Prosthetic Limb Vacuum Systems

Number: 0630

Policy

Aetna considers the eVAC, the Harmony Vacuum Management System (Vacuum Assisted Socket System (VASS)), and the LimbLogic VS Prosthetic Vacuum Suspension System, specialized vacuum pump residual limb volume management and moisture evacuation systems medically necessary for use with lower limb prostheses when any of the following criteria are met:

• Excessive pistoning of the socket to residual limb interface that cannot be resolved by adjustments in the current suspension system; or
• Excessive residual limb hyperemia from prior socket use; or
• Excessive skin hyperhidrosis from prior socket use; or
• Multiple falls in below-knee amputees (trans-tibial amputation).

Note: The use of prosthetic limb vacuum systems for multiple falls in above-knee amputees (trans-femoral amputation) is considered experimental and investitgational.

See also CPB 0578 - Lower Limb Prostheses.

Background

A residual limb volume management and moisture evacuation system (e,g,, Vacuum Assisted Socket System [VASS]) is a specialized device used with artificial limbs in an attempt to manage residual limb volume fluctuation. The system consists of a liner, suspension sleeve and air evacuation pump. The device creates an elevated vacuum between the liner and the socket wall. The elevated vacuum attempts to promote natural fluid exchange to regulate volume fluctuation in the residual limb, reduce forces to the residual limb and increase suspension and balance.

The Vacuum Assisted Socket System (VASS), developed by Total Environmental Control (TEC), is a specialized device used with artificial limbs to manage residual limb volume fluctuation in amputees. The manufacturer claims that the enhanced linkage from the vacuum between the liner and the socket wall decreases weight and promotes an improved gait.

Murphy (2014) stated that elevated vacuum systems are a form of suspension that is becoming more often used and seen in the younger population of wearers requiring a continued level of suspension throughout a variety of activities. An elevated vacuum system uses a draw pump to draw air out of the socket pulling air from between the residuum and the inner socket to maintain the tissue against the walls of the socket at a desired level of avacuum within the confines of the socket, thus preventing movement in all directions. The suspension is not for those with inconsistent volume loss requiring frequent sock ply management.

According to the manufacturer, studies conducted at St. Cloud (MN) State University indicate a daily volume loss of 6 to 12% in the residual limb (wearing liner, sealing sleeve and expulsion valve).  The same sample group (with VASS Technology) lost less than 1 % of residual limb volume.  Current published peer-reviewed evidence for the VASS consists of two small un-blinded studies.  One study involving 9 amputees compared peak pressures between skin and liner during stance and swing phases during a 20-min walk with a standard prosthetic socket and a vacuum-assisted socket (Bell et al, 2002).  Another study examined stump volume in 10 amputees before and after a 30-min walk (Board et al, 2001).  Neither of these studies examined the effect of VASS on clinical outcomes (reductions in disability or improvement of function).

1. total surface-bearing socket with a VASS, and
2. modified patellar tendon-bearing socket with a pin lock suspension system.

Main outcome measures included activity level, residual limb volume before and after a 30-min treadmill walk, residual limb pistoning, and Prosthesis Evaluation Questionnaire.  Activity levels were significantly lower while wearing the VASS system than the pin suspension (p = 0.0056; 38,000 +/- 9,000 steps per 2 wk versus 73,000 +/- 18,000 steps per 2 wk, respectively).  Residual limb pistoning was significantly less while wearing the VASS system than the pin suspension (p = 0.0021; 1 +/- 3 mm versus 6 +/- 4 mm, respectively).  Treadmill walking had no effect on residual limb volume.  In general, participants ranked their residual limb health higher, were less frustrated, and claimed it was easier to ambulate while wearing a pin suspension compared with the VASS.  The authors concluded that the VASS resulted in a better fitting socket as measured by limb movement relative to the prosthetic socket (pistoning), although the clinical relevance of the small but statistically significant difference is difficult to discern.  Treadmill walking had no effect, suggesting that a skilled prosthetist can control for daily limb volume fluctuations by using conventional, non-vacuum systems.  Participants took approximately 50 % as many steps while wearing the VASS which, when coupled with their subjective responses, suggests a preference for the pin suspension system.

