Carnes arm and function
The Carnes arm is a sophisticated and mechanical prosthetic arm. It was developed by William T. Carnes and patented from the year 1911 on under the US Patents 760102 (artifical limb), 1046966 and 10469672287781 (artificial arm and hand). Interestingly, the more intricate mechanism that the Germans bought from William Carnes (see below) does not appear to surface in the US Patent files until 1942 (US Patent 2287781).
- Carnes arm and function
- Germany evaluates, buys and mass produces the Carnes arm
- Review of the Carnes arm after the productive post WW-I years
- Current status of the Carnes arm
- Teaching points
- Future of the Carnes arm
Arms of that design were produced in relatively large numbers both in the USA and, after the German government had bought patent licenses, by German factories.
The Carnes arm got a lot of exposure. Many orthopedists ruled the Carnes arm to be the ideal prosthesis for "intellectual professions" ("Kopfarbeiter"). But, how came that many orthopedists said that?
Because German evaluation (by non-disabled people working for a government agency around 1916) preceded advertising of the idea to purchase the patent rights (which was done rather aggressively as it appears) which preceded the actual purchase of patent rights from William Carnes by the German government (in 1916) which then preceded German mass production of Carnes derived prosthetic arms (after 1916) only after which one could see that as fine an arm this was it was most likely not the right thing for everybody. It had become outdated and relatively unpopular by 1922 and obsolete by 1935.
As current body powered technology is even older (and not outdated, superseded by better technology nor unfunctional because of that), as current myoelectric technology also builds on old ideas (and still suffers the same issues since years), old prosthetic designs per se are not necessarily a bad thing. Just because the German government built so many of these arms, and maybe sometimes for the wrong people, does not mean this clever work of art should not be inspected closely. So a closer look is warranted into what the Carnes arm was reported to offer and to be, and maybe what to learn from the history.
Germany evaluates, buys and mass produces the Carnes arm
Prüfstelle für Ersatzglieder Charlottenburg 
Germany - as a consequence of World War I - had a particular interest in prosthetic arms. So the temporary Prüfstelle für Ersatzglieder Charlottenburg was founded on February 1st 1916.
This was a governmental agency that primarily tested and recommended products and strategies for prosthetic limbs. The Prüfstelle was founded with considerable support by the VDI (Verein der Ingenieure, Germany's engineer association). About 4 years later, it was dissolved according to a board resolution on October 5th 1920, as all its (initial) tasks had been completed. After that, German government and officials continued to support amputees - but not any longer under that agency: in their final report , the author of the Prüfstelle noted that out of their initial activities, a more permanent research agency (Forschungsgesellschaft für Ersatzglieder und Arbeitshilfen) had started to take over tasks and become active in the areas of research, funding and implementation in the field of orthopedic means of support.
The work shop (Konstruktionswerkstätte) associated with the Prüfstelle was lead by Otto Schlegelmilch.
Evaluation of the Carnes arm 
The Carnes arm does not appear to be so much a brand new ground breaking invention than it seems to be an end point reached by previous prosthetic development at the time.
Cable controlled arms were known to be used since the Royal Court Mechanic Carl Heinrich Klingert in Breslau tried to imitate hand motion with his construction of a prosthesis that used 9 gut strings and a number of manually operated control switches, for an aristrocrat around 1712-1786.
The German dentist and surgical technician Pierre Ballif established in 1812, that an externally placed cable operated by remaining muscles (then fixed to a chest strap) was the way to operate a movable hand which he designed, that, in its closed position, must have appeared like a clenched fist.
The Dutch sculptor Van Peetersen developed the idea of using a shoulder (rather than chest) harness to operate the Ballif type cable controlled prosthetic parts in 1844. He also introduced the voluntary opening system and a hand shaped with thumb and finger tips somewhat extending and touching (rather than clenching a fist which was viewed as threatening gesture).
In 1860, Count de Beaufort in Paris built lightweight and affordable arms built on the aforementioned design principles then called "prothese de pauvre" (prosthesis for poor). These were the first prosthetic arms that became popular, widespread and that could be used in labor and work jobs.
Charrière built a significantly advanced arm in 1860 for an Opera singer who had an elbow exarticulation after a hunting accident. Except thumb motion and wrist flexion, all movements of a natural arm were incorporated. Most notably, elbow flexion and extension was combined with wrist pronation and supination. At the time, this arm was to be considered perfect for an Opera singer but for daily work it seemed less practical.
After Germany lead three wars in rapid succession (1864 - against Denmark; 1866 - against Italy; 1870/1 - against France) prosthetic technology was developed more rapidly.
Oskar Dalisch (who lost his left hand at the age of 14 due to an explosion) built a prosthetic hand where he used metal rods instead of strings and cables. He used pronation and supination to drive the fingers; while this forced the user to pronate to close and supinate to open the hand, the appearance of this constraint was commented as "hitherto unachieved natural appearance" (H. Gocht, 1907).
