Oblique lumbar interbody fixation: a biomechanical study in human spines

In vitro spine biomechanics.

To determine the biomechanical properties of oblique lumbar interbody fixation (OLIF) in human cadaveric spines.

OLIF has been used for stabilization of degenerative spondylolisthesis at the lumbosacral junction. Biomechanical properties and mode of failure of OLIF as a standalone device for motion segments without sagittal deformity has not yet been investigated. We hypothesize that the biomechanical properties of OLIF will be comparable with the contemporary standard of pedicle screw (PS) fixation.

Randomly matched motion segments from L1 to L5 were allocated into 2 groups: (A) OLIF (group 1, n=5) or (B) PS (group 2, n=5). The intact and instrumented motion segments with and without anterior interbody graft were first tested under a combination of 200N axial compression and 5 Nm bending moments in flexion-extension and in lateral bending. Range of motion (ROM) and neutral zone were determined and compared between intact, OLIF and PS. A final load to failure test was carried out for each motion segment in either flexion or extension.

OLIF resulted in reduction of flexion-extension ROM to 36%±14% of intact whereas PS resulted in reduction to 27%±22% of intact. The reduction of lateral bending ROM were 32%±13% and 32%±24% of intact with OLIF and PS. There were no significant difference in ROM between OLIF and PS (P=0.39). The mean failure loads with OLIF and PS in flexion were 1284 and 1158N, and in extension were 1879 and 1934N, respectively. Failure occurred at the ventral screw bone interface without pedicle fracture.

These results indicate that stiffness and load to failure of the OLIF is comparable with PS fixation. OLIF failure occurred ventrally through the anterior cortical rim without concomitant pedicle fracture.