Immediate Restoration of Lordosis in Single-level Minimally Invasive Transforaminal Lumbar Interbody Fusion (MI-TLIF): A Comparison of Expandable and Static Interbody Cages

Presented at SMISS Annual Forum 2018
By Sheeraz Qureshi MD, MBA
With Avani Vaishnav MBBS, Philip Saville MD, Steven McAnany MD, Roger Härtl MD, Sertac Kirnaz MD2, Rodrigo Navarro-Ramirez MD, Catherine Gang MPH,

Disclosures: Sheeraz Qureshi MD, MBA A; Cervical Spine Research Society. B; Zimmer-Biomet, Stryker Spiner, Globus Medical, Inc. D; Avaz Surgical. F; RTI, Zimmer-Biomet, Stryker Spine Avani Vaishnav MBBS None, Philip Saville MD None, Steven McAnany MD None, Roger Härtl MD B; Brainlab, DePuy-Synthes, Ulrich, Sertac Kirnaz MD2 None, Rodrigo Navarro-Ramirez MD None, Catherine Gang MPH None,

Introduction:

Minimally invasive (MIS) techniques are becoming popular in spine surgery because they are associated with reduced morbidity. However, a common concern with MIS techniques is the failure to adequately restore lordosis.

Aims/Objectives:

To compare lordosis generated with non-articulating expandable cages and static cages and determine if intra-operative cage-positioning affects radiographic parameters.

Methods:

Upright lateral radiographs of patients undergoing single-level MIS-TLIF with non-articulating expandable or static interbody cages were reviewed. Segmental lordosis (SL), regional lordosis (RL) and Posterior Disc Height (PDH) were measured pre- and post-operatively. Distance from anterior edge of vertebral body to the front of the cage was measured. Based on pre-operative SL, patients were divided into: low-lordosis (<15o), moderate-lordosis (15-25o) and high-lordosis (>25o). Mann Whitney u-test was performed to compare radiographic parameters between static and expandable cages. Linear regressions were conducted to assess the effect of pre-operative SL on post-operative SL, and the effect of cage-position on post-operative SL and PDH. Multivariate regressions were conducted with SL and PDH as dependent variables.

Results:

A total of 171 patients, 60 in the expandable cohort and 111 in the static cohort, were included. In the expandable group, in patients with low lordosis (n=29) SL increased (10.5o to 13.7o, p=0.01), while RL was unchanged (48o). In patients with moderate lordosis (n=21) SL (18.3o to 20.2, p=0.34) and RL (57o to 52o, p=0.07) were unchanged. In patients with high lordosis (n=10) SL decreased (29.5o to 25.3o, p<0.03), while RL was unchanged (59 to 57o, p=0.49). In the static group, in patients with low lordosis (n=28) SL increased (10.6o to 13.7o, p<0.05), while RL was unchanged (47o to 48o). In the moderate lordosis group (n=48) SL (19.1o to 17.5o, p=0.08) and RL (56o to 55o, p=0.47) were unchanged. In patients with high lordosis (n=38) SL (29.5 to 25.3o, p=0.02) and RL (62o to 58o, p=0.002) decreased. When the static and expandable group were compared, there were no significant differences. PDH increased in both groups (Static: 5.9 to 8.2mm, Expandable: 3.6 to 7.5mm). Linear regressions showed that pre-operative SL moderately correlated with post-operative SL (R2=0.41, p<0.00001), but cage-position was not correlated with post-operative SL (R2=0.02) or PDH (R2=0.03). Multivariate regression for post-operative SL confirmed that pre-operative SL was predictive of post-operative SL, as was RL to a lesser extent; cage-position, cage-type, and pre-operative PDH were not. Multivariate regression for post-operative PDH showed that cage-type, pre-operative PDH and pre-operative SL were related, but cage-position was not.

Conclusions:

Pre-operative SL was predictive of post-operative SL. There was no difference in lordosis generated by non-articulating expandable cages and static cages. Expandable cages resulted in a significantly improved PDH but showed no benefit in SL.