Reflections on CAD/CAM in Prosthetics and Orthotics

John W. Michael, M.Ed., C.P.O.

The computerization of contemporary manufacturing has been termed the Third Industrial Revolution.¹ The rapid advance in microchip technology over the past five years, combined with drastic reductions in cost, have helped make Computer Aided Socket Design (CASD) and Computer Aided Manufacturing (CAM) a clinical reality in prosthetic practice.²

As recently as 1985, such efforts were widely viewed as experimental, even by the developers, and most CASD sockets were not comfortable enough for long-term use.³ However, at present there are several software/hardware packages available which permit successful fitting of below-knee prostheses after an average of two check sockets.⁴ In some instances, the patients prefer the "experimental" prosthesis to their definitive one!⁵

What is the Certified Prosthetist-Orthotist to make of all this? Although no one has any definitive answers to such questions, this author will offer some observations and opinions for consideration in hopes of stimulating additional discussion and exploration of this rapidly evolving area.

The author's first opinion is that:

1. Computerization will come to P & O whether we want it or not.

There are numerous reasons for this view, not the least of which is observation of the inexorable infiltration of computerization into other fields. As recently as 20 years ago, internal experts pontificated about the poor quality and unreasonable cost of digital watches. But while the Swiss tried to protect their centuries-old skilled craftsman approach, others pursued technological innovation. Today, only a few Swiss watchmakers remain, catering to a miniscule number of upscale clients.⁶ For every Rolex sold, there are literally hundreds of digital watches produced.

In a similar fashion, computerized typesetting has largely displaced an entire profession of commercial typesetters. Electronic synthesizers and multi-track recording have reduced the number of professional musicians necessary to produce a given performance, as well as the skill necessary to do so. The implications for prosthetics and orthotics are obvious.

Another factor is the growing separation of the prosthetic-orthotic consumer from the source of funding. In a very provocative and thought-provoking essay, Bo Klasson of Sweden noted that the third party funding agency has only second or third hand information about prosthetics and orthotics services, and no personal involvement.⁷ A new system providing 80% of the quality at 20% of the cost (or the reverse) will be very attractive. Only the consumer has as strong a commitment to the pursuit of excellence as the practitioner, and the rise of third party payors tends to weaken this focus.

The author's second opinion is that:

2. Current CASD/CAM techniques provide mediocre-quality prostheses at greater cost than conventional methods.

The top-notch U.S. prosthetist has absolutely nothing to gain, in the short run, by adopting computerized methods. At best, current systems are successful only for the easy-to-fit below-knee residual limb. Numerous technical barriers prevent computerized treatment of irregularly shaped limbs, grossly over or under-sized remnants, or cases complicated by poor quality skin coverage, neuromas, etcetera.⁸

Thus, the clinical prosthetist must maintain all current facilities and expertise to treat the majority of patients. CASD becomes an expense in addition to sustaining a conventional practice, and works only for the cases that currently present few if any difficulties.

However, this is not true in every practice situation. For example, under the British system of socialized medicine, the prosthetist typically takes the plaster impression, but has no direct control over its modification, socket fabrication, or bench alignment; these tasks are performed by technicians at a remote, central location.⁹ Given this customary practice, the ability to measure, modify, fabricate, and fit a check socket during one visit-all under direct prosthetist control-is a significant enhancement. The University College of London's pioneering work in this area may reflect this fact.

Another situation where CASD/CAM may hold initial promise is in developing countries. Faced with an overwhelming need for prosthetic and orthotic services, it may be possible to digitize scores of residual limbs in a brief period of time, and transmit the data electronically via modem to the capital city, where CAM facilities can rapidly produce simplified definitive limbs. ¹⁰

A third observation is that:

3. Current systems reduce the complexity of socket design by disregarding crucial data.

All currently available systems base the socket design on surface topography of the residual limb. Even the beginning prosthetic student quickly realizes that the external appearance of a residual limb offers only a primitive view of the ultimate socket. Our task as practitioners is to fit the skeletal anatomy, allowing for functional changes in the musculature, while maintaining the broadest distribution of dynamic forces possible. Tissue density, tissue mobility, and underlying structure are all evaluated by tactile examination and captured, to some degree, in the hand-molded cast.

