KAFO Knee Extension Assist
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We know from our prosthetic experience that when patients walk more quickly with a free swinging knee, heel rise during initial swing phase quickly becomes excessive, and the gait pattern is severely disrupted while the person if forced to wait for the leg to reach full extension. One common prosthetic solution is the addition of an adjustable extension assist.
During the SCOKJ Qualification Course, I usually mention that the same principle can be applied to lower limb orthoses. But, many orthotists are unfamiliar with prosthetic principles so this comment sometimes draws puzzled looks.
Fortunately, I recently had the chance to meet one of Pam Lupo CO's patients who has used just such a knee extension aid for many years, who confirmed that he would not consider walking with a free-knee KAFO without this adaptation. He and Pam kindly granted permission to post some photos of his system in this month's Corner.
Like the LEMA strap, 2 inch elastic webbing provides the external power for this orthosis. In addition to being inexpensive and reliable, this approach is readily adjusted by the user to modulate the knee extension moment created. This is particularly useful as the webbing ages and loses elasticity. Two closures on the proximal thigh segment permit the wearer to increase or decrease the spring effect.
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The straps originate in the supramalleolar region and cross at the patellar tendon, where they are tacked together with a few stitches. One advantage of such long elastic straps is that this provides maximum stretch capabilities, increasing the durability of this power source.
Much like the normal quadriceps muscle, the elastic provides increasing resistance as the knee flexion angle increases. When the tension is properly adjusted, this will limit heel rise very effectively and permit the patient to walk at a faster cadence. The elastic tension also helps accelerate the shin forward so it reaches full extension more quickly, shortening the duration of swing phase further. As the knee extends, the straps provide progressively diminishing extension force because the elastic elements approach their relaxed length. To reduce terminal impact, it is usually best to initially adjust the straps to have little or no tension with the knee fully extended.
This gentleman, who is a very active full-time worker in the Detroit area, prefers to have his extension aid quite snug because this supplements knee stability during stance phase. Horton's SCOKJ offers another alternative for stance stability, and might allow him to reduce the tension significantly if the straps are only intended to provide swing phase control.