BIOMECHANICAL ASSESSMENT OF TITANIUM AND STAINLESS-STEEL POSTERIOR SPINAL CONSTRUCTS - EFFECTS OF ABSOLUTE RELATIVE LOADING AND FREQUENCY ON FATIGUE LIFE AND DETERMINATION OF FAILURE MODES/
Jl. Stambough et al., BIOMECHANICAL ASSESSMENT OF TITANIUM AND STAINLESS-STEEL POSTERIOR SPINAL CONSTRUCTS - EFFECTS OF ABSOLUTE RELATIVE LOADING AND FREQUENCY ON FATIGUE LIFE AND DETERMINATION OF FAILURE MODES/, Journal of spinal disorders, 10(6), 1997, pp. 473-481
The goal of this study was to examine the effects of absolute/relative
loads and frequency on the fatigue life of titanium and stainless ste
el posterior spinal constructs, and to determine the failure fracture
modes. The stainless steel constructs had higher stiffness and yield s
trength than the titanium constructs, but the ultimate static strength
was almost equal for both types of constructs. Titanium constructs, h
owever, exhibited higher variability than the stainless steel construc
ts. In fatigue tests, the stainless steel constructs were significantl
y affected by the external load and were frequency independent. It app
ears from fatigue curves that 500 N can be approximated as the enduran
ce limit for the stainless steel constructs. Titanium constructs were
load-frequency dependent, and their endurance limit was somewhere betw
een the 500 and 750 N load levels. There were no differences in perfor
mance between the stainless steel and titanium constructs at 16 Hz. At
4 Hz, titanium constructs performed as well or better than stainless
steel constructs. Also, the titanium constructs resulted in better per
formance than the stainless steel constructs in the elastic region, an
d with smaller differences in the plastic region. Most of the failure
modes for stainless steel constructs were in screw bending at 16 Hz wi
th a smaller percentage of rod fractures at high loads, with a higher
percentage of rod fractures observed for the stainless steel construct
s at 4 Hz. Most of the failure modes for titanium constructs occurred
in screw bending or fracture.