The Carnes hand (1911) combined these elegant looking features with rather complex mechanism that did achieve the same as the previous inventions. It was crafted relatively well.
Technically, warfare had changed considerably in 1870/1. A higher degree of penetrance of projectiles and increased usage of explosivs such as grenades lead to a sharp rise of injured and dead. Shortly after World War I broke out (1914), the German government realized their upper extremity prosthetics was not keeping pace with actual requirements.
The German surgeon O. Witzel (1915) wrote about the Carnes arm "the newest American hands show several special achievements such as for dressing, eating, drinking or writing that - if presented in clever succession - create the appearance of functional replacement. In reality, the many expensive and very fragile prosthetic parts do not achieve a lot more than simple prostheses".
Requirements were also clearly formulated. Dr. Ing. e..h. K. Hartmann (1919) said that "We do not just require a simple shape of the supportive device but also long durability, light weight, comfortable adjustments, rapid donning/doffing, cheap mass production, replacement materials for missing materials (leather, rubber, brass, ..) as well as easy to perform maintenance, ordering of normed spare parts, and unlimited and danger free use of the prosthetic arm for activities of daily living and for particular types of work".
Sauerbruch and cineplasty
To understand why the Carnes arm got famous, one has to consider the other big achievement and prosthetic alternative at the time: cineplasty.
The Italian Giuliano Vanghetti (1861-1940) called a new procedure he had just invented "cinematic prosthesis" or "plastic amputation" - it consisted in using remaining tendons and muscles to move a prosthetic limb. His experiments after 1896 were performed on chicken and resulted in 52 different surgical approaches.
His director - Professor Antonio Ceci, University of Pisa - praised these not yet very practical ideas as beautiful and original, and relabelled them as "cineplasty". Ceci later tested this new method on three patients (1900 to 1906); in one of the three, gangrene developed and the result was destroyed.
Italians and Germans (Payr) then continued to use cineplasty. At first, the method was reported to fail - also due to the patients not being keen on the numerous experimental re-operations necessary to reach the required result.
After World War I had started, all hell broke loose in 1915 - Sauerbruch had just returned to his newly appointed post at the University of Zürich (Switzerland) from some German military medical experience in Greifswald. He had become dedicated to help arm amputees and seemed possessed with that thought.
On a Zürich tram, he accidentally met Prof. A. Stodola, professor for mechanics at the Technical University of Zürich. Stodola suggested to use the stump's remaining muscles to operate a prosthetic hand - while it remains unclear whether Stodola had the same idea as Vanghetti earlier, or whether he had already learned about this new method previously. Both Sauerbruch and Stodola agreed that only close cooperation between surgery and technologoy could lead to the proposed innovation - as the stump would have to be fashioned to the needs of technology and the prosthesis would have to match medical requirements as well.
Sauerbruch - allegedly unaware of Vanghetti's previous work - started to conduct cineplasty experiments on sheep and dead human bodies. Encouraged from these experiments, he went back to the German war hospitals where he tested the feasibility of conducting cineplasty on war victims' arm stumps. Three slightly different techniques emerged, all of which resulted in a skin pocket that residual muscles and tendons could pull on.
To combine his main job - head of surgery at the University Hospital of Zürich - with his new calling and oportunity to become famous - use cineplasty on arm amputees - he managed to get the Germans to relocate some of their arm amputees to the war hospital in Singen between 1915 and 1918 - just north of the Swiss-German border, not too far from Zürich. In dedicated rooms ("Sonderlazarett"), Sauerbruch had taken on the tasks of (1) extending and improving his surgical technique, and (2) seeing to it that useful prosthetic hands were built that then could be used on stumps with cineplasty.
Within this setup, Dr. Alfred Stadler contributed significantly to the further development of the cineplasty technique while Dr. Stadler's wife Angela Stadler as head nurse reportedly contributed necessary dedicated nursing power to the cineplasty operations. At that time, prosthetic engineering was not anywhere near to match the new requirements of muscle power by cineplasty. So amputees spent a long time in the Singen army hospital (1915: about 16 months!, after they installed their own prosthetic workshop in 1916: about 4 months).
Sauerbruch encountered some resistance against his technique. Firstly, some amputees feared that being equipped with a prosthesis they would have to go back to work and miss out on their government disability support. Others were reluctant due to the bad condition of their stumps. After conditioning exercises, treating skin problems and healing infections, patients were then ready for surgical revision sometimes after 4 weeks already, sometimes only later. Success required intensive muscle training of the amputees. Operations were done in locoregional plexus anesthesia or general ether anesthesia. Getting skin canals to stay straight, refashioning muscles so they could actually pull real weight in people with various problematic stumps, daily cleaning of the skin channels with disinfectant and vaseline to avoid infections, babysitting of skin necroses, all that provided lots of additional work.
