This article is written by an actual amputee who wears these items. There are quite a few things to consider in selecting a prosthetic knee.
Certainly the most well known knee on the market is the C-Leg from Otto Bock, but it may not be the best for you because if your insurance will not pay for all it's needs of service, you'll find yourself dipping into your pocket uncontrollably. This article will only address the three most popular knees, the C-leg, the Rheo Knee and the Adaptive - or Smart Adaptive as it is known these days.
The first microprocessor-controlled prosthetic knees became available in the early 1990’s. The Intelligent Prosthesis Knee was first commercially available microprocessor controlled prosthetic knee. It was released by Chas. A. Blatchford & Sons, Ltd., of Great Britain, in 1993 and made walking with the prosthesis feel and look more natural. An improved version of the knee was released in 1995 by the name Intelligent Prosthesis Plus (IP+). Blatchford released another knee, the Adaptive Prosthesis, in 1998. T
he Adaptive prosthetic knee utilized hydraulic controls, pneumatic controls, and a microprocessor to provide the amputee with a gait that was more responsive to changes in walking speed. Blatchford is known by the name Endolite in America - behind the fact most of it's knee frame are strong carbon fiber designs. Endolite took the approach to give the amputee some control of there knee with hand held programmers and modular replacement parts anyone can install.
The Otto Bock Orthopedic Industry introduced the C-Leg during the World Congress on Orthopedics in Nuremberg in 1997. The company began marketing the C-Leg in the United States in 1999. the C-Leg is a complete in house controlled service and setup proposition.
You cannot get parts, the software to program it or any parts yourself from the company - it all has to go through an Otto Bock certified prostheticist who has to send the knee to Otto bock for all service and repair. Other microprocessor controlled knee prostheses include Ossur's Rheo Knee, released in 2005, the Power Knee by Ossur, introduced in 2006, the Plié Knee from Freedom Innovations and DAW Industries’ Self Learning Knee (SLK).
The C-Leg is probably the best developed emulating knee on the market. It has dynamic stance support controlled by the sensor in the lower pylon foot connector, and this makes all the difference in the world. Having the sensor in a sensitive leverage point at the ankle area allows the hydraulics to be switched and controlled by the sensor input more predictably and dynamically fine tuned. This lets the leg "know" better how to support and lock or give dynamically.
Let it be made clear - the C-leg, is the only Microprocessor controlled knee which is ALWAYS in support mode (unless you change to modes by remote or the triple tapping of the toe), and all other knees on the market - with the strange exception of the Rheo Knee - defaults to swing phase, and if it is not setup statically to lock, the slightest shift in weight may cause the knee to completely go out from under you unexpectedly. A properly setup C-leg will NOT do this. It will always provide support.
That being said . . . The other two competing well known microprocessor controlled knees - the Rheo Knee from Ossur and the Adaptive2 - or now known as the "Smart Adaptive" do not use sensors in the ankle and cannot do true dynamic stance support for this reason. The Rheo knee uses software to try to detect when to lock, or stiffen or not. Many wearers of the Rheo Knee say the Rheo Knee behaves unpredictably.
The Adaptive by Endolite, is a dual knee. It uses pneumatics for the swing, and hydraulics for the stance and flexion support functions. The Endolite Knee has its sensor in the knee at the top and to the rear of the hinge area of the knee. The early knees could basically only detect and switch between five modes - standing, walking, stairs, stumble recovery, or ramps and slopes; and it did this by the way the weight pressed on that sensor and how fast.
The Endolite Adaptive does have a "standing mode" - based on weight on the force sensor and will hydraulically lock while standing still - if setup right. While the Endolite was/is a self learning knee, the initial stiffness of the knee was/is set up manually using a Bluetooth communicating programmer box. The Endolite Adaptive Knee however had/has no way to monitor dynamic stance support.
Thus when it locks or unlocks it has to switch modes - or at least try to. It has to guess at which mode to switch to by how sensitive you have set it up to change to based on your walking style. This author owns the first generation Endolite Adaptive 2, which will soon be upgraded to the latest Smart Adaptive by changing the hydraulic cylinder and programming card which is attached to it and a firmware upgrade by Endolite to the programmer box, and has walked on all three.
The price is really reasonable - only a few thousand dollars for basically a new, latest and greatest - Smart Adaptive knee. Still remember it does NOT do "dynamic stance support" however. This is the nice feature of the Endolite Adaptive knee - the cylinder is a completely field replaceable item that can be swapped out by anyone with the removal and replacement of three bolts. The bolts are exposed and accessible and can be done in 30 minutes.
