Brendan McHugh

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.

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.

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.

Analysis of body-device interface forces in the sagittal plane for patients wearing ankle-foot orthoses

An ankle-foot orthosis (AFO) is employed principally to treat musculoskeletal disorders of the ankle and/or subtalar joints although, occasionally, it may be prescribed to provide stance phase control of the knee. In order to function satisfactorily, an AFO must apply appropriate forces to the lower leg in a manner which does not cause local tissue damage or discomfort. Equally the leg will apply forces to the AFO which it must be capable of withstanding without breakage or loss of function. Thus it is useful to know where the body-device interface forces act during walking and to be able to estimate their magnitudes. This is not well understood and has not been satisfactorily documented. This paper explains the force actions between the AFO and the leg, in the sagittal plane, where there is absence of muscle power. Furthermore, it explores the possibility of estimating the magnitudes of these forces. It is found that the forces are greatest when orthotic assistance is needed to compensate for plantar flexor insufficiency in late stance phase. On the other hand, where the AFO is used to support the foot, in the absence of dorsiflexion power in swing phase, the forces are relatively small. Understanding these force levels is relevant to the design of the AFO in terms of choice and use of materials and components.

Measuring the daily stepping activity of people with transtibial amputation using the ActivPAL™ activity monitor

ABSTRACT This study compared the general activity during 1 week and detailed activity during a 24-hr period of 48 established unilateral transtibial prostheses users. Activity was measured by instrumenting their prescribed prosthesis, which they have been using for a minimum of 6 months, with the ActivPAL™ activity monitor. Half (n = 24) were fitted with a prosthesis with total surface bearing (TSB) pressure-cast sockets (“hands-off” group), and the other half (n = 24) had been wearing prostheses with hand-cast patellar tendon-bearing (PTB) sockets (“hands-on” group). As a prerequisite, the long-term reliability of the ActivPAL activity monitor was assessed, and it was found to exhibit a high level of consistency between devices (intraclass correlation coefficient [ICC] of 0.997 during the 24-hr period). The monitors were used to examine the activity levels of the two groups of transtibial prostheses users wearing their own prosthesis. The results indicated that both subject groups were active throughout the day, walking a mean of more than 8000 steps. No statistically significant difference in daily stepping activity was seen between the two groups (p = 0.173). Despite differences in prosthetic socket design, the daily activity profiles of both subject groups were similar.

Design of manikin for testing of residual-limb shape-capture method: technical note.

Consensus is still lacking on how best to capture the shape of a residual limb. Computer-aided design systems have not proven more accurate, repeatable, or reliable than traditional plaster of paris methods. Research is limited in design, relates to clinical trials, and is based on opinions and clinical experience. Many outcome measurements are based on qualitative estimations of prosthetic fit or patient feedback rather than quantitative measurements. Research must identify the most accurate, repeatable, and reliable methods for residual-limb shape capture under conditions most likely to enhance socket fit. Measurement is difficult because a reference grid is required for identifying the residual limbs axis for ensuring direct comparison. This article describes a manikin production method for testing the shape capture of the residual limb. Diameters and volume were measured at specific levels with a programmable computer numerical control milling machine and a displacement tool, with a combined accuracy of 5 micrometers.