Adjacent Segment Motion of Stand-Alone ALIF Versus TLIF in the Degenerative Spine: A Biomechanical Study.

Study DesignBiomechanical human cadaveric study.ObjectivesTransforaminal lumbar interbody fusion (TLIF) is a well-established procedure for treating degenerative lumbar spine pathologies. However, posterior fixation has been reported to accelerate adjacent segment degeneration (ASD). Posterior fixation can be omitted in screw-anchored stand-alone anterior lumbar interbody fusion (ALIF). The present study aimed to compare the cranial adjacent segment motion of ALIF vs TLIF in specimens with reduced bone mineral density (BMD).MethodsSixteen fresh-frozen lumbosacral spines with reduced BMD (donors' age 71 ± 13years, BMD 95.7 ± 34.5 mg HA/cm) were used. Range of motion (ROM) and Neutral Zone (NZ) of the cranial adjacent segment were analyzed in flexion-extension, lateral bending, and axial rotation in native state and after TLIF or stand-alone screwed ALIF instrumentation.ResultsNo significant differences between TLIF and stand-alone screwed ALIF were observed for both absolute ROM and NZ of the cranial adjacent segment in instrumented state across all tested motion directions (  ≥ .267). Decreased relative ROM of the fused segment - normalized to the corresponding segmental ROM in native state - resulted in compensatory increased relative ROM of the cranial adjacent segment after instrumentation. However, the relative adjacent segment ROM did not differ significantly between TLIF and stand-alone screwed ALIF ( ≥ .172).ConclusionsThis study found no clinically significant difference in adjacent segment motion when comparing TLIF with stand-alone screwed ALIF. Hence, both techniques appear to have a negligible impact on adjacent segment motion in poor bone quality. This suggests that neither TLIF nor stand-alone screwed ALIF increase the risk of ASD due to compensatory motion resulting from an operated adjacent segment.