Conventional lower limb prostheses employ exclusively mechanical control: these may include a pneumatic or hydraulic damping cylinder, which is adjusted by a prosthetist, to provide optimum gait parameters at the patient's conventional walking speed. If a patient walks at a different speed, the patient must compensate for the pendulum action of the prosthesis to alter stride length or step rate by tilting the pelvis, or by other maneuvers, to delay extension to ensure that the foot is in the right place for the next step. These maneuvers lead to an abnormal gait and require extra effort and concentration. Aetna’s policy on standard lower limb prostheses is based on Medicare DME MAC criteria.
The microprocessor-controlled lower limb prosthesis (also known as computerized lower limb prostheses) is relatively new to the United States, although a different brand of microprocessor-controlled lower limb prosthesis has been in use in Europe for many more of years. These prostheses employ a microprocessor-controlled knee extension damper, which is designed to detect step time and alter knee extension level to suit walking speed. More advanced microprocessor controlled lower limb prostheses, such as the C-leg, also have multiple sensors that gather and calculate data on, for example, amount of vertical load, sagittal plane ankle movement, and specifics of knee joint movement. These prostheses are claimed to be a significant improvement over the conventional mechanically controlled prostheses.
Claimed advantages of the microprocessor-controlled lower limb prostheses include: decreased effort involved in walking; improved gait symmetry; increased confidence by the patient in the prosthesis; more natural movement, including on stairs, inclines, and uneven terrain; the perception that participation in activities such as sports is possible; and the avoidance of falls.
The Otto Bock C-leg was cleared by the Food and Drug Administration (FDA) based on a 510(k) application; FDA clearance was based on the Otto Bock C-leg's substantial equivalence to a predicate device that was on the market prior to the date of enactment of the 1976 Medical Device Amendments to the Food, Drug and Cosmetic Act.
A number of systematic evidence reviews have identified limitations in current literature on microprocessor controlled knees. The majority of this literature evaluates intermediate outcomes, although some studies have focused on actual functional outcomes. However, the bulk of all of these studies show improvement in outcomes when the microprocessor-controlled knee is used as compared to a more traditional non-microprocessor-controlled knee.
The first systematic evidence review of microprocessor controlled knees was prepared by the Department of Veterans Affairs Technology Assessment Program (VA TAP) (MDRC, 2000). The VA TAP assessment reviewed the evidence supporting the use of computerized lower limb prostheses such as the Otto Bock C-leg and the Intelligent Prosthesis, a microprocessor-controlled lower limb prosthesis that is slightly different than the Otto Bock C-Leg (MDRC, 2000). The VA TAP found, upon review of published studies, that users' perceptions of the microprocessor-controlled prosthesis are favorable. They also found that, although the energy requirements for ambulation (compared to requirements for conventional prostheses) are decreased at walking speeds slower or faster than the amputee's customary speed, energy requirements are not significantly different at customary speeds. The VA TAP found that the reported results on ability to negotiate uneven terrain, stairs, or inclines are "mixed."
At that time, the VA TAP found the evidence of effectiveness of the microprocessor-controlled lower limb prostheses (Intelligent Prosthesis, Otto Bock C-leg) to be limited (MDRC, 2000). Regarding the evidence of effectiveness, the report drew the following conclusions: “The published research is a small body of work. Less then 3 % of the published and indexed articles represent structured research, with the larger fraction of published articles being purely descriptive or frankly promotional. Most of the available structured research is based on a slightly different microprocessor-controlled prosthesis (the [Endolite] Intelligent Prosthesis (IP), Blatchford, United Kingdom). The IP is associated with many of the same potential benefits as the C-LEG.”
The VA TAP reported (MDRC, 2000): “Published studies have enrolled highly selected samples of amputees who do not have additional medical problems, whose amputations were secondary to trauma or congenital defects, and who are fit and active. These and similar characteristics have been shown to be independently predictive of successful rehabilitation or return to normal living after amputation, and may confound the results of the non-randomized, uncontrolled microprocessor-controlled prosthesis studies that have been published to date.
- Results in the highly selected patients who have participated in the available published studies may not be directly transferable to VA amputees, who are likely to have multiple additional medical problems and amputations secondary to vascular disease.
