Influence of prior activity on residual limb volume and shape measured using plaster casting: results from individuals with transtibial limb loss.

INTRODUCTION Advances in computer-aided design/manufacturing (CAD/CAM) may advance prosthetics and allow imaging tools to take a more dominant role in clinical care. For example, quantification of changes in residual limb shape over time, determined by comparing limb shapes, potentially provides insight into a person's needs for socket replacement or volume accommodation [1-2]. In addition, characterization of shape change may serve as an outcome measurement for testing new technologies and treatment strategies intended to stabilize or compensate for volume fluctuation (e.g., fluid-filled inserts, air-filled inserts, and elevated vacuum systems) [3]. 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. It has been noted clinically that after a socket is doffed, the residual limb tends to swell over time [2,4]. 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 measurements. METHODS Participants Participants were volunteers who had a transtibial amputation more than 15 mo prior to entry in the study and who were considered by their practitioner to have reached a stable residual limb volume. Participants were required to meet a Medicare Functional Classification level of at least K-1 (limited or unlimited household ambulation) [5], and to be capable of ambulating on level surfaces at a fixed cadence. Volunteers were excluded from the study if they had recent injury or existing skin breakdown. Enrollment of participants for whom a socket replacement was imminent was deferred until the new socket fitting was completed. Procedures Casting Each participant was seated comfortably with the prosthesis donned until all materials were prepared. A nylon stocking was donned on the residual limb to serve as a barrier between the plaster of Paris bandage and the limb. No liner was worn. Using the thumb to lift the starting end loosely, the practitioner submerged the bandage (Ortho-Care extra-fast setting plaster of Paris bandages 15 cm x 4.6 m; Manchester, New Hampshire) in clean, tepid water (approximately 26[degrees]C) for approximately 5 s. The excess water was squeezed out, and the bandage was applied in a left to right fashion, the right hand always holding the bandage. At each bandage turn, the layers were massaged to obtain a smooth surface. A timer was used to document the length of time of the casting procedure. The timer was started when the practitioner began to wrap the bandage around the residual limb and stopped when the completed cast was removed from the residual limb. The casting procedure took less than 4 min to complete on all test subjects. Care was taken to ensure that the times for different castings for each subject were consistent. After the cast was dry and removed from the subject's residual limb, the practitioner applied a fine layer of talcum powder to the inside surface to serve as a mold release agent. A bucket of tepid water was filled, and dental grade plaster of Paris was added and stirred into the bucket until a thick consistency was achieved. The cast was filled, and an identifying label placed on the mold. After the mold set, the casting bandages were removed by cutting two strips down the length of the cast using a Dremel and saw blade and prying the bandages off with a flat-head screwdriver and pliers. Care was taken to ensure the mold was not distorted. …