Building the individually crafted prostheses for each and every Sauerbruch cineplasty patient then was the ultimate bottle neck at first - and that is when the Carnes arm came into play.
At first the Sauerbruch patients were sent to orthopedic technicians all over Germany who were hopelessly overwhelmed when they saw the cineplasty results. This lead to the realization that the necessary money, mechanics specialists and a suitable setup for a dedicated Singen based prothetics factory simply could not be provided. Even though Dr. Rudolf Ritter von Aberle financially supported the installation of a dedicated factory in Singen, they only built 26 finished and 22 incomplete arms between April 1916 and June 1917.
The consequences of this massive delay in building prosthetic arms to get the Sauerbruch technique going were serious: (1) the amputees started to get used to living with one arm and thus were increasingly difficult to get trained with a prosthetic arm, (2) the amputees were missing as laborers or workers as long as they spent time waiting, (3) the mood in the hospital was bad.
Despite all that, waiting times were down to 6 to 8 weeks in 1917. Then, and as a consequence of good publicity, Sauerbruch stumps were made by other surgeons all over Germany. And amputees were sent to the Singen hospital for prosthetic fitting in increasing numbers (1915: 27, 1916: 51, 1917: 155, 1918: 241). Problem was that with World War I going on towards 1918, resources and raw materials were increasingly hard to round up. After 1918, Sauerbruch moved prosthetic factory to Munich where it operated under the name of "Orthopädische Werkstätte Sauerbruch". Prosthetic hands remained a real problem.
Prof. Stodola's first prosthetic hand was interesting but did not make it past the prototype stages. Apparently, Stodola had offered his cooperation under firm humanistic ideals and retracted all his patent applications (obviously, Stodola represented a previous manifestation of today's open prosthetics idea); Sauerbruch and other developers of prosthetic hands kept patenting their ideas and collecting the reputation and fame that war had brought them - Stodola did not want any of that and apparently felt repulsed so much that he withdrew from prosthetic business altogether.
Felix Rohrmann built a first useful hand (thumb opposing fingers 1 and 2, with passive fingers 3 and 4) that provided a pincer grip just as today's Otto Bock system hand does. However, everybody and their grandmother at the time patented their hand constructions and that showed to be a significant problem for Sauerbruch who was after modifying different designs for his own purpose. At that time everyone was trying to get a piece of what they felt was part of big business.
Purchase of the Carnes patent licenses
Given the circumstances one can understand that Sauerbruch did not find it cool to see the opening of the Prüfstelle für Ersatzglieder Charlottenburg far away in Berlin. Everyone was getting antsy about finally getting prosthetic arms. Besides, not everyone was a good candidate for cineplasty.
On February 13th in 1902, the US American mechanic William Carnes had lost his right arm above the elbow. After he had replaced an initial cosmetic arm with a satisfying arm he had constructed himself, he started to build this type of arm for other people. It just so happened that a wealthy warehouse owner, a certain Mr. Prescott, was equipped with a left sided Carnes arm. Prescott was so happy about this that he suggested to Carnes to mass produce the arm rather than manually crafting single models. When they founded a company to build Carnes arms in Kansas City, they made sure to hire as many arm amputees as they could. Thus they tried to show that the Carnes arm would allow the amputee to do shop work. This company then found Dr. Binnie, a medical doctor, as consultant. The combination of inventor (Carnes), capitalist (Prescott) and medical advisor (Binnie) was nothing new for the USA at the time - a combination unheard of in Germany.
While Sauerbruch was really in his earliest stages getting started with a very promising but risky method and unable to provide innovative prosthetics as fast as many would have wished for, the Carnes arm was already patented and then factory produced. It was extremely well packaged (though a bit outdated) technology. The Carnes arm was presented in Europe at the British-American surgeons' conference in 1913.
In 1916, it appeared that Dr. Max Cohn - a doctor and himself an amputee - published and demonstrated the performance of the Carnes arm. Due to that, countless amputees wanted the Carnes arm and the Prüfstelle had to find an affordable way to produce suitable prosthetic arms.
In a lengthy analysis, Dr. Rudolf Ritter von Aberle noted the many advantages of the Carnes arm: numerous levers and intricate gears enabled the wearer to perform more detail oriented movements that were beyond the scope of tool-like work prostheses. These activities apparently included tying a necktie (not everyone needs a prosthesis for that), picking up coins from a flat surface (hard to do even with real hands), riding a bicycle (can be done with prostheses that are not very sophisticated as well) and taking banknotes out of a wallet (check it out). As it emerged, it may well be that these tricks were more part of advertising than everyday experience.
This was apparently the type of dexterity more appropriate for "intellectual professions" ("Kopfarbeiter"). According to von Aberle, an arm as delicate and finely crafted as the Carnes arm could not withstand the heavy labor of the field and factory. Furthermore, its high price and costly repairs should reserve this arm for those patients in "intellectual professions". In short, the Carnes arm was a middle-class arm. Also, Dr. P. Guradze of Wiesbaden defined the Carnes arm as strictly for "intellectual professions" ("Kopfarbeiter").
