Timothy M. Barker

Defining the Neutral Zone of sheep intervertebral joints during dynamic motions: an in vitro study

OBJECTIVE To make an experimental assessment of the Neutral Zone of intervertebral joints during dynamic spinal motion in flexion/extension, lateral bending and axial rotation and to develop a criterion for its definition. DESIGN Dynamic mechanical testing of sheep intervertebral joints with a six-degree of freedom robotic facility under position control. BACKGROUND The Neutral Zone is defined as a region of no or little resistance to motion in the middle of an intervertebral joints range of movement. Previous studies have used quasi-static loading regimes that do not model physiological activity. This study simulated physiological movements using a robotic testing facility to address this issue. METHODS Five spines from mature sheep were used and three motion segments were tested from each spine. The robotic facility enabled the testing regime to be defined for each individual joint based on its geometry. The joints were tested by cycling through the full range of physiological movement in flexion/extension, lateral bending and axial rotation. RESULTS A Neutral Zone was found to exist during dynamic movements only in flexion/extension. The results suggested that a Neutral Zone does not exist in lateral bending or axial rotation. The zygapophysial joints were shown to be significant in determining the mechanics of the intervertebral joints as their removal increased the Neutral Zone in all cases. A new criterion for defining the size of the Neutral Zone during dynamic motion was proposed and its implications for spinal movements in life discussed. CONCLUSIONS A Neutral Zone exists in flexion/extension during dynamic movements of intervertebral joints and is a feature of the natural range of joint motion. This has important implications for the muscular control of the spine consisting of several intrinsically lax joints stacked on one another. RELEVANCE The existence of a Neutral Zone is a feature of the natural range of joint motion and requires complex control of intervertebral joints by the spinal muscles. Defining the biomechanical response throughout the physiological range of motion (RoM) is important in understanding possible injury and rehabilitation mechanisms.

Walking and running inter-limb asymmetry for Paralympic trans-femoral amputees, a biomechanical analysis:

The aim of this project was to further the research and understanding of the trans-femoral amputees ability to walk and run by comparing the changes in walking and running inter-limb asymmetry. An objective biomechanical analysis was conducted on four male trans-femoral amputees, all members of the Australian Paralympic training squad for the 1996 Atlanta Paralympic Games. The data was collected in the biomechanics laboratories at Queensland University of Technology and the Australian Institute of Sport. The main outcomes measure a synchronised 3D kinematic (200Hz), kinetic (600Hz) and temporal analysis of walking at self-selected (1.1-1.3m/s), and at maximal running speed (2.5-4.3m/s). The walking and running biomechanical data was summarised into 27 indices of symmetry. The results showed that for all subjects the inter-limb asymmetry was significantly different at running speed, when compared to the walking speed. Using indices of symmetry 79% of the kinematic, 67% of the kinetic, and 67% of the temporal measurements identified better inter-limb asymmetry when the subjects walked, compared to running. This study objectively identified that when Paralympic level amputees ran on their standard running prosthesis, the inter-limb asymmetry was exacerbated.

Preservation of Residual Foot Length in Partial Foot Amputation: A Biomechanical Analysis

Background: Partial foot amputation may be preferred to more proximal amputation because of the perceived improvement in function associated with preserving foot length and the ankle joint complex, thus enabling normal gait and push-off. Clinically, partial foot amputees display significant wasting of the triceps surae musculature, strongly indicative of disuse. This investigation aimed to examine the belief that preserving residual foot length should be the primary operative objective necessary to maintain normal foot and ankle function. Method: The gait patterns of eight partial foot amputees and a cohort of matched nonamputee control subjects were analyzed using a peak three-dimensional (3D) motion analysis system incorporating an AMTI force platform (Advanced Mechanical Technology Inc., Waterton, MA). Amputee subjects used their own prostheses for the evaluation. Results: Amputations disarticulating the metatarsophalangeal (MTP) joint had little impact on the normal pattern of ankle power generation. However, amputation proximal to the MTP joint level resulted in virtually negligible power generation across the ankle, regardless of residual foot length. Subjects compensated for the lack of ankle power generation by adopting strategies in which the hip became the primary source of power to advance the body forward. Conclusions: The primary reason for a partial foot amputation is to preserve the normal function of the foot and ankle complex associated with push-off. As such, surgery should strive to preserve the metatarsal heads to allow amputees to use the ankles contribution to walking. Given that amputation proximal to the metatarsal heads compromised the normal propulsive function of the foot and ankle, surgery should not strive to preserve residual foot length to maintain function but should instead aim to achieve good distal tissue coverage and healing, particularly given that the hip joint(s), not the ankle, become the primary source of power for walking.

