Comments regarding: The benefits of using a vacuum-assisted socket system to improve balance and gait in elderly transtibial amputees by Samitier et al

In the United States there is much debate regarding the potential benefits of vacuum-assisted suspension, hence it was with great interest that we read the recent publication by Samitier et al., ¹ “The benefits of using a vacuum-assisted socket system to improve balance and gait in elderly transtibial amputees.”

While the authors conducted a potentially useful clinical study, description of the interventions hampers meaningful interpretation and clinical application of the results. This study compared the subjects’ usual prosthesis to a prosthesis fitted with vacuum-assisted socket system (VASS). This was accomplished by duplicating the regular socket. Unfortunately, the design of the regular socket and the suspension mechanism used as part of the usual prosthesis were not described. Additionally, it was not mentioned whether other prosthetic components were standardized. Insufficient intervention description has been highlighted in a number of systematic reviews as a common issue in the reporting of prosthetic research. ² We agree with the authors and recognize from our own investigations that outcomes on performance-based measures, such as the Berg Balance Scale, are influenced by device fit and function, ³ and so these details are important for interpretation of the main and sub-analysis results.

It is not clear whether the comparator socket was an exact duplicate of the usual socket or not given the statement that “the VASS was adapted following the manufacturer’s instructions” ¹ (p. 84). Does this mean that after socket duplication, modifications were made to the socket design as recommended by the manufacturer to ensure that it was total surface weight bearing? ⁴ With regard to the subjects who experienced blisters, was testing completed before or after a distal valve was installed in their VASS? This information is important since the appearance of blisters in some subjects may have resulted from lack of total contact between the socket and limb.

We are also concerned that the statistical analysis in which multiple paired comparisons were made to address the primary study hypothesis results in a high risk of type 1 error (i.e. false positives). The authors have compared results on seven outcome measures (evaluating balance, gait, transfers, etc.) to assess the main effect of suspension type on the construct of ambulation/mobility, in which implementing a critical alpha correction would have been appropriate. This concern is exacerbated by the secondary analysis separating the subjects based on Medicare Functional Classification Level (MFCL), for which an additional 14 paired comparisons were conducted. This analysis should have been included as part of the primary study hypothesis and a more appropriate inferential statistical analysis implemented to properly address interaction effects.

We believe that the prosthetic community would benefit from clarification of these issues by the authors.