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 novel portable sensor to monitor bodily positions and activities in transtibial prosthesis users.

BACKGROUND: Step activity monitors provide insight into the amount of physical activity prosthesis users conduct but not how they use their prosthesis. The purpose of this research was to help fill this void by developing and testing a technology to monitor bodily position and type of activity. METHODS: Thin inductive distance sensors were adhered to the insides of sockets of a small group of transtibial prosthesis users, two at proximal locations and two at distal locations. An in-lab structured protocol and a semi-structured out-of-lab protocol were video recorded, and then participants wore the sensing system for up to 7 days. A data processing algorithm was developed to identify sit, seated shift, stand, standing weight-shift, walk, partial doff, and non-use. Sensed distance data from the structured and semi-structured protocols were compared against the video data to characterize accuracy. Bodily positions and activities during take-home testing were tabulated to characterize participants' use of the prosthesis. FINDINGS: Sit and walk detection accuracies were above 95% for all four participants tested. Stand detection accuracy was above 90% for three participants and 62.5% for one participant. The reduced accuracy may have been due to limited stand data from that participant. Step count was not proportional to active use time (sum of stand, walk, and standing weight-shift times). INTERPRETATION: Step count may provide an incomplete picture of prosthesis use. Larger studies should be pursued to investigate how bodily position and type of activity may facilitate clinical decision-making and improve the lives of people with lower limb amputation.

Modeling the mechanics of elevated vacuum systems in prosthetic sockets.

Elevated vacuum (EV) is suggested to improve suspension and limb volume management for lower limb prosthesis users. However, few guidelines have been established to facilitate configuration of EV sockets to ensure their safe and proper function. A benchtop model of an EV socket was created to study how prosthetic liner tensile elasticity, socket fit, and socket vacuum pressure affect liner displacement and subsequent pressure on the residual limb. A domed carbon fiber layup was used to represent an EV socket. Inserts were used to simulate various air gaps between the socket and liner. Various prosthetic liner samples were placed under the carbon fiber layup. Liner displacement and the corresponding pressure change underneath the liner were measured as vacuum was applied between the liner sample and socket wall. Tissue vacuum pressure increased linearly with socket vacuum pressure until the liner contacted the socket wall. Predicted tissue vacuum pressure matched well with experimental results. Findings suggest that the effect of vacuum pressure on the residual limb is primarily determined by air gap distance. The developed model may be used to assess effects of EV on residual limb tissues based on an individual's socket fit, liner characteristics, and applied vacuum. Understanding the physiological effects of EV on the residual limb could help practitioners avoid blister formation and improve EV implementation.

Does actively enlarging socket volume during resting facilitate residual limb fluid volume recovery in trans-tibial prosthesis users?

BACKGROUND: Residual limb volume loss is a source of prosthetic socket fit problems in people with lower-limb amputation. The aim of this study was to investigate a novel volume recovery strategy for people with trans-tibial amputation. METHODS: Test sockets for people with trans-tibial amputation were created that allowed panels of an adjustable socket and the underlying elastomeric liner to be pulled radially outward, using small motors mounted to the socket. One Control and one Intervention session were conducted with each participant. During Intervention sessions, panel-pull was executed during the sits of a multi-cycle sit/walk protocol. No panel-pull was executed during the Control sessions. Residual limb fluid volume was monitored in anterior and posterior regions using bioimpedance analysis. FINDINGS: Results from 12 participants demonstrated that short-term (12 min after the intervention was applied) median posterior residual limb fluid volume change for Intervention (0.44%) was higher than that for Control (-0.02%) (P = .015). Long-term (40 min after the intervention was applied) median posterior residual limb fluid volume change for Intervention (0.95%) was higher than that for Control (-0.26%) (P = .002). INTERPRETATION: If a panel-pull mechanism that was easy to assemble and operate could be created, then panel-pull may be an effective accommodation strategy to reduce daily limb volume loss in trans-tibial prosthesis users.

Effectiveness of elevated vacuum and suction prosthetic suspension systems in managing daily residual limb fluid volume change in people with transtibial amputation.

BACKGROUND: Previous studies investigating limb volume change with elevated vacuum have shown inconsistent results and have been limited by out-of-socket volume measurements and short, single-activity protocols. OBJECTIVES: To evaluate the effectiveness of elevated vacuum for managing limb fluid volume compared to suction suspension with an in-socket measurement modality during many hours of activity. STUDY DESIGN: Fixed-order crossover design with a standardized out-of-laboratory activity protocol. METHODS: Transtibial electronic elevated vacuum users participated in two sessions. Elevated vacuum was used during the first session, and suction suspension in the second. Participants completed a 5.5-h protocol consisting of multiple intervals of activity. In-socket residual limb fluid volume was continuously measured using a custom portable bioimpedance analyzer. RESULTS: A total of 12 individuals participated. Overall rate of fluid volume change was not significantly different, though the rate of posterior fluid volume change during Cycle 3 was significantly lower with elevated vacuum. Although individual results varied, 11 participants experienced lower overall rates of fluid volume loss in at least one limb region using elevated vacuum. CONCLUSION: Elevated vacuum may be more effective as a volume management strategy after accumulation of activity. Individual variation suggests the potential to optimize the limb fluid volume benefits of elevated vacuum by reducing socket vacuum pressure for some users. CLINICAL RELEVANCE: A better understanding of how elevated vacuum (EV) affects residual limb fluid volume will allow prosthetists to make more informed clinical decisions regarding accommodation strategies designed to improve daily socket fit.