The selective inclusion for research patients noted above undoubtedly introduce bias into study results, precluding definitive attribution of improvements in gait, energy expenditure, etc., to the computerized prosthesis."
An assessment conducted by the Washington State Department of Labor and Industries (2002) concluded "[d]ue to the small number of studies and study participants, evidence of the broad effectiveness of microprocessor-controlled prosthetic knees remains inconclusive."
An evidence review prepared by the Evidence Based Group of the Workers Compensation Board of British Columbia (Martin, 2003) concluded that, "[t]o date, the published research on computerized knee prosthesis is very limited. Less than 3 % of published and indexed research represents structured research. Most published articles are purely descriptive or promotional in nature." The evidence review noted: “Published studies enrolled highly selected sample of amputees who did not have additional medical problems and who were fit and active. These characteristics have been shown to be independently predictive of successful rehabilitation or return to ‘normal’ living after amputation. Thus, these variables are most likely to confound the results of the non-randomized, uncontrolled studies on microprocessor controlled knee prosthesis that have been published to date.” The evidence review concluded that, "[a]t present, the small number of studies on computerized knee prostheses does not conclusively show the effectiveness of the prostheses" in reducing energy expenditure particularly in normal speed walking, improving ability to walk on uneven terrain, improving ability to climb and descend stairs, and increasing walking distance.
Additional studies have been published since these technology assessments were published. Although each of these studies have flaws, the bulk of the studies show improvement in outcomes when the microprocessor-controlled knee is used as compared to a standard hydraulic knee. Similar to previously published studies, Stinus (2000) authored an uncontrolled descriptive study involving a selected group of 15 patients, reporting on their subjective assessments of the microprocessor-controlled lower limb prosthesis compared with previously fitted mechanically controlled prosthetic knee joints. This study did not include objective assessments of improvements in function and reductions in disability compared with conventional prostheses. Schmalz, et al (2002) reported on the results of a randomized controlled clinical study comparing conventional hydraulic knees with electronically controlled knee joints during walking on a treadmill. The investigators reported reductions in oxygen consumption in persons with electronically controlled knees compared to patients with conventional hydraulic knees when walking at speeds other than the amputee’s customary walking speeds. This study, however, did not assess differences in function between these groups. Similarly, a study by Chin et al (2003) of 8 traumatic amputees fitted with an Intelligent Prosthesis compared to 14 normal non-amputee controls reported a 24 % greater energy expenditure compared to controls walking at equal speeds. However, this study did not assess reductions in disability and improvements in function with the Intelligent Prosthesis.
In a subsequent study, Chin et al (2005) reported on changes in oxygen consumption of 3 amputees after prescription of a microprocessor-controlled prosthesis. The change in energy expenditures reported was highly variable among subjects, with 1 subject reporting a minor (4.9 %, 11.6 % and 105 %) reductions in oxygen consumption, another reporting changes in energy expenditures of 10.3 %, 14.9 % and 23.3 % depending upon speed, and the third subject reporting larger changes in energy expenditures (39.6 %, 24.6 % and 23.3 %). The study provided no details about how these cases are selected. Thus, one is not able to determine whether one can generalize from this selected set of individual cases to other amputees. The study suffers from the same flaws as the previous study by the same investigator group; it does not represent a stronger study, in terms of design, than previous published studies. The study by Chin et al (2005) is a pre-/post-study, without concurrent controls; other factors may have accounted for changes in energy expenditures after prescription of the microprocessor controlled prosthesis, including the training program and practice subjects received to improve their ability to walk with a microprocessor-controlled prosthesis before their energy expenditures were re-assessed. The study by Chin et al also suffered from the limitations of his previous study in that it assessed differences in oxygen consumption, an intermediate endpoint, and did not assess clinically relevant endpoints of reductions in disability and improvement in function.
