Alan Turner-Smith

Clinical investigation of the pressure and shear stress on the trans-tibial stump with a prosthesis.

A system for measuring pressures and bi-axial shear stresses at the body support interfaces has been developed. This system has been used, in five unilateral trans-tibial amputees, to investigate the stresses at multiple points on the residual limb and prosthetic socket interface during standing and walking. The subjects investigated regularly used a patellar-tendon-bearing socket. The maximum peak pressure at the measured points was 320 kPa over the popliteal area during walking. The maximum shear stress was 61 kPa over the medial tibia area. Variable wave-forms of stress during walking were observed at the different measured points. The influence of the angular alignment on the stresses was investigated on one subject. It was found that a miss-alignment of +/- 8 degrees produced a change in peak longitudinal shear stress of between 8% and 11.5%.

Development of a non-linear finite element modelling of the below-knee prosthetic socket interface

A non-linear finite element model has been established to predict the pressure and shear stress distribution at the limb-socket interface in below-knee amputees with consideration of the skin-liner interface friction and slip. In this model, the limb tissue and socket liner were respectively meshed into 954 and 450 three-dimensional eight-node isoparametric brick elements, based on measurements of an individuals amputated limb surface; the bone was meshed into three-dimensional six-node triangular prism elements, based on radiographic measurements of the individuals residual limb. The socket shell was assumed to be a rigid boundary. An important feature of this model is the use of 450 interface elements (ABAQUS INTER4) which mimic the interface friction condition. The results indicate that a maximum pressure of 226 kPa, shear stress of 53 kPa and less than 4 mm slip exist at the skin-liner interface when the full body weight of 800 N is applied to the limb. The results also show that the coefficient of friction is a very sensitive parameter in determining the interface pressures, shear stresses and slip. With the growth of coefficient of friction, the shear stresses will increase, while the pressure and slip will decrease.

Frictional action at lower limb/prosthetic socket interface

The frictional action at stump/socket interface is discussed by a simplified model and finite element model analyses and clinical pressure measurements. The friction applied to the stump skin produces stresses within tissue and these stresses may damage the tissues and affect their normal functions. The combination of normal and shear stresses is considered to be a critical factor leading to amputees discomfort and tissue damage. However, friction at the stump/socket interface has a beneficial action. A simplified residual limb model and a finite element model using real geometry have been developed to analyse the support action of friction. Both results show that the friction plays a critical role both in supporting the load of the amputees body during the support phase of the gait cycle and in preventing the prosthesis from slipping off the limb during swing phase. Pressure at the below-knee socket during walking were measured with conditions of different friction. The results reveal that a larger pressures was produced at the lubricated interface than at the normal interface. A proper choice of coefficient of friction will balance the requirements of relief of load stress and reduction of slip with the general ability to support loads.

The reaction of skin and soft tissue to shear forces applied externally to the skin surface

The reaction of skin and soft tissue to shear force applied externally to the skin surface has been investigated by the experimental measurement of skin blood flow and model analysis of internal stresses. Skin blood flow has been measured using laser Doppler flowmetry while variable shear forces and normal force were applied to the skin surface. The experimental results show that the skin blood flow is reduced by increasing either normal force or shear force; the magnitude of the reduction being nearly proportional to the resultant of the normal and shear forces. The internal stresses were analysed by simplified models incorporating elasticity theory. The analyses indicate that shear force changes the stress distribution mainly in the superficial layer of the soft tissue and increases the stress in the area ahead of the direction of application; the maximum internal compression stress was found to be determined by the resultant of normal and shear forces. The study suggests that the resultant force is the most critical parameter in assessing the effect of load applied to the skin; and shear force has the same effect on skin and underlying tissue as normal force.