Sauerbruch's engaged work had indeed somewhat stalled at the prosthetic end - so imagine when the Gemeinnützige Gesellschaft für Beschaffung von Ersatzgliedern m.b.H. in Berlin (founded also by initiative of the VDI) went to buy Carnes arm patents for a whopping 1,75 million Mark (roughly equivalent to about 9 million US dollars today, then considered an absolutely insane amount of money) on July 14th 1916. Sauerbruch must have been livid and outraged.
With money going in the wrong direction, Sauerbruch struggled to find a suitable prosthetic hand for cineplasty. Public competitions open to engineers did not produce convincing results - hand model constructions that were judged as not useful included models by Schulz, Troendle, Kauffmann and Spickermann, and Funk.
Given the stuation Schlesinger and Reichel of the Prüfstelle advised Sauerbruch to consider the Carnes arm as add-on to his surgical technique rather than losing too much time evaluating. They said to consider not just the current Carnes arm but - as patent licenses were bought - to also consider taking the Carnes arm a step further and working with it, modifying it. But Sauerbruch himself rejected the idea of modifying a Carnes hand for his purpose as the locking mechanisms would take away from the proprioceptive qualities of an optimal stump-prothesis combination. After this rejection, the Prüfstelle für Ersatzglieder Charlottenburg charged ahead and advertised and supported their newly acquired Carnes arm design.
Sauerbruch as well as other specialists were of the clear opinion that the real potential of the Carnes arm was greatly overjudged. While Sauerbruch at the time had no money, no workers and no factory, as he stated, he found the degree and amount of Carnes arm advertising that was conducted by Schlesinger from the Prüfstelle für Ersatzglieder Charlottenburg inaequately high.
Conversely, Schlesinger appeared to be unable to appreciate Sauerbruch's work. In fact, Schlesinger denied both Sauerbruch's cineplasty as well as Krukenberg's forearm cineplasty (1917) his recognition of their innovative and useful potential.
At any rate, Krukenberg must have been a rather original spirit as he not only came up with a highly innovative and useful surgical procedure, but he was also way ahead of his time by using interrupted galvanic currents to activate the healing muscles to give his amputees a head start; "electrogymnastics" was brand new at the time and entirely unheard of. But he mentioned that "who does this plastic operation needs to have a good understanding of the anatomy of the forearm". At that time, competitive aspects and a dynamics inside the Prüfstelle für Ersatzglieder Charlottenburg may have overrided any consideration of the amputees themselves. The Krukenberg procedure was rated by Schlesinger as an ugly result. Even more, it appears that rumors were started, and doctors and patients were actively discouraged from the Krukenberg procedure. As it emerged the hierarchy of methods was encouraged to be (1) Carnes arm first, (2) Sauerbruch's cineplasty second, (3) no prosthesis third, and (4) only then Krukenberg's forearm split.
Reality turned out differently; indeed a Krukenberg arm may appear as a new appearance to an uninformed person confronted with this situation - but both amputees and their immediate friends or relatives often do not appear to think so, and with a very few exceptions amputees that had the Krukenberg procedure done would do this again, or if they were double amputees, often requested the procedure on the other stump as well. To this day, the Krukenberg procedure can give amputees back a degree of dexterity unmatched by any prosthesis.
Besides, these surgeons must have had a strange humor related to the appearance of their surgeries; Krukenberg once remarked that "an amputated stump will always appear as disfigurement and not be aesthetic - but that is true for every stump. I still prefer the looks of my own method resembling two large fingers to the appearance of a Sauerbruch stump that features these ridges and that hole that always remind me of an asshole stitched on in the wrong spot". Conversely, Sauerbruch commented on the Krukenberg method as resulting in "two large Bratwursts". Despite these strange and humorous views, generally and by and large, surgeons eventually seemed to agree that longer forearm stumps were best treated with the Krukenberg method, shorter forearm or above elbow stumps were better treated using the Sauerbruch method.
Sauerbruch had warned that the Carnes arm not be overjudged. He was of the opinion that exploiting stump muscles was a big advantage whereas prostheses using the Baliff cable such as the Carnes arm were only for amputees that had a short or useless stump, or that did not want another operation. Along the same lines, General Medical Doctor Schultzen wrote in the year 1916 that "cosmetic arms with more or less useful features were only worn for a short amount of time as they were felt to be a burden; it would be better to advise amputees that better solutions were under development and they had to wait until these were ready". He added that "many amputees already manage well without prosthesis" so no rush was in order.
Sauerbruch broke with the Berlin establishment after the Carnes arm license purchase. His contemporary fellows in Berlin stated that "several parallel ways can lead to the goal" (of equipping amputees with useful prostheses).