A study by Johansson et al (2005) compared the magnetorheological-based Ossur Rheo prosthesis to the hydraulic-based Otto-Bock C-Leg microprocessor-controlled prosthesis to a standard hydraulic-based (Mauch) prosthesis. The study found no statistically significant difference between the C-Leg microprocessor controlled prosthesis and a standard hydraulic (Mauch) prosthesis in metabolic expenditure (as measured by oxygen consumption) with walking, the primary study endpoint. The investigators (from a group headed by an inventor and patent-holder of the Ossur Rheo microprocessor-controlled leg prosthesis) reported a 5 % lower average metabolic consumption with walking using the Ossur Rheo prosthesis, and a 2 % lower average metabolic consumption with walking using the C-leg microprocessor-controlled prosthesis compared to a standard hydraulic (Mauch) prosthesis; the latter difference did not achieve statistical significance. There is also a question about the clinical significance of such small differences in metabolic consumption, especially among the younger active amputees for whom microprocessor-controlled prostheses are most commonly prescribed.
The study by Johansson et al (2005) also evaluated differences in kinetics, kinematics, and electromyographic data between the C-Leg, the Ossur Rheo prosthesis, and standard hydraulic prostheses in walking sessions performed in the laboratory. However, the study fails to show how any identified differences in these intermediate outcomes, while statistically significant, translated into tangible, clinically significant reductions in disability and improvements in function. The small size of the study (n = 8) may limit one's ability to generalize its findings to other amputees. Observed differences between microprocessor-controlled prostheses and the standard hydraulic-based Mauch prosthesis may be due, in part, to the fact that half of the study subjects had been using a microprocessor-controlled prostheses as their usual prosthesis prior to study initiation, and only 1 study subject used the Mauch hydraulic prosthesis as her usual prosthesis prior to study initiation. In addition, laboratory-based evaluation of prostheses and their components may not necessarily reflect the characteristics of the prostheses when used outside of the clinical setting (in real life situations), and in subjects with more experience with use of these particular prosthetics.
A study by Datta et al (2005) comparing the Intelligent Prosthesis microprocessor-controlled prosthesis to conventional pneumatic leg prostheses in 10 amputees found no significant difference in metabolic expenditures (oxygen consumption) at average walking speeds. The study also found no significant differences in temporal and spatial parameters of gait between the 2 types of knee joint, nor any significant differences in gait by observational video analysis. The study found statistically significantly lower energy expenditures using the Intelligent prosthesis (0.30 ml/kg.m) compared to the standard pneumatic prosthesis (0.33 ml/kg.m) only when subjects walked at about half normal speed. However, the clinical significance of this degree of difference in metabolic expenditure, which is only manifest at slow walking speeds, is in question, especially for younger, healthy subjects.
A study by Swanson et al (2005) evaluated body image and function in 8 amputees using the Otto-Bock C-Leg. However, the study did not include a comparison group of individuals using a standard hydraulic-based prosthesis. Thus, no conclusions can be drawn regarding differences in body image and function levels of individuals using the C-Leg and individuals using a standard hydraulic-based prosthesis.
In a randomized, controlled cross-over study comparing the C-leg to a standard mechanical knee (Mauch SNS knee), Orendurff et al (2006) found that, at measured walking speeds, the C-Leg did not significantly improve gait efficiency in transfemoral amputees (TF). Eight TF amputees were randomized to the Mauch SNS knee and the C-Leg microprocessor-controlled knee. The subjects were given a 3-month acclimation period in each knee. Then, their net oxygen cost (mL/kg/m) was measured while they walked overground at 4 speeds in random order: 0.8 m/s, 1.0 m/s, 1.3 m/s, and self-selected walking speed (SSWS). The C-Leg caused small reductions in net oxygen cost that were not statistically significant compared with the Mauch SNS at any of the walking speeds (p > 0.190). Subjects chose higher SSWSs with the C-Leg compared with the Mauch SNS (mean +/- standard deviation = 1.31 +/- 0.12 m/s versus 1.21 +/- 0.10 m/s, respectively, p = 0.046) but did not incur higher oxygen costs (p = 0.270), which suggests greater efficiency only at their SSWS.
