Vacuum Suspension: Effect on Tissue Oxygenation, Activity and Fit - Center for Limb Loss and MoBility
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Vacuum Suspension: Effect on Tissue Oxygenation, Activity and Fit

PI: Glenn K. Klute, Ph.D.
Agency: Department of Veterans Affairs

Objectives: Many amputees live with an ill-fitting socket and can experience limb pistoning within the socket, which in turn may result in skin irritation, tissue breakdown, discomfort, and a reduction in activity. The Otto Bock Harmony® Vacuum Management System (Harmony System), a novel suspension system utilizing sub-atmospheric pressure, may have the potential to alleviate these conditions for healthy and dysvascular amputees. The research described herein will allow us to understand how suspension systems influence prosthetic socket fit and residual limb tissue health and to formulate a knowledge base on two suspension systems providing prosthetists and clinicians the objective data to make better prescription decisions. The specific objectives of this research are to characterize the response of the lower residual limb to a vacuum suspension system and to measure its performance as compared to a typical distal locking pin suspension system.

Research Design: The Harmony System’s purported benefits include, but are not limited to: improved suspension (reduction in the amount of pistoning), maintenance of limb volume throughout the day, and increased tissue oxygenation to the residual limb. However, to date, the Harmony System and its supposed merits have escaped formal study. This research uses (1) a within-subject crossover design to compare the Harmony System to a distal locking pin suspension and a pseudo-patellar bearing socket and (2) a between-subject design to explore the effect of pressure within a socket on residual limb transcutaneous oxygen tension (TcPO2) levels.

Methodology: Our first objective was to characterize performance, as related to socket fit, of the Harmony System using objective and subjective measures. This is done by conducting a within-subject experiment to measure pistoning in three dimensions while walking, overall and regional changes in limb volume before and after a thirty-minute treadmill walk, mobility (step counts) and the perception of socket fit (questionnaire) as a function of prosthetic prescription (Harmony System vs. distal locking pin suspension system). This objective required the development of a novel, near real-time limb scanning instrument.

Limb volume as well as the 3D shape of the residual limb is collected using a six projector, 12 camera custom scanner developed in conjunction with the University of Washington CSE department. The scanner allows a subject to be scanned in a matter of seconds. The projectors emit a line pattern alternating on and off which the cameras use to create partial 3D surfaces. Six of these surfaces are registered together to give a 3D surface of the residual limb. This surface is used to quantify any significant volume change and potentially the areas where the volume change is the most substantial.

Transtibial amputee participating in limb scanning protocol

Transtibial amputee participating in the limb scanning protocol.

Findings: Five subjects completed the protocol (4 traumatic and 1 dysvascular, 56±9 years, 84±11kg wt). Reasons for the 15 withdrawals included: problems achieving an adequate fit or had issues with the VASS (n=6), time commitments (n=2), or illness, limb ulcers, or personal reasons (n=7). Limb pistoning was smaller (p=.0021) for the VASS (1±3 mm) compared to the PIN (6±4 mm). The limb volume was not statistically different (p>.05) for the VASS (0.72±0.13 liters) compared to the PIN (0.68±0.14 liters). The 30 minute treadmill walk at self-selected speed had no effect on limb volume (p>.05); pre-treadmill volume was 0.70±0.14 liters compared to post-treadmill volume 0.69±0.13 liters. The activity level was significantly less (p=.0056) when subjects wore the VASS (38k±9k steps/2 weeks) when compared with the PIN (73k±18k steps/2 weeks). Subjects opined their residual limb health was healthier while wearing the PIN (90 ± 5) compared to the VASS (77±20), less frustrating while wearing the PIN (9±11) compared to the VASS (43±29), and found it easier to ambulate with the PIN (95±6) compared to the VASS (67±22).

Milestones: Manuscript preparation is continuing and submission is expected in early 2010. Further analysis of volume change location is continuing.