Proper suspension is critical to maintaining socket comfort and fit. Vacuum-assisted socket suspension (VASS) improves fit and comfort by reducing peak socket pressure and pistoning of the residual limb. The purpose of this study was to quantify the effects of VASS on metabolic costs of gait and performance-based outcomes by evaluating changes in these measures immediately after altering suspension and to compare self-reported outcome measures between groups of VASS and non-VASS users.Materials and Methods
Eighteen current VASS users and 18 non-VASS users, all of whom were active community ambulators, participated in two related studies. For study 1, VASS users completed three tasks in the following order: 1) a quantitative gait analysis, 2) function and mobility tests (10-m walk test [10MWT] and timed up and go [TUG]); and 3) 6 minutes of walking at self-selected speed (SSS) to determine energetic costs of walking and socket comfort. Participants performed each task under three suspension conditions, in random order, before proceeding to the next task. The conditions were altering VASS by inactivating the vacuum and blocking the one-way valve. Participants completed tasks immediately after alterations in suspension; that is, we provided no specific accommodation period. All tasks in study 1 were completed during a single testing session. For study 2, both VASS and non-VASS subjects completed electronic versions of surveys to assess prosthetic use and locomotor function including sections of the Prosthetic Evaluation Questionnaire.Results
Study 1: There was no effect of suspension on cost of transport (p = 0.47 for main effect of suspension). However, participants performed TUG in shorter time using VASS and suction (p = 0.02 VASS vs. sleeve; p = 0.049 suction vs. sleeve; p = 0.54 VASS vs. suction) and performed the 10MWT with greater speed while using VASS compared with both suction (p = 0.027) and sleeve (p = 0.011). The use of VASS resulted in a significant within-subject increase of 1.5 and 3 points in socket comfort compared to suction (p = 0.001) and sleeve (p = 0.001), respectively. Study 2: There were no significant differences in any self-reported outcomes measures between VASS and non-VASS users.Conclusions
In absence of active vacuum, current users of VASS experience an immediate reduction in comfort, presumably reflecting worse fit, which may limit their ability to attain faster walking speeds but which does not have an immediate negative affect on the cost of transport. The self-reported measures used to quantify the effects of suspension on prosthetic use, locomotor capabilities, and domains reflecting prosthesis-related quality of life may have been ill-suited for identifying difference in the high-functioning heterogeneous population considered.