development of knee osteoarthritis (OA) by increasing the external knee adduction moment during walking. The purpose of this study was to test the hypothesis that reduced function of the gluteus medius (GM) muscle would lead to increased external knee adduction moment during level walking in healthy subjects. Reduced GM muscle function was induced experimentally, by means of intramuscular injections of hypertonic saline that produced an intense short-term muscle pain and reduced muscle function. Isotonic saline injections were used as non-painful control. Fifteen healthy subjects performed walking trials at their self-selected walking speed before and immediately after injections, and again after 20 min of rest, to ensure pain recovery. Standard gait analyses were used to calculate three-dimensional trunk and lower extremity joint kinematics and kinetics. Surface electromyography (EMG) of the glutei, quadriceps, and hamstring muscles were also measured. The peak GM EMG activity had temporal concurrence with peaks in frontal plane moments at both hip and knee joints. The EMG activity in the GM muscle was significantly reduced by pain (?39.6%). All other muscles were unaffected. Peaks in the frontal plane hip and knee joint moments were significantly reduced during pain (?6.4% and ?4.2%, respectively). Lateral trunk lean angles and midstance hip joint adduction and knee joint extension angles were reduced by ?1°. Thus, the gait changes were primarily caused by reduced GM function. Walking with impaired GM muscle function due to pain significantly reduced the external knee adduction moment. This study challenge the notion that reduced GM function due to pain would lead to increased loads at the knee joint during level walking.     

Static optimization underestimates antagonist muscle activity at the glenohumeral joint: A musculoskeletal modeling study

Static optimization is commonly employed in musculoskeletal modeling to estimate muscle and joint loading; however, the ability of this approach to predict antagonist muscle activity at the shoulder is poorly understood. Antagonist muscles, which contribute negatively to a net joint moment, are known to be important for maintaining glenohumeral joint stability. This study aimed to compare muscle and joint force predictions from a subject-specific neuromusculoskeletal model of the shoulder driven entirely by measured muscle electromyography (EMG) data with those from a musculoskeletal model employing static optimization. Four healthy adults performed six sub-maximal upper-limb contractions including shoulder abduction, adduction, flexion, extension, internal rotation and external rotation. EMG data were simultaneously measured from 16 shoulder muscles using surface and intramuscular electrodes, and joint motion evaluated using video motion analysis. Muscle and joint forces were calculated using both a calibrated EMG-driven neuromusculoskeletal modeling framework, and musculoskeletal model simulations that employed static optimization. The EMG-driven model predicted antagonistic muscle function for pectoralis major, latissimus dorsi and teres major during abduction and flexion; supraspinatus during adduction; middle deltoid during extension; and subscapularis, pectoralis major and latissimus dorsi during external rotation. In contrast, static optimization neural solutions showed little or no recruitment of these muscles, and preferentially activated agonistic prime movers with large moment arms. As a consequence, glenohumeral joint force calculations varied substantially between models. The findings suggest that static optimization may under-estimate the activity of muscle antagonists, and therefore, their contribution to glenohumeral joint stability.     

On the estimation of joint kinematics during gait.

In gait analysis, the concepts of Euler and helical (screw) angles are used to define the three-dimensional relative joint angular motion of lower extremities. Reliable estimation of joint angular motion depends on the accurate definition and construction of embedded axes within each body segment. In this paper, using sensitivity analysis, we quantify the effects of uncertainties in the definition and construction of embedded axes on the estimation of joint angular motion during gait. Using representative hip and knee motion data from normal subjects and cerebral palsy patients, the flexion-extension axis is analytically perturbed +/- 15 degrees in 5 degrees steps from a reference position, and the joint angles are recomputed for both Euler and helical angle definitions. For the Euler model, hip and knee flexion angles are relatively unaffected while the ab/adduction and rotation angles are significantly affected throughout the gait cycle. An error of 15 degrees in the definition of flexion-extension axis gives rise to maximum errors of 8 and 12 degrees for the ab/adduction angle, and 10-15 degrees for the rotation angles at the hip and knee, respectively. Furthermore, the magnitude of errors in ab/adduction and rotation angles are a function of the flexion angle. The errors for the ab/adduction angles increase with increasing flexion angle and for the rotation angle, decrease with increasing flexion angle. In cerebral palsy patients with flexed knee pattern of gait, this will result in distorted estimation of ab/adduction and rotation. For the helical model, similar results are obtained for the helical angle and associated direction cosines.(ABSTRACT TRUNCATED AT 250 WORDS)     

Sensitivity analysis of hip joint centre estimation based on three-dimensional CT scans

In morphological analysis of the femur, the hip joint centre (HJC) is generally determined using a 3D model of the femoral head based on medical images. However, the portion of the image selected to represent the femoral head may influence the HJC. We determined if this influence invalidates the results of three HJC calculation methods, one of which we introduce here.

To isolate femoral heads in cadaver CT images, thresholds were applied to the distance between femur and acetabulum models. The sensitivity of the HJC to these thresholds and the differences between methods were quantified.

For thresholds between 6 and 9 mm and healthy hips, differences between methods were below 1 mm and all methods were insensitive to threshold changes. For higher thresholds, the fovea capitis femoris disturbed the HJC. In two deformed hips, the new method performed superiorly. We conclude that for normal hips all methods produce valid results.     

Sensitivity analysis of hip joint centre estimation based on three-dimensional CT scans

In morphological analysis of the femur, the hip joint centre (HJC) is generally determined using a 3D model of the femoral head based on medical images. However, the portion of the image selected to represent the femoral head may influence the HJC. We determined if this influence invalidates the results of three HJC calculation methods, one of which we introduce here. To isolate femoral heads in cadaver CT images, thresholds were applied to the distance between femur and acetabulum models. The sensitivity of the HJC to these thresholds and the differences between methods were quantified. For thresholds between 6 and 9?mm and healthy hips, differences between methods were below 1?mm and all methods were insensitive to threshold changes. For higher thresholds, the fovea capitis femoris disturbed the HJC. In two deformed hips, the new method performed superiorly. We conclude that for normal hips all methods produce valid results.     

In-vitro experimental assessment of a new robust algorithm for hip joint centre estimation

Hip joint centre (HJC) localization is used in several biomedical applications, such as movement analysis and computer-assisted orthopaedic surgery.The purpose of this study was to validate in vitro a new algorithm (MC-pivoting) for HJC computation and to compare its performances with the state-of-the-art (least square approach–LSA). The MC-pivoting algorithm iteratively searches for the 3D coordinates of the point belonging to the femoral bone that, during the circumduction of the femur around the hip joint (pivoting), runs the minimum length trajectory. The algorithm was initialized with a point distribution that can be considered close to a Monte Carlo simulation sampling all around the LSA estimate.The performances of the MC-pivoting algorithm, compared with LSA, were evaluated with tests on cadavers. Dynamic reference frames were applied on both the femur and the pelvis and were tracked by an optical localizer.Results proved the algorithm accuracy (1.7 mm±1.6, 2.3—median value±quartiles), reliability (smaller upper quartiles of the errors distribution with respect to LSA) and robustness (reduction of the errors also in case of large pelvis displacements).     

Angular orientation of trabecular bone in the femoral head and its relationship to hip joint loads in leaping primates

The elastic properties and mechanical behavior of trabecular bone are largely determined by its three-dimensional (3D) fabric structure. Recent work demonstrating a correlation between the primary mechanical and material axes in trabecular bone specimens suggests that fabric orientation may be used to infer directional components of the material strength and, by extension, the hypothetical loading regime. Here we quantify the principal orientation of trabecular bone in the femoral head and relate these principal fabric directions to loading patterns during various locomotor behaviors. The proximal femora of a diverse sample of prosimians were scanned using a high-resolution X-ray computed tomography scanner with resolution of better than 50 mum. Spherical volumes of interest were defined within the femoral heads and the 3D fabric anisotropy was calculated using the mean intercept length and star volume distribution methods. In addition to differences in bone volume and anisotropy, significant differences were found in the spatial orientation of the principal trabecular axes depending on locomotor behavior. The principal orientations for leapers (Galago, Tarsius, Avahi) are relatively tightly clustered (alpha(95) confidence limit: 8.2; angular variance s: 18.2 degrees ) and oriented in a superoanterior direction, while those of nonleapers are more variable across a range of directions (alpha(95): 16.8; s: 42.0 degrees ). The mean principal directions are significantly different for leaping vs. nonleaping taxa. These results further suggest a relationship between bone microstructure in the hip joint and locomotor behavior and indicate a similarity of loading across leapers despite differences in kinematics and phylogeny.     

Failure of total hip arthroplasties. Numerical modeling of debris formation through plastic strains

The life span of a total hip prosthesis is one of the main points on which the long-term success of arthroplasties depends. It is, by now, widely recognized that hip arthroplasty failure is mainly due to the aseptic loosening resulting from the presence of wear debris forming at the contact interface between the femoral head and the cup of the acetabulum. The size of these particles varies from a few micrometers to some tens of micrometers or more. The main aim of this study was therefore to investigate the formation of debris in the microscopic size range. For this purpose, a numerical study was carried out on various mechanisms leading to plastic deformations, which can lead to damage and wear in material. Numerical analyses were performed with a laboratory software program LMGC90, on the evolution of the plastic strains involved in various wear mechanisms on the microscopic scale.     

HAPLOPOOL: improving haplotype frequency estimation through DNA pools and phylogenetic modeling

MOTIVATION: The search for genetic variants that are linked to complex diseases such as cancer, Parkinson's;, or Alzheimer's; disease, may lead to better treatments. Since haplotypes can serve as proxies for hidden variants, one method of finding the linked variants is to look for case-control associations between the haplotypes and disease. Finding these associations requires a high-quality estimation of the haplotype frequencies in the population. To this end, we present, HaploPool, a method of estimating haplotype frequencies from blocks of consecutive SNPs. RESULTS: HaploPool leverages the efficiency of DNA pools and estimates the population haplotype frequencies from pools of disjoint sets, each containing two or three unrelated individuals. We study the trade-off between pooling efficiency and accuracy of haplotype frequency estimates. For a fixed genotyping budget, HaploPool performs favorably on pools of two individuals as compared with a state-of-the-art non-pooled phasing method, PHASE. Of independent interest, HaploPool can be used to phase non-pooled genotype data with an accuracy approaching that of PHASE. We compared our algorithm to three programs that estimate haplotype frequencies from pooled data. HaploPool is an order of magnitude more efficient (at least six times faster), and considerably more accurate than previous methods. In contrast to previous methods, HaploPool performs well with missing data, genotyping errors and long haplotype blocks (of between 5 and 25 SNPs).