Sauerbruch replied on November 18th 1916 (excerpted translation from ) after meeting with engineers in Baden:
I was invited to a presentation that aimed at showing the potential and performance of the Carnes arm. I decided to bring along some of my own operated soldiers to compare the Carnes arm performance with my Sauerbruch method. Already previous impressions of this Carnes arm had not convinced me. Instead, converting arm stumps into useful artificial limbs appears to be a much better goal.
So I visited the presentation where I met a certain Mr. Smith (an American) who had presented the Carnes arm in various presentations so far. Comparing the (low) performance of Mr. Smith and our own soldiers, several other gentlemen agreed with me that your evaluation of the Carnes arm was incorrect and unscientific and at this moment in time your evaluation is also outdated.
Mr. Smith acts as an acrobat or juggler when he presents the Carnes arm. After producing manual demonstrations for fifteen minutes his heart rate was 140 beats per minute, and he sweated profusely. Also I noted that you (the gentlemen of the ) had missed the fact that his stumps were covered with sores and eczema. Mr. Smith asked me about these as he said he frequently could not use and move the prostheses as the stumps were painful.
I therefore have to say that all of us that witnessed this demonstration had asked ourselves how you all could spend such a large amount of money for the patents of this Carnes arm and instead impede our own developments.
When Mr. Smith went on to demonstrate the Carnes arm for engineers in Mannheim, one of the engineers present wrote this about the meeting:
Mr. Smith (the American who was in Germany to show off the Carnes arm) offered important looking demonstrations of very simple looking activities of daily living. He was visibly exerted by the demonstration. The Carnes arm caused significant soreness on his stumps. Despite an almost acrobatic proficiency in juggling the Carnes arms for 5 years, Smith admitted that he was not happy with the arms himself. He had seen the success of Sauerbruch's operations and considered becoming a patient of Sauerbruch himself. [...] When comparing both, the Carnes arm may be the suitable prosthesis for a very few cases - but the Sauerbruch method is by far better, and if the prosthesis is improved, will win over the Carnes arm construction.
Sauerbruch's demonstration patients were ex-soldiers that only wore their prostheses since a few days or weeks and despite that, they could hold cards when playing cards or light matches. The difference must have been striking. Smith apparently told Schlesinger also that he wanted to get a Sauerbruch operation but it appears he ended up not doing it after all.
And even though it took him a while, Sauerbruch did find suitable prosthetic terminal devices.
In 1917, Jacob Hüfner built the legendary Hüfner-Hand. From pincer grip type hands, the Hüfner hand emerged as the best. The fingers 2 and 3 are approximated to the thumb and thus delivers grip power.
In March 1918, an ingenious hook type device (Arbeitsklaue) was published by Sauerbruch's prosthetic factory, that was then supplemented by a tension device that allowed gradual increase of tension developed by Dipl.-Ing. Müller-Gleiwitz, an amputee and a Sauerbruch patient himself. In September 1918, Müller had developed a Rohrmann based fine-grip hand with a maximal grip power that could be operated even with the smallest muscle action. The mechanism was that of repeated pull and locking as we know it today from Otto Bock's two-way hand, from Physionetic's Low Energy Sequential Action prehensor (LESA) and others. It is notable that for unknown reasons, Sauerbruch ignored these particular developments and did not mention them. - Later, the hook type device saw development of a range of add-ons that allowed even musicians to play their instruments (organ; violin).
In 1919, the DERSA ("Deutsche Ersatzgliedergesellschaft Sauerbruch) was founded - as it turned out later, with the support of the Swiss company Brown-Boveri which, as Dr. W. Boveri requested in a letter to Sauerbruch 1922, was to be kept a secret.
So despite other perceptions, both cosmetic and functional requirements finally were very well covered by Sauerbruch's method.
As it appears, the Carnes arm as well as other prostheses were well combined with the Sauerbruch technique. Many were of the opinion that the clear dichotomy - "either one is for the Carnes arm or for the Sauerbruch method" - did not play out in real life. Really, several prosthetic solutions were seen as helpful. For some patients, some were better, for others, the Carnes arm worked well, yet others required a combination. The orthopedic surgeon Biesalski wrote in 1915 that "the decisive moment in arm prosthetics was the will power of the amputee; the amputee was the one who had to exert the will power to get his stump equipped".
German factory manufacturing of Carnes arm copies 
Otto Schlegelmilch built a number of arms using design variants of the Carnes arm: He built an "arm for short below elbow stumps by Schlegelmilch", an "arm for wrist exarticulation by Schlegelmilch", an "arm for elbow exarticulation by Schlegelmilch", an "arm for Krukenberg operations by Schlegelmilch" (using the Krukenberg pincer to open and close the prosthetic hand), an "arm for exarticulation in the shoulder joint without Sauerbruch canal by Schlegelmilch" , an "arm for exarticulation in the shoulder joint using the pectoralis muscle" (a Sauerbruch canal in the pectoralis muscle was used to close fingers of the prosthetic hand) and an "arm for exarticulation in the shoulder joint using the pectoralis and the latissimus dorsii muscles" (Sauerbruch canal in pectoralis muscle to close fingers, Sauerbruch canal in the latissimus dorsii muscle to open fingers of prosthetic hand).
