Beyond step counts: Including wear time in prosthesis use assessment for lower-limb amputation.

Introduction: The purpose of this study was to test a novel activity monitor that tracks the time a prosthesis is worn, and the nature of the ambulatory activity conducted with the prosthesis. These capabilities allow prosthesis users' wear and accommodation practices (e.g., temporary doffing) to be monitored, and the intensity of their activities to be assessed. Methods: A portable limb-socket motion sensing system was used to monitor doffs, walk bouts (≥5 steps), low locomotion (2-4 steps), stationary positions, and weight shifts in a group of transtibial prosthesis users. The relationship between doff time and active motion time was investigated, and durations of low and high intensity active motions were compared. Results: For the 14 participants tested, the median prosthesis day duration ranged from 12.8-18.8 h. Eleven participants typically doffed five or fewer times per day, and three participants typically doffed 10 or more times per day. Nine participants demonstrated a positive correlation between daily doff duration and active motion duration. Six participants spent more time in weight shifts than walk bouts, while eight participants spent more time in walk bouts than weight shifts. Conclusion: Capturing don time and temporary doffs and distinguishing weight shifts from walks may provide insight relevant to patient care. Longer-term monitoring studies should be conducted, and the clinical utility of the data evaluated.

A Bioimpedance Analysis Platform for Amputee Residual Limb Assessment.

OBJECTIVE: The objective of this research was to develop a bioimpedance platform for monitoring fluid volume in residual limbs of people with trans-tibial limb loss using prostheses. METHODS: A customized multifrequency current stimulus profile was sent to thin flat electrodes positioned on the thigh and distal residual limb. The applied current signal and sensed voltage signals from four pairs of electrodes located on the anterior and posterior surfaces were demodulated into resistive and reactive components. An established electrical model (Cole) and segmental limb geometry model were used to convert results to extracellular and intracellular fluid volumes. Bench tests and testing on amputee participants were conducted to optimize the stimulus profile and electrode design and layout. RESULTS: The proximal current injection electrode needed to be at least 25 cm from the proximal voltage sensing electrode. A thin layer of hydrogel needed to be present during testing to ensure good electrical coupling. Using a burst duration of 2.0 ms, intermission interval of 100 µs, and sampling delay of 10 µs at each of 24 frequencies except 5 kHz, which required a 200-µs sampling delay, the system achieved a sampling rate of 19.7 Hz. CONCLUSION: The designed bioimpedance platform allowed system settings and electrode layouts and positions to be optimized for amputee limb fluid volume measurement. SIGNIFICANCE: The system will be useful toward identifying and ranking prosthetic design features and participant characteristics that impact residual limb fluid volume.

Assessment technique for computer-aided manufactured sockets.

This article presents an assessment technique for testing the quality of prosthetic socket fabrication processes at computer-aided manufacturing facilities. The assessment technique is potentially useful to both facilities making sockets and companies marketing manufacturing equipment seeking to assess and improve product quality. To execute the assessment technique, an evaluator fabricates a collection of test models and sockets using the manufacturing suite under evaluation, then measures their shapes using scanning equipment. Overall socket quality is assessed by comparing socket shapes with electronic file (e-file) shapes. To characterize carving performance, model shapes are compared with e-file shapes. To characterize forming performance, socket shapes are compared with model shapes. The mean radial error (MRE), which is the average difference in radii between the two compared shapes, provides insight into sizing quality. Interquartile range (IQR), the range of radial error for the best-matched half of the points on the compared socket surfaces, provides insight into regional shape quality. The source(s) of socket shape error may be pinpointed by separately determining MRE and IQR for carving and forming. The developed assessment technique may provide a useful tool to the prosthetics community and industry to help identify problems and limitations in computer-aided manufacturing and give insight into appropriate modifications to overcome them.

Central fabrication: carved positive assessment.

BACKGROUND: It is estimated that only 24% of practitioners use CAD/CAM regularly. Socket manufacturing error may be a source of the limited use of central fabrication. OBJECTIVES: The purpose of this study was to investigate the differences in shape between computer-manufactured, centrally fabricated carved models and electronic file shapes, to determine if carving was a major source of socket manufacturing error in central fabrication. STUDY DESIGN: Experimental, mechanical assessment. METHODS: Three different trans-tibial model shapes were sent electronically to each of 10 central fabrication facilities for the fabrication of positive foam models. A custom mechanical digitizer and alignment algorithm were used to measure the model shapes and then compare them with the electronic file shapes. RESULTS: Volume differences between the models and the electronic file shapes ranged from -4.2% to 1.0%, and averaged -0.9 (SD = 1.1)%. Mean radial error ranged from -1.2 mm to 0.3 mm and averaged -0.3 (SD = 0.3) mm. Inter-quartile range was between 0.3 mm and 2.7 mm and averaged 0.6 (SD = 0.5) mm. The models were significantly smaller than sockets made from the same electronic file shapes (p < 0.01), but the range of mean radial error and the interquartile range were not significantly different between the models and sockets. CONCLUSIONS: The results demonstrated that there was considerable variability in model quality among central fabricators in the industry, and that carving was not the sole source of socket fabrication error. CLINICAL RELEVANCE: The results provide insight into the severity and nature of carving error by central fabrication facilities. Because we found a wide range of model quality, there is not a consistent fabrication problem across the industry, but instead some central fabrication facilities practice the art of model fabrication better than others.

Assessment of residual-limb volume change using bioimpedence.

We investigated electrical bioimpedance as a potential measurement modality to assess residual-limb volume change in lower-limb amputees. Four strip electrodes were positioned across the anterior lateral to posterior lateral aspects of the proximal lower leg or residual limb such that the outer pair applied current and the inner pair sensed voltage. A commercial bioimpedance analyzer supplied current at 50 fre quencies between 5 kHz and 1 MHz and then used a well-validated model to determine fluid resistance. From these data, extracellular fluid volume (V(ECF)) could be estimated. Bench test evaluation showed the instrument to have a root-mean-square error of less than 0.014% over a 1 h interval. Tests of subjects who had been transtibial amputees for at least 2 yr showed V(ECF) changes from postural adjustments well outside the instrument error and normal minute-to-minute biological variability. The rate of V(ECF) change while standing with the prosthesis donned was greater for diabetic subjects than for nondiabetic subjects. Bioimpedance analysis may have use in prosthetics research, where comparing residual-limb volume at different time points or under different treatment conditions is of interest.