503 - Use of Expandable Interbody Spacer for MIS TLIF: Preliminary Radiograp...

#503 Use of Expandable Interbody Spacer for MIS TLIF: Preliminary Radiographic Results of Lordosis Correction at L5-S1

Oral Posters: Deformity

Presented by: J. Sclafani

Author(s):

J.A. Sclafani (1)
H. Kang (2)
C.W. Kim (1)

(1) Spine Institute of San Diego, Center for Minimally Invasive Spine Surgery, San Diego, CA, USA
(2) New York University, New York, NY, USA

Abstract

Introduction/Purpose: Minimally invasive fusion at the L5-S1 level comes with inherent challenges to the surgeon including the correction of sagittal and coronal alignment, achievement of solid bony fusion and recreation of focal lordosis at the operative level. A previous meta-analysis performed on open versus minimally invasive TLIF has shown a comparable rate of arthrodesis at L5-S1 when traditional open and MIS techniques are used (Wu et.al.,2010).

Minimally invasive Anterior approaches have been shown to significantly increase focal lordosis at the L5-S1 level but traditional MIS posterior approaches utilizing static spacers have not achieved similar success in this respect. The posterior MIS approach with static cage implantation is limited mainly through the narrow posterior annulotomy and wedge shaped posterior bony architecture. Expandable cages have been developed to overcome these logistical limitations by passing through posterior structures in a collapsed form and expanding to maximal diameter in the anterior most aspect of the intervertebral space. This study was designed to evaluate recreation of focal lordosis at the L5-S1 level by expandable spacers implanted through the MIS TLIF procedure.

Methods: Multiple retrospective lordosis angle measurements were taken by 2 separate observers at L5-S1 on MIS TLIF patients with static cage implantation and expandable Caliber cage implantation. A single surgeon performed all fusions with expandable spacer implantation and procedures with static spacer implantation were extracted from a practice group of four fellowship trained spine surgeons. All measurements were averaged at the pre-operative and post-operative time points and entered into an Excel spreadsheet. A statistical analysis was performed on the data using GraphPad Prism softwear.

Results: Preoperative and postoperative lordosis angle measurements were averaged for MIS TLIF patients with static spacer (n=15, postoperative follow-up average of 55 weeks) and expandable spacer (n=20, postoperative follow-up average of 54 weeks) implants. A significant correction in lordosis (absolute change of 9.25°, p=0.007, n=4) was obtained with expandable spacer implantation when pre-operative focal lordosis was less than 15°. A significant increase in lordosis angle was not achieved with expandable spacer implantation when pre-operative lordosis angle was greater than 15° but focal lordosis angle was maintained in all cases (n=16). Static spacers did not achieve a significant correction of focal lordosis except for cases when pre-operative lordosis was 16-20° (absolute change of 3.38°, p=0.05, n=4).

Conclusion: Restoration of focal lumbar lordosis at the L5-S1 level is challenging when utilizing posterior MIS techniques. This study demonstrates an expandable spacer can be utilized to gain a significant improvement in focal lordosis when pre-operative lodosis angles are less than 15° at the L5-S1 level. An expandable spacer can be used together with other strategies such as performing a thorough discectomy, serial disk release and cantilever techniques to attain maximal lordosis with MIS lumbar reconstruction.