Microprocessor Controlled Prosthetic Knees circa 1977

In preparing for the presentation on microprocessor-controlled knees, I was struck by how clearly earlier researchers had anticipated the present state of the art in prosthetic components. In particular, the work of Professor Woodie Flowers at the Massachusetts Institute of Technology was full of insights. I vaguely remembered being aware of the work of his group in the mid-1970s, when I first entered the field, but I lacked the experience and vision to appreciate the contribution at that time.

His publication titled "Feasibility of an Active Control Scheme for Above Knee Prosthetics [Grimes, Flowers & Donath; J Biomedical Eng; Nov 1977; pp 215-221] is an excellent primer to help understand the concepts and advantages of today's microprocessor-controlled knees. A quarter of a century ago, Professor Flowers' group built a massive electrohydraulic controller that was connected by flexible lines to an experimental prosthetic knee that could be mounted on a SACH foot and connected to a duplicate of the socket of that era. The several hundred pound controller was in turn connected to a computer, which was inordinately expensive and was the size of a small room - in those pre-PC days.

Two young, active unilateral transfemoral amputees walked on the simulator-controlled knee, as least within the limits of the hydraulic umbilical lines that tethered them to the electrohydraulic controller. [One of Dr. Flowers research subjects was a traumatic amputee who graduated from Northwestern University the year before I did, and is now a successful CPO in New England. Ironically, he had to wait nearly a quarter of a century for the commercial availability of the self-contained microprocessor controlled stance and swing control hydraulic knee in his current prosthesis.]

Dr. Flower's experiment was intended to determine if such a complex system offered any discernable advantages for the amputee. He used three sets of sensors for input to determine how to adjust the hydraulic knee resistances: a knee position sensor, a load cell, and a shoe instrumented with simple footswitches to determine heel strike, foot flat, heel off, and toe off respectively. It is interesting to note that today's microprocessor-controlled SNS units also use knee position and loading inputs. [One of the major accomplishments of these experiments was to prove that a sufficiently powerful computer could make the necessary calculations and control the servo motor that opened and closed the hydraulic valves in real time. Today, a microchip weighing a few grams has sufficient computing power to perform such calculations dozens of times per second!]

After instrumented gait analysis verified that the apparatus itself did not alter the amputees' gait from that with their conventional prostheses, Flowers then wrote a program so the tethered knee would provide sufficient stance control to permit controlled knee flexion in early stance, as well as respond instantly to changes in the amputee's cadence. Both amputee subjects quickly learned to walk on this apparatus, the world's first microprocessor-controlled prosthetic knee, and both expressed a preference for such a device over their own prostheses. Gait analysis demonstrated much more normal kinematics that are possible with simpler knees.

This paper concluded by noting that the results were very promising when the amputees walked on the level ground in the laboratory, and that the power requirements suggested that it would be feasible to develop such a component. The authors also concluded that, "There is no appreciable difference in the peak displacement of the body c.g....These factors indicate that the extend-flex-extend pattern at the knee may not be as important to energy consumption as previously thought....For level walking, additional swing control may be necessary to abolish the c.g. peak during midstance on the amputee's natural limb."

Reader Comments: Read all user comments Help me please! I´m 18 years old girl from Finland I paralysed 3 years ago in a snowboarding accident. My injury is in the area of TH 11-12. I would want to know if UTX Swing orthosis is good for me. I can move (swing) my feet from the hip and another (lef... read more - Ulla Kulju   12/26/2004 Re: Help me please! Thank you for this inquiry, Ms. Kulju. It is possible that you would be a candidate for the UTX or for one of the other Stance Control Orthoses, but the only way to answer this question would be to arrange a personal examination by an orth... read more - John Michael   12/27/2004 I want to find a Journal about UTX orthoses I want to find a Journal about UTX orthoses. Where can I find a paper? - Kang sungjae   1/15/2003 Re: I want to find a Journal about UTX orthoses help - hashem   2/12/2006 Re: I want to find a Journal about UTX orthoses To the best of my knowledge, any refereed articles on the UTX will be in Dutch. I don't have access to that literature. You may be able to contact Ambroise Holland for more information. --John Michael CPO - John Michael CPO   1/19/2003 Microprocessor leg Hi, I am trying to do a project on microprocessor legs. Can you please let me know which knees are the best out in the market? I will like to compare them and try to understand how they work. - Yesenia   12/9/2002 Re: Microprocessor leg There's no short answer to such a question. As of December 2002, there are basically three MP controlled prosthetic knees commercially available in North America. The Blatchford IP+ is a pneumatic swing phase control knee; the Blatchford ... read more - John Michael   12/9/2002 false leg 1967 Dear John Michael, Can you help me , I am the costume designer for the play 'Buried Child' by Sam Shephard.[ Belvoir St Theatre in Sydney , Australia][set in 1967] One of the key characters is an amputee, he has false leg from above ... read more - Julie Lynch   7/13/2002 Re: false leg 1967 The external appearance of prostheses did not change much until the 1960s. Prior to that time, almost all artificial limbs were made primarily from wood. Due to the hard out structure, this type is termed "exoskeletal" construction. Most... read more - John Michael   7/14/2002 UTX orthosis I have read a few articles about the UTX technology. I am a polio victim and wear a full leg brace. Where would I find out more and perhaps be able to purchase such a brace? - Ron Rensink   1/24/2002 Re: UTX orthosis help me - hashem   2/12/2006 Re: UTX orthosis UTX is available from Becker in the USA as of September 2002, and a variation called the FreeWalk is available from Otto Bock as of March 2002. --John Michael CPO - John Michael   12/9/2002 microprocessor leg hi john, is there a picture existing of this microprocessor leg ? i could not find picture material concerning this product. thank you robert - Robert KAITAN   10/18/2001 Re: microprocessor leg Happy Holidays Robert! I apologize for the delayed reply, but I have just now realized that people might post queries many months after these Corners are archived. Unless I happen to stumble onto an old Corner, I have no way to tell when... read more - John Michael CPO   12/18/2001 Thanks I m working in Honduras with Handicap International, it s really nice that some book are translated in spanish, we dowload the all the part we could and we used it as reference for a manual of procedure that we are doing. Thanks for all t... read more - Isabelle Couture cpo   5/1/2001 Re: Thanks Delighted to know that you have found this resource helpful. --John Michael CPO - John Michael   12/9/2002