Re: Total Surface Bearing Modifications- Ray Francis
Stan LaCount
Description
Collection
Title:
Re: Total Surface Bearing Modifications- Ray Francis
Creator:
Stan LaCount
Date:
3/1/2001
Text:
The GOAL of a TSB socket should be to distribute and equalize all the forces. Slightly tighter at the top than distally is not a TSB socket per se. Clients often have numb areas after amputations that have little or no feeling in areas of the residuum. Correct socket fit should not be left to their analysis alone as to whether they are aware of any initial discomfort. Tissues and bony prominences may not feel like they are being loaded under excessive shear or compression. However, after years of faulty fittings, they may develop subcutaneous cysts and recurrent skin problems that may have to be corrected surgically or not at all. It can be argued that a good fit will not be determined while the client is being looked at in the check socket for minutes or even an hour but can only be proven in weeks or months. The goal of the prosthetist should be to develop quantitative methods that scientifically determine and ensure that the pressure distributions are equal. There are several such pressure measurement systems in existence today such as the Renco STS. Looking subjectively through a clear check socket can only determine where there are areas of NO support, not in determining what those values are or how they are distributed. Although I have not attended the OWW class, I have attended Ossur's and had years of experience using the Alpha liners in both TSB and PTB sockets. Please allow me to pass on some observations.
It can been seen that there is indeed a significant difference between initial test patient comfort and a well fitting definitive socket for use in long term ambulation. Only time will tell if a looser fit proximally will ensure that the simplified methodology you espouse is worthwhile and it has been my experience that it isn't. I suggest that what you describe is not a TCB fit and that M/L instabilities as well as excessive pistoning will result. I can agree that the TSB socket and gel liner approach has the immediate benefit in allowing one to spend 10 minutes in the socket revision process with generally good results but any flaws in the definitive socket will eventually telegraph through the gel liner to the residuum with long term use. I submit further that a TSB socket can not be adequately developed from a male plug poured using a conventional female casting process.
When the fit is looser proximally excessive pistoning develops as the tissues are displaced upwards. This creates a vacuum within the sleeve distally, especially when the forces on the pin are other than axial. The Alpha is notorious for its longitudinal stretch characteristics and has no distal strength matrix to prevent it. The soft mineral oil impregnated gel material has low adhesion characteristics (lower than silicone anyway) and flakes apart in the distal end by the low pressures needed in a suction suspension system. The failure of the sleeve will of course be in the distal end as the proximal end is not sealed, but the excessive pistoning by not pre-tensioning the pin in the original casting process over the residuum is a major cause of blowouts in the Alpha. A fleshy residuum needs to be pre-shaped in a tensioned configuration during the casting process and the socket needs to be as tight at the top as it is at the bottom. Why does the OWW video detail a specific proximal trim & popliteal shelf procedure that, when followed, extends the warranty of the Alpha from 6 months to 12 if the liner failures are primarily in the distal area as you stated?
In transitioning from a PTB to a TSB fabrication methodology the simple procedure of removing a percentage of the material from the male plug IS oversimplified and not consistent with the 1/2 reduction method. Either method does not get us close enough, in my humble opinion, and will not provide a well designed socket or cure the warranty problems inherent in this liner. It is excellent advice that you should cast over the liner that you are going to use on the patient, but I suggest the use of a substitute for the Alpha to get the best results I am sure that OWW has developed many good products in their time and continue to do so, but the Alpha Liner has been less than successful. Just my two cents.
Stan LaCount
PRE
Beach Biotech
Raymond Francis writes:
Mr. Burdette is technically correct. If accurately measured the socket would be very slightly tighter at the bottom than at the top. Practically speaking, I am not sure that is of any significance in terms of fitting and patient comfort. When we fit our test sockets one of the questions we ask every patient is, are they aware of any place in the socket that is tighter than any other? When we are finished with the test fitting they can not tell us of any place in the socket that is tighter than another. In a successful fitting the patient is not aware of any place in the socket that is carrying more weight then any other. To me this is the goal of a Total Surface Bearing Socket.
In teaching this principal of fitting and socket fabrication we wanted to come up with the simplest and easiest method to change most prosthetist from the P.T.B. design (which does not provide longevity to our liners) to the total surface bearing socket. It is ours, as well as other prosthetist's experience that the total surface bearing socket does provide the longevity that we were looking for. Having said that, we selected a simple system that works very well for us. It is just a matter of
removing about 1/2 inch (and that number can vary from 3/8 to 3/4 of an inch depending on different prosthetist) from the circumference for the positive cast after it has been poured. We also suggest that the prosthetist can use a percentage of between four to six percent. These variances are to allow for the differences in casting tensions and techniques. As we have studied the wear issues of the Alpha Liner we have found most of the problems come from the distal section of the socket. Movement at the bottom of the socket will cause early failure of the liner more than any other single issue of the fit. Most of the soft tissue is also at the distal end. In truth if this section ends up just a bit tighter than the proximal section we don't think that is all too bad. You must remember, we are talking about a very small amount.
All of these issues are discussed in length at the Alpha Liner seminars that we offer to the prosthetist in the field. We also offer a video on the subject. Certainly, the video does not go into the depth of detail that the seminar covers. We strongly encourage any prosthetist that is using our Alpha Liners to attend one of our seminars on the subject.
I have read the responses from Mr. McFarland's post. I have to agree with some of the responses that suggest you should cast over the liner that you are going to use on the patient. If you use a substitute of some sort you are not going to get the best results. Cast modification time for me is down to less then ten minutes. I really think we are getting ourselves in trouble if we keep trying to second guess the simple system. I know that I go on the road and cast and produce test sockets on people that I have never seen before. I, in my opinion, end up with a socket that the test patients say has and feels as though the pressures are evenly distributed to them. I also feel that no system is designed to remove that talent and knowledge of any experienced prosthetist. The suggestions that we make are to bring you very close to a good fitting socket. You still have to fit the test socket. You still have to be a prosthetist.