A randomized crossover study by Segal et al (2006) comparing the C-Leg to a standard mechanical knee (Mauch SNS knee) found no significant differences in gait biomechanics. After subjects had a 3-month acclimation period with each prosthetic knee, typical gait biomechanical data were collected in a gait laboratory. The investigators reported that, at a controlled walking speed (CWS), peak swing phase knee-flexion angle decreased for the C-Leg group compared with the Mauch SNS group (55.2° +/- 6.5° versuss 64.41° +/- 5.8°, respectively; p = 0.005); the C-Leg group was similar to control subjects' peak swing knee-flexion angle (56.0° +/- 3.4°). Stance knee-flexion moment increased for the C-Leg group compared with the Mauch SNS group (0.142 +/- 0.05 versus 0.067 +/- 0.07 N²m, respectively; p = 0.01), but remained significantly reduced compared with control subjects (0.477 +/- 0.1 N²m). Prosthetic limb step length at CWS was less for the C-Leg group compared with the Mauch SNS group (0.66 +/- 0.04 versus 0.70 +/- 0.06 m, respectively; p = 0.005), which resulted in increased symmetry between limbs for the C-Leg group. Subjects also walked faster with the C-Leg versus the Mauch SNS (1.30 +/- 0.1 versus 1.21 +/- 0.1 m/s, respectively; p = 0.004). The C-Leg prosthetic limb vertical ground reaction force decreased compared with the Mauch SNS (96.3 +/- 4.7 versus 100.3 +/- 7.5 % body weight, respectively; p = 0.0092). The investigators concluded: "Our study demonstrated minimal differences between the gait biomechanics of subjects walking with the C-Leg compared with the Mauch SNS, a non-computerized prosthetic knee, during constant speed ambulation at approximately TF amputee SSWS."
Klute et al (2006) found that a microprocessor controlled knee had no effect on amputees functional level compared to mechanical knees. To investigate the effect of prosthetic interventions on the functional mobility of lower-extremity amputees, the investigators conducted a cross-over study involving 5 transfemoral amputees comparing a microprocessor controlled knee (C-Leg) to a non-microprocessor controlled knee (Mauch SNS). The investigators reported that knee type had no effect on the daily activity level or duration for transfemoral amputees.
A study by Seymour et al (2007) (n = 13) comparing the C-leg to various non-microprocessor controlled knees reported decreased oxygen consumption with the C-leg. However, this study is of weaker design than the studies by Orendurff et al (2006) and Segal et al (2006) described above, in that it was a simple pre-post study, which is of weaker design than a randomized controlled clinical trial. Another recently reported study comparing functional performance of microprocessor controlled and mechanical knees is also of weaker design (Hafner et al, 2007) (n = 21).
There is limited evidence for the use of microprocessor-controlled knees in patients with unilateral hip disarticulation. Chin et al (2005) compared the energy expenditure during walking in 3 patients, aged between 51 and 55 years, with unilateral disarticulation of the hip when using the mechanical-controlled stance-phase control knee (Otto Bock 3R15) and the microprocessor-controlled pneumatic swing-phase control knee (Intelligent Prosthesis, IP). All had an endoskeletal hip disarticulation prosthesis with an Otto Bock 7E7 hip and a single-axis foot. The energy expenditure was measured when walking at speeds of 30, 50, and 70 m/min. Two patients showed a decreased uptake of oxygen (energy expenditure per unit time, ml/kg/min) of between 10.3 % and 39.6 % when using the IP compared with the Otto Bock 3R15 at the same speeds. One did not show any significant difference in the uptake of oxygen at 30 m/min, but at 50 and 70 m/min, a decrease in uptake of between 10.5 % and 11.6 % was found when using the IP. The use of the IP decreased the energy expenditure of walking in these patients.
The California Technology Assessment Forum (CTAF, 2007) recommended the use of a C-Leg microprocessor-controlled prosthetic knee in otherwise healthy, active K3-K4 community ambulating adults with a trans-femoral amputation from a non-vascular cause (usually trauma or tumor) for whom this prosthesis can be fit and programmed by a qualified prosthetist trained to do so. (Note: Medicare level K3 refers to unlimited community ambulator, while level K4 refers to active adult, athlete, who has the need to function at a K3 level in daily activities).
