Aetna considers the Vacuum Assisted Socket System (VASS), a specialized vacuum pump residual limb volume management and moisture evacuation system that is used with an artificial limb to increase suspension and proprioception and improve gait, experimental and investigational because there is insufficient evidence in the medical literature that these specialized components improve the function of the artificial limb or provide any other clinically significant benefits. 

Note: An artificial limb that is used with the VASS is covered as a prosthetic when medically necessary for amputees, on the same basis as any other artificial limb.

See also CPB 0578 - Lower Limb Prostheses.

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 system consists of a TEC liner, suspension sleeve and air evacuation pump.  The device creates an elevated vacuum between the liner and the socket wall.  The elevated vacuum promotes natural fluid exchange that regulates volume fluctuation in the residual limb, reduces forces to the residual limb, and increases suspension and proprioception.  The manufacturer claims that the enhanced linkage from the vacuum between the liner and the socket wall decreases weight and promotes an improved gait.

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).

In a randomized cross-over study, Klute et al (2011) examined the effect of a VASS system as compared with pin suspension on lower extremity amputees.  Unilateral, trans-tibial amputees (n = 20 enrolled, n = 5 completed).  Interventions were (i) total surface-bearing socket with a VASS, and (ii) 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.