Axial bone-socket displacement for persons with a traumatic transtibial amputation: The effect of elevated vacuum suspension at progressive body-weight loads

Background: Elevated vacuum suspension 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 elevated vacuum suspension systems decrease limb displacement uniformly during transitions from unloaded to full-body-weight support. Objectives: To compare limb-socket motion between elevated vacuum and passive suction suspension sockets using a controlled loading paradigm. Study design: Comparative analysis. Methods: Persons with transtibial amputation were assessed while wearing either an elevated vacuum 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. Results: Total axial displacement (0%-100% body weight) was significantly lower using the elevated vacuum (vacuum: 1.3cm, passive suction: 1.8cm; p<0.0001). Total displacement decreased primarily due to decreased motion during initial loading (0%-20%; p<0.0001). Other body-weight intervals were not significantly different between systems. Conclusion: Elevated vacuum suspension 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. Clinical relevance Excessive bone-socket motion contributes to poor residual limb health. Our results suggest elevated vacuum suspensions can reduce this axial displacement. Visual assessment of the images suggests that this occurs through the reduction or elimination of the air pocket between the liner and socket wall while the limb is unloaded.