Developed and fabricated by Otto Bock HealthCare GmbH, the C-Leg® is the central component of a highly sophisticated leg prosthesis system. The “C” in C-leg stands for the “Computerized” leg. The microprocessor controls the C-Leg® in real time throughout the entire walking cycle, controlling the types of movements that healthy people take for granted.

The other knee joint that utilizes C-Leg® technology is called ‘Compact’ because its offering of features is more compact. During the development of this innovative knee joint, highest priority was given to safety. The advantages of the C-Leg® Compact are particularly beneficial for prosthesis users who require a high degree of stability, for example, elderly people with lower walking speeds or amputees with additional, physical limitations.

The C-Leg® Compact utilizes the proven advantages of the electronic stance phase control and always provides high stability, such as when negotiating stairs, inclines and other walking surfaces.

The C-Leg® is an intelligent leg prosthesis system that contains sensors, which can tell what phase of gait the user is in at any given moment. The knee joint sensor measures step length and frequency and transmits this information for the dynamic control of the swing phase. To ensure stance phase stability, a moment sensor measures heel strike and forefoot load. Changing resistance within the joint—which allows the leg to stiffen for support of flex out of the way when necessary—is created by an hydraulic system.

Servo motors regulate the valves of the hydraulic unit, which increase or decrease the flow of hydraulic fluid, thus changing the resistance available. The opening and closing of these valves ensures that the damping adapts in real time to the respective situation – whether the C-Leg® user is walking quickly or slowly, or taking large or small steps. The microprocessor coordinates all measurement and control processes. The C-Leg® is powered by a lithium-ion battery.

The C-Leg® allows users to walk naturally. Unlike conventional prosthesis users, C-Leg® users no longer have to concentrate on every step. This allows them to move freely in their everyday life. Whether taking small steps, for example when shuffling through crowded shopping areas, or walking briskly, C-Leg® users can transition smoothly between different walking speeds. The computer-controlled, hydraulic stance phase stability allows them to conquer steep terrain with ease and security – without the C Leg® buckling involuntarily if they hit uneven ground. With this feature, prosthesis users can catch themselves before stumbling and falling. Moreover, a study has shown that C-Leg® users expend considerably less energy when walking, allowing them to cover longer distances with the C-Leg® than with a conventional prosthesis.

In just a moment, the C-Leg® can easily be switched from normal operation into one of the additional special modes. One individually adaptable mode, for example, enables the user to perform activities such as cycling or cross-country skiing. An additional standing mode provides more stability and security while standing. This standing mode lets C-Leg® users stabilize the C Leg® with little energy expenditure in any flexion angle – in spite of dynamic alignment.

The C-Leg® prosthesis system offers users permanent control of the movements of their prosthesis. For amputees this means that they can walk more smoothly and comfortably, changing speed and step length so that they can closely approximate normal walking.

Every 0.02 seconds, electronic sensors provide the data required for swing phase control and stance phase stability. That means that the C-Leg® always recognizes what walking phase the user is in, and adapts to the individual requirements in real time. For this reason, the prosthesis user can pay more attention to where he or she is going, and less on his or her prosthesis. At the same time, the C Leg® provides a maximum of security in all everyday situations, for example when walking on uneven surfaces or when walking down stairs or inclines step-over-step. The continuously present stance phase stability reduces the risk of falling, while the more natural gait helps relieve the sound side of the body.

The C-Leg® can be used by transfemoral (above the knee) amputees who weigh up to 275 lbs./125 kg. It was primarily designed for active prosthesis users of any age, who can be assigned to Mobility Grades 3 or 4 (unrestricted outdoor walkers and unrestricted outdoor walkers with especially rigorous demands).

When developing the C-Leg® Compact, the increased need for security of those who are less mobile was the main priority. The mechatronically-controlled stance phase stability is a result of this focus. In contrast to the C-Leg®, its hydraulic swing phase control is not electronically controlled. Furthermore, the C Leg® Compact does not include any additional modes available to the more active users who use the C-Leg®.

The C-Leg® Compact features intelligent control and allows the prosthesis user to walk smoothly. However, the C-Leg® Compact was designed to provide increased security for amputees with restricted mobility. The mechatronically controlled, hydraulic stance phase, in particular, is a special feature that stabilizes the joint from heel strike up to the exact point of switching over to swing phase, helping the user to avoid stumbles or falls for example, when walking on uneven ground or over door sills.

The C-Leg® Compact is powered by a lithium-ion battery with a capacity for 40 to 45 hours. Users generally recharge the prosthesis overnight by plugging it into a wall outlet. If need be, it can also be recharged using a 12 Volt connection in a car, for example.

The C-Leg® Compact allows for comfortable walking downhill or down stairs while always offering the highest possible security. As with the sound leg, knee flexion is dampened, resulting in a natural gait pattern that efficiently relieves the sound side of the body. In addition, the prosthesis user can concentrate less on his or her prosthesis, and more on where he or she is going.

The C-Leg® Compact was designed for transfemoral amputees with Mobility Grade 2 (restricted outdoor walkers). However, it can also be used by less active amputees of Mobility Grade 3 (i.e. unrestricted outdoor walkers). It is approved for a patient weight of up to 275 lbs./125 kilograms.

The Lithium-Ion battery that powers both knees generally operates from 40-45 hours. In case of power failure, the C-Leg® and C-Leg® Compact automatically switch to a safety mode. Beforehand, a vibration alarm informs the prosthesis user several times that the battery is running low. In this mode, the C-Leg®/C-Leg® Compact extends and maintains stance phase resistance, providing the user with a stable leg. Switching from stance to swing phase is no longer possible while the safety mode is active.