Manufacturers' Workshops
Wednesday was filled with 28 different workshops providing 2-3 hours of technical information about a variety of new and old P&O products. Those with some measure of scientific content were best attended, with some of the newer topics drawing 50-75 active participants. One of the best attended was Ossur's program on transfermoral prostheses introducing their new TF suspension liners.
I attended Cascade's new program on their versions of the Intelligent Prosthesis based on the familiar Kobe steel patents also used by Blatchford and Seattle Orthopedic Group, Inc. I was pleasantly surprised to discover that this is not simply another "me too" offering, but represents a refinement in microprocessor control logic for pneumatic swing phase flexion resistance. John Hattingh CP did a very good job of both explaining the principles and making the knees seem much more "prosthetist friendly" than might have been expected.
While Blatchford has gone to a wireless programmer with the IP Plus, Cascade elected to stay with an adjustment unit that physically connects to the knee via telephone cables. But, for a patient who can easily walk at a range of cadences, the initial adjustments were so straightforward that this is not much of a disadvantage. John had his model simply walk continuously, starting at a very slow pace and then gradually increasing cadence on command. After a sample of 7 steps at a particular pace, pressing the button captures that data and sampling of the next group of steps begins.
The Cascade ProAdvantage IP knees have three innovative features. First, they are available in a polycentric configuration, offering an alternative to the friction brake stance controls previously available under these licenses. In addition, Cascade's friction brake looks like an Otto Bock 3R15 that has been rotated ninety degrees, with the brake axis and swing axis stacked vertically over one another. This is reported to result in faster brake release in late stance, in an effort to overcome the "braking lag" - inherent in existing mechanical brake knees - that often disrupts preswing knee flexion. By tipping the knee in the sagittal plane, using the alignment screws, the prosthetist can increase or decrease how quickly the Ground Reaction Force passes the brake axis and causes it to release.
More significantly, Cascade's ProAdvantage uses a different control logic than the original Intelligent Prosthesis. In the original design, the knee measured step timing [from full knee extension to full extension again] to determine when to adjust the flexion valve. This meant that one full step was needed for the baseline timing and a second full step to detect a cadence change. The valve adjustment then took effect during the third step.
The ProAdvantage estimates stance phase duration instead, by timing how long it takes the knee to go from full extension to a few degrees of flexion in late stance. It then estimates the time for swing phase, and adjusts the valve as necessary. This means that the valve is readjusted during the same step, so swing phase timing is optimized more quickly. I watched the model demonstrating this knee carefully, and could not detect any "cadence lag" such as occurred with the earlier control logic.
Since these microprocessor-controlled knees are also priced commensurately with the more elegant hydraulic stance and swing control knees, we may see more widespread clinical use of these IP variations.
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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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