Ben Stansfield

Sagittal joint kinematics, moments, and powers are predominantly characterized by speed of progression, not age, in normal children.

Twenty-six healthy 7-year-old children were enrolled in a 5-year longitudinal study to examine the importance of age and speed in the characterization of sagittal joint angles, moments, and powers. In 740 gait trials, children walking at self-selected speeds were examined on the basis of age and normalized speed [speed/(height ×g)1/2]. The kinematics and kinetics in these children were characterized predominantly by normalized speed of progression and not age. The clinical relevance of these findings is that normalized speed of walking, rather than age, should be considered when comparing normal with pathologic gait.

Normalisation of gait data in children

The comparative effect of semi-dimensional (SD) and non-dimensional (ND) normalisation on the results of a longitudinal study of gait in 5-12-year old children was investigated. The use of both height and leg length in the normalisation was examined. Only ND analysis could be used to identify subjects with the same accelerations. ND analysis of the childrens gait indicated that there was little change in the combination of step length and cadence used to achieve a particular velocity between 5 and 12. The first peak and mid-stance trough values of the vertical component of ground reaction force did not change with age. We recommend the use of ND normalisation rather that SD to allow comparisons between individuals of differing size and mass.

Normalized speed, not age, characterizes ground reaction force patterns in 5-to 12-year-old children walking at self-selected speeds.

Twenty-six healthy 5-year-old children were enrolled in a 7-year longitudinal study to examine the importance of age and speed in the characterization of ground reaction forces. One thousand forty gait trials of children walking at self-selected speeds were examined on the basis of age and normalized speed [speed/(height ×g)½]. Results, presented as discrete peak and trough values and as continuous trace plots over the stance phase, indicated that there was little change in ground reaction forces with age, but there were significant changes in vertical force and anterior-posterior force values with normalized speed. The ground reaction force patterns in these children were characterized predominantly by normalized speed of progression and not age. The clinical relevance of these findings is that normalized speed of walking, rather than age, should be considered when comparing normal with pathological gait.

Intra-rater repeatability of the Oxford foot model in healthy children in different stages of the foot roll over process during gait

BACKGROUND The repeatability of the Oxford foot model has been reported, but possible variations in the repeatability during the foot roll over process have not been examined. The aim of this study was to determine the relative and absolute repeatability of the model for each stage of the foot roll over process during gait and to compare foot kinematic data from this study with that from another centre as a preliminary examination of the models inter-centre repeatability and validity. METHOD Eight healthy children were tested twice at the gait laboratory. Foot kinematics from this study were plotted against those from an earlier repeatability study and repeatability statistics calculated for the three rockers of stance phase and swing phase. RESULTS Foot kinematics from this study and an earlier repeatability study produced similar kinematic patterns and joint angle ranges, but there were offsets in the absolute joint angles in the frontal and transverse planes. Relative and absolute repeatability were best in the sagittal plane (flexion/extension) with the poorest repeatability in the transverse plane (rotation and abduction/adduction). There was little difference in repeatability between the three rockers. Typical error of measurement varied between planes and segments from 0.9 degrees for maximum forefoot dorsiflexion in second rocker to 8.6 degrees for maximum hindfoot internal rotation in first rocker. DISCUSSION Repeatability varied markedly between planes and segments but was consistent throughout the gait cycle. Further studies are needed to determine the inter-centre repeatability and validity of the model.

Finite element model creation and stability considerations of complex biological articulation: The human wrist joint

The finite element method has been used with considerable success to simulate the behaviour of various joints such as the hip, knee and shoulder. It has had less impact on more complicated joints such as the wrist and the ankle. Previously published finite element studies on these multi-bone joints have needed to introduce un-physiological boundary conditions in order to establish numerical convergence of the model simulation. That is necessary since the stabilizing soft tissue mechanism of these joints is usually too elaborate in order to be fully included both anatomically and with regard to material properties. This paper looks at the methodology of creating a finite element model of such a joint focussing on the wrist and the effects additional constraining has on the solution of the model. The study shows that by investigating the effects each of the constraints, a better understanding on the nature of the stabilizing mechanisms of these joints can be achieved.

Development of temporal and distance parameters of gait in normal children

Temporal and distance parameters of 33 normal children were obtained from instrumented gait analysis prospectively over five consecutive years. The parameters were normalised to minimise the confounding effects of increasing height and leg length. Rank correlations were performed on normalised speed, normalised stride length, normalised cadence and normalised walk ratio across consecutive pairs of years to examine the ranking of these parameters for an individual child over time. Consistent trends of increasing rank correlation were observed in normalised stride length and normalised walk ratio suggesting that individual children were continuing to adjust these gait parameters towards their own characteristic position within the normal range. Consistent trends were not observed in the rank correlations for normalised speed and normalised cadence. These findings support the concept that individual children predominantly adjusted their cadence to effect changes in speed, while the development of stride length was dictated by other factors specific to the individual child. Rank correlation coefficients for walk ratio between consecutive years increased from the ages of 7-11 years of age and hence walk ratio appears be a feature of gait that matures beyond the age of 7 years. This accords with the proposal that it is an invariant parameter for an individual.