Sanders et al (2011) employed bioimpedance analysis to measure the residual limb fluid volume of 7 transtibial amputee subjects using elevated vacuum sockets and non-elevated vacuum sockets.  Fluid volume changes were assessed during sessions with the subjects sitting, standing, and walking.  In general, fluid volume losses during 3- or 5-min walks and losses over the course of the 30-min test session were less for elevated vacuum than for suction.  Numerous variables, including the time of day that data were collected, soft tissue consistency, socket-to-limb size and shape differences, and subject health, may have affected the results and had an equivalent or greater effect on limb fluid volume compared with elevated vacuum.  Researchers should well consider these variables in the study design of future investigations on the effects of elevated vacuum on residual limb volume

The results from this series of case studies did not consistently demonstrate that elevated vacuum maintained or increased limb fluid volume nor do they consistently demonstrate that elevated vacuum had no effect.  Instead, elevated vacuum maintained or increased limb fluid volume on 6 of the 7 subjects and affected some measures of limb fluid volume change but not others.  Results from these cases suggested that in future research efforts evaluating elevated vacuum, researchers need to consider a number of study design variables that may influence limb volume change measurements.  These variables need to be considered when test results between 2 different conditions (e.g., elevated vacuum versus suction) are compared.  Variables include:

• Limb soft tissue mechanical consistency
• Size of residual limb relative to size of socket
• Socket shape
• Subject health
• Time after doffing that measurements are taken (if out-of-socket measurement technique used)
• Time into session that measurements are made and ordering of interventions within a session
• Time of day of test
• Use of elevated vacuum as the regular prosthesis (i.e., subject accommodation)
• Weight differences between prostheses tested

The authors concluded that this series of case studies on 7 subjects showed that some subjects demonstrated less decrease (or more increase) in limb fluid volume using sockets with elevated vacuum compared with suction sockets or lock-and-pin suspension sockets, while others did not.  Some measures of limb fluid volume changed consistently, while others did not.  A number of variables may affect limb fluid volume change.  When designing future research studies, investigators need to consider these variables in study design, particularly when comparing elevated vacuum to another socket design.

1. the experimental group was trained to use a VASS prosthesis in the presence of open ulcers/wounds on the stump; and
2. the control group was trained to use a standard suction socket system prosthesis following ulcers/wounds healing.

At the end of the 12-week rehabilitation program, all VASS users were able to walk independently with their prosthesis as reflected by a median Locomotor Capability Index (LCI) value of 42, whereas only 5 participants in the control group were able to walk independently with a median LCI value of 21.  At the 2-month follow-up, the participants used their VASS prostheses for 62 hours a week (median; range of 0 to 91), which was significantly longer than the control group using the standard prosthesis for 5 hours per week (range of 0 to 56, p = 0.003).  At the 6-month follow-up, the difference between VASS-users (80, range of 0 to 112 hours a weeks) and control-users (59, range of 0 to 91) was no longer significant (p = 0.191).  Despite more intense use of the prosthesis, pain and wound healing did not significantly differ between the 2 groups.  The authors concluded that these findings showed that the VASS prosthesis allowed early fitting with prompt ambulation recovery without inhibiting wound healing or increasing pain.

Residual limb wounds are typically treated by suspension of prosthetic use until healing occurs, increasing the risk of long-term prosthesis nonuse. Sockets with vacuum-assisted suspension may reduce intra-socket motion and be less disruptive to wound healing. Hoskins, et al. (2014) conducted a case series to measure residual limb wound size over time in persons with transtibial amputation while using prostheses with vacuum-assisted suspension. Six subjects with residual limb wounds were fit with vacuum-assisted suspension sockets. Wound surface area was calculated using ImageJ software at the time of fit and each subsequent visit until closure. Average wound surface area at initial measurement was 2.17 ± 0.65 cm(2). All subjects were instructed to continue their normal activity level while wounds healed, with a mean of 177.6 ± 113 days to wound closure. The investigators concluded that results suggest that well-fitting sockets with vacuum-assisted suspension in compliant individuals did not preclude wound healing. The investigators stated that further research is required to substantiate these case-based observations.

