Jl. Stambough et al., EFFECTS OF CROSS-LINKAGE ON FATIGUE LIFE AND FAILURE MODES OF STAINLESS-STEEL POSTERIOR SPINAL CONSTRUCTS, Journal of spinal disorders, 11(3), 1998, pp. 221-226
This study tested the effects of cross-linkage on the fatigue performa
nce of posterior spinal constructs (i.e., AcroMed stainless steel Isol
a systems). The failure modes encountered during fatigue were also exa
mined. The results of this study confirmed earlier findings that the u
se of cross-linkage does not significantly affect the stability of pos
terior constructs during axial loading. Their influence in torsion loa
ding is much more pronounced. During the fatigue tests, posterior stai
nless steel spinal implants instrumented without cross-linkage reached
1 million cycles at 500- and 750-N loads. When the load was increased
to 1,000 N, the number of cycles to failure dropped by two-thirds. Th
ese findings demonstrate that the endurance limit was between 750 N an
d 1,000 N for spinal constructs without cross-linkage, with the limit
being closer to 750 N. Devices equipped with one or two cross-linkages
reached 1 million cycles at 500 N. The number of cycles to failure dr
opped dramatically as the load was increased to 750 and 1,000 N. It ap
pears that the endurance limits for spinal devices using cross-linkage
should be 500 and 750 N, with the Limit closer to the 500-N load. All
rod fractures occurred near the junction between the longitudinal and
transverse rods. Stress concentration was greatly in the vicinity of
that contact point. These results should provide a basis for future im
provement in endurance Limits of spinal implants equipped with cross-l
inkage. Higher endurance limits will reduce the toxic effects encounte
red during fracture modes. The implants will also be better able to wi
thstand the high physiologic loads experienced by obese individuals.