Researchers Find Variability in Who Benefits From Sub-Ischial and Ischial Prosthesis Designs

ORLANDO, Fla. – People with amputations present with mobility limitations. According to Edward Strachan, CPO, this is partially the result of balance impairment.

“If we are able to maximize their balance, we will likely be able to minimize their energy cost,” Strachan explained during his presentation, here, at the 2011 Annual Meeting and Scientific Symposium of the American Academy of Orthotics and Prosthetics. “As prosthetists we affect this balance through prosthetic alignment, components and socket design.”

One way of measuring this balance, Strachan explained, is through gait variability.

“As an individual’s capacity to maintain balance decreases, steps become less consistent in length, width and timing. Lower gait variability is indicative of improved balance and decreased energy expenditure. Therefore, ideally a prosthesis should be designed to minimize this stride-to-stride temporal special gait variability.”

For his study, which was supported by University of Michigan Orthotics and Prosthetics Center and the Ohio Willow Wood Company, Strachan measured the stride-to-stride gait variability of seven unilateral transfemoral amputees throughout the course of 10 walking trials. New prosthetic sockets were fabricated for each participant as they repeated these measures for both the sub-ischial elevated vacuum suspension and the ischial containment suspension,

“Neither socket consistently resulted in more variability,” Strachan said. “Some [participants] performed better in the ischial containment and some performed with less variability and improved balance in sub-ischial.”

He reported that three of the seven participants walked better with ischial containment while four of the seven walked better with sub-ischial sockets with less variability.

“The [participants] who performed better with ischial containment where those with short residual limbs, muscle strength impairments or any type of physical de-conditioning,” he said. “Those who benefitted from the sub-ischial design had longer residual limbs, physical conditioning, normal muscular strength and good muscular endurance.”

In conclusion, Strachan explained that socket trim line heights, which were not consistently relative to vacuum pressure, should reflect specific patient characteristics.


It’s good to see somebody do a vacuum study that compares ischial containment to sub-ischial. Everything I’ve seen so far has not compared the two and I’d often wondered, is the vacuum affecting the results or is this trim line affecting the results? It’s a good attempt at starting to compare the two.

— Michael E. Hansen, LPO
American Orthopedics

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