Arjan Buis

Calibration problems encountered while monitoring stump/socket interface pressures with force sensing resistors: Techniques adopted to minimise inaccuracies

Force sensing resistors (FSR) have been used to measure dynamic pressures at the interface between appliance and patient. Inaccuracies using FSRs have been reported. This paper summarises both the calibration problems encountered and the techniques adopted to minimise inaccuracies. It is considered that, by calibrating the transducers attached to the socket, and by adopting a strict test protocol, FSRs may provide a guide to the dynamic pressure distribution applied to the trans-tibial stump during gait.

Socket/stump interface dynamic pressure distributions recorded during the prosthetic stance phase of gait of a trans-tibial amputee wearing a hydrocast socket.

Force sensing resistors (FSR) have been used to measure dynamic stump/socket interface pressures during the gait of a trans-tibial amputee. A total of 350 pressure sensors were attached to the inner wall of a hydrocast socket. Data were sampled at 150Hz during approximately 0.8 seconds of prosthetic stance of gait. The dynamic pressure distributions within a hand cast socket reported by Convery and Buis (1998) are compared with those monitored within a hydrocast socket for the same amputee. The pressure gradients within the hydrocast socket are less than that of the hand cast Patellar-Tendon-Bearing (PTB) socket. The proximal “ring” of high pressure in the hand cast PTB socket is replaced with a more distal pressure in the hydrocast socket.

Dynamic interface pressure distributions of two transtibial prosthetic socket concepts

In this study, we investigated and compared the dynamic interface pressure distribution of hands-off and hands-on transtibial prosthetic systems by means of pressure mapping. Of the 48 established unilateral amputees recruited, half (n = 24) had been wearing pressure-cast prostheses (IceCast Compact) and the other half (n = 24) had been wearing hand-cast sockets of the patellar tendon bearing design. We measured the dynamic pressure profile of more than 90% of the area within each prosthetic socket by means of four Tekscan F-Scan socket transducer arrays. We compared the interface pressure between socket concepts. We found that the distribution of dynamic pressure at the limb-socket interface was similar for the two intervention (socket prescription) groups. However, a significant difference was found in the magnitude of the interface pressure between the two socket concepts; the interface pressures recorded in the hands-off sockets were higher than those seen in the hands-on concept. Despite the differences in interface pressure, the level of satisfaction with the sockets was similar between subject groups. The sockets instrumented for this study had been in daily use for at least 6 months, with no residual-limb health problems.

Conventional patellar-tendon-bearing (PTB) socket/stump interface dynamic pressure distributions recorded during the prosthetic stance phase of gait of a transtibial amputee

Force sensing resistors (FSR) have been used to measure dynamic stump/socket interface pressures during the gait of a trans-tibial amputee. A total of 350 pressure sensor cells were attached to the inner wall of a patellar-tendon-bearing (PTB) socket. Data was sampled at 150 Hz during the approximate 0.8 seconds of prosthetic stance of gait. A total of 42,000 pressures were recorded during a single prosthetic stance. This paper describes the distribution of the pressure patterns monitored during the prosthetic stance phase of gait.

Measurement of the consistency of patellar-tendon-bearing cast rectification

The quality of fit of a trans-tibial patellar-tendon-bearing (PTB) socket may be influenced by consistency in casting, rectification or alignment. This paper quantifies, for the first time, the variations in the rectified casts between two experienced prosthetists and the variation between the rectified casts of each individual prosthetist. Prosthetists A and B observed the hand casting of a typical trans-tibial amputee. Each prosthetist was supplied with 5 previously measured duplicated plaster models. The two prosthetists rectified the supplied plaster models based on their own interpretation of basic rectification guidelines. Both prosthetists operated in isolation. The re-measured rectified plaster model data was compared with the unrectified data. The extent of rectification at each of 1800 locations per plaster model was calculated. In zones of major rectification, the mean difference between prosthetists was quantified as 2mm and the standard deviation (SD) about that mean was ±1mm for each prosthetist. The co-ordinates of the apex of the fibular head for the 10 modified casts indicated that the maximum variation was in the axial direction with a SD of 4.3mm for prosthetist A and a SD of 2.8mm for prosthetist B. The lengths of the 5 plaster models rectified by prosthetist A indicated a SD of 0.2mm whereas the lengths of the 5 plaster models rectified by prosthetist B indicated a SD of 2.9mm.

