A “Triple Swivel” connector that I have, of which Fillauer apparently even claims that they treat it as a class I medical device and therefore cannot sell it to users/amputees, just came apart.

Simple as that.

Almost by itself.

I pulled it, obviously — that is what it is there for, in order to pull on it — while lifting something that was somewhat heavy, and it came right out. The damage and failure problem could have caused serious damage, but I prevented it by being cautious.

The only connection that no one other than the manufacturer had had their fingers on? That is the one that came apart.

Not the prosthetist’s crimped on little wire stop sleeve. Certainly not my prosthetic control cable mount. Notably, I had gotten myself consulting and advice, on how to correctly mount my steel cable. I would recommend that also to Fillauer.

So I’m obviously puzzled by a “Triple Swivel” connector I possess that just came apart. But also, Fillauer treats this connector as a class I medical device, meaning it’s seen as low-risk, and because of this, they don’t sell it directly to users or amputees. However, despite these “precautions”, it malfunctioned.

So in other words, when I tried to use it as intended, pulling on it to lift an object of some weight, it unexpectedly came apart.

Notably, the part that failed was the original manufacturer’s connection, untouched by any modifications from my prosthetist or myself.

This raises concerns about the connector’s inherent quality.

Table of Contents

Triple Swivel, as offered by Fillauer

The device in question is shown in its correct and intact assembly.

Remember how these look, because below, you see images of this stuff just after it “came out”, failed, disconnected, came apart.

Catalog: https://fillauer.com/products/triple-swivels/

When I had asked them to just send me ten of these (along with their bill, of course – I was not asking to get these for free), they refused, saying it was only allowed to give them to certified prosthetists and not to me as a licensed medical doctor (that can legally buy any class I device) and also end user (with parts that we designed and built ourselves, that I wear, and that insurance inspected, and pays for, and so on).

Now it is interesting to see just who the engineering rookies are here! When I lifted something that was just a bit (but not overly) heavy, maybe ~30 kg, their shit just came apart.

In other words, I had approached them with a request to purchase ten of these connectors, fully intending to pay. However, they declined my request, explaining that only certified prosthetists could receive them.

This was surprising, given that I am a licensed medical doctor with the authority to buy class I devices.

Moreover, I’m an end user with custom parts that I personally wear which have been vetted by insurance and are covered by them.

Yet, Fillauer’s product’s reliability came into question when I used it to lift an item weighing roughly ~30 kg. It simply fell apart.

It makes one wonder about their engineering expertise!

Triple Swivel, that had come apart

Here you can see the top and bottom part, clearly separated from each other.

Fact is that the hollow top portion simply had slid out of the bottom part (that with the cable attached), just like that.

The top portion is shaped as a spherical end of a barbell shaped piece.

The attached portion has a round rim whereas the spherical part is supposed to reside inside the hollow rim at all times.

It is never supposed to come out, like, at all.

As things are, I pulled a bit and *plop* the thang just came out.

So I keep it for further evaluation and examination.

The rim of the enclosure looks fine by eye. Also the barbell shaped piece looks fine. Both appear symmetrical.

Both seem to lack damage, such as fractures, cracks, or tears that would explain the failure.

Details of hollow part

It does not exhibit relevant deformation, nor is there a crack or tear, missing part or other relevant damage visible.

There are superficial scratches which may indicate that the metal is relatively soft.

Details of the barbell bit

There appears to be no deformation, relevant indentation or fracture.

There are superficial scratches which may indicate that the metal is relatively soft.

Purpose

Medical purpose

The medical device legislation has one particular specific and explicit intent and goal: to protect the user and the user’s interest. Nowhere does medical device legislation state a particular intent to protect a manufacturer. That alone should make clear where the focus should be: medical device manufacturers should help users understand their product so the user (not necessarily the manufacturer) is safe. Here, all that’s protected are sales channels.
The user has usually one goal, interest or requirement: that the medical device fulfils its designated purpose. That “purpose” boils down to, according to Swiss legislation and court decisions, the actual medical prescription. It is set equal to this, when philosophically there could be any purpose. So if a medical doctor prescribes a prosthetic arm “to allow the user to use it for his/her work”, that means, that whatever it is that they do at work, will directly impact the type of exposure and challenges that not only the worker as a whole, but also their prosthetic arm, will be subjected to.
A prosthetic arm is a piece of engineering, if ever, so only those aspects from the user’s work or other designated use, that are technical, and that directly relate to the engineering, are of further interest here. These however can be of utmost interest. I don’t know of any manufacturer that exhibited an actual understanding of this.
The exposure levels that a worker or arm prosthesis user will be subjected to, as far as technical figures go, are known, for a range of occupations. They are known in technical terms, that then can be applied to technical testing, and results of testing can be given. If they are not known, the people that build the prosthetic arm are in charge of evaluating that with the user. As long as (registered) medical devices are as overpriced, as they are, the manufacturers’ duty to provide documentation that allows the user and prosthetist to easily understand the capabilities and limitations of a particular component, from a technical view when focusing on the work application of the prosthetic arm, are included in the price.
In other words, as long as my prosthetic arm is prescribed for work, I will use it for whatever is associated with work. Law actually restricts me to using the prosthesis for the intended purpose. This is probably intended to delimit the exposure. But as long as no one really checks what I work, it also is what puts the play d’oh they sell as “robust” medical devices directly in harm’s way.
A medical device documentation will thus have to describe the purpose of the component such as a Triple Swivel connector “to allow pulling forces up to (… kg …) with safety”, and, “The connector was found to disassemble when a pulling force of … kg … is exceeded”. To write “this device’s purpose is to be used as part of a prosthetic arm” shows in essence, that the manufacturer has no idea what they are doing, really. They act in a void.

