Preliminary characterization of the relationship between clinical assessment of prosthetic fit using plasticine and in-socket pressure measurement in transtibial amputation.

Background: Currently, clinicians use a ball of plasticine to measure contact between the end of amputated residual limbs and prosthetic sockets to assess distal-end fit.

Objectives: This study characterizes the forces required to deform plasticine and relates these to clinical decisions made about socket fit.

Study design: Cross-sectional study.

Methods: Loading thresholds for plasticine deformation were identified. Three different sized check sockets were loaded with a phantom limb, distal-end sensors, and in-situ plasticine. Three transtibial prosthesis users were recruited and completed a socket fitting assessment with distal end sensors and in-situ plasticine. Forces and deformations were recorded and compared with the thresholds and with prosthetist and prosthesis users' ratings of fit.

Results: Plasticine deformation associated with a "good fit" was associated with loads of 4.8-48.5 N for 7- to 8-mm balls and 15.5-148 N for 10- to 11-mm balls. Plasticine deformation magnitudes alone could not detect differences between sockets of various sizes for a standardized limb model. Distal-end force sensors could differentiate between sockets to some extent. In the 3 transtibial prosthesis users, plasticine and force measurements aligned with the "good fit" reported by the prosthetist and the end user.

C onclusions: This study has characterized the forces required to achieve clinically relevant types of plasticine deformation at the distal end of a socket. It has also related these plasticine deformations and distal-end force measurements to clinical judgements about socket fit in the clinic and end user ratings of comfort and fit. Future work should test these thresholds on end user and clinician ratings of poor fit.