Feasibility study for a controllable orthotic knee joint.

PURPOSE: The purpose of this study was to demonstrate the feasibility of producing an orthotic knee joint that could lock and unlock during ambulation for eventual use in a reciprocating gait orthosis (RGO) for severely disabled patients. METHOD: Three prototype orthotic knee joints incorporating braking mechanisms were designed and manufactured to demonstrate their ability to withstand a maximum calculated sagittal plane bending moment of 73 Nm. Each was then subjected to bench trials to test their performance against the required specification. RESULTS: Although all three joints achieved the requirement to sustain the specified externally applied bending moments, the hydraulic disc brake system proved significantly superior and was selected for more comprehensive testing. CONCLUSIONS: The results confirmed the feasibility of utilising a hydraulic braking mechanism within an orthotic knee joint to withstand the knee flexing moments during walking in a lower limb orthosis. This gave the development group confidence to progress to the prototype design phase with the specific aim of eventually incorporating such a joint in an RGO designed for severely disabled patients such as those with complete paraplegia up to level T4 and those with severe neurological dysfunction.

A rehabilitation device data logging system.

PURPOSE: The difficulty of recording service history of rehabilitation devices makes it impractical for prescribing centres to monitor treatment effectively, or implement maintenance and replacement policies that permit safety and economic viability to be fully complementary. An approach to providing such a facility has been investigated, so that specified treatment can be monitored or device replacement matched to the functional activity of the patient. METHODS: A two-channel data logger has been developed that can record, over periods in excess of 12 months, information in an event-monitoring channel; and in the second channel a varying analogue signal at the time an event occurs. In addition a downloading interface allows data to be transferred and then processed in a personal computer during a routine patient visit. RESULTS: Laboratory testing demonstrated that the system recorded events accurately. Field trials verified a battery life exceeding 12 months for continuous routine monitoring of twice daily orthosis application in the event logging channel. The analogue channel was tested by applying known signals to the logger at the time events were monitored, and comparing the output to the input signal. OUTCOME: The feasibility of routinely monitoring the use of rehabilitation devices was successfully demonstrated and production development is now being undertaken.

Reciprocal walking orthosis with composite material body brace: initial development.

Reciprocal walking orthoses are routinely used by thoracic lesion patients for ambulation using crutches. A primary reason for their prescription is to provide therapeutic benefit and improved independence. To achieve this, maximum efficiency of walking and acceptance of the device is necessary to promote long-term compliance. Lateral rigidity in the orthosis influences walking efficiency, but the structural properties of conventional techniques for producing a sufficiently rigid body brace makes them unattractive. Currently patients and clinicians are forced to choose between greater efficiency or cosmesis of the orthosis. Composite materials have the potential to permit the required rigidity in a structure that is less obtrusive. However, their material properties could lead to unsafe forms of failure unless suitable manufacturing methods are devised. It is therefore inappropriate to supply prototypes to patients for field evaluation until laboratory investigation of innovative production methods has ensured that the orthosis is safe. A production technique has been devised that is ostensibly suitable. Prototype body braces have been tested and have been shown to have improved structural properties and safe failure modes. A test programme implemented on a complete concept orthosis has confirmed that improved lateral rigidity can be achieved with a less obtrusive body brace, and that it will behave safely for long enough to permit field evaluation.

Transportable two-dimensional gait assessment: routine service experience for orthotic provision.

PURPOSE: The purpose of the pilot service was to establish the potential of the newly developed system to achieve, in a community setting, more effective orthotic outcomes for patients in whom alignment of ground reaction force is an important treatment objective. METHODS: Twelve visits were arranged to a paediatric community physiotherapy department. Up to six patients at each visit were selected for assessment of their lower limb orthotic prescription. The patient's gait was assessed using the video vector generator to determine alignment of ground reaction force. Where necessary, adjustments to the orthotic set-up were made to achieve more closely the stated objective. At the conclusion a specification of the orthosis was agreed. RESULTS: In only two of 61 assessments that were conducted was it not possible to achieve a useful outcome. CONCLUSIONS: Improvements in biomechanical alignment were achieved in more than 68% of assessments. The pilot service was sufficiently successful for it to be extended to a routine clinical service.

Evaluation of safety and reliability in an infant reciprocal walking orthosis.

In response to new demands for infant walking orthoses consideration was given to the development of a device for this category of patient. A specially developed hip joint with the required structural properties (Woollam et al., 2001) provided an opportunity for this development. Earlier structural assessment, and limited cyclic load testing of key elements of the orthosis (primarily the body brace), confirmed that a safe device for evaluation with patients could, theoretically, be produced. A provisional prototype was therefore designed and manufactured for initial structural testing of the complete infant orthosis (Stallard et al., 2001). Efficiency of walking is strongly influenced by the lateral rigidity of the orthosis. Monitoring the structural performance of the provisional infant design indicated it would equal or improve on the stiffness of that achieved in the adult specification. Additionally, relative strength was comparable with the adult version, which has proven to be safe and reliable in many years of routine prescription. This, together with the limited cyclic testing of the complete orthosis (Stallard et al., 2001), gave confidence that it was safe to proceed with controlled field evaluation of the infant design when supplied as a rehabilitation engineering device within the provisions of an ISO9001 and EN46001 QA System. This additional study of controlled patient use, and further representative cyclic load testing in parallel with the field evaluation, had established the long-term structural safety of the orthosis. Wider application is now to be introduced through completion of the EC (European Community) Medical Devices Directive formalities.

