The Effects of Interbody Device Design and Placement on Lumbar Lordosis and Disc Height in Transforaminal Lumbar Interbody Fusion

Abstract

There are a wide variety of interbody devices available for use in transforaminal lumbar interbody fusion (TLIF). While traditionally these interbodies are bullet-shaped, crescent-shaped cages have become increasingly common. There is a paucity of literature comparing the effect of cage geometry with substratification for surgical approach (minimally invasive (MIS) vs. open). The aim of this study was to determine the effect of implant geometry, positioning, and surgical approach on the correction of different spinal alignment parameters in patients undergoing TLIF. A retrospective chart and imaging review was performed on 103 patients with a total of 131 instrumented segments performed by a single surgeon. Preoperative, initial postoperative, and final postoperative standing lateral lumbar radiographs were evaluated for lumbar lordosis (LL), segmental lordosis (SL), anterior disc height (ADH), and posterior disc height (PDH). Anterior-posterior implant positioning was recorded for initial and final postoperative radiographs. These measurements were compared among four groups: open bullet (OB), MIS bullet (MB), open crescent (OC), and MIS crescent (MC). SL increased in all groups by a mean of 2.9° at initial imaging and 2.2° at final imaging. The OC group had greater initial improvement in SL compared to the MB group (p = 0.02), though this effect was lost at final follow-up (p = 0.11). The OB and OC groups conferred greater initial improvement in ADH (p = 0.02; p = 0.04), while the OC group had greater final improvement in ADH compared to the MB and MC groups (p = 0.01; p = 0.01). The OC group had less initial improvement in PDH compared with the other groups (p = 0.03, p = 0.02, p < 0.01). The MB group provided greater final improvement in PDH compared with the MC and OC groups (p = 0.04, p = 0.01). Cage geometry, surgical approach, and implant position all demonstrated a statistically significant but clinically minor impact on segmental alignment for TLIF procedures.