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It can been seen that there is indeed a significant difference between initial test patient comfort and a well fitting definitive socket for use in long term ambulation. Only time will tell if a looser fit proximally will ensure that the simplified methodology you espouse is worthwhile and it has been my experience that it isn't. I suggest that what you describe is not a TCB fit and that M/L instabilities as well as excessive pistoning will result. I can agree that the TSB socket and gel liner approach has the immediate benefit in allowing one to spend 10 minutes in the socket revision process with generally good results but any flaws in the definitive socket will eventually telegraph through the gel liner to the residuum with long term use. I submit further that a TSB socket can not be adequately developed from a male plug poured using a conventional female casting process.
When the fit is looser proximally excessive pistoning develops as the tissues are displaced upwards. This creates a vacuum within the sleeve distally, especially when the forces on the pin are other than axial. The Alpha is notorious for its longitudinal stretch characteristics and has no distal strength matrix to prevent it. The soft mineral oil impregnated gel material has low adhesion characteristics (lower than silicone anyway) and flakes apart in the distal end by the low pressures needed in a suction suspension system. The failure of the sleeve will of course be in the distal end as the proximal end is not sealed, but the excessive pistoning by not pre-tensioning the pin in the original casting process over the residuum is a major cause of blowouts in the Alpha. A fleshy residuum needs to be pre-shaped in a tensioned configuration during the casting process and the socket needs to be as tight at the top as it is at the bottom. Why does the OWW video detail a specific proximal trim & popliteal shelf procedure that, when followed, extends the warranty of the Alpha from 6 months to 12 if the liner failures are primarily in the distal area as you stated?
In transitioning from a PTB to a TSB fabrication methodology the simple procedure of removing a percentage of the material from the male plug IS oversimplified and not consistent with the 1/2 reduction method. Either method does not get us close enough, in my humble opinion, and will not provide a well designed socket or cure the warranty problems inherent in this liner. It is excellent advice that you should cast over the liner that you are going to use on the patient, but I suggest the use of a substitute for the Alpha to get the best results I am sure that OWW has developed many good products in their time and continue to do so, but the Alpha Liner has been less than successful. Just my two cents.
Stan LaCount
PRE
Beach Biotech
Raymond Francis writes:
Mr. Burdette is technically correct. If accurately measured the socket would be very slightly tighter at the bottom than at the top. Practically speaking, I am not sure that is of any significance in terms of fitting and patient comfort. When we fit our test sockets one of the questions we ask every patient is, are they aware of any place in the socket that is tighter than any other? When we are finished with the test fitting they can not tell us of any place in the socket that is tighter than another. In a successful fitting the patient is not aware of any place in the socket that is carrying more weight then any other. To me this is the goal of a Total Surface Bearing Socket.
In teaching this principal of fitting and socket fabrication we wanted to come up with the simplest and easiest method to change most prosthetist from the P.T.B. design (which does not provide longevity to our liners) to the total surface bearing socket. It is ours, as well as other prosthetist's experience that the total surface bearing socket does provide the longevity that we were looking for. Having said that, we selected a simple system that works very well for us. It is just a matter of
removing about 1/2 inch (and that number can vary from 3/8 to 3/4 of an inch depending on different prosthetist) from the circumference for the positive cast after it has been poured. We also suggest that the prosthetist can use a percentage of between four to six percent. These variances are to allow for the differences in casting tensions and techniques. As we have studied the wear issues of the Alpha Liner we have found most of the problems come from the distal section of the socket. Movement at the bottom of the socket will cause early failure of the liner more than any other single issue of the fit. Most of the soft tissue is also at the distal end. In truth if this section ends up just a bit tighter than the proximal section we don't think that is all too bad. You must remember, we are talking about a very small amount.
All of these issues are discussed in length at the Alpha Liner seminars that we offer to the prosthetist in the field. We also offer a video on the subject. Certainly, the video does not go into the depth of detail that the seminar covers. We strongly encourage any prosthetist that is using our Alpha Liners to attend one of our seminars on the subject.
I have read the responses from Mr. McFarland's post. I have to agree with some of the responses that suggest you should cast over the liner that you are going to use on the patient. If you use a substitute of some sort you are not going to get the best results. Cast modification time for me is down to less then ten minutes. I really think we are getting ourselves in trouble if we keep trying to second guess the simple system. I know that I go on the road and cast and produce test sockets on people that I have never seen before. I, in my opinion, end up with a socket that the test patients say has and feels as though the pressures are evenly distributed to them. I also feel that no system is designed to remove that talent and knowledge of any experienced prosthetist. The suggestions that we make are to bring you very close to a good fitting socket. You still have to fit the test socket. You still have to be a prosthetist.
********************
To unsubscribe, send a message to: <Email Address Redacted> with
the words UNSUB OANDP-L in the body of the
message.
If you have a problem unsubscribing,or have other
questions, send e-mail to the moderator
Paul E. Prusakowski,CPO at <Email Address Redacted>
OANDP-L is a forum for the discussion of topics
related to Orthotics and Prosthetics.
Public commercial postings are forbidden. Responses to inquiries
should not be sent to the entire oandp-l list.
Citation
Stan LaCount, “Re: Total Surface Bearing Modifications- Ray Francis,” Digital Resource Foundation for Orthotics and Prosthetics, accessed November 5, 2024, https://library.drfop.org/items/show/216230.
