238. Interbody spacers and instability: is there a difference in subsidence and range of motion between various cages for osteotomy techniques?

Abstract

BACKGROUND CONTEXT Several types of spine osteotomy techniques have been described to maintain sagittal alignment, varying regarding degree of deformity correction and invasiveness. Intradiscal osteotomy (IDO) is an alternative osteotomy technique for correcting thoracolumbar deformity. Lordotic interbody spacers provide anterior column support and act as a fulcrum around which an osteotomy can be reduced. Partial removal of the posterior endplate during IDO may increase subsidence risk. PURPOSE The purpose of this cadaveric study was to compare the biomechanical stability of bilateral IDO with static and expandable oblique interbody spacers to that of standard Smith-Petersen osteotomy (SPO) with transforaminal lateral interbody fusion (TLIF) using a static, banana-shaped spacer, pre- and postsubsidence. STUDY DESIGN/SETTING Biomechanical cadaveric study PATIENT SAMPLE N/A OUTCOME MEASURES N/A METHODS Eighteen cadaveric functional spine units (FSU) were divided into three equal groups (n=6): SPO-TLIF, bilateral IDO and static cage (sIDO), or bilateral IDO and expandable cage (eIDO). Bilateral pedicle screws were placed proximally and distally for all specimens. Subsidence was created by cyclically loading between 400N and 1200N compression for 20000 cycles at 2Hz, and was defined as the amount of implant settling between the first 1200N cycle and last 1200N cycle. Range of motion (ROM) was captured for flexion/extension (FE), lateral bending (LB), and axial rotation (AR), pre- and postsubsidence. RESULTS ROM in FE, LB, and AR was similar for all three groups, with no significant differences in motion pre- or post-subsidence (p>.05). The eIDO group had the largest loss of stability following subsidence, with motion increasing by 111.9±50.7% in FE, 91.4±42.6% in LB, and 65.5±29.9% in AR. Motion following subsidence was significantly higher than pre-subsidence for eIDO for all three bending planes (p=.003). sIDO motion increased by 103.0±104.3% in FE, 70.3±71.4% in LB, and 73.9±72.8% in AR. SPO-TLIF motion increased by 42.0±33.9% in FE, 27.7±20.1% in LB, and 19.4±17.8% in AR. Motion following subsidence was significantly higher than pre-subsidence for SPO-TLIF for LB (p=.037). CONCLUSIONS In this cadaveric model of a single FSU, IDO with both static and expandable interbodies showed similar biomechanical stability to SPO-TLIF both pre- and postsubsidence. Motion in the eIDO group significantly increased following subsidence in all three bending modes, while sIDO did so in none, and SPO-TLIF did so in only LB. This may be due to larger amounts of subsidence in the eIDO group. Expandable spacers in the eIDO group may have been overexpanded, causing endplate damage upon reducing the osteotomy. Further studies are required to elucidate clinical significance. FDA DEVICE/DRUG STATUS RISE (Globus Medical Inc.) (Not approved for this indication), SUSTAIN (Globus Medical Inc.) (Not approved for this indication), SIGNATURE (Globus Medical Inc.) (Not approved for this indication)