Following a lower-limb amputation and after the appropriate healing of the surgical site, an individual may consider the use of a prosthetic leg to begin rehabilitation efforts in learning to ambulate. There are many different component types of a prosthetic limb, with more than 100 different prosthetic knee devices currently available on the market, and still other devices are under investigation.
MICROPROCESSOR-CONTROLLED PROSTHETIC KNEES
Multiple prosthetic devices are available that use varying degrees of computer technology to enhance basic mechanical knee designs. Recently, prosthetic devices with a microprocessor-controlled knee have become available, including the C-Leg® and Genium™ Bionic Prosthetic System (Otto Bock Orthopedic Industry, Minneapolis, MN), the Intelligent Prosthesis (IP) (Blatchford & Sons, UK), the Rheo Knee ® (Ossur, Iceland), and Seattle Powered Knees (3 models include Single Axis, 4-bar and Fusion, from Seattle Systems). These devices are equipped with a sensor that can detect when the knee is in full extension and automatically adjust the swing phase of the individual's gait, allowing for a more natural walking pattern at varying speeds. The C-Leg® is also designed to improve stance control. In addition, sensors may be able to detect a stumble and stiffen the knee to avoid a fall.
Hafner et al (2007) investigated the differences in function, performance, and preference between mechanical and microprocessor-controlled prosthetic knees for transfemoral amputees. Subjects were fully accustomed to a mechanical knee system (various types) and were required to show proficiency in ambulating on level ground, inclines, stairs, and uneven terrain prior to enrollment. Of the 17 subjects (81 percent) who completed the study, patient satisfaction was significantly better with the microprocessor-controlled prosthesis as measured by the Prosthesis Evaluation Questionnaire (PEQ). In addition, subjects reported fewer falls, reduced frustration with falls, and improved concentration on tasks other than knee control and stability while walking. Average performance on stair descent improved from a step-to pattern with a rail to a step-over-step pattern with a rail and assistive device. Also, the C-Leg® improved hill descent from requiring an assistive device to using a step-to pattern without an assistive device.
All lower-limb amputees returning from Operation Iraqi Freedom and Operation Enduring Freedom currently receive a C-Leg® from the Department of Veterans Affairs (VA). Subjective assessment revealed a perceived reduction in attention to walking while performing the cognitive test (effect size of 0.79) and a reduction in cognitive burden with the microprocessor-controlled prosthesis (effect size of 0.90). Seven of the eight subjects preferred to keep the microprocessor-controlled prosthesis at the end of the study. The authors noted that without any prompting, all of the subjects had mentioned that stumble recovery was their favorite feature of the C-Leg®.
Although it is similar to the C-Leg®, the Intelligent Prosthesis (IP) is not currently distributed in the United States. One study (Kirker, et al) reported on the gait symmetry, energy expenditure, and the subjective impression of the IP with 16 subjects who presented with an above-the-knee (AK) amputation related to trauma or congenital anomaly. These individuals had been functioning adequately with a pneumatic swing phase control unit and were offered a trial of the IP. At the commencement of the study, they had been using the IP for between one and nine months. A questionnaire was provided to the individuals to rate how much effort was required to walk at slow, normal, and fast speeds on multiple surfaces (e.g., smooth level, outdoors or at work, up and down a slope, up and down the stairs). The individuals indicated an overall preference for the IP over the pneumatic swing phase unit. They reported that considerably less effort was required when using the IP to walk at normal or high speeds, but no difference was noted for a slow gait. Reduced effort was required when the IP was used outdoors or at work.
Literature researching microprocessor-controlled prosthetic knees indicates that selected individuals strongly prefer prosthetic knees that control both stance and swing, with perceived benefits such as a decrease in falls, an increase in stability, and a decrease in the cognitive burden or effort associated with monitoring the prosthesis. The VA short report states: “Users’ perceptions may be particularly important for evaluating a lower limb prosthesis, given the magnitude of the loss involved. A difference between prostheses sufficient to be perceived as distinctly positive to the amputee may represent the difference between coping and a level of function recognizably closer to the preamputation level.”
Microprocessor-controlled prosthetic knees may provide incremental benefits for individuals who meet the need for the technological or design features of the device. Individuals who are considered most likely to benefit from this prosthesis have both the potential and the need for frequent ambulation at variable cadence, frequent negotiation of uneven terrain, and/or recurrent usage of stairs. The potential to achieve a high functional level with a microprocessor-controlled prosthetic knee requires the appropriate physical and cognitive abilities to utilize the advanced technology.
POWERED AND PROGRAMMABLE FLEXION/EXTENSION ASSIST-CONTROL PROSTHETIC KNEES
In development are lower-limb prostheses that also replace muscle activity in order to bend and straighten the prosthetic joint. For example, according to the manufacturer, the Power Knee™ (Ossur Foothill Ranch, CA), is designed to replace muscle activity of the quadriceps. It is proposed that the Power Knee™ delivers active lifting power for stairs, resistance for downhill slopes and gentle propulsion for level ground walking. These devices use artificial proprioception with sensors similar to the Proprio Foot® (Ossur, Alsio Viejo, CA) in order to anticipate and respond with the appropriate movement required for the next step in time and space. The Power Knee™ is currently in the initial launch phase in the United States.
MICROPROCESSOR-CONTROLLED PROSTHETIC ANKLE-FOOT SYSTEMS
Microprocessor-controlled prosthetic ankle-foot systems for lower-extremity amputees are devices designed to adjust to environmental impediments such as uneven terrain, inclines, and stairs. The device usually consists of four parts; a power storing foot, a lithium battery and charger, a battery-powered prosthetic flexing ankle, and a microprocessor with Terrain Logic™ that controls both dorsiflexion and plantarflexion in response to changing landscape conditions. The Proprio Foot® (Ossur, Alsio Viejo, CA) is currently available for low- to moderate-impact use for transtibial amputees who are classified as Level K3 (ie, community ambulatory, with the ability or potential for ambulation with variable cadence). Available published peer-reviewed literature evaluating the use of microprocessor-controlled prosthetic ankle-foot systems is limited and consists mainly of pilot studies and case series involving small samples sizes (Fradet et al 2010, Alimsuaj et al 2009, Wolf et al 2009).
POWER-ASSIST ANKLE-FOOT PROSTHETIC SYSTEMS
Power-assist ankle-foot prosthetic systems replace muscle activity of the foot, Achilles tendon, and calf muscle in order to bend and straighten the prosthetic joint. For example, transtibial amputees use muscle activity from the remaining limb for the control of ankle movement. Power-assist ankle-foot prosthetic systems are designed to propel the foot forward as it pushes off the ground during the gait cycle, which is proposed to improve efficiency, and has the potential to reduce hip and back problems arising from an unnatural gait with use of passive prostheses. This power-assist technology may be limited by the size and the weight required for a motor and batteries in the prosthesis.
The limited evidence with small sample size in available published peer-reviewed literature does not support an improvement in functional outcomes with a power-assist ankle-foot prosthetic system compared to
standard prostheses (Gates et al 2013, Aldridge et al 2013).