Biomechanics of lateral interbody spacers: going wider for going stiffer

Abstract

This study investigates the biomechanical stability of a large interbody spacer inserted by a lateral approach and compares the biomechanical differences with the more conventional transforaminal interbody fusion (TLIF), with and without supplemental pedicle screw (PS) fixation. Twenty-four L2-L3 functional spinal units (FSUs) were tested with three interbody cage options: (i) 18 mm XLIF cage, (ii) 26 mm XLIF cage, and (iii) 11 mm TLIF cage. Each spacer was tested without supplemental fixation, and with unilateral and bilateral PS fixation. Specimens were subjected to multidirectional nondestructive flexibility tests to 7.5 N·m. The range of motion (ROM) differences were first examined within the same group (per cage) using repeated-measures ANOVA, and then compared between cage groups. The 26 mm XLIF cage provided greater stability than the 18 mm XLIF cage with unilateral PS and 11 mm TLIF cage with bilateral PS. The 18 mm XLIF cage with unilateral PS provided greater stability than the 11 mm TLIF cage with bilateral PS. This study suggests that wider lateral spacers are biomechanically stable and offer the option to be used with less or even no supplemental fixation for interbody lumbar fusion.

Figure 1

Axial view of cages used in testing (CoRoent, NuVasive, Inc, San Diego, CA): (a) 26 mm XLIF cage, (b) 18 mm XLIF Cage, and (c) 11 mm TLIF cage.

Figure 2

Lateral fluoroscopy images during testing of (a) 18 mm XLIF cage, (b) 26 mm XLIF cage, and (c) 11 mm TLIF cage, implanted at L2-L3 intervertebral space.

Figure 3

Range of motion (ROM) results normalized to intact motion: (a) flexion extension, (b) lateral bending, and (c) axial rotation. Bars represent means ±1 standard deviation. Intact spine ROM (100%) indicated by solid line.