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Stand-alone interbody cage provides sufficient stability, stiffness for lumbar fusion
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In their finite element analysis, researchers from South Korea found promising results with a stand-alone interbody cage with anterior fixation.
The researchers modified a 3-D, non-linear finite element model of the L2-5 segment to simulate anterior lumbar interbody fusion (ALIF) in L3-4 and tested the model with an intact spine, destabilized spine, with the interbody cage alone (type 1), with the stand-alone cage with anterior fixation (type 2) and with type 1 in addition to pedicle screw fixation (PSF; type 3). Using external loading, researchers quantified measures such as range of motion and the stiffness of the operated level, range of motion of the adjacent segments, load-bearing distribution and vertebral body stress.
Compared to those of the destabilized spine, the implanted models had decreased range of motion and increased stiffness, according to study results. Researchers found differences in range of motion limitation of 8% in flexion, 10% in extension, 4% in axial rotation and 6% in lateral bending in type 2 vs. type 3. Type 2 also had decreased range of motion of the upper adjacent segments by 3% to 11% and the lower adjacent segments by 3% to 6% vs. type 3.
The investigators found the greatest reduction in facet load at the operated level was observed in type 3 with 71%, followed by type 2 at 31% and type 1 at 23%. Type 3 also had the highest increase in facet load at the adjacent level, followed by type 2 and type 1. While type 2 showed a similar distribution of load sharing to that of the intact spine, type 3 migrated posterior to the normal. Fifteen percent of the stress on the lower vertebral endplate was reduced by type 2 compared to type 1. However, the stress of type 2 increased two-fold vs. the stress of type 3, especially in extension, according to study results.
“In conclusion, the stand-alone cage with reinforced anterior fixation provided sufficient stability and stiffness necessary to carry out lumbar fusion and at the same time, reduced the excessive motion of the adjacent segments and the stress on the adjacent segment joints by exhibiting similar load sharing characteristics to a normal lumbar,” the researchers wrote in their study. “Therefore, the stand-alone cage can supplement with the shortcomings of the anterior lumbar interbody cage with no fixation device and have the advantage of parallel use with pedicle screw fixation.”
Disclosure: The researchers reported no relevant financial disclosures.
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