Komolafe et al (2013) noted that despite increasingly widespread adoption of vacuum-assisted suspension systems in prosthetic clinical practices, there remain gaps in the body of scientific knowledge guiding clinicians' choices of existing products.  In this study, these researchers identified important pump-performance metrics and developed techniques to objectively characterize the evacuation performance of prosthetic vacuum pumps.  The sensitivity of the proposed techniques was assessed by characterizing the evacuation performance of 2 electrical (Harmony e-Pulse [Ottobock; Duderstadt, Germany] and LimbLogic VS [Ohio Willow Wood; Mt. Sterling, OH, USA]) and 3 mechanical (Harmony P2, Harmony HD, and Harmony P3 [Ottobock]) prosthetic pumps in bench-top testing.  Five fixed volume chambers ranging from 33 cm(3) (2 in(3)) to 197 cm(3) (12 in(3)) were used to represent different air volume spaces between a prosthetic socket and a liner-clad residual limb.  All measurements were obtained at a vacuum gauge pressure of 57.6 kPa (17 in Hg).  The proposed techniques demonstrated sensitivity to the different electrical and mechanical pumps and, to a lesser degree, to the different setting adjustments of each pump.  The authors concluded that the sensitivity was less pronounced for the mechanical pumps, and future improvements for testing of mechanical vacuum pumps were proposed.  The authors noted that overall this study offered techniques that are feasible as standards for assessing the evacuation performance of prosthetic vacuum pump devices.

Kuntze Ferreira and Neves (2015) compared gait deviations between Kondylen Bettung Münster (KBM) and vacuum prosthetic fitting using the Gait Profile Score (GPS), the Movement Analysis Profile (MAP) and temporal-spatial parameters. Seventeen transtibial amputees that received their prosthesis from the Brazilian governmental health system participated in this study. Twelve of them used KBM prosthetic fitting on their prosthesis and five used vacuum prosthetic fitting. Kinematic and temporal-spatial parameters data were captured by a six-camera Motion Analysis system (Santa Rosa, CA). The results showed that the vacuum group walked faster than the KBM group but the differences in temporal-spatial parameters between them were not significant. The GPS for the intact limb (IL) and the overall GPS differentiated between the groups of prosthetic fitting. Hip flexion/extension and knee flexion/extension were higher in KBM group than in the vacuum group, although only knee flexion/extension for the intact limb revealed significant difference between the groups. In KBM group, the major deviations were in hip flexion/extension for both limbs, knee flexion/extension for both limbs and ankle dorsi/plantar flexion for the prosthetic limb. The vacuum group showed deviations especially in ankle dorsi/plantar flexion for both limbs, knee flexion/extension for the prosthetic limb and hip rotation for the prosthetic limb. Besides, the vacuum group was more symmetrical than the KBM group. This study concluded that subjects who used vacuum prosthetic fitting presented smaller gait deviations and a more symmetrical gait than those who used KBM prosthetic fitting.

Samitier et al (2016) investigated the effect of vacuum-assisted socket system on transtibial amputees' performance-based and perceived balance, transfers, and gait.  Subjects were initially assessed using their prosthesis with the regular socket and re-evaluated 4 weeks after fitting including the vacuum-assisted socket system.  These researchers evaluated the mobility grade using Medicare Functional Classification Level, Berg Balance Scale, Four Square Step Test, Timed Up and Go Test, the 6-Min Walk Test, the Locomotor Capabilities Index, Satisfaction with Prosthesis (SAT-PRO questionnaire), and Houghton Scale.  A total of 16 unilateral transtibial dysvascular amputees, mean age of 65.12 (standard deviation = 10.15) years were included.  Using the vacuum-assisted socket system, the patients significantly improved in balance, gait, and transfers: scores of the Berg Balance Scale increased from 45.75 (standard deviation = 6.91) to 49.06 (standard deviation = 5.62) (p < 0.01).  Four Square Step Test decreased from 18.18 (standard deviation = 3.84) s to 14.97 (3.9) s (p < 0.01).  Timed Up and Go Test decreased from 14.3 (standard deviation = 3.29) s to 11.56 (2.46) s (p < 0.01).  The distance walked in the 6-Min Walk Test increased from 288.53 (standard deviation = 59.57) m to 321.38 (standard deviation = 72.81) m (p < 0.01).  The investigators concluded that vacuum-assisted socket systems are useful for improving balance, gait, and transfers in over 50-year old dysvascular transtibial amputees.

