Interview: Bruce "Mac" McClellan, CPO
(Mr. McClellan's answers are in blue)
10/17/07
Question: I am curious about the reception of your research 17 years ago when the article "Does Socket Configuration Influence the Position of the Femur in Above-Knee Amputation?" was published in the JPO (as well as the reception at lectures given at the meetings). I ask this because it is difficult to understand how entrenched the beliefs on this subject were (and still are).
The research was met with some disdain by those advocating the efficacy of the new socket design(s). I recall that the ischial containment/NML [Narrow Medial – Lateral] designs had been touted as a breakthrough and that the design concepts were tightly held by the “originators” as proprietary information. This resulted in a “if you want this technology-you can only get it here” situation which was dimly viewed by much of the profession. In part because practitioners wanted to have the technology to try with their patients and partly because significant fee increases accompanied prostheses with these socket designs.
I specifically recall when Frank Gottschalk presented our paper at a national convention; it was not well received by those who were vested in the new socket designs. Indeed, during an open discussion period following the presentation, advocates openly challenged the study. There were rather vociferous outbursts along with the claim that they were doing their own study and would be presenting it in the future to refute our findings. I do not recall ever seeing the promised study or outcomes that proved our conclusions to be invalid.
Question: After 17 years how do you view the research as applied to your building of AK limbs?
As a result of spending a few days with Ivan Long (and five other practitioners) in an informal “course” that he gave, we were able to gain some insight into “Long's line” and his socket design techniques. The casting procedure and modifications were, as you might imagine, completely different than the more traditional quadrilateral design. His concepts made sense from a bio-mechanical standpoint and he indicated he had improved outcomes with this approach. Though the incorporation of this method into practice was difficult and somewhat prolonged, the rationales appeared legitimate as did the critical re-analysis of the non-anatomic quad socket configuration. I continue to use the more anatomic approach in my sockets to this date in conjunction with flexible wall design.
Question: Was there any consideration about changing the alignment or shape of the socket of the limbs X-rayed in this study?
No, there was no consideration given to changing the alignment or socket shape of the prostheses evaluated in the study. The reason for this is quite straight forward. This was an analytical study to determine whether or not the claims made by the CAT-CAM/Narrow M-L advocates were more that just anecdotal. It was not an attempt to present a new socket design or offer different alignment criteria. It was strictly a comparative evaluation of two categories of sockets (ischial containment vs. quadrilateral) that were provided by multiple practitioners. None of these prostheses were made with the idea that they would be used in a study. We simply randomly evaluated existing prostheses and patients.
Question: you think the socket has any influence in supporting the femur?
I fully support the findings of our study done in 1997. It was objective and unbiased and done for the purpose of seeking answers. The numbers of amputees and sockets evaluated were adequate to draw conclusions and the study was scientifically sound with regard to the methodology used for the specific information being sought.
Having said that, one enhancement to the study (not available to us at that time) would have been a dynamic evaluation displaying full single limb stance loading of the femur in the socket. This indeed is the situation where femoral control is the most critical and may have shed some additional light on individual socket control capability.
I do hold the belief that some control is exercised on the femur in prosthetic sockets. Whether this is significant enough to make any appreciable functional difference is open to debate. It is my opinion and experience that an intimately fitted socket with appropriate tissue compression will result in an improved gait pattern as opposed to a poorly designed and loosely fitting socket. The socket/knee/foot (alignment) relationship is also influential with regard to the gait pattern, energy expenditure and socket comfort and function. Prosthetic alignment in my opinion is equal in importance to appropriate socket fit and design with regard to achieving an optimal gait pattern and reduced energy consumption. However, it is my firm belief (and the conclusion of our study) that nothing has a greater effect upon a person’s prosthetic ambulation potential than the post-amputation reconstructive techniques employed with regard to limb angulations and the reattachment method used for the surgically cut muscles.
Question: Dr. Gottschalk recently sent me a scan of four sheets from a yellow legal pad that was used for X-ray data collection, or summarization, in your study. I've just finished compiling all the patient abduction / adduction angles into a spreadsheet. The quadrilateral sockets are all identified, obviously, as quadrilateral. However, the Ischial Containment sockets are classified into the following subcategories (parenthetical numbers represent the number of patients in these categories):
- CAT-CAM (7)
- Narrow ML (11)
- Ischial Containment (1)
- Ischial Containment Narrow ML (1)
- NSNA (2)
I realize that this data was collected over a period of time and hand recorded, thus the might not represent distinct rigid categories. I also know that you tried to find sockets made by as many different practitioners as you could. Might you have any recollection on how these sockets were identified and classified? The CAT-CAM socket is distinctive, but the Narrow ML / IC / ICNML and NSNA would be tough to pick out. Do you have any recollection you could share on the how the categorization of these types of sockets were undertaken in your study?
I can offer this information to the best of my recollection. In each case, we would interview the patient with regard to which practitioner was responsible for designing/fabricating their prosthesis. If it were Sabolich or Guth or other identifiable CAT-CAM practitioners then the classification was made accordingly. Likewise, if the practitioners had attended Ivan Long's course, the socket designs were categorized as NSNA. With regard to the other classifications, I frankly can't recall specifically what nuances were identified to separate the remaining socket designs. Having said that, I do believe that sockets that were not definitively specific to the aforementioned categories were classified as NML if the medial - lateral socket dimension was narrower than the anterior - posterior dimension. I do not believe however, that any of the sockets we evaluated were actually designed and fabricated by Ivan Long himself.
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