Aetna considers lower limb prostheses medically necessary for performing normal daily activities when the following criteria are met:

1. Member is motivated to ambulate; and
2. Member meets the specific criteria for lower limb prostheses set forth below; and
3. Member will reach or maintain a defined functional state within a reasonable period of time.

Aetna considers lower limb prostheses experimental and investigational because of insufficient evidence in the peer-reviewed literature when these criteria are not met.

Aetna does not cover a replacement prosthesis unless the member's medical needs are not being met by the current prosthetic or it is broken and can not be repaired.

Aetna considers "water leg" (an attachment for persons with lower limb prostheses to shower) a convenience item, and not medically necessary.

Foot Prosthesis:

• A solid ankle-cushion heel (SACH) foot is considered medically necessary for persons whose functional level is 1* or above.
• An external keel SACH foot or single axis ankle/foot is considered medically necessary for persons whose functional level is 1* or above.
• A flexible-keel foot or multi-axial ankle/foot is considered medically necessary for persons whose functional level is 2* or above.
• A flex foot system, energy storing foot, multi-axial ankle/foot, dynamic response, or flex-walk system or equal is considered medically necessary for persons whose functional level is 3* or above.

Knee Prosthesis:

• A fluid or pneumatic knee is considered medically necessary for persons whose functional level is 3* or above.
• A single axis constant friction knee and other basic knee systems are considered medically necessary for persons whose functional level is 1* or above.
• A high-activity knee control frame is considered medically necessary for members whose function level is 4*.

Ankle Prosthesis:

• An axial rotation unit is considered medically necessary for persons whose functional level is 2* or above.
•  An user-adjustable heel height feature is considered not medically necessary. 

Sockets:

• Test (diagnostic) sockets for immediate post-surgical or early-fitted prostheses are considered not medically necessary.
• Two test (diagnostic) sockets for an individual prosthetic are considered medically necessary.  Additional documentation of medical necessity is required for more than 2 test sockets.
• No more than 2 of the same socket inserts per individual prosthesis at the same time are considered medically necessary.
• Socket replacements are considered medically necessary if there is adequate documentation of functional and/or physiological need, including but is not limited to: changes in the residual limb; functional need changes; or irreparable damage or wear/tear due to excessive weight or prosthetic demands of very active amputees.

Prostheses have no proven value for persons whose potential functional level is 0.*

Accessories:

Stump stockings and harnesses (including replacements) are considered medically necessary when they are essential to the effective use of the artificial limb.

Prosthetic sheaths/socks, including a gel cushion layer (prosthetic gel stockings; 6 in 6 months) are considered medically necessary.

Microprocessor-Controlled Lower Limb Prostheses:

Aetna considers microprocessor-controlled leg prostheses (e.g., Otto Bock C-Leg (Otto Bock HealthCare, Minneapolis, MN), Intelligent Prosthesis (Endoliete North America, Centerville, OH), and Ossur Rheo Knee (Ossur-Flexfoot, Aliso Viejo, CA)) medically necessary in otherwise healthy, active community ambulating adults (18 years of age or older) (functional level 3* or above) with a knee disarticulation amputation or a trans-femoral amputation from a non-vascular cause (usually trauma or tumor) for whom this prosthesis can be fitted and programmed by a qualified prosthetist trained to do so.

Aetna considers microprocessor-controlled leg prostheses (e.g., Otto Bock C-Leg, Intelligent Prosthesis, and Ossur Rheo Knee) experimental and investigational for gait management in spinal cord injury because of insufficient evidence in the peer-reviewed literature.

Aetna considers bilateral microprocessor-controlled leg prostheses experimental and investigational because of insufficient evidence in the peer-reviewed literature.

Aetna considers microprocessor-controlled ankle-foot prostheses (e.g., Proprio Foot®, Ossur, Aliso Viejo, CA) experimental and investigational because there is inadequate evidence of their effectiveness.

*Note: Clinical assessments of a member’s rehabilitation potential should be based on the functional classification levels listed in the appendix. 

See also CPB 0399 - Myoelectric Prosthesis, and CPB 0630 - Vacuum Assisted Socket System (VASS).

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."

Appendix

Clinical assessments of a member’s rehabilitation potential should be based on the following classification levels: 

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.