Lumbar Foraminal Morphology Can Affect Outcomes of Indirect Decompression: A Systematic Review and Novel Classification.

Study DesignSystematic review.ObjectiveTo identify and classify intervertebral foraminal morphologies associated with failed indirect decompression (IND), with the goal of developing a preoperative classification system to assess candidacy for this procedure.MethodsA systematic review of PubMed, EMBASE, and Google Scholar was conducted. All reported cases of failed indirect decompression secondary to abnormal foraminal morphology were included. Imaging findings were reviewed to identify distinct morphological patterns.ResultsThirteen studies describing 22 patients with failed indirect decompression due to abnormal foraminal morphology were identified. Four distinct imaging patterns were observed: (1) hypertrophic superior articular process variant, (2) prominent posterior inferior osteophyte variant, (3) osseous ring variant, and (4) foramen crowded by disco-ligamentous material variant.ConclusionsWe propose a simple, intuitive classification system for preoperative evaluation of the foramen in candidates for indirect decompression. Each variant is presented with supporting literature implicating it in failed indirect decompression. Future studies should aim to determine the prevalence, clinical significance, and failure rates associated with each morphology type.