P20. Titanium expandable interbody spacers placed via bilateral-TLIF provides stability similar to ALIF: an in-vitro range of motion analysis

Abstract

BACKGROUND CONTEXT The transforaminal lumbar interbody fusion (TLIF) approach was developed to avoid the risks of the anterior lumbar interbody fusion (ALIF) and posterior lumbar interbody fusion (PLIF) approaches, and their potential for damage to the major vessels and the neurological elements, respectively. Construct stability of these various lumbar interbody fusion techniques is paramount to promote arthrodesis. Placement of two titanium expandable interbody spacers intradiscally following a bilateral facetectomy has the theoretical advantage of increased stability. PURPOSE This biomechanical study aims to compare the stability of bilateral-TLIF with titanium expandable interbody spacers compared to various standard constructs in an in-vitro range of motion kinematic analysis in cadaveric models. STUDY DESIGN/SETTING In vitro biomechanics study. OUTCOME MEASURES Range of motion in flexion-extension (FE), lateral bending (LB), and axial rotation (AR) was captured for each specimen. METHODS Twenty-four fresh frozen cadaveric spines (L3–L4/L5–S1) were divided into four groups with equivalent bone mineral density average scores (n=6). Specimens were instrumented with either (1) one static ALIF spacer; (2) one static oblique TLIF spacer (Ob); (3) two static bilateral-TLIF spacers (BiSt); or (4) two expandable bilateral-TLIF spacers (BiEx). Constructs were tested according to a load control protocol (±6.0Nm) before and after posterior fixation in FE, LB, and AR. Motion was captured for the (1) intact condition, (2) interbody spacer with posterior pedicle screw and rod fixation (Spacer+PI), and (3) spacer-alone (Spacer). Motion was normalized to intact, change in stability from intact to Spacer+PI and Spacer constructs was calculated, and statistical analyses were performed (p RESULTS All groups with PI reduced motion from intact in all modes. BiST resulted in comparable stability to ALIF in FE and AR. BiEX Spacer increased stability in all modes and was the only group to gain stability in FE (31% vs. -74%[ALIF], -46%[Ob], and -20%[BiST]). BiEX Spacer added significantly more stability than Ob Spacer in LB (49% vs. -7% [p=0.014]). CONCLUSIONS The proposed bilateral-TLIF technique resulted in comparable stability to an ALIF spacer. Adding posterior fixation to the construct notably increased stability in all modes, emphasizing the need for supplemental fixation. When examining the sole effect of the spacer, only the expandable bilateral-TLIF spacer group gained stability from intact in all modes of motion, illustrating the biomechanical benefits of expandable technology. FDA DEVICE/DRUG STATUS Interbody spacers are indicated for this application (Approved for this indication)