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® microcessor-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 adjustments to knee function, using algorithms developed from studies of how thousands of people walk, fine-tuned for the wearer’s unique needs and characteristics.
For example, data from the knee angle sensor is used to adjust dynamic swing phase control any time the wearer changes cadence.
And a force sensor in the C-Leg’s shin component measures toe and heel loading to inform the system when it is both safe and efficient to transition from stance phase to swing phase.
The latest version of the C-Leg enables wearers to select between two preset options optimized by their prosthetist for a particular activity. Typically, one is set for everyday, all-around use and the other for a specific activity, such as bicycling. An intentional tap of the foot induces the mode switch, which is confirmed by a beep tone and vibration.
Two studies have been undertaken to evaluate the C-Leg’s performance relative to different conventional hydraulic knees also made by the C-Leg’s manufacturer, Otto Bock Health Care. In one, 10 unilateral transfemoral amputees completed four tests in each of three knees, the single-axis C-Leg, the 3R45 single axis knee with integrated hydraulic swing-phase control, and the 3R80 single-axis knee with rotary swing and stance-phase control.
The 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 Otto Bock 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.
In addition, an ongoing Prosthetic Research Study project is comparing the activity level of patients using the C-Leg with those using conventional knee units.
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.
For additional information on this exciting advance in prosthetic componentry, we invite you to contact us. Offices are located in Beaumont, Nederland and Jasper, Texas.