Background The retrodural space of Okada is a potential space posterior to the ligamentum flavum that allows communication with the bilateral facet joints. However, the actual anatomy of this space has not been clearly visualized to date. We sought to investigate the characteristics of patients showing contrast spreading to the facet joint space during epidural injection and to clarify the anatomical structures of the retrodural space and adjacent ligamentous tissues in cadaveric specimens.
Methods Fluoroscopic images of patients who underwent fluoroscopy-guided lumbar interlaminar epidural injection were assessed for contrast flow to the facet joints. Patient demographics, preprocedural imaging study findings, and epidural approaches were analyzed. The anatomical study included the sectional dissection, micro-CT imaging, and histological evaluation of lumbar spine specimens from 16 embalmed cadavers.
Results Fluoroscopic images of 605 epidural injections were analyzed. Among them, 36 with inadvertent spread into the facet joints (5.9%) were identified. Multivariate analysis revealed that facet joint pathologies were significantly associated with inadvertent spread into the facet joints (OR 4.382; 95% CI 1.160 to 16.558; p=0.029). Micro-CT and histological findings consistently showed a retrodural space between the ligamentum flavum and interspinous ligament. Various anatomical communication routes in the posterior ligamentous complex leading to this space were observed in specimens with degenerative and pathological changes.
Conclusion Degenerative and pathological facet joint changes were associated with a higher incidence of spread into the retrodural space during epidural injection. Our findings confirm anatomical evidence for a false loss of resistance before the needle enters the epidural space.
- regional anesthesia
- pain management
- nerve block
Data availability statement
Data are available on reasonable request. Data are available on reasonable request. Deidentified data will be made available on reasonable written request submitted to the corresponding author.
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SHK and T-HC contributed equally.
Contributors SHK and T-HC (these authors contributed equally to this work) were involved with study conception, design, clinical and anatomical data acquisition, data analysis, interpretation, and figure preparation, drafting of the paper. HJK was involved with clinical data acquisition, clinical data analysis/interpretation and drafting of the paper. H-JK was involved with anatomical data acquisition, anatomical data analysis, interpretation, and figure preparation. H-HK was involved with anatomical data acquisition, anatomical data analysis, interpretation, and figure preparation. K-JS was involved with anatomical data acquisition, anatomical data analysis, interpretation, and figure preparation. YSL was involved with clinical data acquisition, clinical data analysis/interpretation. H-MY: study conception, design, anatomical data acquisition, anatomical data analysis, interpretation, figure preparation, and drafting of the paper and is guarantor. All authors read and gave final approval of the version to be published.
Funding This work was supported by grants from the National Research Foundation Korea, funded by the Korean government (No. 2020R1F1A1058123 to H-MY and No. 2021R1F1A1045873 to SHK).
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
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