In their desire to avoid subjective variations, current CASD designers have disregarded crucial data necessary for optimal socket fittings. Laser tomography,¹¹ passive soft-tissue plaster wraps,¹² and moire' techniques¹³ all provide external data only. The passively unsupported residual limb has such different contours from the dynamically loaded residual limb, that this data is truly superficial-in every sense of the word. Virgil Faulkner, C.P.O. warned at a recent conference about one well-recognized risk of computerization: Garbage In-Garbage Out (GIGO).¹⁸ Poor data is simply multiplied more rapidly by computer, but never corrected.

Foort's approach of generating stored video "prototype shapes" based on simple caliper and tape measurements, ¹⁴ Is even less precise. In essence, it is a reincarnation of his previously published view that most below-knee patients could be fitted with a series of prefabricated sockets. ¹⁵ Thanks to computerization, the modular blanks can now be stored on disk rather than on a shelf, and "stretched" to accommodate various girths and lengths of residual limb.

Although adjustable prefabricated sockets have found some measure of acceptance in clinical prosthetics, few will argue that the precision of their fit is equal to any custom-molded approach. Much the same criticism can be levelled at current CASD/CAM approaches.

However, this may only be a temporary problem. Krouskop, et al. have been investigating ultrasound techniques, particularly for the above-knee amputee, which provide three-dimensional data about internal and external structures, as well as tissue density approximations. ¹⁶ Others are independently pursuing similar internal imaging techniques, including Computer Aided Tomographic Scanning (CATSCAN)¹⁷ and Magnetic Resonance Imaging (MRI).¹⁸ CASD could result in an improved socket if the input data were more precise or more complete than that currently gathered manually by the clinician.

A fourth caveat would be:

4. We tend to be so enamored with computerization that we imagine benefits that really don't exist yet.

Prosthetics and orthotics is not unique in the tendency to view the world of high technology through rose-colored glasses. The authors of a recent book entitled In Search of the Most Amazing Thing: Computers, Education, and Children conclude that:

"In fact, the computer has done little that is educationally significant. What it has done is captured our imagination, and prompted us to finance possibly the biggest unfocused research effort in the world at a cost, for hardware and software alone, projected to exceed $8 billion in 1987. So compelling are the continuing fantasies that they overshadow debate about the merits of educational computing relative to other priorities."¹⁹

The authors go on to argue that although the schools should continue to explore the value of computerization, they should do so in an atmosphere of healthy criticism and pay attention to the costs involved. They note that a number of technological marvels failed to enhance education as much as originally hoped. The President of Harvard University, Derek Bok, is quoted as saying:

"Experience should make us wary of dramatic claims for the impact of new technology. Thomas Edison was clearly wrong in declaring that the phonograph would revolutionize education. Radio could not make a lasting impact on public schools even though foundations gave generous subsidies to bring programs to the classroom. Television met a similar fate in spite of glowing predictions heralding its powers to improve learning.²⁰

Given this bleak experience in the past, and the genuine limitations of current CASD systems, should the Certified Prosthetist-Orthotist ignore this emerging area or even actively oppose it? This author would advise precisely the opposite approach:

5. We should embrace, encourage, and adapt computer-aided approaches to prosthetics and orthotics, starting immediately.

There are many reasons for this recommendation, but the primary one is that, if we fail to accept and enhance this technology, other less-qualified individuals will simply fill the void. Computerization seems almost like a freight train, barreling down the tracks, directly toward prosthetics and orthotics. Today we have some chance to influence the path that train takes; at the very least, we can see it coming and plan a response other than simply being run over.

An additional reason is that all current criticisms are based on fledgling efforts. Despite genuine shortcomings in the current state-of-the-art in CASD/CAM, there may well be long-term advantages we cannot even imagine at this stage of development. To return to an earlier simile, no one anticipated-prior to the widespread availability of inexpensive, digital wristwatches-that it might become commonplace to have multiple watches, in various styles, to complement different wardrobes and social occasions. Perhaps the reproducibility of CAD/CAM devices could foster the development of specialized sockets for different sporting or recreational activities.

If current systems are relatively crude, perhaps we can test their utility by applications where a "generic" prosthesis represents an improvement. This is certainly true in many developing countries. Closer to home, CASD/CAM may be most appropriate for preparatory devices, where the rapidly changing volume and contours of the immature residual limb make precise fitting a temporary state of affairs.

Only by active involvement in the early stages of development can we hope to influence the ultimate outcome of new technology. Without the constant urging of clinical practitioners to use the computer to increase the quality of socket fitting, it may become a tool to multiply only the quantity produced. Without the continual urging of consumers for maximum options and effectiveness in prosthetic-orthotic design, we may see an era of cookbook surgical amputation followed by unimaginative pre-programmed prostheses

A final suggestion is:

6. We should resist the tendency to develop a new orthodoxy or bring computerized development under an artificial set of "standards."

