P36. Interbody spacers placed via bilateral-TLIF provide higher vertebral endplate contact: a micro-CT 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. Contact between the entire spacer and the adjacent endplates of these various techniques is paramount to providing stability, increasing fusion rates, and reducing subsidence. A novel bilateral-TLIF technique includes reconstruction via a bilateral facetectomy and the placement of two interbody spacers along the lateral margins of the disc space. Bone graft is pre-packed in the graft chamber as well as between spacers. PURPOSE The goal of this study was to assess spacer and graft contact with the endplate of the proposed technique compared to various standard constructs. STUDY DESIGN/SETTING In vitrobiomechanics study. OUTCOME MEASURES Spacer and graft contact percentage was calculated from sagittal images across the entire width of the disc space 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 standard TLIF static oblique spacer (Ob); (3) two static bilateral-TLIF spacers (BiSt); or (4) two expandable bilateral-TLIF spacers (BiEx). Specimens were scanned using the SkyScan-1173 (Bruker microCT, Belgium) with an isotropic resolution of 35um. Quantitative analysis was performed using DataViewer (Bruker microCT) and CTAn software (Bruker microCT). Based on sagittal images, spacer and graft contact percentage was calculated by dividing the contact length of graft and spacer on the endplate, by endplate length. The relative percentage was averaged across the entire width of the disc space for each specimen. Statistical analysis was performed (p RESULTS BiST (27.5%) exhibited the highest spacer and graft contact percentage followed by BiEX (21.4%) > ALIF (19.6%) > Ob (9.9%) (Figure 1). ALIF, BiST, and BiEX groups had significantly higher contact with the vertebral endplate compared to Ob (p=0.005, 0.000, and 0.001, respectively). CONCLUSIONS The proposed bilateral-TLIF technique resulted in relative spacer and graft contact area comparable to ALIF and significantly increased contact with the endplate compared to an oblique spacer. A benefit to the proposed approach is higher graft contact with the endplate due to graft packed between the spacers. It can be suggested that because of higher graft contact, this unique approach may potentially increase fusion rates. FDA DEVICE/DRUG STATUS Interbody spacers (Approved for this indication)