C-Leg

The C-Leg is a microprocessor-controlled knee prosthesis, developed by the Otto Bock Healthcare company, that enables moderately active amputees to vary walking speeds and travel over changes in terrain. The C-Leg uses hydraulic cylinders to control the flexing of the knee. Sensors send signals to the microprocessor that analyzes these signals, and communicates what resistance the hydraulic cylinders should supply. C-Leg is an abbreviation of 3C100, the model number of the original prosthesis, but has continued to be applied to all Otto Bock microprocessor-controlled knee prostheses.

Technical aspects of the C-Leg

The versatility of the C-Leg is possible due to the advanced technology incorporated into different components of the prosthesis.

Sensors in the C-Leg

The C-Leg uses a knee-angle sensor to measure the angular position and angular velocity of the flexing joint. Measurements are taken up to fifty times a second. The knee-angle sensor is located directly at the axis of rotation of the knee. [http://www.ottobockus.com/products/lower_limb_prosthetics/c-leg.asp “Otto Bock Microprocessor Knees”] , Otto Bock, retrieved 16 March 2008]

Moment sensors are located in the tube adaptor at the base of the C-Leg. These moment sensors use multiple strain gauges to determine exactly where the force is being applied to the knee, from the foot, and the magnitude of that force.

Hydraulics in the C-Leg

The C-Leg controls the resistance to rotation and extension of the knee using a hydraulic cylinder. Small valves control the amount of hydraulic fluid that can pass into and out of the cylinder, thus regulating the extension and compression of a piston connected to the upper section of the knee. Pike, Alvin (May/June 1999). “The New High Tech Prostheses”. InMotion Magazine 9 (3)]

Microprocessor in the C-Leg

The microprocessor receives signals from each sensor and uses proprietary algorithms to determine the type of motion being employed by the amputee. The microprocessor then signals the hydraulic cylinder to act accordingly. The whole process happens instantaneously.

The microprocessor also records information concerning the motion of the amputee that can be downloaded onto a computer and analyzed. This type of information allows the user to determine how to make the most of the prosthesis.

Power source in the C-Leg

The C-Leg is powered by a lithium-ion battery housed inside the prosthesis below the knee joint. On a full charge, the C-leg can operate for up to 45 hours, depending on the intensity of use. A charging port located behind the knee joint can be connected to a charging cable plugged directly into a standard outlet. An optional adapter can also be used enabling the C-Leg to be charged from the 12-volt cigarette lighter outlets found in automobiles. [http://www.ottobock.com/cps/rde/xchg/ob_com_en/hs.xsl/7071.html “FAQ: Questions and Answers on the C-Leg.”] , Otto Bock, retrieved 1 April 2008]

Advantages of the C-Leg

The C-Leg provides many advantages over conventional mechanical knee prostheses. The C-Leg provides a close approximation to an amputee’s natural gait. The C-Leg allows amputees to walk at higher speeds, approaching that of non-amputees. Variations in speed are also possible and are taken into account by the C-Leg’s sensors and communicated to the microprocessor, which adjusts to these changes accordingly. It also enables the amputees to walk down stairs with a step-over-step approach, rather than the one step at a time approach used with mechanical knees. Martin, Craig W. (November 2003) “Otto Bock C-leg®: A review of its effectiveness”. WCB Evidence Based Group ] The C-Leg’s ability to respond to sensor readings can help amputees recover from stumbles without the knee buckling. Without having to concentrate on each step, C-Leg users can focus on other activities while walking. [ [http://www.ottobock.com/cps/rde/xchg/ob_com_en/hs.xsl/1913.html?id=2897#t2897 “High-Tech for more Quality of Life”] , Otto Bock, retrieved 16 March 2008]

Amputees using the C-Leg can take on hills and slopes with better stability, due to the real-time dynamic response of the system. The C-Leg also has the ability to adjust to changes in terrain directly. The system that the C-Leg employs allows amputees to gain freedoms otherwise unattainable with a mechanical knee prosthesis.

Disadvantages of the C-Leg

The C-Leg has some significant drawbacks that impair its use. The C-Leg is susceptible to water damage and thus great care must be taken to ensure that the prosthesis remains dry. Otto Bock recommends that each amputee use the C-Leg for up to two months before the system can fully become accustomed to the individual’s unique gait. Becoming accustomed to the C-Leg is especially difficult when walking downhill, and amputees should seek help while becoming familiar with the system to avoid injury.

Appropriate users of the C-Leg

A wide range of amputees can make use of the C-Leg; however, some people are more suited to this prosthesis than others.

Types of amputees

The C-Leg is designed for use on people who have undergone transfemoral amputation, or amputation above the knee. The C-Leg can be used by amputees with either single or bilateral limb amputations. In the case of bilateral amputations, the application of C-Legs must be closely monitored. In some cases, those who have undergone hip disarticulation amputations can be candidates for a C-Leg. [http://www.ottobockus.com/PRODUCTS/LOWER_LIMB_PROSTHETICS/C-LegTechnical.asp “Clinical and Technical Information”] , Otto Bock, retrieved 16 March 2008]

Levels of activity

The C-Leg is designed for amputees who lead an active lifestyle. The prosthesis is recommended for amputees that vary their walking speeds and can reach over 3 miles per hour; however, it is not to be used for running. For amputees that walk long distances, up to 3 miles a day, the C-Leg is also practical. Amputees that routinely walk on uneven ground, slopes, or stairs are also excellent candidates. Active amputees, such as bikers, rollerbladers, and those responsible for young children, can also benefit from the mobility the C-Leg provides.

Amputees’ physical characteristics

Certain physical requirements must be met before considering the C-Leg for use. The amputee must have satisfactory cardiovascular and pulmonary health. The balance and strength of the amputee must be sufficient to take strides while using prosthesis. The C-Leg is designed to support amputees weighing up to 275 pounds.

Development of microprocessor-controlled prosthetic knees

The C-Leg is a result of continuing innovation in the field of prosthetics. Knee prostheses have developed significantly from their humble beginnings to the technological devices that exist today. The first microprocessor-controlled prosthetic knees became available in the early 1990’s.

The Intelligent Prosthesis 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. [ [http://www.blatchford.co.uk/company/history/history.html “History of Prosthetics”] , Blatchford & Sons, Ltd, retrieved 16 March 2008] An improved version was released in 1995 by the name Intelligent Prosthesis Plus. Blatchford released its most advanced prosthesis, the Adaptive Prosthesis, in 1998. The Adaptive Prosthesis utilizes hydraulic controls, pneumatic controls, and the microprocessor to provide the amputee with a gait that is responsive to changes in walking speed.

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. Other microprocessor controlled knee prostheses include Ossur's Rheo Knee, released in 2005, the Power Knee by Ossur, introduced in 2006, and DAW Industries’ Self Learning Knee (SLK). [ [http://www.daw-usa.com/Pages/SLK3.html “The SLK, The Self-Learning Knee”] , DAW Industries, retrieved 16 March 2008]

See also

Prosthesis

Otto Bock

Amputation

References

External links

* [http://www.ottobockus.com/PRODUCTS/LOWER_LIMB_PROSTHETICS/c-leg2.asp C-Leg]
* [http://www.ottobockus.com/ Otto Bock]
* [http://www.oandp.org/ American Academy of Orthotists and Prosthetists]