Elevated Vacuum Suspension in Lower Limb Prosthetics

Rink and associates (2016) stated that a growing number of clinical trials and case reports support qualitative claims that use of an elevated vacuum suspension (EVS) prosthesis improves residual-limb health on the basis of self-reported questionnaires, clinical outcomes scales, and wound closure studies.  These researchers reported first efforts to quantitatively assess residual-limb circulation in response to EVS.  Residual-limb skin health and perfusion of people with lower-limb amputation (n = 10) were assessed during a randomized cross-over study comparing EVS with non-EVS (control) over a 32-week period using non-invasive probes (trans-epidermal water loss, laser speckle imaging, transcutaneous oxygen measurement) and functional hyperspectral imaging approaches.  Regardless of the suspension system, prosthesis donning decreased perfusion in the residual limb under resting conditions.  After 16 weeks of use, EVS improved residual-limb oxygenation during treadmill walking.  Likewise, prosthesis-induced reactive hyperemia was attenuated with EVS following 16 weeks of use.  Skin barrier function was preserved with EVS but disrupted after control socket use.  The authors concluded that these outcomes suggested that chronic EVS use improved perfusion and preserved skin barrier function in people with lower-limb amputation.

Darter and co-workers (2016) stated that EVS systems use a pump to draw air from the socket with the intent of reducing bone-socket motion as compared to passive suction systems.  However, it remains unknown if EVS systems decrease limb displacement uniformly during transitions from unloaded to full-body-weight support.  These researchers compared limb-socket motion between EVS and passive suction suspension sockets using a controlled loading paradigm.  Persons with trans-tibial amputation were assessed while wearing either an EVS or passive suction suspension socket.  Digital video-fluoroscopy was used to measure axial bone-socket motion while the limb was loaded in 20 % body-weight increments.  An analysis of variance model was used to compare between suspension types.  Total axial displacement (0 % to 100 % body weight) was significantly lower using the elevated vacuum (vacuum: 1.3 cm, passive suction: 1.8 cm; p < 0.0001).  Total displacement decreased primarily due to decreased motion during initial loading (0 % to 20 %; p < 0.0001).  Other body-weight intervals were not significantly different between systems.  The authors concluded that EVS reduced axial limb-socket motion by maintaining position of the limb within the socket during unloaded conditions; elevated vacuum provided no meaningful improvement in limb-socket motion past initial loading.

Gholizadeh and colleagues (2016) noted that an optimal suspension system can improve comfort and quality of life (QOL) in people with limb loss.  To guide practice on prosthetic vacuum suspension systems, assessment of the current evidence and professional opinion are required.  PubMed, Web of Science, and Google Scholar databases were explored to find related articles.  Search terms were amputees, artificial limb, prosthetic suspension, prosthetic liner, vacuum, and prosthesis.  The results were refined by vacuum socket or vacuum assisted suspension or sub-atmospheric suspension.  Study design, research instrument, sample size, and outcome measures were reviewed.  An online questionnaire was also designed and distributed worldwide among professionals and prosthetists (www.ispoint.org, OANDP-L, LinkedIn, personal email).  A total of 26 articles were published from 2001 to March 2016.  The number of participants averaged 7 (SD = 4) for trans-tibial and 6 (SD = 6) for trans-femoral amputees.  Most studies evaluated the short-term effects of vacuum systems by measuring stump volume changes, gait parameters, pistoning, interface pressures, satisfaction, balance, and wound healing.  A total of 155 professionals replied to the questionnaire and supported results from the literature.  Elevated vacuum systems may have some advantages over the other suspension systems, but may not be appropriate for all people with limb loss.  The authors concluded that EVS could improve comfort and QOL for people with limb loss.  However, they stated that future investigations with larger sample sizes are needed to provide strong statistical conclusions and to evaluate long-term effects of these systems. 

The above policy is based on the following references: