When casting an individual’s residual limb for socket design and prosthetic fitting, practitioners should be mindful of prior activity and doffing history, which could influence the cast shape, according to study results published in the Journal of Rehabilitation Research & Development.
Using imaging tools such as CAD/CAM to understand limb shape change may not only provide insight into a patient’s need for socket replacement or volume accommodation, but it could also “serve as an outcome measurement for testing new technologies and treatment strategies intended to stabilize or compensate for volume fluctuation,” according to researchers.
“A challenge toward accomplishing these goals is to clinically measure limb shape in a way that other variables, ones outside the clinician’s interest, do not confound interpretation. For example, the time between doffing the prosthesis and the initiation of casting is likely to influence cast volume,” the researchers wrote. “It has been noted clinically that after a socket is doffed, the residual limb tends to swell over time. Ambulation that occurred before the casting might also affect the measurements. It is important to know the influence of prior activity in limb volume and shape assessment. If these factors significantly affect results and a practitioner does not carefully plan the measurements to account for them, then the changes in volume and shape might not be measured correctly, leading to a false interpretation of the clinical measurement.”
Doffing and casting differences
Twenty-four transtibial amputees had plaster casts taken twice in one day, with 5 seconds between doffing and casting (PDI-5s) in one trial and 20 minutes (PDI-20m) in the other trial. Researchers randomly assigned the order of the trials among the patients.
Study results showed time between doffing and casting and order of testing affected cast volume. Researchers found the mean radial difference (MRD) between the two casts was only statistically significant when casting 5 seconds after doffing was performed first and casting 20 minutes after doffing performed second. The range of difference was 0.06 mm to 0.68 mm, with a mean MRD between PDI-5s and PDI-20m of 0.34 mm and a median difference of 0.30 mm. The order of testing was statistically significant according to a repeated measure analysis of variance, with larger values obtained when PDI-5s was conducted first.
“We were surprised by the consistency of the result. Almost all subjects showed this trend,” Joan Sanders, PhD, professor of bioengineering at the University of Washington, told O&P Business News. “We did not expect this result because we thought that pressure applied to the residual limb during casting would be enough to counter volume gain. We expected the volume gained to be mainly blood filling the vasculature and thus we thought that it would be easily pushed out of the residual limb during casting. That was not the case.”
According to Sanders, doffing may be a highly effective way to recover and maintain limb volume for patients who experience volume loss over the day.
“A practitioner may be able to manipulate a patient’s limb volume and thus volume measured by casting while they are within the clinic through activity and doffing history,” Sanders said. “Activity history and doffing history are important factors to consider before casting a patient for a new socket. It is not reasonable to expect that re-donning the prosthesis after a period of doffing will quickly reduce limb volume.”
Another step for research is to evaluate whether information about volume and shape differences over time can be used to clinical advantage through extended imagine analysis and interpretation, the researchers wrote. Finally, BMI, limb length, limb circumference, type of prosthesis, suspension, cause of amputation and sex should be considered in future studies to test for possible associations between the variable and MRD. — by Casey Tingle
Disclosure: Sanders has no relevant financial disclosures.