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Shoulder Disarticulation Fitting with Utah Servo Control
I recently spent a very hectic week fitting several amputees with new prostheses. On of the largest challenges was to come up with a system that would offer a husky gentlemen more active function than his old body powered system. Although John wore his old prosthesis regularly for a number of years, like many high level amputees, he found that it was just too much struggle to operate a body powered elbow and body powered terminal device.
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Despite having broad shoulders and powerful musculature, this gentlemen could not generate sufficient excursion to raise the body powered elbow and fully open the terminal device.
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Prior myotesting had revealed a number of potential control sites including fairly strong anterior, middle, and posterior deltoid signals. Unfortunately, even with practice, John had a hard time separating one myosource from another. This is not uncommon when many decades have elapsed since the original amputation, particularly if the transected muscles have not been attached to bone [myodesis]. Often, all the patient can do is generate one massive contraction of all available remnant muscles. It is sometimes worth delaying fitting a few weeks longer to see if the muscle control improves, but in this case John was eager to complete the fitting and start using the prosthesis for bimanual tasks.
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Regardless of the harnessing and cabling, this gentleman could barely flex a body powered elbow more than 90 degrees.
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The initial plan, then, was to create a hybrid arm using Otto Bock's ErgoArm elbow combined with a single site electronic terminal device. Unfortunately, even with careful harnessing, John could barely flex the elbow to 100 degrees: hardly more than with his old prosthesis. Because he was straining even to flex the elbow this much, we agreed that he would be more functional with a powered elbow.
So, we then created a diagnostic prosthesis using a loaner Utah Arm system. Because John was very satisfied with his old abduction shoulder joint, and had durability problems in the past with other shoulder options, we elected to stay with this configuration.
To simplify the diagnostic fitting, I made a quick trip to the hardware store and purchased a T-hinge. When combined with a drilled aluminum bar [discarded from an orthosis sidebar] and my standard slotted humeral adapter, this created a good simulation of the function of an abduction joint. From hindsight, this was a very good decision because we discovered that it would improve John's functional work envelope if the abduction angle was moved obliquely so the arm moved anteriorly as well as laterally.
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This simple T-hinge simulated the motion of an abduction shoulder joint during the diagnostic fitting.
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In fact, we moved the shoulder joint 3 times until we were all satisfied with its placement. Once the joint axis location was established, it was a simple matter to transfer in the dual single axis hinges that comprise the abduction joint for the definitive prosthesis.
John was accustomed to a socket that rested on his chest wall and to using uniscapular protraction to operate his prosthesis. We discussed other alternatives with him, but it quickly became clear that he would be most comfortable and confident with a similar socket and control scheme. Due to the limitations in his myo signals, a trial with Servo control was in order.
Because John had such limited excursion available, the Servo sensor was routed across the inferior third of his scapula. This allowed us to keep the control strap fairly loose to minimize the chance of inadvertent operation, yet John could readily generate sufficient force to operate both elbow and terminal device pretty easily.
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The gray elastic webbing provides sufficient resistance to suspend the socket comfortably and securely. The black Velcro strap is rigidly connected to the Servo sensor. When the patient rounds his shoulders, the forces generated on the Servo sensor control operation of the electronic elbow and terminal device. Because the Utah Servo is strictly force-based, this requires zero excursion.
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With the Servo control, applying force to the sensor flexes the elbow while relaxing the force extends it. The speed of movement is directly proportional to the force the amputee generates, so they quickly learn to control the forearm position. When the elbow is held steady for a little less than a second, it automatically locks and control is transferred to the terminal device. To unlock the elbow, the amputee generates a quick force pulse.
It took a few hours of practice for John to get the hang of unlocking the elbow and moving the terminal device without dropping whatever he was holding. Fortunately, he was willing to persist, and by the end of the second day he could place the hand in space, open, and close it on command. Based on this initial success, he was very eager to move on to the definitive components and have the prosthesis finalized.