Structural design and performance of a rear support walking frame.

Rear support walking frames provide predetermined vertical support for patients with dysfunctional lower limbs that have limited active control; the support is provided through a spring-loaded boom hinged on an upright stanchion mounted at the rear of a wheeled frame within which the patient ambulates. The application of these frames for total-body-involved cerebral palsy patients, in combination with a walking orthosis, has highlighted a number of practical problems that need to be addressed for the system to become fully viable. A composite material prototype walking frame has been developed that permits the patient to be transferred by a single carer without the need to use inappropriate manual handling techniques. The frame has improved structural properties, with stiffness in the sagittal and coronal planes increasing by between 50 and 100 per cent. Evaluation with patients showed that the greater structural stiffness permitted the objective of improved continuity of walking to be achieved. The strength of the frame is such that it can accommodate patients of up to 80 kg, more than twice that possible in the earlier system. Since the structural yield point is approximately twice the maximum working load, the device should not be prone to unacceptable fatigue characteristics. Despite the use of carbon composite materials (which have brittle failure characteristics), the mode of failure is of progressive collapse and is therefore inherently safe. The successful outcome of prototype testing has justified production development. Work is now proceeding on a design that incorporates further improvements in structural performance and ease of manufacture.

An infant reciprocal walking orthosis: engineering development.

The growing trend of prescription of reciprocal walking orthoses for children under the age of 5 years has created a requirement for a new design of orthosis in this category. In response to this new demand, a prototype orthosis for infants, incorporating a specially developed hip joint and manufactured as a rehabilitation engineering device within the provisions of the EC Medical Devices Directive, has been produced and tested. A design feature that strongly influences the efficiency of walking is the rigidity of the body brace structure. Monitoring the specific structural performance of the body brace intended for infants showed that it would equal or improve the stiffness achieved in an orthosis for adults. Additionally its strength was comparable with the adult design, which has proven to be safe and reliable in many years of routine prescription. Incorporation of the infant body brace within a complete orthosis provided a structure of more acceptable physical dimensions for these more diminutive patients. The orthosis showed no incipient sign of failure after 100,000 cycles of representative service loading equivalent to that imposed by a 20 kg (5-year-old) patient. The results of structural assessment and cyclic load testing confirm that the design of the orthosis sufficiently satisfies the statutory requirements for devices that are safe and fit for purpose to permit field trials with patients.

A rear support walking frame for severely disabled children with cerebral palsy: initial development.

Ambulation for patients with total body involved cerebral palsy poses greater problems than those encountered in providing reciprocal walking for thoracic lesion paraplegic subjects. Experience with a prototype system showed that an orthosis which controls the movement of the lower limbs, in combination with a walking frame giving anterior support, enables such patients to walk. Despite shortcomings which restricted the use of the system to an indoor environment it provided a sound basis on which to examine walking frames to address the problems which had been identified. A review of these devices showed that the most effective means of achieving this aim is the use of a wheeled walking frame which provides vertical support and truncal alignment via a sprung pantograph mounted to the rear of the patient (rear support walking frames). Trials were conducted with two existing rear support walking frames. These indicated their potential for severely disabled patients, but also identified the need for higher stiffness in the structure and more sensitive control of vertical support to be achieved if effective ambulation in a wider range of environments was to be made possible for the target group. Prototypes based on an existing frame, which took account of the specification requirements, were produced for four new total body involved cerebral palsy patients with the same degree of walking dysfunction. Three of the patients were able to walk in a much wider variety of environments than any patient in the original system. A number of other issues related to transfer and steering were identified as requiring further development.

Feasibility study on a composite material construction technique for highly stressed components in reciprocal walking orthoses for paraplegic patients.

Reciprocal walking for thoracic level paraplegic patients using reciprocal walking orthoses has become a routine treatment option. Two general design options are currently deployed within an overall treatment regime. Research has shown that one has better walking efficiency but is cosmetically less acceptable to the patient. Design analysis and experimental data have shown that a major factor in improved walking efficiency is the lateral stiffness of the body brace section of the orthosis. This is the area where problems of cosmesis in the more efficient orthosis are perceived because of the employment of metallic structures. The use of composite material structures to achieve shapes which are more closely conforming to the patient is an attractive option. However the brittle nature of these materials makes it unlikely that the requirement for the ductile failure mode will be achieved from a straightforward moulding. A new construction technique has been devised which has the potential to provide a safe failure mode with greater stiffness and lighter weight. This feasibility study has been undertaken to demonstrate its potential so that further work can be justified which will provide sufficient evidence to support a patent application. The successful outcome of the study, in which stiffness was increased by 60 per cent with a weight reduction of 50 per cent and a failure mode comparable with the original metal structure, suggests that further work will enable the dilemma in the choice of orthosis to be resolved.