A technology assessment of microprocessor-controlled prosthetic knees prepared by the CTAF (2007) noted that the majority of available literature evaluated intermediate outcomes; however, 3 studies were identified that focused on actual functional outcomes. The CTAF assessment found that the bulk of all of these studies show improvement in outcomes when the microprocessor-controlled knee is used as compared to a more traditional non-microprocessor-controlled (NMC) knee. The CTAF assessment reported: "While it is unclear how some of the intermediate outcomes impact on clinical or functional outcomes, the functional outcomes of improved gait biomechanics, improved balance, few falls, improved performance on an obstacle course and going down stairs and hills, as well as fewer self-reported falls have obvious benefit for the prosthetic users. While none of the studies is without flaws; however, the bulk of the evidence is in favor of the studied microprocessor-controlled prosthetic knees for the populations enrolled." The CTAF assessment concluded that it appears that healthy, active adults with a trans-femoral amputation for a non-vascular cause (usually trauma or tumor) derive functional benefit from wearing a microprocessor-controlled knee.
According to the CTAF assessment, there are questions remaining about microprocessor-controlled prosthetic knees (CTAF, 2007). The CTAF assessment notes that many of the studies attempted to enroll more individuals, but some of their enrollees either could not be fit with the prosthesis or could not adapt to it. It is unclear whether there are particular predictors of who these people might be -- is it something to do with the interface between stump and socket, or are there other important predictors? The CTAF assessment also observed that all of the studies were of individuals who were long-term users of an NMC previously; is there a population who should be offered a microprocessor-controlled prosthetic knee as their initial prosthesis? The CTAF assessment commented that most of the studies enrolled active adults, and only a few enrolled moderately active or older dysvascular adults -- is there a group of moderately active adults whose activity level would improve even more with this technology? "Perhaps these researchers would have observed even greater differences if they had studied somewhat less active individuals with the potential for enhanced mobility with a more responsive prosthesis."
The Proprio Foot (Ossur, Alsio Viejo, CA) is a microprocessor-controlled prosthetic ankle-foot system for lower-extremity amputees. It is designed to adjust to uneven ground, ramps, stairs, and other environmental obstacles. It consists of 4 parts: (i) an energy storing prosthetic foot, (ii) a battery-powered prosthetic ankle that dorsiflexes and plantarflexes during swing phase, (iii) a microprocessor that controls dorsiflexion and plantarflexion in real time and in response to changes in the underlying terrain by sampling ankle position more than 1,000 times per second, and (iv) a lithium-ion battery and charger. Its Terrain Logic software permits the adjustment to surface gradients of up to 20 degrees.
Published evidence on microprocessor-controlled ankle-foot orthoses is limited to small studies examining the short-term effects on kinematic parameters, which are considered short-term surrogate outcomes (Fradet et al, 2010; Alimusaj et al, 2009; and Wolf et al, 2009). However, there is a lack of data on other relevant aspects of ambulation (e.g., daily step frequency, estimated step distance, stopping and standing safely, adaptation to different walking speeds, and fall frequency). In addition, there is a lack of reliable published evidence of the impact of microprocessor-controlled ankle-foot prostheses compared to standard ankle-foot prostheses on other relevant outcomes, including energy expenditure, cognitive requirements of ambulation, and patient-centered outcomes (quality of life, impact on activities of daily living, work, and work performance).
A systematic evidence review prepared for the Washington State Health Technology Advisory Committee (Henrickson, et al., 2011) found no studies of the Proprio Foot or other microprocessor controlled foot devices that met inclusion criteria for the systematic evidence review. The review stated that "[t]here is insufficient evidence to evaluate the comparative effectiveness, safety, or cost effectiveness of microprocessor-controlled foot devices."
