Thranhardt Lectures
All the Thrandardt lectures were well done. This series has improved in quality each year and is now predictably among the most scientifically valuable group of presentations in the field. Tom Gavin CO updated his efforts to develop a lightweight, low cost, self-contained device to reliably record actual wearing time with a body jacket or similar device. This key measurement is likely to be able to discriminate between patients who seem compliant and those who actually are compliant, helping to explain some of the outcomes we see when treating idiopathic scoliosis with a custom TLSO.
Steven Gard, PhD from Northwestern reviewed his recent work investigating the biomechanical causes and implications of vertical displacement of the center of gravity. Although this was well explained in his article in JPO, it is always good to hear the author elaborate on such original research. In summary, in contrast to Eberhart and Inman's speculation half a century ago, it appears that knee flexion in early stance does NOT reduce the magitude of vertical oscillation of the CG.
Some in the audience had trouble accepting that one of the "gospels according to Inman" did not withstand scientific scrutiny, but I found Steve's data compelling. His conclusion was, in part, that stance flexion makes a significant contribution to shock absorption in early stance but since that is the wrong time in the gait cycle to have much effect one way or the other on maximum rise of the CG.
Interestingly, while preparing for a lecture I will be presenting in Sweden in a few days, I was rereading some of Woodie Flowers' work from the Massachusetts Institute of Technology that I read decades ago as a novice prosthetist-orthotist. The MIT experiments with a microprocessor-controlled hydraulic prosthesis simulator in the 1970s led them to the same conclusion.
Speaking of MIT, one of the most interesting talks of the entire meeting was the presentation by Hugh Herr, PhD from the MIT "Leg Lab". Although best known for making a number of clever ambulatory robots, the MIT group has also been working on a prosthetic knee that is self-adjusting. Dr. Herr briefly reviewed their results to date in developing an "auto-adaptive" device that uses an on-board microprocessor to compare the amputee's gait analysis data to a database from a large group of non-amputee subjects, gradually re-adjusting the prosthetic knee to encourage the amputee to walk in a more symmetrical pattern.
In some ways, this is the culmination of concepts first proposed by Professor Flowers based on research he conducted at MIT more than 25 years ago. It appears that actuators, power sources, and microprocessors are just now becoming small enough and sufficiently reduced in price that a self-contained prosthetic knee with these features may become a reality in the near future.
The short video clips looked quite smooth and natural, both on level ground and during stair descent. Reportedly, this knee will be able to sense and accommodate automatically for changes in the patient's weight, the addition of a heavier shoe, donning or doffing a backpack, and similar changes in the location of the center of mass. Dr. Herr summarized the concept by saying that this knee has "a virtual biomechanist and a virtual prosthetist on-board, constantly collaborating to tune the knee for each task that the amputee wants to accomplish." This approach is intended to allow the prosthetist to focus primarily on socket design, suspension, and alignment - and permit the amputee to concentrate on walking. Adjustments to the knee resistances will happen automatically, so it will no longer be necessary for the amputee to come back to the facility just to have the knee resistances fine-tuned as their gait pattern improves or changes.
This knee uses magnetorheologic fluid that thickens in response to electromagnetic signals to increase knee stiffness. Dr. Herr described this as a "virtual hydraulic unit" with the advantage that there are no high pressures generated that might cause wear on the seals in the unit.
But, by far the most outstanding presentation of the entire meeting was given by Robert Gailey, MSPT. Bob and his student researchers have been working for quite some time to try and develop a simple test instrument that will objectively document an amputee's functional level. Based on the results from the first 170 some amputees, this will likely be feasible.
This work has tremendous potential to validate the judgments we make as clinicians, and to add irrefutable credibility to our determinations about a patient's potential by offering an objective tool that is easily used in the clinic setting. The first part of Bob's research showed a very high correlation between a simple battery of tasks the amputee must perform with the prosthesis and the opinions of experienced, ABC Certified Prosthetists.
More surprisingly, and even more importantly, Bob was able to identify a set of tasks that the amputee can complete without a prosthesis that seem to have nearly the same validity. If continuing studies with larger numbers of subjects verify this instrument, we will then have a practical series of tests to conclusively demonstrate that an amputee has the potential to achieve a specific level of functioning - prior to fitting the preparatory prosthesis.
This would insure that patients receive functionally appropriate components with every prosthesis, and eliminate the old fashioned attitude that "amputees must walk on simple components first, to prove they are rehabilitation candidates". This "conservative" bias of requiring amputees to first use a primitive device not only fails to give marginal candidates a fair chance to demonstrate their potential, it is also much more costly for the overwhelming majority who become long term ambulators than to start them out with the components they will ultimately need.
In an intriguing sidebar discussion, Bob noted that he had done a analysis of the actual components these 170+ amputees received versus their measured functional level. There has always been suspicion and subterranean speculation that amputees may be receiving components that are "too good"; that is, that they might demand components that are high cost that they cannot use functionally. Bob's analysis showed quite the opposite.
In this group of lower limb amputees, 80% received knee, ankle, and foot components that were commensurate with their predicted and measured functional abilities. However, about 1 in 5 received a foot or knee component that was at least one functional level lower than is eligible for reimbursement under present Medicare policy guidelines. In other words, not only was there no evidence of a tendency to "overprescribe", in fact many patients received components that may have been rather conservative compared to their actual functional capabilities.
Bob is actively recruiting additional subjects to conclude this landmark research. If these trends continue and are verified as statistically significant, we may be able to prescribe functional components with far greater precision than seemed possible previously. This would be a tremendous contribution to clinical practice and to amputee's quality of life.
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Thank You
John,
As you probably recall I was unable to attend our Academy meeting. I would like to take this opportunity to thank you for your enlightening review of the meeting. I called many of my colleagues to see how the meeting went, and was pl... read more
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