The Carnes arm was the design principle behind all arms at that time, but it was Schlegelmilch who went behind the designs and adapted them for various levels of amputation.
- For short above elbow arm stumps, control of the Carnes hand is described to be a bit tricky: a lifting motion (such as by lifting the shoulder) was required to switch the hand into a different mode - however to achieve that, soft leather sockets appeared to be not as useful as hard wooden sockets and cables appeared to be not as useful as wires for the "cable control".
- For below elbow amputees with short stumps, Carnes did not provide a mechanism to take advantage of the additional mobility the stump could provide. Schlegelmilch started to work on this but first attempts appeared to require cumbersome swinging motions. Ultimately, Sauerbruch canals (cineplasty) was found to offer most control.
- Below elbow amputees with mid forearm amputations were built in huge amounts by German factories particularly after November 9th 1918 (when the production went to a large scale). However, the original Carnes arm was hand made and carefully adapted to the amputee which had to be abandoned due to a big success and everyone asking for that arm on one hand, and prosthetic parts having to be normed and standardized for cheap production on the other hand. This lead to variations of the original Carnes arm that appeared to be not acceptable any more so the German factories had to take measures to produce better copies of the original Carnes arm.
- Below elbow amputees with a long stump were not noted to particularly benefit from the Carnes arm whose main feature appeared to be a clever way to automate pro-/supination based on elbow flexion which was not necessary so much for people with long stumps. Later, modifications by Biesalski used wooden sockets to improve control of pro-/supination for below elbow amputees with long stumps.
Experiences with the Carnes arm copies 
Bandages, locks: material used for bandages turned out to be crucial. Good bandage material has to be thin, soft and must not allow for stretch. Locks have to be stainless and thin not as to bulge out or damage the clothes worn over them. A real problem at the time was to pad the shoulder strap so it would not cause problems. An extra bandage was used to allow for the "Carnes-Stoss" - a special kick one would have to administer to the Carnes arm to change wrist modes.
Sockets: Wherever possible, wooden sockets were used. On one hand it provided insulation and on the other, the stiff quality allowed for optimal control.
Elbow: The original Carnes arm provided an elbow lock that many amputees found heavy and useless. While Schlegelmilch at first had the elbow locks included with the arm, many users requested that lock to be removed later. Apparently the prosthesis became significantly lighter and more useful that way.
Joint (Drehgelenk): Firstly, the joint contains some screws that are under heavy load. These lack proper securing so they come loose and repairs are frequent. The problem could be solved by using proper nuts or locking washers. Secondly, the joint contains a turning bar that requires very careful mounting by a skilled mechanic.
Wrist (Handgelenk): Compared to the original American construction, the German modification includes a lock mechanism that allows to lock the wrist in any position rather than only in certain positions. That way, even a hand bent towards the palm (volar flexion) can be locked such as when carrying a heavy load.
Hand: The original Carnes arm hand consists of Vulcan Fibre whereas the German copy was built from Electron Metal. Professor Schlesinger modified the gearbox in that a spring mechanism was added to the thumb, and an additional spring was used to avoid the hand falling out of gear. Despite that, a lot of force was required by the amputee to close the hand. With a short thumb and the way thumb and index fingers are shaped, the ability of the Carnes hand to grasp small or minute objects was well known as low. Only with certain tricks a very well trained user could grasp smaller objects. Carnes apparently tried already back in 1914 himself to modify finger shape and geometry to improve this situation - but without success. Considerable experiences collected in the prosthetic arm training ("Armschule") lead to a modification of the original Carnes hand design around 1920, that resulted in a finger/thumb geometry that we still see in the current Otto Bock system hand with a curved shape and elongated thumb. In terms of repairs, the inner parts of the hand broke at times; finger leverage axes appeared to have broken rather often.
Overall usage: The Carnes arm did require lengthy training. Also it use a lot more power to operate than other prostheses. The result was that users would regularly sweat when performing.
Review of the Carnes arm after the productive post WW-I years
In hindsight, Sauerbruch had been absolutely right.
The filigrane inner workings of the Carnes arm and its outer almost life like appearance exuded a type of fascination that many doctors (including, initially, Sauerbruch himself) and many technicians could not resist (see my post about the Mesmerized Bunny Effect).
The Carnes arm was found to indeed use a similar means of power transmission to the Dahlisch-Hand. But the Carnes arm was extremely complex, had 147 little cogwheels, screws and springs and was constructed on basis of previous prosthetic designs, thought over cleverly and built with loving care.
