Progress for Prosthetic Knees

The elevator door opens and a squat Latino man almost kicks my head off.   Odd as it may sound, this is a pleasant greeting at the office where I have come to obtain a new prosthetic leg.   Martin is a single leg below-the-knee amputee with a black belt in Karate, and his feisty roundhouse kick is a welcome sight for someone of the same affliction.  This is my first visit in a while, and after seven years I’m excited to see what superpowers a modern prosthetic has to offer.

Of the several recent advancements in leg technology, including those of foot and socket, microprocessor knees are the big deal.  These knees use embedded motion sensors to collect spatial and positioning data of a wearer’s limb at up to 50 times a second.  A microprocessor interprets this data according to a predefined algorithm and appropriately adjusts the flexion and extension of a central hydraulic piston.   The result is a knee that can optimize its state to give the wearer a smoother experience with reduced effort.

This is a big change from my usual mechanical unit so I’m excited to feel the difference.   My prosthetist, Chris, has arranged for me to trial two microprocessor knees, the C-Leg and the newer, more advanced Genium.   I strap on the C-Leg and pace up and down the small office hallway.  It’s buttery smooth and I’m impressed how it carries me through the swing phase of my gait.  I burst into a run and almost end up flying out the window at the end of the hall.  A good sign.  I test out the incline traversal capabilities on the office ramp and enjoy not having to do my usual beleaguered half-skip.  After an hour I switch to the sexy and compact Genium, which utilizes an accelerometer and gyroscope to better refine its input.  I pause in semi-crouched position and revel as the leg clenches and applies an opposing, supportive force.  Nice.  I try and run but its so sensitive it freezes on every first step. Not nice. The Genium is obviously badass but it’s so expensive I strike it from my list of possibilities.

After two hours with the microprocessor knees (not much time to get used to a prosthetic) I was impressed.  To compare I went back to my knee of 12 years, the 3R95 and maneuvered around a bit.  With only a simple hydraulic pump, the 3R95 offers no support when in a flexed position, forcing my biological leg to support my entire body.   But it’s light (about three pounds lighter than the C-Leg) and less bulky; I feel noticeable quicker.  I jump off the mini staircase and run up and down the floor a few times and pivot like I am playing basketball.  Decisions…decisions….

I would come to learn there are other benefits to the 3R95 over the microprocessors.  Cost is one (the C-Leg is approximately $15-20k more than the 3R95) but another is versatility.  Microprocessors can’t be submerged in water and they necessitate an ion battery that carries a limited charge.  For certain activities like biking you need to utilize a special preset that is pre-programmed.   As Chris lists these caveats my mind drifts away to a recent vacation, canoeing down the Delaware River, and I realize the C-Leg would require unacceptable sacrifices.   I relay my decision and a quick frown slides across Chris’s face.

Undoubtedly I just cost Chris some insurance money, but he is cool about it and understands.  It occurs to me my cell phone wasn’t much help on my last vacation either, and as I walk into the elevator with my shiny new prosthetic, I can’t help but wonder how much of my decision was guided by a subconscious stubbornness to keep my body parts computer free.