Bellmann et al (2012) examined the immediate biomechanical effects after transition to a new microprocessor-controlled prosthetic knee joint. Subjects were men (n = 11; mean age ± SD, 36.7 ± 10.2 years; Medicare functional classification level, 3 to 4) with unilateral transfemoral amputation. Two microprocessor-controlled prosthetic knee joints: C-Leg and a new prosthetic knee joint, Genium were used in this study. Main outcome measures included static prosthetic alignment, time-distance parameters, kinematic and kinetic parameters, and center of pressure. After a half-day training and an additional half-day accommodation, improved biomechanical outcomes were demonstrated by the Genium: lower ground reaction forces at weight acceptance during level walking at various velocities, increased swing phase flexion angles during walking on a ramp, and level walking with small steps. Maximum knee flexion angle during swing phase at various velocities was nearly equal for Genium. Step-over-step stair ascent with the Genium knee was more physiologic as demonstrated by a more equal load distribution between the prosthetic and contralateral sides and a more natural gait pattern. When descending stairs and ramps, knee flexion moments with the Genium tended to increase. During quiet stance on a decline, subjects using Genium accepted higher loading of the prosthetic side knee joint, thus reducing same side hip joint loading as well as postural sway. The authors concluded that in comparison to the C-Leg, the Genium demonstrated immediate biomechanical advantages during various daily ambulatory activities, which may lead to an increase in range and diversity of activity of people with above-knee amputations. Results showed that use of the Genium facilitated more natural gait biomechanics and load distribution throughout the affected and sound musculoskeletal structure. This was observed during quiet stance on a decline, walking on level ground, and walking up and down ramps and stairs.
Powered prosthetic devices, which utilize signals from muscle activity in the remaining limb to bend and straighten the device, are being researched. These devices use sensors and electronics to process data and control movement and power of the knee. Examples of these devices are the Power Knee (Ossur, Foothill Ranch, CA). According to the manufacturer, the Power Knee is the first motorized prosthetic knee available for transfemoral amputees weighing up to 275 pounds. It is designed for use by functional level K3 individuals with a documented co-morbidity in their sound limb or spine and by bilateral amputees. The knee houses an electro-mechanical actuator that actively initiates and controls all aspects of the user's gait. It also provides powered knee flexion and extension under full user load. The motor initiates appropriate movement and function based on data collected through accelerometers, gyroscopes, a torque sensor, and a load sensor. When users walk with the Power Knee, the device samples knee position and loads at the rate of 1,000 times/second to provide appropriate power for the user in all 3 phases of the extension portion of the gait cycle. At heel strike, the motor permits and encourages active stance flexion, functioning to replace foot/ankle, knee, and hip muscles. This allows a flexion moment that more accurately replicates able-bodied gait while simultaneously providing full support and stability for users. The motor-controlled knee flexion at heel strike also reduces the impact on users, permitting a smoother transition from the sound side to the prosthetic side, facilitating a more symmetrical gait. When users walk down declines and stairs, the Power Knee allows leg-over-leg descent. When users stand still, it permits them to stand with the prosthetic knee flexed, as the electro-mechanical motor actively support the user's weight. The Power Knee’s motor actively extends the knee from a flexed (seated) position into an extended (standing) one. The motor provides an affirmative, dynamic response that resists gravity, lifting the user up. Upon initial use, a practitioner must program and align the knee. Once programming and alignment are complete, the user needs only to press the power button to use the device. The user must also charge the lithium-polymer batteries that power the device. A 3.5-hour charge is recommended to ensure maximum battery life. On a full charge, battery life is up to 12 hours depending on the user's activities. Each Power Knee comes with 2 batteries.
The BiOM is a below knee robotic prosthesis that designed for use by individuals with lower extremity amputation. This prosthesis, which includes the foot, ankle, and lower calf, uses robotics to replicate the calf muscles and Achilles tendon. With each step, the BiOM provides a powered push-off which propels the wearer forward. Powered plantar flexion enables the prosthesis to normalize the gait and metabolic demands to those of non-amputees. With its bionic functionality, this prosthesis can resolve clinical issues faced by amputees, including tiredness, slowness, and a feeling of being unstable on their feet. The robotic muscle power provided by the BiOM during toe-off requires less energy from the user. It also provides more power when the user walks faster and less when the user walks slower, which produces a natural gait at variable speeds. Users are able to negotiate stairs and inclines with increased confidence and stability due to improved articulation and the design’s ability to mechanically yield and conform. http://www.abledata.com/abledata.cfm?pageid=19327&top=12677&ksectionid=19327&productid=203704&trail=0&discontinued=0.