Its concept however was indeed outdated already in the 1920s. Only six years after the Carnes arm patent licenses were purchased by the German government, orthopedic surgeons Hohmann and Schede wrote already in 1922, that "today, the Carnes arm frenzy is over, only a very few amputees still wear the Carnes hand".
At the beginning of World War II (1939) the Carnes arm had become entirely obsolete. The Sauerbruch method was used throughout Germany until 1957.
Current status of the Carnes arm
The Carnes arm currently is not produced any more.
The role of the Carnes arm at the time may have been more that of a technologically advanced prop that obviously failed more stringent and hard performance tests while it was presented and worn as the penultimate in high tech performance - a role that nowadays is taken by TouchBionics' iLimb or Otto Bock's Michelangelo hand: both do not go further than working with two electrodes (open, close), they use relatively frail myoelectric technology, they are heavily protected by patents, they sell outdated technology at absolutely staggering dream prices, and they are not constructed for prolonged use, nor are they rugged in any way.
Also, the DARPA project that outsourced prosthetic development to DEKA was born out of a (post) war government guilt, it employs illustrious figures such as Ling who can get neither technology nor stereotypes right (he ignores body powered technology and compares hooks to a pirate captain), and these guys produce very interesting constructions for arm prosthetics that serve as TV docudrama footage but so far do not have a lot of practical impact particularly for many below elbow amputees that - as 150 years ago - require affordable and sturdy but modern outfits regarding their prostheses.
So, these modern "bionic" products today attempt to take the role the Carnes arm once had. None of these - including the Carnes arm - seemed / seems to withstand closer analysis of their actual grip function - and that function is in no way superior relative to competitive products to justify the extreme costs - so quite obviously, logically, function is not what you pay for. If nothing else they are a manifest for displaying one peculiar aspect of disability: that society supports and "arms race of arm prosthetics" as an open appreciation of that particular disability. That is absolutely endearing, don't get me wrong here, it's as fabulous as things can ever be. I also watch the Transformers' movies with delight. But that doesn't get a report typed, the garbage taken out, the eggs cracked open or the oil checked in the car.
And again: this is not a blog that attempts to solve all prosthetic problems. I am purely interested in what fits a pain sensitive and long below elbow amputee stump which is halfways useful (prosthetics manufacturers: for you, this spells out as "ultra extreme super dynamo space XTX mega titanium" rather than "run-of-the-mill cheap blech" or "plastic wires that snap within seconds").
So let us not be confounded as to such products' ultimate goal. These prostheses are not there to be used and wrecked when lugging parts, doing work or crafts - they are primarily there to sell expensively, to soothe the wounded spirit and to represent the idea of technology.
- When you evaluate prosthetics, please try to separate overal impression, emotional gut reaction, critical technical evaluation, wearing comfort, every day actions and performance, price evaluation and support effort and cost.
- Old robust technology can be great if it is carried out in a perfect manner and does not cost too much. But it has to be carried out in a perfect manner. Usually, precision manufacturing is costly.
- There exists such a thing as a public run for gadgets. Gadgets don't have to be carried out in a perfect manner. They just have to be cool.
- Governments, engineers, doctors and companies can work themselves up to a situation that the clouds all judgement. Such seems to exist. If it happens, try to step back and take a deep breath.
- Always be aware of the other people's agendas. Prosthetics may be performed as societal feel-good excuse, as tax write-off branch of a big plastics company, as obsessive activity or as idealistic realisation. Main thing should be an at least halfways matter-of-factual orientation.
- People wearing prosthetic arms themselves can probably better judge what is going on. Particularly if they are technically inclined or engineers. If you are a prosthetic company and if you have dissatisfied customers that are technically inclined, and the problem is your technical proficiency, then asking them e.g. to pay 6000$ for shipment to get non functional goods repaired or asking them to get stuffed and try ergo-therapy is just outrageously offensive. In case you were cluelessly wondering? Instead you should listen to these people's concerns and listen very carefully. Or just build their arms so they do not crap out. That'd be a good alternative.
Future of the Carnes arm
As opposed to the heavy, strenuous to use, sensitive if not fragile show case of modern technology that the Carnes arm was, the Becker hands are a well developed and sturdy piece of equipment that should not be missing from any household. Both are body powered prostheses.
The current status of body powered arm prosthetics is that (a) not nearly as much money can be made from selling disabled people and their insurances body powered technology compared to grossly overpriced wares as when selling "bionic" (i.e., myoelectric) material and (b) due to that, I am under the strong impression that big prosthetic part providers and their representatives and associates belittle and neglect product development and customer service. While some people clearly benefit from myoelectric arms, other people like me clearly do not.
The planet does not stand still, and since last year we have seen a number of notable improvements in body powered technology: Becker Mechanical Hands now has a website, Bradley Veatch of Physionetics / ADA Technologies Inc. now developed the V2P prehensor, Dan Horkey (GTOPI) is well established in providing artwork for your prosthesis, and we are moving forward with a new wrist quick release unit.