The influence of the length of lower-limb prosthesis on spinal kinematics

OBJECTIVE To examine the immediate effects of a change in prosthetic length on the kinematics of the lumbar spine in lower-limb amputees. DESIGN An experimental study with repeated measurements of lumbar spine movements under conditions of different prosthetic lengths. SETTING A free-standing rehabilitation center in the United Kingdom. PARTICIPANTS Twenty unilateral below-knee amputees. INTERVENTION Patients performed anatomic movements of the lumbar spine in standing and a sit-to-stand activity. Changes in prosthetic length were produced by placing a wooden block under the prosthetic and sound legs. MAIN OUTCOME MEASURES The positions of the pelvis and the lumbar spine in standing and the movement patterns of the lumbar spine were recorded by an electromagnetic tracking device. RESULTS A change in prosthetic length produced lateral tilt of the pelvis and lateral bending of the spine in standing. The mean maximum magnitudes of lateral bending and axial rotation toward the sound and prosthetic sides were different. Subjects exhibited lateral bending and axial rotation when they performed the flexion movement. There were also changes in the direction of coupling between lateral bending and axial rotation in some subjects. CONCLUSION A change in prosthetic length or leg-length inequality altered the kinematics of the lumbar spine.

Adapting the homes of older people: a case study of costs and savings

Meeting the demand for independent living from the increasing number of older people presents a major challenge for society, government and the building industry. Older peoples experience of disabling conditions can be affected by the design and layout of their accommodation. Adaptations and assistive technology (AT) are a major way of addressing this gap between functional capacity and the built environment. The degree of adaptability and the differences in the average cost of adaptation of different types of property are large and there is major variation within property type. Based on a series of user profiles, it was found that a comprehensive package of adaptations and AT is likely to result in significant economies arising from a reduction in the need for formal care services. This finding is sensitive to assumptions about how long an individual would use the adaptations and AT, as well as to the input of informal care and the nature of their accommodation. The present study, which focused on social housing, has implications for how practitioners specify ways of meeting individual needs as well as providing a case to support the substantial increase in demand for specialist adaptation work.

Older people and mobility in the home: in search of useful assistive technologies

A number of assistive technologies exist to help older people with their indoor mobility needs and there is an increasing recognition that older people are capable of being critical and active consumers of these technologies. This paper reports on a study that used focus groups and informal trials to explore older peoples perspectives on their indoor mobility problems, their ideas on what assistive technologies might resolve these problems and their evaluation of assistive technologies that were developed in response to these ideas. The analysis of the results from the four focus groups led to the development of a stair-climbing aid and a new cataloguing aid. The analysis of the results from the informal trials produced useful feedback on the design of the two products and indicated some limitations to the focus group methodology which could be addressed in future research.

Assistive technology and older people: Listening to their views

The growing proportion of older people in the United Kingdom requires policies that are cost‐effective and responsive to their needs. Both these factors have led to growing emphasis on policies which enable older people to remain in homes of their own. Older people are becoming more vociferous in expressing their views and are being encouraged to do this. This article reports on three pieces of research funded by the Engineering and Physical Science Research Council (EPSRC) which have attempted to draw on the views of older people about assistive technology and its role in staying at home policies.

Review of Wheelchair Services in England

This article reviews the results of investigations into wheelchair service provision in the United Kingdom since its devolution to National Health Service trusts in 1991. The following key issues persist: – Funding: The existing dilemma is to find how far a comprehensive service can be provided in a climate with decreasing, real-term funding. – Staffing: The availability of specialist staff on a multidisciplinary team is variable across the country. Some people are not being used in a manner that is suitable to their education and training. – Education and training. Educational backgrounds are variable; however, guidelines for standards have been published for occupational therapists, physiotherapists and rehabilitation engineers. – Accessibility: Users are often not provided with enough information to feel that they have been able to contribute to the prescription of their wheelchairs. – Assessment and prescription: This procedure varies from being based on a referral form to individual meetings between the therapist and the user. – Audit. User satisfaction and the provision of data for purchasers are the advantages of doing regular audits. Where the standards of provision are decided at local level without national guidelines, it is important that information about successful outcomes on limited resources is shared among service managers, therapists and rehabilitation engineers.