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MATERIAL FATIGUE In the prosthetic SACH foot
1997Download the complete report (1,03 MB, PDF format) |
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The effects of material fatigue on the prosthetic foot appear to have received little attention. The purpose of this study was to examine fatigue effects in term of their infuence on amputee gait. It was hypothesised that the mechanical characteristics of the prosthtic SACH feet would be compromised after fatigue loading and that the artifical 'aging' of these feet woul influence biomechanical characteristics of gait.
Kingsley SACH type KO51 and Otto Bock SACH type IS49, right side, size 26, were tested. Three specimens of each were fatigued by a cycle tester which approximated forces on the foot during the gait cycle. Static compliance of the heel and forefoot was measured and impact tests were performed to evaluate the shock absorption capacity of the prosthetic feet. Four trans-tibial amputees were recruited and each fitted with new and fatigued prosthetic feet fo both types. Temporal data was collected via the Stride Analyser System and ground reaction force data was obtained using a Kistler force platform. A two-way (foot type x foot age) repeated measures ANOVA was performed.
The Kingsley prostehtic feet were found to undergo premature delamination and failure without recommended interface plate between the foot and the pyramid adapter. Further tests incorporating an interface plate solved this problem. Drop test results indicated that Kingsley feet provided significantly better shock absorption and that shock absorption increased with a minimal amount of fatigue. The Otto Bock feet were significantly stiffer in the forefoot region. Both brands of feet followed a similar trend of an initial increase in stiffness after 5.000 cycles, then a decrease after 10.000 cycles. The mean duration of the heel loading phase of the 'new' Kingsley test sample was significantly longer than the fatigued test sample. It was also demonstrated that as the stiffness of the rearfoot increases, so does the duration of the loading phase (r=0.952)
