From the development of the first artificial knee device long ago, walking with a transfemoral prosthetic limb has either required a great deal of concentration or been extremely awkward. Either the wearer walked stiff-legged with the knee locked, or he/ she had to think, and often worry, about controlling the limb in swing phase...on a level surface at a constant speed. Changing cadence or ambulating on uneven terrain introduced a whole new
degree of difficulty!

The introduction of the 3C100 C-Leg® microprocessor-controlled knee-shin system in 1999 initiated a revolution of sorts in transfemoral ambulation. Essentially, the C-Leg’s on-board circuitry does the thinking and lets the above-knee amputee concentrate on other things while walking.

The C-Leg functions through real-time gait analysis to control hydraulic swing- and stance phase resistance. Built-in sensors provide information to the microprocessor 50 times per second to determine the precise phase of gait.

The microprocessor then makes instantaneous adjust-ments to knee function, using algorithms developed from studies of how thousands of people walk, fine-tuned for the wearer’s unique needs and characteristics.

Two studies have been undertaken to evaluate the C-Leg’s performance relative to different conventional hydraulic knees.

The first series of tests included two gait analysis trials, a kinetic test for stance-phase loading, and another kinetic test for swing-phase performance while walking 1000 meters on a treadmill at three different speeds.

The most telling results showed the C-Leg clearly superior at higher speeds on the swing-phase treadmill test, in swing-phase behavior, and in reduction of residual limb forces. The second analysis sought to compare the physiological cost of ambulating in the C-Leg with that of another conventional single-axis hydraulic knee, the 3C1. Six experienced 3C1 wearers were involved in the study. After gaining experience in the C-Leg for several weeks, the subjects were evaluated at three walking speeds on a treadmill, first in the 3C1, then the C-Leg. All other aspects of the wearers' prostheses were as identical as could be provided.

Results show the C-Leg to be more energy-efficient with a significant reduction in oxygen consumption ranging from 7 percent at slow walking speed to 4 percent at the fast speed.

Clearly, the C-Leg is a good option for vigorous, healthy amputees, but it is also applicable to many other transfemoral amputees as well. Of course, not everyone is a candidate, but for those who are, an increase in ability of one functional level is certainly possible.

Read Dr. Wheatley's Article on Computer Legs