Dynamic alignment using external socket reaction moments in trans-tibial amputees.

BACKGROUND: Prosthetic alignment is used to optimize prosthetic functioning and comfort. Spatio-temporal and kinematic gait parameters are generally observed to guide this process. However, they have been shown to be influenced by compensations, which reduces their sensitivity to changes in alignment. Alternatively, the use of moments working at the base of the prosthetic socket, external socket reaction moments (ESRM), has been proposed to quantify prosthetic alignment. RESEARCH QUESTION: To investigate if a predetermined kinetic alignment criterion, 0Nm averaged over the stance phase, can be used to fine-tune prosthetic alignment. METHODS: 10 transtibial amputees were included in this intervention study. Firstly, their prostheses were aligned using conventional alignment procedures. Kinetic parameters and Socket Comfort Score (SCS) were measured in this initial alignment (IA) condition. Subsequently, the coronal plane ESRM during gait was presented to the prosthetist in real time using a Gait Real-time Analysis Interactive Lab. The prosthetist iteratively adapted the prosthetic alignment towards a predetermined average ESRM during the stance phase of 0 Nm. At the Final Alignment (FA), kinetic parameters and SCS were measured again and a paired sample t-test was performed to compare ESRMs and SCSs between alignments. RESULTS: A significant (p < 0.001) change was found in the absolute coronal plane ESRM (mean ± SD) from IA (|0.104| ± 0.058 Nm/kg) to FA (|0.012| ± 0.015 Nm/kg). In addition a significant (p < 0.001) change of the external coronal adduction knee moments was observed from IA (-0,127 ± 0.079 Nm/kg) to FA (-0.055 ± 0.089 Nm/kg), however this change was more variable among participants. On average, no significant (p = 0.37) change in the SCS was observed. SIGNIFICANCE: While this study shows the potential of quantifying and guiding alignment with the assistance of kinetic criteria, it also suggests that a sole reliance on the ESRM as a single alignment criterion might be too simple.

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 intra-prosthetist 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.

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.

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 150 Hz 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.

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

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.