A three-dimensional finite element model of maximal grip loading in the human wrist

Abstract The aim of this work was to create an anatomically accurate three-dimensional finite element model of the wrist, applying subject-specific loading and quantifying the internal load transfer through the joint during maximal grip. For three subjects, representing the anatomical variation at the wrist, loading on each digit was measured during a maximal grip strength test with simultaneous motion capture. The internal metacarpophalangeal joint load was calculated using a biomechanical model. High-resolution magnetic resonance scans were acquired to quantify bone geometry. Finite element analysis was performed, with ligaments and tendons added, to calculate the internal load distribution. It was found that for the maximal grip the thumb carried the highest load, an average of 72.2 ± 20.1 N in the neutral position. Results from the finite element model suggested that the highest regions of stress were located at the radial aspect of the carpus. Most of the load was transmitted through the radius, 87.5 per cent, as opposed to 12.5 per cent through the ulna with the wrist in a neutral position. A fully three-dimensional finite element analysis of the wrist using subject-specific anatomy and loading conditions was performed. The study emphasizes the importance of modelling a large ensemble of subjects in order to capture the spectrum of the load transfer through the wrist due to anatomical variation.

Re-attachment of the tuberosities of the humerus following hemiarthroplasty for four-part fracture

This study evaluated the effect on movement under load of three different techniques for re-attachment of the tuberosities of the humerus using test sawbones. In the first, the tuberosities were attached both to the shaft and to each other, with one cerclage suture through the anterior hole in the prosthesis. The second technique was identical except for omission of the cerclage suture and in the third the tuberosities were attached to the prosthesis and to the shaft. An orthogonal photogrammetric system allowed all segments to be tracked in a 3D axis system. The humeri were incrementally-loaded in abduction, and the 3D linear and angular movements of all segments were calculated. Displacement between the tuberosities and the shaft was measured. The first and second techniques were the most stable constructs, with the third allowing greater separation of fragments and angular movement. Separation at the midpoint of the tuberosities was significantly greater using the latter technique (p < 0.05). The cerclage suture added no further stability to the fixation.

Characteristics of very slow stepping in healthy adults and validity of the activPAL3™ activity monitor in detecting these steps

The use of activity monitors to objectively measure stepping activity allows the characterisation of free-living daily activity performance. However, they must be fully validated. The characteristics of very slow stepping were examined and the validity of an activity monitor, the activPAL3™ (PAL Technologies Ltd., Glasgow, UK) to detect these steps was assessed. 10M/10F healthy adults (36±10 y) performed a treadmill walking protocol from 1.0m/s down to 0.1m/s (0.1m/s increments) whilst wearing the monitor under video observation (gold standard). Within the 800 stepping periods recorded the proportion of the steps correctly detected by the activPAL3™ was explored against speed and cadence. Below 0.4 m/s walking began to be intermittent, stepping interspersed with stationary postures. At 0.1 m/s almost 90% of walking periods were intermittent. The percentage of steps detected was over 90% for walking speed at or above 0.5m/s and cadence at or above 69 steps/min. However, below these limits % steps detected reduced rapidly with zero steps detected at 0.1m/s and at or below 24 steps/min. When examining the stepping activity of groups with limited stepping cadence the above thresholds of performance should be considered to ensure that outcomes are not misinterpreted and important very slow stepping activity missed.

Use of biomechanical data in the Inclusive Design process: packaging design and the older adult

Biomechanical data may be used to inform the design process to ensure Inclusive Design. Yet many products are clearly not designed inclusively, one possible reason being that biomechanical data are not used, is not available or offers insufficient benefits to merit integration into the design process. This study investigates designers’ use of biomechanical data to inform the process of Inclusive Design in the consumer packaging industry. Packaging design professionals were interviewed to elicit information regarding their use of biomechanical data and to establish if they followed Inclusive Design principles. Biomechanical data were collected using observational study and customised force and motion measurement tools. Finally, biomechanical data were presented to the designers to establish the best/preferred format for use in the design process. Biomechanical data were rarely used by the designers and Inclusive Design principles were not routinely incorporated into company procedures. There was clear preference for visual data with imagery of real subjects. Most quantitative force and motion data formats were considered to be unsuitable for routine use due to commercial priorities and lack of technical appreciation. The use of biomechanical testing to develop standards to allow Inclusive Design may be the way forward.