Mark Lesek of Tasmania now has started to redesign a very lightweight myoelectric arm to be used for his osseo-integrated upper arm stump. For that, he will use modern lightweight materials and he will exploit design ideas of both the Carnes arm and the Becker hand. He went to Sweden to get osseo-integrated by Dr Rickard Branemark against the advice of his doctors in Tasmania and Australia. Of course, nothing bad happened and they got over it. As it appears it just took Mark to show them the way.
Mark's idea is very clever - the Carnes arm's features are particularly great for above elbow amputees, any drawbacks due to outdated string pulling can be overcome with myoelectric power, and any issues with grip alleged from historical documents may be better solved by modifying the prosthetic hand and the Becker hand has relevant features that can be combined with Carnes technology. Check out the current discussion at ModernMechanis titled 'Shop Work with a CARNES ARTIFICIAL ARM'.
Some images (C) Copyright by Mark Lesek to give an idea about what is being done:
Parts in construction: hands require careful analysis and an anatomical copy.
Using Mark's belly as significant add-on for prosthetic control.
"Plastic is fantastic" :)
Update June 2010
Update July 2010
Update November 2010
Images (C) Copyright BBC UK / Link to broadcast
Mark now has some skeletal parts ready to show off, and some more carbon fiber. Black looks great, I sense Cult Appeal - while Otto Bock has a white Michelangelo arm, this is a black rein"carn"ation - very cool, also in terms of competitive development.
Of course, the Carnes arm was as ingenial as it was short lived - for good reasons some of which may have gotten lost to history. If anything survived to this day it was the superb marketing of the Carnes arm - not its usefulness. It was marketed by the honest appearingest, mechanical work showingest men that the manufacturers could round up. Yet, the Sauerbruch cineplasty was far more sustainable, popular and in demand by amputees. Today, any modern carbon fiber socket and an aluminum hook are provenly, reportedly and measurably more useful than a whole bunch of other parts, particularly for hard work, and I have to say that I particularly like Hosmer's work hook for hard work.
But the current commercially available choice of arms does not cover underactuated controls for complete elbow / wrist / hand combinations and there are absolutely no robust hands for such prosthetic arms. Both of my current Otto Bock hands that I only wear for presentation type events started to fail (!) - that is how they are manufactured. All heavy duty parts currently available are ideal for a below elbow amputee like me - but underactuated control setups such as the Carnes arm are not available - particularly not for mechanically controlled arms as any researcher or manufacturer these days assumes that amputees will not do heavy work.
Besides, it is an open question what is portrayed as heavy work and what actually is. Best to try it out, measure loads and weights, measure actually what work is done and how many times per hour. Just sitting at a desk and typing recommendation mails for Swedish surgery as such is not heavy work.
But if one has to reinvent the Carnes arm, one particular difficulty consists in re-inventing its combined motions, in re-designing the already highly complex mechanism, in joining elbow, wrist and hand, so it will not cause the same problems as the original versions. And so far, that is the really interesting part that is the next big step here. A lossy mechanical contraption may just be lossy again if rebuilt from the same drawings.
Mainstream research for shoulder level amputation nowadays addresses control and sockets. For better control, targeted reinnervation now is available. That then seems to allow the user to control elbow, wrist and hand in a relatively relaxed fashion using mostly prosthetic standard components. However, at prices of current commercial prosthetic parts, performance does not warrant the price tag the slightest bit. The products were alright were they affordable. So one does have to go to the shed and do one's own work.
Personally, I would wonder whether separating arm, elbow and wrist coordination from choice or build of terminal device would not be a more interesting way to go. That would allow the user to do one thing I find extremely useful with my arm - I can wear a Becker hand (already optimized and available), or one out of a range of really useful hooks, or other hand models that are ready to use, and swap them depending on the need. That would reduce the complexity of the task to using elbow motion and position sensors to control the wrist and pull the terminal device's cable. And that should be no problem to construct after one defines position spaces, switch/transition spaces and switch/transition motions. Ah, you read that here first ;)
Update April 2011
Another portrait of Mark and the current development of a re-engineered Carnes arm.
 (21. 6. 1921) Tätigkeitsbericht der Prüfstelle für Ersatzglieder Charlottenburg, Archives of Orthopaedic and Trauma Surgery 19(2): 551- 578
 Karpa M (2004) Die Geschichte der Armprothese unter besonderer Berücksichtigung der Leistung von
Ferdinand Sauerbruch (1875-1951). Dissertation, Hohe Medizinische Fakultät, Ruhr-Universität, Bonn, Deutschland.
 Monika Burri - Aurel Stodolas Entwurf für eine Handprothese [ETHZ]
 Gocht H, Radike R, Schede F (1920) Kuenstliche Glieder. Stuttgart: Ferdinand Enke (with 689 figures and 2 tables).