How do transtibial residual limbs adjust to intermittent incremental socket volume changes?

BACKGROUND: Strategies to maintain prosthesis users' daily limb volume are needed. OBJECTIVES: Test how intermittent incremental socket volume adjustments affect limb fluid volume and limb-socket distance. STUDY DESIGN: Repeated measures. METHODS: People with transtibial limb loss walked on an outdoor trail wearing a motor-driven adjustable socket that they adjusted a small amount, approximately 0.3% socket volume, every 2 min using a mobile phone app. Limb fluid volume and sensed distance between the socket and a target in their elastomeric liner were monitored. A gradual socket enlargement phase was followed by a gradual socket reduction phase. RESULTS: An incremental socket enlargement significantly increased limb fluid volume (p < 0.001) but not sensed distance (p = 0.063). An incremental socket reduction significantly decreased both limb fluid volume (p < 0.001) and sensed distance (p < 0.001). CONCLUSION: Participants' residual limb fluid volume increases during ambulation compensated for incremental socket volume increases. For incremental socket volume decreases, residual limb fluid volume decreases did not compensate and the socket fit became tighter. CLINICAL RELEVANCE: Results support the hypothesis that for people without co-morbidities, intermittent incremental socket volume enlargements are an effective accommodation strategy to increase limb fluid volume while maintaining socket fit. Intermittent incremental socket volume reductions decreased limb fluid volume but also made the socket fit tighter.

A motor-driven adjustable prosthetic socket operated using a mobile phone app: A technical note.

Sockets that allow incremental size adjustment during ambulation may help prosthesis users improve management of their changes in limb volume and the quality of their prosthetic fit. A platform system was developed that allowed people with trans-tibial limb loss to adjust the radial positions of socket panels during ambulation in small increments via a motor mounted beneath the socket. The motor altered the length of a cable running through the socket panels according to commands communicated from a mobile phone. A proportional-integral-derivative controller adjusted the voltage applied to the motor via pulse-width modulation to achieve target settings. Bench test results showed that when the system was subjected to loads comparable to those expected during clinical use, maximum absolute steady state error was 0.036 mm. Treadmill testing on 16 people with trans-tibial limb amputation demonstrated that the range of cable lengths over which participants deemed fit clinically acceptable varied between 24 mm and 114 mm depending on the user. In field testing 11 of 13 participants were comfortable making socket size adjustments while walking. The developed system achieves incremental socket size adjustments appropriate for research and development of ambulatory adjustable sockets.

Socket size adjustments in people with transtibial amputation: Effects on residual limb fluid volume and limb-socket distance.

BACKGROUND: Small intermittent adjustments of socket size using adjustable sockets may be a means for people with transtibial amputation to better maintain residual limb fluid volume and limb position while using a prosthesis. METHODS: Socket size, limb fluid volume, and distance from the limb to the socket, termed "sensed distance," were recorded while participants with transtibial amputation walked on a treadmill wearing a motor-driven, cabled-panel, adjustable socket. Researchers made frequent socket size adjustments using a mobile phone app to identify participants' acceptable socket size range. Limb fluid volume and sensed distance were then monitored as incremental adjustments were made to the socket. FINDINGS: Prosthesis users in this study (n = 10) accepted socket sizes between -5% and +5% of their neutral socket volume. There was a rapid increase in limb fluid volume and sensed distance upon socket enlargement, and a rapid decrease upon reduction. Subsequently, there were gradual changes in fluid volume and sensed distance. While visually monitoring limb fluid volume data in real time, researchers were able to adjust socket size to maintain consistent limb fluid volume within a -0.7% to +0.9% volume change for 24 min. INTERPRETATION: Participant residual limbs compensated to socket size adjustment. Using socket-mounted sensors to monitor limb-socket mechanics, an automatic adjustable socket that maintains limb fluid volume may be possible and may improve socket fit in instances where fit deteriorates during use.

Adjustable sockets may improve residual limb fluid volume retention in transtibial prosthesis users.

BACKGROUND: Loss of residual limb volume degrades socket fit and may require accommodation. OBJECTIVES: To examine if either of two accommodation strategies executed during resting, socket release with full socket size return and socket release with partial socket size return, enhanced limb fluid volume retention during subsequent activity. STUDY DESIGN: Two repeated-measures experiments were conducted to assess the effects of socket release on limb fluid volume retention. METHODS: Limb fluid volume was monitored while participants wore a socket with a single adjustable panel. Participants performed eight activity cycles that each included 10 min of sitting and 2 min of walking. The socket's posterior panel and pin lock were released during the fifth cycle while participants were sitting. In one experiment (Full Return), the socket was returned to its pre-release size; in a second experiment (Partial Return), it was returned to 102% of its pre-release size. Short-term and long-term limb fluid volume retention were calculated and compared to a projected, No Intervention condition. RESULTS: Partial Return and Full Return short-term retentions and Partial Return long-term retention were greater than those projected under the control condition ( p < 0.05). CONCLUSION: Socket release during resting after activity, particularly when the socket is returned to a slightly larger size, may be an effective accommodation strategy to reduce fluid volume loss in transtibial prosthesis users. CLINICAL RELEVANCE: This study suggests that existing prosthetic technologies' adjustable sockets and locking pin tethers can be used in novel ways to help maintain residual limb fluid volume in active prosthesis users.