A study in the current issue of the Journal of Rehabilitation Research & Development, Volume 50, Number 7 2013, concludes that prior activity influences the residual limb cast shape. Given this, the researchers stated “that practitioners should be mindful of prior activity and doffing history when casting an individual’s limb for socket design and prosthetic fitting.”
The study cohort comprised 24 individuals with transtibial amputation with various suspension systems. Each was casted for a socket while in a comfortable seated position; the casting method and variables were controlled and replicated for each participant. Two trials were performed on each person in a single day. To ensure consistent activity before casting was started, at the outset of each study day, participants were submitted to a 40-minute protocol of about equal durations of sitting with the prosthesis donned, standing, walking on a treadmill at a self-selected walking speed, and sitting with the prosthesis doffed. Then, the participant redonned the prosthesis and walked for up to one minute until he or she was comfortable, sat down, doffed the prosthesis, and after a prescribed interval-five seconds in one trial and 20 minutes in the other-was casted. Participants wore their prosthesis but were not active for the five to 30 minutes between castings, other than a walk to a waiting area, a few minutes of rest, and then a walk to return to the laboratory. The interval between castings was typically 15 minutes, but varied between five and 30 minutes because of differences in the time the subjects required to prepare and don their prosthesis and time to walk the distance between the waiting area and laboratory. Depending on their availability, some participants underwent two more castings on a different day with the ordering of the prescribed interval between casting reversed (20 minutes in the first trial and five seconds in the next). The molds were then scanned using a commercial, tabletop, high-performance laser scanner.
The researchers found that when casting five seconds after doffing was performed first and casting 20 minutes after doffing performed second, then the mean radial difference (MRD) between the two casts was statistically different from zero (mean 0.34mm). But when casting 20 minutes after doffing was performed first and casting five seconds after doffing performed second, then the MRD between the two casts was not statistically different from zero (mean −0.02mm). A repeated measures analysis of variance showed that order of testing was statistically significant (p = 0.008), with larger values obtained when casting after five seconds was conducted first.
