Mechanical testing of a flexible fixation device for the lumbar spine.
The aim of this study was to test mechanically a new flexible fixation system for the lumbar spine. This device incorporates loops of polyester braid which are secured by a crimped titanium sleeve. In tensile tests, all loops failed, by slippage through the crimped sleeve, at 434 +/- 25 N (mean +/- standard deviation from five loops) for a single crimp and 415 +/- 15 N (from five loops) for two crimps. The intact system was then tested according to the ASTM standard. In a static test, all five specimens failed by slippage of the braid through the sleeve. Initial slippage occurred between 600 and 700 N, but the mean maximum load sustained was 1090 +/- 140 N. Dynamic tests were performed on ten constructs at a frequency of 5 Hz, under a range of loading conditions. The maximum load applied in any of the tests was 825 N. Two constructs did not complete the required 5 x 10(6) test cycles because of fracture of their spinous process hooks. However, other tests, under the same conditions, showed no signs of failure. Fracture occurred as a result of fretting damage from the recommended stainless steel roll pins.
Leahy
J C
JC
Department of Bio-Medical Physics and Bio-Engineering, University of Aberdeen, Scotland, UK.
Mathias
K J
KJ
Hukins
D W
DW
Shepherd
D E
DE
Deans
W F
WF
D001696:Biomechanical Phenomena; D004867:Equipment Design; D004868:Equipment Failure; D006801:Humans; D016268:Internal Fixators / Q000592:standards*; D008159:Lumbar Vertebrae / Q000601:surgery*; D008422:Materials Testing; D011091:Polyesters; D011095:Polyethylenes; D013123:Spinal Fusion / Q000295:instrumentation*; D013718:Tensile Strength; D016474:Weight-Bearing
D011091:Polyesters; D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene