Seeing tissue as a 'phase of matter': exploring statistical mechanics for the cell.

The field of tissue engineering aims to produce living, biological constructs which possess the appropriate spatial ordering of cells and their extra cellular matrix products. The complexity of a single cell and its interactions in a large collective have made development of useful models to assist in tissue culture difficult, and consequentially most tissue culture endeavors are limited to trial and error approaches. Some cell types display a natural tendency to spontaneously self-assemble into large domains of parallel-oriented cells. In this work, we show that these cell culture systems can be studied in the context of continuous disorder-order phase transformations. We suggest that collective ordering of the cells is controlled by the amount of noise in the walk of the individual cells (directional persistence) because undifferentiated mesenchymal stem cells display a seven-times higher directional persistence than mature fibroblasts and have a 24-times larger final-oriented domain size, an observation that corresponds with collective ordering in self-propelled particle systems. The study of cell culture systems using analogies derived from statistical mechanics yields simple, practical models offering insight into how a long-range order can be obtained in tissue-engineered constructs, providing a new paradigm for managing operations with large collectives of living cells.

New insights into the plantar pressure correlates of walking speed using pedobarographic statistical parametric mapping (pSPM).

This study investigates the relation between walking speed and the distribution of peak plantar pressure and compares a traditional ten-region subsampling (10RS) technique with a new technique: pedobarographic statistical parametric mapping (pSPM). Adapted from cerebral fMRI methodology, pSPM is a digital image processing technique that registers foot pressure images such that homologous structures optimally overlap, thereby enabling statistical tests to be conducted at the pixel level. Following previous experimental protocols, we collected pedobarographic records from 10 subjects walking at three different speeds: slow, normal, and fast. Walking speed was recorded and correlated with the peak pressures extracted from the 10 regions, and subsequently with the peak pixel data extracted after pSPM preprocessing. Both methods revealed significant positive correlation between peak plantar pressure and walking speed over the rearfoot and distal forefoot after Bonferroni correction for multiple comparisons. The 10RS analysis found positive correlation in the midfoot and medial proximal forefoot, but the pixel data exhibited significant negative correlation throughout these regions (p<5x10(-5)). Comparing the statistical maps from the two approaches shows that subsampling may conflate pressure differences evident in pixel-level data, obscuring or even reversing statistical trends. The negative correlation observed in the midfoot implies reduced longitudinal arch collapse with higher walking speeds. We infer that this results from pre- or early-stance phase muscle activity and speculate that preferred walking speed reflects, in part, a balance between the energy required to tighten the longitudinal arch and the apparent propulsive benefits of the stiffened arch.

Mechanical and morphological properties of the triceps surae muscle-tendon unit in old and young adults and their interaction with a submaximal fatiguing contraction.

The purposes of this study were to examine (a) whether the morphological properties of the muscle gastrocnemius medialis (GM) contribute to the known enhanced muscle fatigue resistance during submaximal sustained isometric plantar flexion contraction of old compared to young adults and (b) whether a submaximal fatiguing contraction differently affects the mechanical properties of the GM tendon and aponeurosis of old and young adults. Fourteen old and 12 young male subjects performed maximal voluntary isometric plantar flexions (MVC) on a dynamometer before and after a submaximal fatiguing task (40% MVC). Moments and EMG signals from the gastrocnemius medialis and lateralis, soleus and tibialis anterior muscles were measured. The elongation of the GM tendon and aponeurosis and the morphological properties of its contractile element were examined by means of ultrasonography. The old adults showed lower maximal ankle joint moment, stiffness and fascicle length in both tested conditions. The submaximal fatiguing contraction did not affect the force-strain relationship of the GM tendon and aponeurosis of either young or old adults. The time to task failure was longer for the old adults and was strongly correlated with the fascicle length (r(2)=0.50, P<0.001). This provides evidence on that the lower ratio of the active muscle volume to muscle force for the old adults might be an additional mechanism contributing to the known age related increase in muscle fatigue resistance.

Sequential processes for controlling distance in multijoint movements.

The purpose of this study was to examine the mechanisms underlying control of distance during multijoint movements in different directions. The findings revealed 2 sequential muscle torque impulses, which correlated with 2 events in the hand acceleration profile. These 2 events occurred prior to peak velocity, characterizing control in the initial acceleration phase of motion. The contribution of shoulder and elbow joint torque to each event varied with movement direction. However, regardless of direction, these 2 torque events appeared to be functionally distinguishable: a preplanned initiation event was responsible for the initial hand acceleration, whereas a 2nd modulation event adjusted acceleration in compensation for variations in acceleration. Thus, the findings support the idea that control of distance during multijoint movement occurs through sequential control mechanisms.

Coupling of the reach and grasp phase during catching in children with developmental coordination disorder.

The authors studied 2-handed catching behavior in 10 children with developmental coordination disorder (DCD), aged 7-10 years old, and their typically developing peers (TDC). Participants performed 15 catches, and the authors examined kinematics of both transport and grasp phases. In terms of the transport phase, movement initiation and movement time was longer and peak deceleration was earlier in children with DCD. In addition, such children initiated the grasp phase earlier, and their maximal grasp aperture was larger. In children with DCD, the time to maximal grasp aperture was more variable, and that aperture was earlier when the authors examined it with respect to the transport phase of the catch. The data suggest that children with DCD may use a decomposition strategy to simplify the movement control of the transport and grasp phases of a catch.

A weighted least squares method for inverse dynamic analysis.

Internal forces in the human body can be estimated from measured movements and external forces using inverse dynamic analysis. Here we present a general method of analysis which makes optimal use of all available data, and allows the use of inverse dynamic analysis in cases where external force data is incomplete. The method was evaluated for the analysis of running on a partially instrumented treadmill. It was found that results correlate well with those of a conventional analysis where all external forces are known.

A neurofuzzy inference system based on biomechanical features for the evaluation of the effects of physical training.

The current study aimed to evaluate physical training effects. For this purpose, a classifier was implemented by taking into account biomechanical features selected from force-plate measurements and a neurofuzzy algorithm for data management and relevant decision-making. Measurements included two sets of sit-to-stand (STS) trials involving two homogeneous groups, experimental and control, of elders. They were carried out before and after a 12-week heavy resistance strength-training program undergone by the experimental group. Pre- and post-training differences were analysed, and percentages of membership to "trained" and "untrained" fuzzy sets calculated. The method was shown to be appropriate for detecting significant training-related changes. Detection accuracy was higher than 87%. Slightly weaker results were obtained using a neural approach, suggesting the need for a larger sample size. In conclusion, the use of a set of biomechanical features and of a neurofuzzy algorithm allowed to propose a global score for evaluating the effectiveness of a specific training program.

Reduction, classification and ranking of motion analysis data: an application to osteoarthritic and normal knee function data.

There are certain major obstacles to using motion analysis as an aid to clinical decision making. These include: the difficulty in comprehending large amounts of both corroborating and conflicting information; the subjectivity of data interpretation; the need for visualization; and the quantitative comparison of temporal waveform data. This paper seeks to overcome these obstacles by applying a hybrid approach to the analysis of motion analysis data using principal component analysis (PCA), the Dempster-Shafer (DS) theory of evidence and simplex plots. Specifically, the approach is used to characterise the differences between osteoarthritic (OA) and normal (NL) knee function data and to produce a hierarchy of those variables that are most discriminatory in the classification process. Comparisons of the results obtained with the hybrid approach are made with results from artificial neural network analyses.

Computational biomechanics of knee joint in open kinetic chain extension exercises.

Open kinetic chain (OKC) extension exercises are commonly performed to strengthen quadriceps muscles and restore joint function in performance enhancement programs, in exercise therapies and following joint reconstruction. Using a validated 3D nonlinear finite element model, the detailed biomechanics of the entire joint in OKC extension exercises are investigated at 0, 30, 60 and 90 degrees joint angles. Two loading cases are simulated; one with only the weight of the leg and the foot while the second considers also a moderate resistant force of 30 N acting at the ankle perpendicular to the tibia. The presence of the 30 N markedly influences the results both in terms of the magnitude and the trend. The resistant load substantially increases the required quadriceps, patellar tendon, cruciate ligaments and joint contact forces, especially at near 90 degrees angles with the exception of ACL force that is increased at 0 degrees angle. At post-ACL reconstruction period or in the joint with ACL injury, the exercise should preferably be avoided at near full extension positions under large resistant forces.

An estimation of joint kinematics for a standing reach task using ground reaction data.

The objective of this work was to derive a procedure able to estimate joint kinematics, relative to a simple, yet functionally relevant, motor task, starting from ground reaction data. The minimum number of input data has been used: force platform data, few and simple measurements relative to the subject, and protocol-specific parameters. Standing reach (SR) is the motor task analysed. The biomechanical model is a two degrees-of-freedom inverted pendulum moving on the vertical sagittal plane. Joint kinematics has been estimated solving the related direct dynamic problem stated in function of ground reaction data. The original nonlinear differential equation system of the model showed a high sensitivity to errors affecting initial conditions and experimental input data. Consequently, an approximate solution has been looked for in order to reduce the coupling between the model differential equations. This was possible taking into account the peculiar characteristics of the motor task. An optimization procedure has been deemed necessary in order to minimize the effects of the assumed approximation. The method has been tested both with simulated and with experimental data. In this latter case the validation of the angular kinematics estimated by the proposed method has been performed by means of data obtained by a stereophotogrammetric system. Results show a satisfactory behaviour of the whole optimization procedure. Very good results have been obtained in the case of slow reaching tasks.

Comparison of force, power, and striking efficiency for a Kung Fu strike performed by novice and experienced practitioners: preliminary analysis.

This paper presents a comparison of force, power, and efficiency values calculated from Kung Fu Yau-Man palm strikes, when performed by 7 experienced and 6 novice men. They performed 5 palm strikes to a freestanding basketball, recorded by high-speed camera at 1000 Hz. Nonparametric comparisons and correlations showed experienced practitioners presented larger values of mean muscle force, mean impact force, mean muscle power, mean impact power, and mean striking efficiency, as is noted in evidence obtained for other martial arts. Also, an interesting result was that for experienced Kung Fu practitioners, muscle power was linearly correlated with impact power (p = .98) but not for the novice practitioners (p = .46).

Observation of high and low passive ankle flexibility in stair descent.

Able-bodied people from the two extremes of the distribution of passive dorsiflexion exhibit biomechanical differences when descending stairs. Whether physical therapists could judge accurately the amount of ankle flexibility from observation of stair descent was examined with physical therapists (20 neurological 20 cardiothoracic) and 20 students. Subjects were 18 able-bodied men with high or low passive dorsiflexion. Raters viewed videotaped subjects descending stairs at normal playback speed and in slow motion and rated ankle flexibility on a 20-point scale. 'Flexible' or 'inflexible' subjects were classified correctly better than chance, but accuracy of rating flexibility was relatively poor. Both experience and slow motion playback improved accuracy. Physical therapists can detect extremes of normal flexibility in the ankle, based solely on observation of stair descent, and experienced therapists are better at this task than less experienced ones. Using slow motion videotape enhanced observational analysis.

In vivo areal modulus of elasticity estimation of the human tympanic membrane system: modelling of middle ear mechanical function in normal young and aged ears.

The quasi-static elastic properties of the tympanic membrane system can be described by the areal modulus of elasticity determined by a middle ear model. The response of the tympanic membrane to quasi-static pressure changes is determined by its elastic properties. Several clinical problems are related to these, but studies are few and mostly not comparable. The elastic properties of membranes can be described by the areal modulus, and these may also be susceptible to age-related changes reflected by changes in the areal modulus. The areal modulus is determined by the relationship between membrane tension and change of the surface area relative to the undeformed surface area. A middle ear model determined the tension-strain relationship in vivo based on data from experimental pressure-volume deformations of the human tympanic membrane system. The areal modulus was determined in both a younger (n = 10) and an older (n = 10) group of normal subjects. The areal modulus for lateral and medial displacement of the tympanic membrane system was smaller in the older group (mean = 0.686 and 0.828 kN m(-1), respectively) compared to the younger group (mean = 1.066 and 1.206 kN m(-1), respectively), though not significantly (2p = 0.10 and 0.11, respectively). Based on the model the areal modulus was established describing the summated elastic properties of the tympanic membrane system. Future model improvements include exact determination of the tympanic membrane area accounting for its shape via 3D finite element analyses. In vivo estimates of Young's modulus in this study were a factor 2-3 smaller than previously found in vitro. No significant age-related differences were found in the elastic properties as expressed by the areal modulus.

Accuracy and repeatability of an optical motion analysis system for measuring small deformations of biological tissues.