Optimising the trans-femoral prosthetic alignment for running, by lowering the knee joint:

For amputees to perform an everyday task, or to participate in physical exercise, it is crucial that they have an appropriately designed functional prosthesis. The aim of this study was to investigate the optimal trans-femoral prosthetic alignment configuration for running. A case study design was implemented as the method to collect data on four male Paralympic level trans-femoral amputee runners. In total 28 synchronised 3D kinematic, kinetic, and temporal biomechanical measures were analysed. A new prosthetic alignment, in which the prosthetic knee axis was lowered longitudinally (moved distally), was evaluated for running. The performance of the symmetry indices and running time for a total of three new modified alignments were compared to the standard prosthetic alignment. The interlimb asymmetry was found to improve when the subjects ran on the modified prosthetic alignment, and most importantly a one way ANOVA found a statistically significant increase in running velocity. This study identified that for all four subjects, who used the same prosthetic components, lowering the prosthetic knee joint centre improved their interlimb symmetry, and subsequently their running velocity by an average of 26%.

Can partial foot prostheses effectively restore foot length

Our understanding of how partial foot prostheses function stems from static force analyses, where assumptions about the location of the ground reaction force during terminal stance have been made. While such assumptions seemed reasonably based on an understanding of normal gait, they are often illogical based on what is observed clinically. As such, the aim of this work was to evaluate the belief that partial foot prostheses are able to restore the effective foot length. Centre of pressure (CoP) excursion data were collected as part of a complete gait analysis incorporating an Advanced Mechanical Technology Inc. force platform. The CoP excursion patterns, observed in a cohort of eight partial foot amputees and matched control subjects, highlight the inability of toe fillers and slipper sockets to restore the ‘effective’ foot length in transmetatarsal and Lisfranc amputees, whereas clamshell prostheses fitted to the Chopart amputees were able to restore the effective foot length. In the transmetatarsal and Lisfranc amputees, the observed CoP excursion patterns could indicate a learned gait strategy necessary to reduce the requirement of the weak triceps surae musculature as well as spare the sensitive distal stump from extreme forces. The toe fillers and slipper sockets fitted to these amputees may not be stiff enough to support the amputees body weight or the device may not be designed appropriately to assist the weakened triceps musculature to resist the external moments caused by loading the forefoot. The clamshell prostheses restored the ‘effective’ foot length due to the rigid toe lever and clamshell socket, which could allow and comfortably support the generation of substantial external moments during terminal stance.

Effect of inaccuracies in anthropometric data and linked-segment inverse dynamic modeling on kinetics of gait in persons with partial foot amputation.

The accuracy of data derived from linked-segment models depends on how well the system has been represented. Previous investigations describing the gait of persons with partial foot amputation did not account for the unique anthropometry of the residuum or the inclusion of a prosthesis and footwear in the model and, as such, are likely to have underestimated the magnitude of the peak joint moments and powers. This investigation determined the effect of inaccuracies in the anthropometric input data on the kinetics of gait. Toward this end, a geometric model was developed and validated to estimate body segment parameters of various intact and partial feet. These data were then incorporated into customized linked-segment models, and the kinetic data were compared with that obtained from conventional models. Results indicate that accurate modeling increased the magnitude of the peak hip and knee joint moments and powers during terminal swing. Conventional inverse dynamic models are sufficiently accurate for research questions relating to stance phase. More accurate models that account for the anthropometry of the residuum, prosthesis, and footwear better reflect the work of the hip extensors and knee flexors to decelerate the limb during terminal swing phase.

