General Session: MIS - Hall F
Presented by: L. Marchi
L. Marchi(1), R. Amaral(1), R. Jensen(1), L. Pimenta(1,2)
(1) Instituto de Patologia da Coluna (IPC) , Sao Paulo, Brazil
(2) UCSD, Dept Neurosurgery, San Diego, CA, United States
Introduction: Lateral lumbar interbody fusion (LLIF) relies on indirect decompression, therefore maintenance of disc height restoration is pivotal. Different study groups have studied cage subsidence but no review was done. The objective was to review and discuss the data published regarding subsidence following LLIF: radiological characteristics, classification, clinical relevance, and risk factors.
Methods: Systematic literature review into Medline, Lilacs and Google Scholar databases. Inclusion: full text articles; clinical studies; thoracolumbar intervertebral fusion with lateral placed cages via transpsoas; reported subsidence rates; articles in English. Exclusion: case report; case series < 10 cases; corpectomy; trauma; tumor; severe deformity correction. Primary endpoint was cage subsidence: overall rate, assessment, consequences and risk factors.
Results: Records identified (n=257); Records screened after duplicates removed (n=190); Full-text articles assessed for eligibility (n=112); Studies included in qualitative synthesis (n=36). Studies dated from 2010-2016. Definition of subsidence/ Methods of assessment: highly heterogenic; at least three grading systems have been proposed with severity (percent of collapse) as the primary consideration; one classification system has been proposed considering the location of subsidence (superior/inferior endplates). Incidence: subsidence rates were extremely variable in the LLIF group, ranging from 0%-52%. Period: subsidence occur either in the surgical procedure (iatrogenic), or gradually in the postoperative course, usually in the first weeks up to 3mos (spontaneous). Clinical relevance: generally, the studies considering subsidence as any compromise of either endplates or small amounts loss of disc height (1mm/2mm) reported no clinical impact of subsidence. In contrast, more severe cases (>25% of loss) could evolve with transient back pain and/or loss of indirect decompression. Radiological
Findings: most articles reported subsidence to appear in the superior endplate of the caudal vertebra (bellow the cage); in some articles cage sinking caused loss of lordosis and instability. Impact in fusion: 7/8 articles (87.5%) reported no impact in fusion, but one reported negative impact if the cage tilts (type 2 subsidence). Vertebral fractures: extreme cases were shown to facilitate coronal plane VB fracture, especially if lateral plates are used. Revision: needed due to subsidence and subsidence leading to the need of revision ranged from 0-100%, depending on which definition of subsidence used. Risk factors: intraoperative endplate damage, taller/narrower cages (antero-posteirior), poor bone quality, advanced age, female gender, bigger construction lengths, spondylolisthesis, and scoliosis. Supplementation role: no study concluded which kind of supplementation leads to the prevention of subsidence, although, higher incidences seen with stand-alone constructions.
Conclusion: It was observed a high heterogeneity in the studies reporting subsidence following LLIF. Graft subsidence following LLIF is a multifactorial process and researcher have found some risk factors. With the current literature, it is not possible either to make a direct comparison or to have a cumulative incidence facing the fact that the different studies used different criteria to report cage subsidence. A low-grade and asymptomatic subsidence (radiological finding) has been the event most reported in LLIF literature. Depending on the magnitude and type of subsidence, it can be a signiﬁcant complication leading to deformity, compromise of neural elements, nonunion, and even vertebral body fracture.