Optical motion analysis techniques have been widely used in biomechanics for measuring large-scale motions such as gait, but have not yet been significantly explored for measuring smaller movements such as the tooth displacements under load. In principle, very accurate measurements could be possible and this could provide a valuable tool in many engineering applications. The aim of this study was to evaluate accuracy and repeatability of the Qualisys ProReflex-MCU120 system when measuring small displacements, as a step towards measuring tooth displacements to characterise the properties of the periodontal ligament. Accuracy and repeatability of the system was evaluated using a wedge comparator with a resolution of 0.25 microm to provide measured marker displacements in three orthogonal directions. The marker was moved in ten steps in each direction, for each of seven step sizes (0.5, 1, 2, 3, 5, 10, and 20 microm), repeated five times. Spherical and diamond markers were tested. The system accuracy (i.e. percentage of maximum absolute error in range/measurement range), in the 20-200 microm ranges, was +/-1.17%, +/-1.67% and +/-1.31% for the diamond marker in x, y and z directions, while the system accuracy for the spherical marker was +/-1.81%, +/-2.37% and +/-1.39%. The system repeatability (i.e. maximum standard deviation in the measurement range) measured under the different days, light intensity and temperatures for five times, carried out step up and then step down measurements for the same step size, was +/-1.7, +/-2.3 and +/-1.9 microm for the diamond marker, and +/-2.6, +/-3.9 and +/-1.9 microm for the spherical marker in x, y and z directions, respectively. These results demonstrate that the system suffices accuracy for measuring tooth displacements and could potentially be useful in many other applications.

Extraction of information on elder motor ability from clinical and biomechanical data through data mining.

This study aimed at evaluating the additional knowledge provided by a biomechanical test coupled with clinical tests for motor ability assessment. A database including clinical test scores and sit-to-stand test variables obtained from 110 medically stable elderly subjects was submitted to data mining by searching for association rules. The presence of rules revealed some redundancies due to sample homogeneity, as mainly observed in the joint analysis of a questionnaire for daily activities assessment (Nottingham test) and the sit-to-stand, and due to similar evaluated information, as resulted from the joint analysis of a balance and gait scale (Tinetti test) and the sit-to-stand. Conversely, when no association rules were found, the tests carried unrelated information. The associations mined while analysing these clinical tests encouraged the integration of biomechanical tests, increasing significantly its clinical applicability and reducing the information redundancy. The information extracted also allowed to highlight rules typical of elderly persons that may serve as a knowledge-based tool for the detection of possible deviation from normality.

Validation of a new protocol for navigated intraoperative assessment of knee kinematics.

BACKGROUND: This study describes a novel method for accurate evaluations of knee kinematics during arthroscopic reconstructions of anterior cruciate ligament (ACL). METHODS: Quantitative evaluation of knee stability was estimated by experimental validation on 30 volunteers and by statistical analysis of test repeatability. RESULTS: Proposed method present short learning time, is minimally invasive and thus suitable for arthroscopic techniques. Computed laxity showed a repeatability of 1.5 degrees for varus-valgus, 3 degrees for internal-external, and 2mm for antero-posterior tests. CONCLUSIONS: This method represents a reliable quantification of knee kinematics in surgery, able to improve present intra-operative assessment of knee stability.

Kinematic patellar tracking from MR images for knee pain analysis.

Kinematic approaches using MR images have been regarded of more accuracy in knee pain (AKP) detection than stationary approaches. However, the challenge in segmenting femur, patellar and tibia due to the intensity non-uniformity caused by magnetic propagation degradation in MR images, and the strong adhesion of the soft tissue around the knee organs, has restricted the use of kinematic approaches. This paper proposes a combinatorial based kinematic patellar tracking (CKPT) for AKP detection. The CKPT uses a hybrid approach for extracting knee organs, where an edge-constrained wavelet enhancement followed by moment preserving segmentation is employed for conquering the soft tissue adhesion for extracting the femur and tibia from axial MR images, and a sliding window based moment preserving for resolving the segmentation difficulty associated with intensity non-uniformity in sagittal MR images. The location constraints are then applied for extracting landmark points from femur and patellar, and three inclination angles reflecting patellar position and orientation, during leg movement, are calculated as the measurement of patellar dislocation. The experiment shows that the hybrid approach can accurately extract femur, patellar and tibia. It also demonstrates the prominent of the calculated inclination angles in detecting AKP.