Part of the inherent value in CASD and CAM is that we don't know what unanticipated byproducts they will create. If sophisticated three-dimensional visualization and measurement techniques are developed, it may become feasible to replace a socket by adding 9% for soft tissue expansion due to weight gain while leaving the bony contours unchanged. The possibility of simultaneous carving of both inner and outer wall contours might allow development of a series of "onion skin" sockets that nestle inside one another. The patient would remove or insert successively smaller sockets as his weight gain or loss dictated.

It may be useful to suggest that the individual elements of a CAD/CAM system measurements, visualization, modification, and CNC milling/manufacturing - all interface similarly, permitting easy interchange of portions from various developers. However, premature development of detailed or rigid criteria or standards will only serve to restrict creativity and experimentation.

The following quote from Snyder and Palmer could apply to prosthetics and orthotics just as well as it does to education:

"The next 15 or 20 years should be a period of intense exploration and experimentation, not of premature commitment to wrap-around software or any other stock format for the use of computers in the schools. With rigidly defined curriculum goals, often accompanied by a prescription for achieving them, there is currently little room for creative endeavor..."
"The next 15 to 20 years should in fact be just the beginning of an endless 'mess around' period. Things are just happening so fast these days that answers seem to be just around the corner There are no answers, just questions and priorities and a small collection of new tricks to help..."²¹

Conclusion

Bo Klasson is probably correct when he writes, "The computer is an instrument of great power and, for good reasons, it frightens many people."²² But the Certified Prosthetist-Orthotist must acknowledge this fear, accept it as realistic, and then move beyond it to explore the brave new world that is dawning.

Computerization does have the potential to significantly improve the state-of-the-art in prosthetics and orthotics, current limitations notwithstanding. The ability to accurately digitize and store shape and volume data opens up the possibility that successive socket fittings over the years could consist of refinements and enhancements of a basic shape proven clinically for a particular patient. It would no longer be necessary to start from scratch, and run the risk of introducing iatrogenic variables into the fitting.

Sophisticated three-dimensional datasensing devices based on ultrasound technology might allow fitting with a precision that is almost unimaginable today. If an arthritic flare-up resulted in bony exostosis, re-digitization of the residual limb could provide a three-dimensional image of the new bone to overlay on the stored image of the socket, thus identifying precisely what modification is required.

Emerging fabrication technologies may well interface with computerized design to dramatically expand our capabilities. A recent television special highlighted the development of "stereolithography," a technique whereby focused laser beams precisely solidified portions of a liquid polyurethane solution, forming a three-dimensional model with precise simultaneous control of both inner wall and outer wall contours.²³ It is but a small conceptual step from the automobile carburetor part demonstrated to an above-knee socket with infinitely variable tapering wall thicknesses: rigid frame and flexible socket created simultaneously from one compatible material.

It is possible to envision a future where CASD/CAM has developed to the point that all levels and shapes of orthopedic impairments could be digitized-from deformed feet to paralyzed trunks to amputated legs and congenital arm anomalies. If the CPO could care for all patients with the same equipment, computerized treatment would quickly become the norm. Particularly over the past 40 years, prosthetists and orthotists worldwide have rapidly incorporated new technologies into mainstream practice, provided they had practical use.

Perhaps our unspoken fears of being displaced by computerized technology will never come to pass. Some other fields have prospered along with computers. Although computerization of the office is now a worldwide phenomena, predictions of the "paperless office" made in the 1970s have failed to come to pass. In fact, computers spewing out reams of printouts have resulted in a boom for the paper industry²⁴ which no one anticipated.

Similarly, the computerized word processor has almost eliminated hand-written manuscripts. Any author can now produce a polished manuscript, legible and free of most common spelling or punctuation errors, with minimal effort. And yet, it remains as difficult as ever to produce and publish the great American novel.

In the final analysis, it is the skill and ability of the author that determines the ultimate quality of the manuscript. Computerization only enhances the process; it does not substitute for the efforts of a dedicated and talented individual.

Optimal design for prosthetic and orthotic devices requires similar skill and knowledge. If we become actively involved with computerization now, while maintaining an open but skeptical mind, it may ultimately become to the practitioner what a word processor is to the author: an incredibly powerful tool to enhance the creative process, and to record successive iterations for future enhancements.

