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 HÃ¤rtl 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 HÃ¤rtl MD B; Brainlab, DePuy-Synthes, Ulrich, Sertac Kirnaz MD2 None, Rodrigo Navarro-Ramirez MD None, Catherine Gang MPH None,
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.
To compare lordosis generated with non-articulating expandable cages and static cages and determine if intra-operative cage-positioning affects radiographic parameters.
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.
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.
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.