I just recieved another call asking me to clarify the recommended height of trimlines on an elevated vacuum transfemoral socket. In the phone call the prosthetist said he asked a number of prosthetists and the responses were "all over the map".

I would like to first argue that it is incorrect to use the term "sub-ischial sockets" when referring to elevated vacuum transfemoral prostheses. One main difference between elevated vacuum and most other designs is that other designs such as the quad socket have specifically designed trimlines. In the case of elevated vacuum, the height is just as critical, but it depends on the individual patient and residual limb characterists. In one case the proper height is ischial level and in another it is 1" below the ischium.Keep in mind that trimlines affect stability, support, and suspension, but also affect comfort and range of motion. Too low, and the socket will not work; too high and there is unecssary restriction and discomfort.

There is no scientific way to determine the exact location, but in my experience there is no reason to go proximal to the ischium even on the short limbs.On short limbs the proximal brim helps to maintain a good seal between the inner gel liner and the sealing sleeve which is taped to the inner vacuum cap. 

On long residual limbs, I begin at ischial level and  then check for hip joint range of motion. If there is any restriction of range of motion even in the extreme limits, I lower the trimlines. Once the socket is comfortable with full range of motion, I do not lower the trimlines any further. I then fabricate the final socket with a flexible proximal brim.

I welcome other input from "the map".