John W. Michael, M.Ed., C.P.O., is Assistant Clinical Professor and Director, Department of Prosthetics and Orthotics, at Duke University Medical Center, Box 3885 DUMC, Durham, North Carolina 27710, (919) 684-6890.

References:

Klasson, B., "Computer-aided Design and Computer-aided Manufacturing in Prosthetics and Orthotics," Amputation, Surgery and Lower Limb Prosthetics, Oxford, Blackwell Scientific Publications, 1988, pp.335-344.
Bererschot, G., "European Experience with CASD/CAM," presented at the ISPO Workshop on CADCAM in Prosthetics and Orthotics, Seattle, Washington, June, 1988.
Foort, J. R. Spiers and M. Bannon, "Experimental Fittings of Sockets for Below-knee Amputees Using Computer Aided Design and Manufacturing Techniques," Prosthetics and Orthotics International, 1985, Volume 9, pp.46- 47.
Wilkinson, Joseph, "Current CADCAM Results at University College London," presented at the ISPO Workshop on CADCAM in Prosthetics and Orthotics, Seattle, Washington, June, 1988.
Holden, J. and G. Fernie, "Result of the Pilot Phase of a Clinical Evaluation of Computer Aided Design of Trans-tibial Prosthesis Sockets," Prosthetics and Orthotics International, 1986, Volume 10, pp.142-148.
Landes, D., Revolution in Time: Clocks and the Making of the Modern World. Cambridge, MA, Harvard University Press, 1983.
Klasson, B., "Computer Aided Design, Computer Aided Manufacture, and Other Computer Aids in Prosthetics and Orthotics," Prosthetics and Orthotics International, 1985, Volume 9, pp.3-lI.
Holden, J. and G. Fernie, Ibid.
Wilkinson, Joseph, CP, personal communication, June 1988. Presently, Research Prosthetist, Bioengineering Centre, University College London, Roehampton Lane, London S215 5PR, England.
Dewar, M., "CADCAM in Developing Countries," report of a subgroup presented at the ISPO Workshop on CADCAM in Prosthetics and Orthotics, Seattle, Washington, June, 1988.
Fernie, G., G. Griggs, S. Bartlett and K. Lunau, "Shape Sensing for Computer Aided Below-knee Prosthetic Socket Design," Prosthetics and Orthotics International, 1985, Volume 9, pp.12-16.
Boone, D., "PRS Approach to CADCAM," presented at the ISPO Workshop on CADCAM in Prosthetics and Orthotics, Seattle, Washington, June, 1988.
Saunders, C., "Reconstruction ofAnatomical Shapes from Moire Contourgraphs." Biostereometrics, '82, SPIE Proceedings, August, 1982.
Saunders, C.,J. Foort, M. Bannon, D. Lean and L. Panych, "Computer Aided Design of Prosthetic Sockets for Below-knee Amputees," Prosthetics and Orthotics International, 1985, Volume 9, pp.17-22.
Foort, J., "Coping With Computer Aided Technology in Prosthetics and Orthotics," presented at the ISPO Workshop on CADCAM in Prosthetics and Orthotics, Seattle, Washington, June, 1988.
Krouskop, T., D. Dougherty and F. Vinson, "A Pulsed Doppler Ultrasonic System for Making Noninvasive Measurements of the Mechanical Properties of Soft Tissue," Journal ofRehabilitation Research and Development, 1987, 24(2), pp.1-8.
Faulkner, V., "Computerized Tomography as an Aid to Prosthetic Socket Design," Progress report in Journal ofRehabilitation Research and Development, 1986, 24(1), p.7.
Faulkner, V., "CAD/CAM of Lower Extremity Prostheses: The San Antonio System," Progress report in Journal of Rehabilitation Research and Development, 1986,24(1), p.6.
Snyder, T. and J. Palmer, In Search of the Most Amazing Thing: Children, Education, and Computers. Reading, MA, Addison-Wesley Publishing Company, 1986, p.13.
Snyder, T. and J. Palmer, op. cit., p.49.
Snyder, T. and J. Palmer, op. cit., p.73.
Klasson, B., "Computer Aided Design, Computer Aided Manufacture, and Other Com puter Aids in Prosthetics and Orthotics," Prosthetics and Orthotics International, 1985, Volume 9, pp.3-Il.
"Beyond Tomorrow," television special on December 12, 1988, Fox Broadcasting Network.
Magid, L., "Facing the Fax: Computers Lose Mail Race," Durham, North Carolina Morning Herald, Sunday, June 19, 1988.