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Tweaking Ossur parts to actually function - Icelock pin lock repeatedly loosening [tip]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Tweaking Ossur parts to actually function - Icelock pin lock repeatedly loosening [tip]; published December 28, 2011, 10:33; URL: https://www.swisswuff.ch/tech/?p=520.

BibTeX: @MISC{schweitzer_wolf_1571396193, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Tweaking Ossur parts to actually function - Icelock pin lock repeatedly loosening [tip]}}, month = {December},year = {2011}, url = {https://www.swisswuff.ch/tech/?p=520}}


Ossur customer service appears to have no time, Ossur Facebook censoring removes relevant request posts - so the company must do their darnedest to create the impression that their parts function and customers happy. It is indeed possible to work with Ossur parts though, despite what definitely comes across as questionable attitude and questionable engineering.

The system that I was set up with to use contains

  • Ossur Upper X silicone liners, and
  • Ossur Icelock pinlocks used for prosthetic arms (Icelock UX 721 and similar)

Both are problematic and yet, prices are massive.

This post is about the pinlock.

Problem description

After just a bit of typing (keyword: vibration) or carrying weights, the pinlock main fastening screw comes loose.

What part are we talking about: the white screw ring that exhibits a cross slit indent here, in this view directly into the prosthetic socket.

Same picture, detail portion of the pinlock screw ring part enlarged.

As steady mechanical use of these locks under prosthetic arm conditions - hard bangs, vibration-like strain when typing, short acceleration/deceleration distances, sudden relatively high loads - tend to always do that (hint to engineers: there are articles about that problem, if you canŽt read it is still not at all safe to assume your customers canŽt) it is a matter of weeks and months until the pin lock loosens again, again and yet again.

There are specific remedies against that, or, alternatively, there is always the option of regularly fastening the screw. If the second option is chosen then why make life difficult for the customer? Just to see your company's name pop up here, on this website? What type of advertising is that!?

Symptoms of mild pin lock loosening

The pin lock coming mildly loose can cause obscure problems. This can be quite unnerving.

The distance between the pin and its metal hole lock and the end of the liner is minimally increased when the white plastic screw ring comes a tad bit off.

Then it might cause jamming of the pin lock but no perceptible rattle or noise as one could assume when a part comes all the way off or loose.

Symptoms of advanced pin lock loosening

Wiggle and obvious lack of firm positioning of the pin lock make it apparent that the pin lock has come loose quite a bit.

I have that problem usually after spending a day of moving furniture or heavy boxes. That is what a prosthetic arm is there for - work. If a manufacturer cannot live with that, they better tell that to someone else. It is a reality and they will learn to deal with it.

Solution

The socket inside contains the entry to the pin lock.

There resides a white plastic screw ring that keeps the pin lock parts in place. It contains a "+" shaped indent that can be used to fasten the screw ring - given the right tool.

Apparently, Ossur sells an adapter for around 80 CHF which is a bit of a rip-off. Given the systematic nature of that problem, and given the huge prices for liners and pin locks, they might consider including these for their customers as a simple act of insight that all of these approximations are limited in stability. Also it would be a sign of respect: why would I - as end user - want to spend 2 hours each time to get the technician to fix this when it happens so often that I should be empowered to do this wherever I want?

Who told the guys at Ossur it is safe practice to sell wiggle-fasten-wiggle-fasten parts and then react surprised when the customer is not amused?

So here is the cross section of a tool (1:1 copy) that is being used to fix loose Ossur pin locks:

Anything shaped similarly will do to fasten the Icelock screw ring.

According to Icelock 621 adaptation kit instructions (a similar looking product), a recommendation of 8 Newton meter torque using an 8 mm ratchet is given for fastening the cross slit plastic screw ring.

I will post further results of where to get suitably shaped metal rods and how to go about them.

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