Subsidence in Nonexpandable, Single-Plane Expandable, and Dual-Plane Expandable TLIFs A Propensity-Matched Cohort Study.

Background: Transforaminal lumbar interbody fusion (TLIF) has become a common tool to achieve interbody fusion in lumbar spine surgery while avoiding the time, expense, and morbidity associated with an anterior approach. Nonexpandable (NE) devices have excellent fusion results but are limited to implant size by spinal anatomy; conversely, expandable implants have been associated with increased intraoperative subsidence. Dual-plane expandable (DPE) devices are theorized to have reduced subsidence risk, but DPE cages have not been directly compared to NE and single plane expandable (SPE) implants in vivo.

Study design: A retrospective review of patients who underwent TLIF at a single metropolitan academic medical center from 2018 through 2021 was conducted to compare intraoperative subsidence between NE versus SPE or DPE devices. Patients were propensity score matched (PSM) by age and bone density according to implant type. A second PSM cohort comparing DPE with SPE devices was performed.

Results: A total of 402 patients underwent PSM with 46 NE and 49 DPE cases matched, and 103 SPE patients were matched with 24 DPE cases. The average age was 59 years with 52.5% female patients. Mean body mass index was 29. Nonexpandable TLIF was the most common device implanted 62%, followed by SPE (26%) and DPE (12.2%). Dual-plane expandable devices had a significantly greater intraoperative subsidence than NE devices (12% vs. 0%). Nonexpandable and SPE devices had significantly larger implant lordosis when compared to DPE (10.93 SPE vs. 6. 17 NE vs. 3.83 DPE). Single plane expandable devices had a significantly greater discrepancy between implant lordosis and interbody level lordosis compared to DPE.

Conclusions: Dual-plane expandable cages are associated with increased intraoperative subsidence compared to NE and SPE implants. Additionally, SPE devices have greater discrepancy between stated implant lordosis and interbody level lordosis compared with DPE devices.