A Static Evaluation of Transtibial Prosthesis Suspension
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Previously, there have been a number of studies comparing different transtibial suspension methods; however, studies using elevated negative pressure (vacuum) as a suspension method are limited. The purpose of this study is to compare three methods of transtibial suspension (vacuum, suction, and knee sleeve) with respect to pistoning. Our hypotheses were: one that vacuum suspension will significantly reduce the amount of pistoning compared to knee sleeve and suction suspensions, and two that a greater magnitude of pistoning would be apparent in individuals with a higher percentage of redundant tissue. Seven subjects with unilateral transtibial amputations were included in this study. A custom made prosthesis was fabricated for each subject that allowed for easy conversion between suspension methods. For each suspension method, radiographic scans of the subject’s limb were produced inside the prosthetic socket using the dual energy X-ray absorptiometry (DEXA) scanner for three conditions. These conditions, designed to simulated dynamic gait, consited of an unweighted, loaded to half body weight, and a 44.5 N distraction. Using a multivariate repeated measures ANOVA along with a Bonferroni post-hoc analysis, statistical significance was shown between both knee sleeve and suction and between knee sleeve and vacuum suspensions with regard to pistoning. Although statistically insignificant, the p value (p=0.063) was very close to the alpha level for significance of 0.05 between suction and vacuum suspensions. In contrast to previous schools of thought this study has also shown that the amount of redundant tissue and pistoning are not strongly correlated.