Loosening of stand-alone ALIF versus TLIF in degenerated lumbar human spines: an in vitro biomechanical study

Biomechanical investigation is needed to determine whether stand-alone anterior lumbar interbody fusion with integrated screws (ALIF) is advisable for use in elderly patients. This study aimed to test three null hypotheses: (1) cyclic loading does not cause loosening of ALIF in degenerated lumbar specimens, (2) cyclic loading does not cause loosening in transforaminal lumbar interbody fusion (TLIF) in degenerated lumbar specimens, and (3) Neutral Zone (NZ) and Range of motion (ROM) of ALIF and TLIF do not differ after cyclic loading.

Twelve fresh-frozen human cadaveric lumbar motion segments (L1-5, donors' age 76.1 ± 6.7 years; trabecular BMD 97.1 ± 36.9 mgHA/cm³) were utilized. NZ and ROM were assessed after ALIF or TLIF and following cyclic loading for flexion-extension (Flex-Ext), lateral bending (LB), and axial rotation (AR). Axial compression of 0-1150 N was applied over 2000 cycles. Loosening was defined as significant increase in NZ.

Cyclic loading significantly increased NZ of ALIF specimens in Flex-Ext (1.69 ± 1.81°, p =.048) and LB (1.84 ± 1.81°, p =.036), and showed a trend to significance in AR (0.46 ± 0.54°, p =.065). NZ of TLIF specimens did not increase significantly in any motion direction (p ≥.112). ROM and NZ did not differ significantly between ALIF and TLIF in post-cyclic states(p ≥.556).

Axial compression loading caused significant loosening of ALIF in Flex-Ext and LB, but not of TLIF in degenerated lumbar human cadaveric specimens. Hence, standalone ALIF cannot be recommended without reservation for the use in elderly patients with degenerative lumbar spines. However, the absolute differences between pre- and post-cyclic states were small, and ROM and NZ of ALIF after cyclic loading were comparable to TLIF.