Mancinelli et al (2011) stated that passive-elastic foot prostheses cannot produce network. Consequently, passive-elastic foot prostheses are limited in their ability to enable a biologically-realistic gait pattern in transtibial amputees. This shortcoming results in difficulties in balance and walking and leads to high levels of oxygen consumption during locomotion. A powered prosthesis has the potential for overcoming these problems and allowing transtibial amputees to achieve a biologically-realistic gait pattern. In this study, these researchers compared the effects of the Ceterus by Ossur, a traditional passive-elastic prosthesis, with those of the PowerFoot Biom (iWalk, Cambridge, MA), a recently-developed powered prosthesis. Gait biomechanics and metabolic cost were compared in a group of 5 transtibial amputees during level-ground walking. The results provided preliminary evidence that the use of a powered prosthesis leads to a decrease in the level of oxygen consumption during ambulation due to improvements in ankle kinematics and kinetics primarily during late stance. An average decrease in oxygen consumption of 8.4 % was observed during the study when subjects used the PowerFoot compared to the Ceterus. An average increase of 54 % was observed in the peak ankle power generation during late stance. The authors concluded that these findings suggested that powered prostheses have the potential for significantly improving ambulation in transtibial amputees.
Aldridge and colleagues (2012) noted that during stair ascent (STA) persons with transtibial amputation (TTA) typically adopt a hip strategy to compensate for the limited ankle motion and joint power that is characteristic of conventional energy storing and returning (ESR) prosthetic feet. The purpose of this investigation was to determine if providing ankle power via a powered prosthetic device (BiOM) normalized STA kinematics and kinetics. A total of 11 individuals with TTA participated in 2 STA gait analysis sessions: (i) using an ESR foot, and (ii) using the BiOM. Eleven height- and weight-matched able-bodied controls (CONT) were also assessed. Lower extremity peak kinematic and kinetic values were calculated at a self-selected and controlled cadence (80 steps/min). Increased prosthetic limb peak ankle plantar-flexion and push-up power were observed while using the BiOM as compared to ESR. Peak ankle power was not significantly different between BiOM and CONT indicating normalization of ankle power generation. However, peak ankle plantar-flexion was significantly lower than CONT. Limb asymmetries including greater prosthetic limb hip flexion and power during stance, and decreased prosthetic limb knee power during stance were observed in the BiOM and ESR conditions. The authors concluded that these findings suggested that the BiOM successfully increased ankle motion and restored ankle power during STA. These differences did not, however, reduce the use of a hip strategy while ascending stairs. They stated that additional device specific training may be necessary to utilize the full benefits of the device.
However, due to the small sample sizes in these studies, it is unclear if these preliminary findings would be observed in the general TTA population. Further investigation is needed to establish a meaningful clinical outcome benefit of the iWalk BiOM prosthetic foot over the conventional ankle-foot prosthesis. Furthermore, the Washington State Health Care Authority (2011) does not cover microprocessor-controlled lower limb prostheses for the feet and ankle (e.g., the iWalk PowerFoot BiOM). http://www.hta.hca.wa.gov/documents/meeting_materials_part_1_031612.pdf.
The ReWalk exoskeleton (Argo Medical Technologies Ltd, Marlborough, MA) is designed for persons with a spinal cord injury (SCI) who retain upper-limb strength and mobility to manage stabilizing crutches. It is worn outside clothing and weighs 44 pounds. It consists of an upper-body harness, lower-limb braces, motorized joints, ground-force sensors, a tilt sensor, a locomotion-mode selector, and a backpack carrying a computerized controller and rechargeable battery. The device is strapped to the user at the waist, alongside each lower limb, and at the feet. Ordinary crutches help maintain stability. The ReWalk exoskeleton comes in 2 sizes: (i) one that fits persons 5 feet 3inches to 5 feet 9 inches in height, and (ii) one that accommodates persons up to 6 feet 3 inches. The ReWalk can be worn by individuals weighing up to 220 pounds. Two types of the ReWalk exoskeletons are available: (i) the institutional version, the ReWalk-I, which is designed for rehabilitation centers and physician private practices, and (ii) a personal version, the ReWalk-P, which is designed for an individual’s sole use.