Impact data for the investigation of injuries in inflatable rescue boats (IRBs)

Inflatable Rescue Boats (IRBs) are arguably the most important rescue tools utilised by Australian Surf Lifesavers. The crews in the IRB are continuously battling the fierce element that is the ocean. This force of nature takes its toll on man and machine. Initial impact data for this unique situation has been gathered as part of a biomechanical study investigating the increasing frequency of injuries to surf lifesavers whilst using an IRB. This paper outlines the scope of the research topic and concentrates on the data gathering equipment and an analysis of this unique data set. This initial testing has revealed impact acceleration peaks up to and exceeding 400m/s2 (40g) for a period of about 20ms. These values were a result of an impact with waves of moderate size (∼1m). It was therefore concluded that the impact is of a significant nature and further work should be performed to determine more concise ride characteristics for the IRB. From that it is hoped that methods will be discovered to lessen the impact on the crew with the aim of decreasing the injury rate.

Inflatable rescue boat-related injuries in Queensland surf lifesavers: the epidemiology – biomechanics interface

The objective was to describe the relationship between epidemiological and biomechanical factors in the causal pathway of inflatable rescue boat (IRB)-related injuries in Australian surf lifesavers; to develop epidemiological and biomechanical methodologies and measurement instruments that identify and measure the risk factors, for use in future epidemiological studies. Epidemiological and biomechanical models of injury causation were combined. Host, agent and environmental factors that influenced total available force for transfer to host were specified. Measurement instruments for each of the specified risk factors were developed. Instruments were piloted in a volunteer sample of surf lifesavers. Participant characteristics were recorded using demographic questionnaires; IRB operating techniques were recorded using a custom-made on-board camera (Grand RF-Guard) and images of operating techniques were coded by two independent observers. Ground reaction forces transmitted to the host through the lifesavers feet at the time of wave impact were measured using a custom-built piezoelectric force platform. The demographic questionnaire was found practical; the on-board camera functioned successfully within the target environment. Agreement between independent coders of IRB operating technique images was significant (p < 0.001) with Kappa values ranging from 0.5 to 0.7. Biomechanical instruments performed successfully in the target environment. Peak biomechanical forces were 415.6N (left foot) and 252.9N (right foot). This study defines the relationship between epidemiological and biomechanical factors in modifying the risk of IRB-related injury in a population of surf lifesavers. Preliminary feasibility of combining epidemiological and biomechanical information has been demonstrated. Further testing of the proposed model and measurement instruments is required.

Automated image analysis technique for measurement of femoral component subsidence in total hip joint replacement

A new technique for the measurement of subsidence of the femoral components is proposed. The method relies on the implantation of two ball markers around the femoral stem. A single radiographic image of the hip is analysed using image-processing techniques to minimize subjectivity related to manual identification of landmarks. Dimensions of the stem are used to correct for magnification and out-of-plane rotations resulting from radiographic positioning. This technique has been applied to a specific design of implant (Exeter). A study of the effect of radiographic positioning has been conducted using a cadaveric bone phantom. Results for the variation in the measurement of axial migration compared to the neutral position (in millimetres) were: 0.942 (10 degrees extension); 0.347 (20 degrees flexion); -0.435 (40 degrees internal rotation); 0.187 (30 degrees external rotation) for distances measured between the bone marker and the implant. Results for distances measured between the implant and the cement centralizer were: 0.107 (10 degrees extension); -0.277 (20 degrees flexion); 0.085 (40 degrees internal rotation); 0.280 (30 degrees external rotation). The variations from within a more realistic range of positions demonstrate that axial migration measurements of ca. 0.5 mm between the bone and implant, and less than 0.3 mm between the implant and the bone cement, may be expected.

Neural Networks in Cardiac Electrophysiological Signal Classification

The aim of this work was to develop a method by which intra-cardiac electrograms could be classified. A new algorithm for training this particular network has been established and applied to the task of finding the onset times of intra-cardiac electrograms. The algorithm is based on adding a choice function to the combination function of each neuron. The choice function enables the network to consider delays in each of its synapses. The gradient of error is then calculated with respect to the weights and delays. A synaptic delay-based artificial neural network was implemented using MATLAB and used to detect the onset times of the atrial, His and ventricular electrograms from the His catheter recordings. Results from a subset of a clinical, 12-channel electrophysiology study demonstrated the ability of the network to successfully identify peak potentials and onset times. Errors in detection of onset times were in the range of 1–2 ms. This method, which does not utilise traditional windowing and/or thresholding operations, can be effectively used to detect temporal patterns in a range of electrophysiological and biological signals.