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Passing an object from the prosthesis to the other hand and back is a good way to verify that the amputee can independently control the elbow and terminal device. The hand shown is too small and for the other side, but was suitable for the trial fitting to verify control prior to ordering the definitive terminal device.
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The definitive design will be laminated with carbon fiber reinforcements to make it as strong and light as possible, and will include a frame socket with ample fenestrations so it will be less "sweaty" than John's old prosthesis. With a little practice, he should be able to do far more two-handed tasks with a modern electronic prosthesis than was possible when he was last fitted, when body powered components were the only available option.
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S.D.
Thank you for sharing info on the S.D.our profession will benefit greatly from sharing the hours of your work. Thanks ,John Micheal !!!
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Re: Options
Thankyou for your info. My 15 year old son started an apprenticeship in September 2003 in November of the same year he was in an accident that resulted in him losing his right arm I have been told a 4 quarter amputaion. Currently he has to... read more
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Re: Re: Options
Forequarter amputation is in many ways a special case in upper limb loss because all of the arm is absent, and only the chest wall remains. The lack of any arm remnant makes it difficult to stabilize the prosthesis and restricts the abilit... read more
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Re: Re: Re: Options
Do you have any suggestions on getting a posthetic shoulder (I am a 4 quarter amputee) that would not strap on but actually beable to adhere to an undershirt and put a shirt over it?
Please email me directly at britseth@aol.com
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Re: Re: Re: Re: Options
Unless you wear a very tight undershirt, I think any shoulder cap attached to it would likely displace and wind up being more annoying than useful. But, with an elastic shirt such as worn for active sports, this might work OK.
I'd be in... read more
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Re: Re: Re: Re: Re: Options
SO helpful...thank you. I have never seen a suspended shoulder cap like that...very refreshing! I am having a difficult time finding the writing about pads in athletic shirts...can you forward a link?
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Re: Re: Re: Re: Re: Re: Options
The URL is http://www.oandp.com/news/jmcorner/2004-06/2.asp . --John Michael CPO
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shoulder disarticulation
Hi
really good info.
i need ur help. my husband met with an accident 3 months before and lost his left hand from shoulder ( almost same as shown in the article)and left leg above knee.
i am in search for upper extremity functional pros... read more
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Re: shoulder disarticulation
Thank you for this inquiry. When both limbs are amputated on the same side, this complicates rehabilitation considerably. I would encourage consideration be given to obtaining an evaluation and opinion from a rehabilitation hospital with ... read more
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Shoudler disarticulation follow up
Very helpful article. Thanks John. Any follow up photos of the finished arm?
THX,
RK
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Re: Shoudler disarticulation follow up
I have a few photos of a S.D.finished If interested email at magur@comcast.net.
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Re: Re: Shoudler disarticulation follow up
i need information i loss my arm shoulder by sarcoma
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Re: Shoudler disarticulation follow up
No, because the patient's prosthetist always does the delivery and follow-up. But, I'll be consulting for them next month, so I'll ask how this gentleman is doing and see if I can get permission to post some "after" shots. --John Michael ... read more
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SD fitting
That was a nicely done article: informative, clear pictures, and realistically written. Thanks
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Re: SD fitting
I'm glad this short summary of many, many hours of work was helpful. Since most practitioners learn visually, I am trying to include photos that show details so the case report narrative can be brief and to the point.
--John Michael CPO
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Re: Re: SD fitting
Sr. John Michael C.O.P. Estimado John, la Sociedad Mexicana de Ortesistas y Protesistas, Asociación Civil, le agradece su participación en el "Foro de Discusión sobre la Educación de Ortesistas y Protesistas en America Latina" celebrado en ... read more
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Re: Re: Re: SD fitting
Gracias, Alberto-
I was very pleased to be present at this important SMOPAC meeting, and will be featuring it in next month's Corner.
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