Fillauer’s description of purpose

Fillauer sent me some documents related to other body-powered components (not this Triple Swivel component, where they lack registration or documentation).

“Intended Use/Purpose — Any or all of these product technologies, in various combinations, are used by certified, professional prosthetists to create custom, individually fit, prosthetic harness and cable systems designed specifically to potentially support a prosthesis and or capture the bio-mechanical elements and energy-power of body motions (prosthetic control motions: Specifically, gleno-humeral flexion, bi-lateral scapular abduction & elbow flexion, as well as other bio-mechanical elements of body motion) and efficiently transfer them, to power, operate and control upper extremity prosthetic terminal device technologies.” They then offer technical dimensions that describe size, weight and color -but no sturdiness, no load capacity, no 100% failure points for push / compression or tensile strength values are given. We can safely conclude that the manufacturer assumes we, users, only wear these devices as counterweight and to look a certain way, and that none of us ever wants to know how much load we can put on these. That can be directly inferred from the documentation.

For their steel cables, purpose statement reads “high strength, abrasion resistant, upper extremity prosthetic control cable”. They simply use a descriptive term, and put that text instead of a statement such as “purpose: to transmit control forces of up to 80 kg”. Furthermore, they have two types of cable here, “Python stainless steel standard” and “Python stainless steel heavy duty” cable, where not even the cable diameter is given. They must think of anyone reading this to be entirely obtuse to all things in life?

None of that, in the context of medical devices, is a proper technical description that allows anyone, including user or prosthetist, to understand the technical capabilities or limitations within the scope of a purpose as explained above. As none of that conforms to any actual requirements, it is, essentially, worthless.

Less obvious is the innocent fun to be had in reading “abrasion resistant”. If a steel cable is mounted properly, there will really not be a lot of abrasion. Did you ever ride a bicycle? Pull brake levers? Coin drop now? Anyone that requires a particularly abrasion resistant steel cable probably should not mount them. That became clear to me when typical commercial steel cable parts and mount parts were used on my prosthetic arm, with the effect that these cables tore up after 4-10 days, repeatedly. When I would not wear the arm for seven days, the fatal tear up would be delayed by, you guessed it, seven days. I understood then why people wear the prosthesis only occasionally: if you can wear it for only 10 days before it breaks again, better to make these days count. Now, we can look at the parts, the components, that are sold to mount these cables on the prostheses, and have a giggle. While they seem to be unable to get a straight understanding of medical purpose to meaningfully spell out as technical failure figures on their spec sheets, they also cannot properly mount steel cables.

Why does a steel triple swivel connector come apart without tear, fracture or crack?

From anecdotal admission of another large prosthetic part manufacturer, we know that other manufacturer gets things fabricated off shore, somewhere far east maybe, and, without quality check / control, sells the stuff for premium prices to users. It was a maneuver in itself to milk the system for that bit of information. Safe to assume that such a type of build/sell strategy is behind the technical failure here. To be transparent in the future, we clearly need certified origins.

The “documentation” as outlined above is technically useless. EU 2017/745 incl annexes should be an easy read.

Conform, bitch! Science, bitch!

Technically, steel is normally softer or harder, give or take.

Steel is an alloy of iron and carbon, sometimes with other elements to impart specific properties. Its strength and hardness can be modified based on its carbon content and the heat treatment it undergoes.

We can distinguish softer steel and hardened steel. It makes sense to understand the difference to see where Fillauer likely went wrong.

This is relevant as users/amputees clearly need to take matters into their own hands – given the way these companies act. Softer steel is the material to be worked on, machined, tooled, milled. Then, when the shape or product is finished, the steel can be hardened in a next step.

Starting with softer steel is often preferred when shaping or machining parts due to its workability. Once the desired shape is achieved, the steel can then be hardened to increase its strength and wear resistance. This hardening process involves heating the steel to change its crystal structure and then rapidly cooling it, followed by a tempering process to improve its ductility and toughness.

Softer Steel (also known as Annealed or Normalized Steel)

This is the initial material that is used to create the first stage of the product.

