The Relationship of Prosthetic Sock Ply Thickness to Percentage of Transtibial Limb Volume Outside of the Socket

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IntroductionProsthetic socks are typically used to accommodate volume fluctuations throughout the day. Clinically, prosthetists often use sock ply thickness to assess the fit of a prosthetic socket and the amount of volume reduction necessary for the next socket iteration. This is done by using various sock plies to determine the proper socket fit. The amount of volume reduction needed for a specific sock ply fit is unclear.ObjectiveThis preliminary study aimed to measure the relationship between sock ply and percentage of volume change.MethodsThe Rodin4D scanner was used to scan three transtibial sample foam models. Each model had an appropriately sized liner, which was scanned as a baseline measurement. Each sock ply combination (one, two, three, five, one + one, one + two, two + three, two + one, and three + two) was scanned six times per model. Scan order was randomly assigned for each model.ResultsSignificant differences in volume change were found between one-ply (5.188%) and three-ply (10.42%) and five-ply (8.83%) socks, but not two-ply socks (7.15%). A significant volume increase was shown for the use of multiple socks (three + two ply, 18.33%, or two + three ply, 18.33%) compared with a single five-ply sock (8.83%). However, no significant differences were found in a similar comparison of a single three-ply sock (10.42%) versus the one + two–ply (11.68%) or two + one–ply (11.57%) socks.ConclusionOur results showed that the use of multiple socks for the same ply, specifically the order of socks donned for the two + three ply and three + two ply, resulted in greater volume than a single sock of the same ply (i.e., five ply). The volumetric change for five-ply is significantly different from one-ply, but not from two-ply and three-ply socks. A limitation of this study was that the scans were completed on foam models with the point of measurement at the distal patella causing potential for the posterior wall to be outside of the socket. This may change on a human subject. The percentage of volume changes based on sock ply thickness that were determined from this study may be used as a starting point for prosthetists during modifications, but further research is needed to determine how this volume changes within the socket.

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