In a pilot study, Zeilig et al (2012) evaluated the safety and tolerance of use of the ReWalk exoskeleton ambulation system in people with SCI. Measures of functional ambulation were also assessed and correlated to neurological spinal cord level, age, and duration since injury. A total of 6 volunteer participants were recruited from the follow-up outpatient clinic. Safety was assessed with regard to falls, status of the skin, status of the spine and joints, blood pressure, pulse, and electrocardiography (ECG). Pain and fatigue were graded by the participants using a visual analog scale pre- and post-training. Participants completed a 10-statement questionnaire regarding safety, comfort, and secondary medical effects. After being able to walk 100 m, timed up and go, distance walked in 6 minutes and 10-m timed walk were measured. There were no adverse safety events. Use of the system was generally well-tolerated, with no increase in pain and a moderate level of fatigue after use. Individuals with lower level of SCI performed walking more efficiently. The authors concluded that volunteer participants were able to ambulate with the ReWalk for a distance of 100 m, with no adverse effects during the course of an average of 13 to 14 training sessions. The participants were generally positive regarding the use of the system. Moreover, the authors stated that the potential benefits of the ReWalk are many, including improved functional mobility, cardio-vascular and respiratory status, bone metabolism, and bowel and bladder function, as well as reduction of spasticity and neuropathic pain, but efficacy still needs to be demonstrated in a larger study. Also, these researchers noted that this study did not include any female subjects, individuals with tetraplegia, children, or older adults; future large-scale inclusive studies are needed.
In an open, non-comparative, non-randomized study, Esquenazi et al (2012) evaluated the safety and performance of ReWalk in enabling people with paraplegia due to SCI to carry out routine ambulatory functions. All 12 subjects have completed the active intervention; 3 remained in long-term follow-up. After training, all subjects were able to independently transfer and walk, without human assistance while using the ReWalk, for at least 50 to 100 m continuously, for a period of at least 5 to 10 mins continuously and with velocities ranging from 0.03 to 0.45 m/sec (mean of 0.25 m/sec). Excluding 2 subjects with considerably reduced walking abilities, average distances and velocities improved significantly. Some subjects reported improvements in pain, bowel and bladder function, and spasticity during the trial. All subjects had strong positive comments regarding the emotional/psychosocial benefits of the use of ReWalk. The authors concluded that the ReWalk holds considerable potential as a safe ambulatory powered orthosis for motor-complete thoracic-level SCI patients. Most subjects achieved a level of walking proficiency close to that needed for limited community ambulation. A high degree of performance variability was observed across individuals. Some of this variability was explained by level of injury, but other factors have not been completely identified. Further development and application of this rehabilitation tool to other diagnoses are expected in the future.
A clinical trial on the ReWalk exoskeletal walking system is currently recruiting participants; the estimated study completion date is April 2014. The objective of this trial is to examine the potential benefits of frequent upright posture and walking on many of the secondary consequences of SCI. The researchers are investigating the ability of persons with paraplegia to learn to stand and walk with the ReWalk-I and the effects of being upright and walking on several of these secondary medical consequences of SCI. http://clinicaltrials.gov/show/NCT01454570.
Clinical assessments of a member’s rehabilitation potential should be based on the following classification levels:
||Does not have the ability or potential to ambulate or transfer safely with or without assistance and a prosthesis does not enhance their quality of life or mobility.
||Has the ability or potential to use a prosthesis for transfers or ambulation on level surfaces at fixed cadence. Typical of the limited and unlimited household ambulator.
Has the ability or potential for ambulation with the ability to traverse low level environmental barriers such as curbs, stairs or uneven surfaces. Typical of the limited community ambulator.
||Has the ability or potential for ambulation with variable cadence. Typical of the community ambulator who has the ability to traverse most environmental barriers and may have vocational, therapeutic, or exercise activity that demands prosthetic utilization beyond simple locomotion.
||Has the ability or potential for prosthetic ambulation that exceeds basic ambulation skills, exhibiting high impact, stress, or energy levels. Typical of the prosthetic demands of the child, active adult, or athlete.
For medically necessary frequency of replacement of prosthetics, see Medi-Cal. Orthotics and prosthetics. Frequency limits on prosthetics. Ortho cd fre 2. Provider Manual. Sacramento, CA: California Department of Health Care Services; August 2010. Available at: http://files.medi-cal.ca.gov/pubsdoco/Manuals_menu.asp. Accessed August 15, 2012.