Contains a lower carbon content.
Is more ductile and malleable.
Easier to shape, form, and machine because of its softer state.
Less likely to crack or break when worked on.

Hardened Steel

After a device has been created from (softer) steel, it then will be hardened.

Has undergone a heat treatment process to alter its microstructure.
Is significantly harder and more wear-resistant.
However, this increased hardness comes at a cost: the steel becomes more brittle and less ductile.
Difficult to cut, shape, or work with using conventional methods.

Process of Hardening Steel

Austenitizing: Steel is heated to a temperature where the iron changes its crystal structure from ferrite to austenite. This is generally above 723°C (1343°F) for plain carbon steels.

Quenching: The steel is then rapidly cooled by immersing it in a quenching medium, which can be water, oil, or air. The rapid cooling traps the carbon atoms within the iron matrix, leading to a very hard and brittle phase called martensite.

Tempering: Just hardening often leaves the steel too brittle for practical uses. So, the hardened steel is reheated to a temperature below the austenitizing temperature and held there for a period of time. This process, called tempering, reduces the brittleness by converting some of the martensite into other microstructures that are less hard but more ductile.

Other anecdotes

Direct sales / soft steel story 1: I have another device (details withheld) that was sold to me directly by the manufacturer. During an accident-critical operation, two of four “soft steel” screws broke and I prevented damage by fast reaction. That could easily have gone side ways, but it did not. Manufacturer then sent me replacement screws that were hardened.
Regular purchase / soft steel story 2: Another device that I had, an Otto Bock Movo2Hook, had a lever, and that lever had caused an indent in the body of the device. Soft steel, right. That, as secondary complication, exposed that the spring of the device was fashioned too long because now the hook fingers would not fully close any more. Shortening that screw would fix the indent problem. I sent the device along proper channels and they first seemed irritated, but I explained again what the problem was. We could have shortened the spring ourselves but I wanted them to learn from their mistake.

Manufacturers really want to perform comprehensive mechanical testing. And if just to avoid me doing it for them.

Conclusion

We here see a case of a seemingly unfractured, undeformed and normal looking separated parts of what should not have been separated as a steel product, a Fillauer Triple Swivel.

The most likely reason I assume for this to occur is that they sell these as steel products without hardening.

That would allow a relatively thin structure as the bottom hollow cylindrical part to just give out to relatively strong pull on the barbell structure that resides, normally, inside the cylindrical part.

In any less irresponsible world, Fillauer would have:

hardened the steel – obviously at extra cost;
tested the device, so we would know under how many kilograms of load invariably all devices fail;
if it fails under less than 100 kg, then it has to designed with more material, be made bulkier; the cylindric part has to be devised to be thicker as that is the part that, here, must have given way; the barbell shape may have to be designed with a less gradual shape change between the spherical part and the connecting part;

Had Fillauer representatives been any competent, …

sales wise, they’d have sold me, as end user, as many triple swivels as I want – obviating any need to make a public medical device drama of this. There is a form I can sign that says “user takes all responsibility”. That’s it. They could even have stated that this is cheap stuff and untested and that I should just apply care and caution myself. That would also have been truthful and as I do that successfully since 15 years (and also here: severe damage could have happened, but, did not happen, guess why). As Fillauer is based on selling (and not on, say, arts, or, moral values, or, academic degrees, etc.), all they should do is “sell”. I told their marketing / sales guy that. He did not comply. That was a mistake.
engineering wise, they would have hardened the device, tested it, and probably made it a bit bigger / bulkier, to sustain up to 100 kg of pulling force; that allows for safe and good marketing across CE marking;
quality accreditation/CE norming wise, they would have either declared it a non-medical device (which it really is, they do not seem to have this documented or tested or anything), so, safe to sell to anyone, or, documented its failure points accordingly and put that into the spec sheet.

Fillauer, however, lacks proper documentation and registration for this bit, as far as I can see in the PDF they mailed me with regard to their body powered parts.

Their sales guy wrote to me that “Rome was not built in a day” and I wrote back to him that it was obvious they weren’t building Rome at all, but exploiting users.

Regardless of lacking cogent documentation, this triple swivel device is also poorly designed and built. If I was them, I would be embarrassed.

They probably cannot just apologize, obviously, as they already claimed something along the lines that they are the good peoples, that want only the best for us users, that they regard us (users, amputees) as too idiotic [link] to handle their obviously overly fragile triple swivels ourselves.

Like all cheap things that aren’t quality checked: just get a bunch.

At the same time, they seem to still have unexplored potential with regard to understanding what the actual purpose of a technical device is, that then will be used in a world full of SI units such as weight, torque, temperatures and the like. What can we say?

At this stage, we are not worried about artificial intelligence taking over the planet. We are at the very other end of that scale of worry.

TECHNICAL RIGHT BELOW ELBOW AMPUTEE ISSUES

Fillauer Triple Swivel comes apart [medical device?]