A data acquisition and analysis system for the biomechanical evaluation of patient moving and transferring equipment and procedures.

Patients and people with various disabilities are frequently moved and transferred by nurses and carers and consequently it is important to assess the risks involved when undertaking such tasks. People with disabilities are often able to bear some of their weight and this has led to the development of non-mechanical aids designed to reduce the load on the nurse or carer when undertaking a transferring manoeuvre. It is essential that aids are assessed thoroughly in order to ensure that transfers are safe and that advice and guidance can be given on the most appropriate equipment in a given situation. This paper describes a data acquisition and analysis system that has been developed to assist in such assessments. The system integrates measurements of spine movements, foot pressure and knee flexion with video recording of a transferring manoeuvre. A biomechanical model provides an estimate of the loading at the bottom of the lumbar spine for comparison with National Institute for Occupational Safety and Health (NIOSH) guidelines. A pilot assessment of non-mechanical aids prior to a full user trial demonstrated that such a system can provide valuable data from which to assess risk during patient transferring manoeuvres.

Specimen-specific beam models for fast and accurate prediction of human trabecular bone mechanical properties.

Direct assessment of bone competence in vivo is not possible, hence, it is inevitable to predict it using appropriate simulation techniques. Although accurate estimates of bone competence can be obtained from micro-finite element models (muFE), it is at the expense of large computer efforts. In this study, we investigated the application of structural idealizations to represent individual trabeculae by single elements. The objective was to implement and validate this technique. We scanned 42 human vertebral bone samples (10 mm height, 8 mm diameter) with micro-computed tomography using a 20 microm resolution. After scanning, direct mechanical testing was performed. Topological classification and dilation-based algorithms were used to identify individual rods and plates. Two FE models were created for each specimen. In the first one, each rod-like trabecula was modeled with one thickness-matched beam; each plate-like trabecula was modeled with several beams. From a simulated compression test, assuming one isotropic tissue modulus for all elements, the apparent stiffness was calculated. After reducing the voxel size to 40 microm, a second FE model was created using a standard voxel conversion technique. Again, one tissue modulus was assumed for all elements in all models, and a compression test was simulated. Bone volume fraction ranged from 3.7% to 19.5%; Young's moduli from 43 MPa to 649 MPa. Both models predicted measured apparent moduli equally well (R2 = 0.85), and were in excellent agreement with each other (R2 = 0.97). Tissue modulus was estimated at 9.0 GPa and 10.7 GPa for the beam FE and voxel FE models, respectively. On average, the beam models were solved in 219 s, reducing CPU usage up to 1150-fold as compared to 40 microm voxel FE models. Relative to 20 microm voxel models 10,000-fold reductions can be expected. The presented beam FE model is an abstraction of the intricate real trabecular structure using simple cylindrical beam elements. Nevertheless, it enabled an accurate prediction of global mechanical properties of microstructural bone. The strong reduction in CPU time provides the means to increase throughput, to analyze multiple loading configuration and to increase sample size, without increasing computational costs. With upcoming in vivo high-resolution imaging systems, this model has the potential to become a standard for mechanical characterization of bone.

Reliability and sensitivity of jerk-cost measurement for evaluating irregularity of chewing jaw movements.

Rate of change in movement acceleration (jerk) is a universally accepted quantity to evaluate irregularities of human limb and eye movements. This study was aimed to attest reliability of the jerk measurement of masticatory jaw movements and to identify its sensitivity to discriminate between movements performed with the presence of varied occlusal interference. Jaw movements during gum chewing were recorded with a 3D tracking device. Twelve adult subjects participated in the experiments. For five subjects, normalized jerk-costs (NJC) during jaw closing were compared between those measured on two separate occasions. For seven subjects, the NJCs during closing were compared with those measured with/without introduction of four different types of occlusal interference. The NJCs did not differ significantly between the two recording occasions. The interference at the canine tooth induced greater increase in the NJCs than that at the molar tooth. The comparison between repeated measures revealed reproducibility of the NJCs. In addition, the NJC was shown to be capable of discriminating between irregularities of the movements induced by occlusal interference at the canine and molar tooth sites. These findings suggest that the NJC is a valid indicator of masticatory jaw movement irregularity induced by disturbances of full intercuspation between upper and lower teeth.