The Endolite unit is a good walking knee, and uses far less electrical power than either the Rheo or C-Leg Knees. It could go up to two weeks without a recharge and the batteries are 3 simple photo CR123A batteries available almost anywhere. You could get a replacement rechargeable set for under $20. BUT - it does not do dynamic stance support. For instance you cannot push in a vehicle clutch and have it respond dynamically to provide resistance support.
Another issue of the Adaptive Knee is that it - like the Rheo Knee must be statically setup properly with body weight to the front of the knee hinge so it locks and presses the weight onto the knee sensor in the various phases of walking and standing. Both the Adaptive and Rheo Knees self program as you walk. The C-Leg is a bit different. It can be setup almost anyway you want - but Otto Bock recommends it most stable about 1.5 inches to the rear of body weight.
However, if the pylon sensor is ever unplugged or goes bad, the knee goes into what is called "native mode" and locks up stiff. It then requires a trip to the prostheticist to re-program it before it will work again. This can also happen on some units if the battery goes completely dead, but it is supposed to go into "standard mode" and respond and work again on a re-charge. The leg does NO self programming on it's own, but the owners of the newer model C-legs that have bluetooth and the remote can do minor programming changes with the remote. No one but an Otto Bock C-Leg certified prostheticist can get the C-Leg software (and training assistance) to program the leg and/or even get service from Otto Bock - meaning they will not even "talk" to a non-certified prostheticist about services or repairs to the C-Leg. They will not - cannot - give you the software.
If they are an Otto Bock C-leg certified prostheticist, there are certain L-codes they use for billing which - if your insurance carrier does not not accept as a microprocessor controlled knee - will cause rejection of the/your claim each and every time. The C-Leg cannot be serviced by you or your prostheticist in any way. ALL service is done by Otto Bock according to their plans, upgrades and service schedule criteria. You cannot control it. Your prostheticist cannot control it either. Most people today have a 20% co-pay.
That can get costly and add up really fast. The Rheo Knee just has not had good success catching on. It uses magnetic fluid - called magneto-rheostatic fluid. The magneto-rheostatic fluid is liquid until a magnetic field is present, it turns solid immediately after being placed in a magnetic field. The Rheo Knee has tried to use this for stance support and stance flexion using varying magnetic fields for hydraulic support. Some vehicles are now using this technology in shock absorbers. The drawback is obvious. If there is no power - there are no magneto-rheostatic properties, and thus the leg goes more towards free swinging. Also not so obvious - is that of the three knees, the Rheo Knee is the most power hungry, and the Endolite Adaptive is the least power hungry.
The Rheo Knee is a radial design similar to the Otto Bock 3R80. So which one is best? Well that depends on your insurance. If you have Medicare or VA benefits, the C-Leg is usually fully covered, and you are best then with the C-Leg. The C-Leg has proven its ability such that it is the only leg to allow a US Air Force pilot to return to flight duty after a motorcycle accident caused him to loose his left leg. If you want a knee that will do dynamic stance and flexion support, but cannot afford the C-Leg lock-in to Otto Bock charges and mandates, you can try the Rheo Knee - but be advised, the software and mode switching of the knee will take quite a bit of getting used to, and you will have to keep it fully charged at all times. If the battery goes dead - you will have NO support at all - and if it is not setup up properly with the body weight to the front of the knee hinge, it will fold on you easily unexpectedly.
Remember - or be advised - the Radial Design has NO ability to mechanically lock at all. The Adaptive Knee on the other hand set up properly will lock - but you will have no stance support - in fact no support at all if the hydraulics blow and leak dry - BUT you can still walk on it - slowly and carefully. It is a variation on a SNS design like the "Ultimate Knee" by Ortho.
The sad reality is the Endolite hydraulics do leak and blow more often than not and you cannot fill the cylinder with oil yourself - but you can swap the unit out yourself for a new one in about 30 minutes. You cannot do any work at all on the C-Leg or the Rheo knee. So, the answer is not an easy one.
The C-Leg is maintained only by Otto Bock and the hydraulics are fairly rugged. When they fix it - they fix it right and upgrade it if required. The Endolite Adaptive is cheaper to buy and easier to get going walking on that many insurances will pay for as comparable to a regular non-microprocessor controlled hydraulic knee because it is self learning and cheaper to buy and set up.
The Rheo Knee has the best of both the C-Leg stance and flexion support and Adaptive Knee's self learning features, but you'll have to get accustomed to manipulating it. If you just want to walk right away at the least expensive, lowest learning curve, then the Endolite Adaptive2 or Smart Adaptive Knee is the one for you. If you need dynamic stance support and the feeling of trust and safe well being from the leg - you need to figure out how to get hold of a C-leg.