Evaluation of the effect of shape on a contemporary CAD system

The TracerCAD system is one of the leading prosthetic CAD systems in the world and is increasingly used in clinics to replace traditional methods of residual limb shape capture. Accurate dimensional capture of the residuum is arguably the most important process in the production of a prosthetic socket. TracerCAD system accuracy has previously been tested on a cylindrical model but not a trans-tibial shape. Residual limbs are irregular in shape therefore it is important to assess if shape has an effect on the accuracy of data collected when using TracerCAD. The objective of this study is to investigate the accuracy of the TracerCAD system in measuring a model of a trans-tibial stump of known dimensions and volume. A model of a trans-tibial stump was produced and filled with plaster and measured using a data acquisition system with an accuracy of five micron (0.005 mm). The model was repeatedly traced using the TracerCAD system by an individual user. The mean value of measures taken by the dynamic indicator was calculated and compared to individual and mean values of TracerCAD measurement. Results showed that the TracerCAD measurement was not as consistent on the more complex trans-tibial model as for the cylindrical model.

Skin Temperature Prediction in Lower Limb Prostheses

Increased temperature and perspiration within a prosthetic socket is a common complaint of many amputees. The heat dissipation in prosthetic sockets is greatly influenced by the thermal conductive properties of the socket and interface liner materials. These materials influence the bodys temperature regulation mechanism and might be the reason for thermal discomfort in prosthetic sockets. Monitoring interface temperature at skin level is notoriously complicated. The problem might be considered notorious because embedding wires and sensors in an elastomer eventually results in elastomer failures because of the high strain induced when donning a liner (amputees roll the liners onto their limbs). Another reason is because placing sensors and wires directly against the skin could cause irritation and chaffing over just a short period of time. We describe a route wherein if the thermal properties of the socket and liner materials are known, the in-socket residual limb temperature could be accurately predicted by monitoring the temperature between socket and liner rather than skin and liner using the Gaussian process technique.

Pilot study: Data‐capturing consistency of two trans‐tibial casting concepts, using a manikin stump model: A comparison between the hands‐on PTB and hands‐off ICECAST compact® concepts

The quality of fit of a transtibial patellar tendon bearing (PTB) socket may be influenced by consistency in casting, rectification or alignment. For this study two distinctive different datacapturing concepts were tested in relation to prosthetist performance. The handson PTB and handsoff ICECAST compact® concept were studied and compared for inter and intraprosthetist consistency using a specially designed manikin stump model. A purpose designed digitiser was used to scan a selected surface area of the produced models, 5 for each concept, 10 in total. The extent of casting consistency at each of 936 locations per plaster model was calculated and the level of consistency was quantified. This study has shown that by using the manikin model there is a clear indication that the investigated handsoff concept produces more consistent results than the handson concept.

Comparison of adaptive neuro-fuzzy inference system (ANFIS) and Gaussian processes for machine learning (GPML) algorithms for the prediction of skin temperature in lower limb prostheses

Monitoring of the interface temperature at skin level in lower-limb prosthesis is notoriously complicated. This is due to the flexible nature of the interface liners used impeding the required consistent positioning of the temperature sensors during donning and doffing. Predicting the in-socket residual limb temperature by monitoring the temperature between socket and liner rather than skin and liner could be an important step in alleviating complaints on increased temperature and perspiration in prosthetic sockets. In this work, we propose to implement an adaptive neuro fuzzy inference strategy (ANFIS) to predict the in-socket residual limb temperature. ANFIS belongs to the family of fused neuro fuzzy system in which the fuzzy system is incorporated in a framework which is adaptive in nature. The proposed method is compared to our earlier work using Gaussian processes for machine learning. By comparing the predicted and actual data, results indicate that both the modeling techniques have comparable performance metrics and can be efficiently used for non-invasive temperature monitoring.

The effect of alignment changes on unilateral transtibial amputee's gait: a systematic review

Introduction Prosthetic alignment, positioning of a prosthetic foot relative to a socket, is an iterative process in which an amputee’s gait is optimized through repetitive optical gait observation and induction of alignment adjustments when deviations are detected in spatiotemporal and kinematic gait parameters. An important limitation of the current prosthetic alignment approach is the subjectivity and the lack of standardized quantifiable baseline values. The purpose of this systematic review is to investigate if an optimal alignment criterion can be derived from published articles. Moreover, we investigated the effect of alignment changes on spatiotemporal, kinematic and kinetic gait parameters. Results A total of 11 studies were included, two controlled before-and-after studies and nine-interrupted time series studies. Discussion The results demonstrate that alignment changes have a predictable influence on the included kinetic parameters. However, the effect of alignment changes on spatio-temporal and kinematic gait parameters are generally unpredictable. These findings suggest that it is imperative to include kinetics in the process of dynamic prosthetic alignment. Partially this can be established by communication with the prosthetic user in terms of perceived socket comfort, but the use of measurement tools should also be considered. While current literature is not conclusive about an optimal alignment, future alignment research should focus on alignment optimisation based on kinetic outcomes.