Issues and themes in computer aided design for external prosthetics and orthotics

Assessment of the non-linear behaviour of plastic ankle foot orthoses by the finite element method

The stiffness characteristics of plastic ankle foot orthoses (AFOs) are studied through finite element modelling and stress analysis. Particular attention is given to the modelling and prediction of non-linear AFO behaviour, which has been frequently observed in previous experimental studies but not fully addressed analytically. Both large deformation effects and material non-linearity are included in the formulation and their individual influence on results assessed. The finite element program is subsequently applied to the simulation of a series of tests designed to investigate the relation between AFO trimline location and stiffness for moderate and large rotations. Through careful consideration and identification of key modelling parameters, the developed finite element solution proves to be a reliable and effective alternative means of assessing variations of a typical plastic AFO design so that particular patient requirements could be met, in the long term.

Clinical evaluation of trans-tibial prosthesis sockets: a comparison between CAD CAM and conventionally produced sockets

This study is an evaluation, from the patient's point of view, of CAD CAM prosthesis sockets compared with conventional sockets. Twenty-two trans-tibial amputees were divided into two groups. One group was provided with a CAD CAM (CAPOD) socket, the other with a conventionally made one. After one month the groups were evaluated with regard to subjective experience, the judgement of a prosthetist and a physiotherapist, social variables and objective gait parameters. Then the groups switched over to the other type of socket, and after another month a new evaluation was performed. The study design was a single-blind study. In total 175 variables were evaluated. No difference was found between the two types of socket, except for a lower number of terry cloth stockings used in the CAD CAM socket. As the standard of conventional prosthetics in Sweden is considered to be high, the results were considered as satisfactory. The quality of the CAD CAM sockets was at least at the same level as conventionally made ones.

Technical evaluation of a CAD system for orthopaedic shoe-upper design

Computer aided design is now employed routinely in the volume shoe trade. New styles are developed on a three-dimensional image of the last followed by automated pattern generation and engineering. It is suggested that such systems could be useful in the orthopaedic footwear industry although the different requirements for these bespoke products need careful consideration. A clinical trial has been conducted on the Shoemaster (Clarks Shoes) upper design system both to assess its technical capabilities and to consider its role in improvement of service and cosmetic appearance. This particular system works throughout on a three-dimensional representation of the shoe last, which offers particular advantages for integration with shape capture and reproduction. The report concentrates on the technical evaluation to assess (a) its ability to work with unusual last shapes dictated by medical requirements and (b) its potential for integration into a complete computer system for design of both shoe lasts and shoe uppers. The trial indicates that this particular system is promising in both respects.

Clinical trial of a computer-aided system for orthopaedic shoe upper design

A trial has been conducted to produce the uppers for orthopaedic shoes using an existing commercial computer-aided design system. The aims of the trial were to confirm that a CAD system developed for the volume shoe trade (Shoemaster from Clarks Shoes) could be used for the upper design of orthopaedic shoes and to assess the contribution of professional shoe design on cosmesis and acceptability of these shoes. A small number of adult diabetic patients and children with foot deformities were selected, all of who had previously been prescribed and issued with special shoes. The existing lasts for these patients were digitised, and new styles developed on the CAD system over a 3D image of the last. Pattern pieces were cut automatically and the uppers closed. Lasting was done as normal at the two collaborating orthopaedic companies and the shoes supplied to the patients. The CAD system proved successful in coping with orthopaedic last shapes and shoe requirements. Professional design produced fashionable and cosmetically-pleasing styles within the constraints imposed by the underlying medical conditions.

An evaluation of computer aided design of below-knee prosthetic sockets

Forty-eight below-knee amputees compared sockets designed using CANFIT computer aided design (CAD) software with sockets designed using conventional methods. Each subject was fitted by one prosthetist who used conventional techniques and one who used the CANFIT system to design the socket. Prosthetists alternated design methods for each new subject. The prosthetist using the conventional techniques was allowed up to 2 design attempts and the prosthetist using the CANFIT system was allowed up to 5 design attempts. After 2 design attempts with each method 21% of the subjects preferred the CANFIT design socket. Following up to 5 attempts 54% preferred the CANFIT designed socket. A jury of experts made an assessment of the CANFIT system and of CAD in prosthetics. The jury did not think that the version of the system tested was cost effective but that at the rate that it was improving it would become such within 3 to 5 years. The jury noted that, as well as monetary benefits, CAD presents the possibility of benefits in other areas such as research and teaching. A number of specific suggestions regarding the use and development of CAD in prosthetics were also made.

Changes in plantar surface shape induced by corrective forefoot eversion

An investigation is presented of the change in shape of the plantar surface of the foot when the forefoot is everted (prohated) from its natural unloaded orientation into a corrected position frequently used during shoe insert fabrication. Both free and corrected casts were made of 13 asymptomatic feet using established casting techniques. Digital scans capture each plantar surface shape into a computer where an analysis of the transverse slope of the plane is made at various longitudinal locations between midheel and metatarsal head regions. The profile of the slopes show results which are consistent with pronation about the midtarsal joint. These results may be useful as a first stage in establishing the appropriate shape corrections to be used in a computer-aided design system for shoe insert design.