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| 21KF-038 |
Retrodural space of Okada and its clinical implication for lumbar epidural injection: a clinical and anatomical analysis
Department of Anesthesiology and Pain Medicine, Anesthesia and Pain Research Institute, Yonsei University College of Medicine, Seoul, Republic of Korea1
Department of Anatomy, Yonsei University College of Medicine, Seoul, Republic of Korea2
Translational Research Unit for Anatomy and Analgesia, Yonsei University College of Medicine, Seoul, Republic of Korea3
Background
A clinical information and an anatomical understanding of the retrodural space of Okada are essential to understand how this space cause a false-positive loss of resistance during interlaminar epidural approach. The purpose of this study was to analyze retrospectively the characteristics of patients with contrast spreading into the space of Okada during fluoroscopically guided lumbar interlaminar epidural injection. Also, we sought to anatomically clarify the 3D structures of this space and adjacent tissues using micro-CT imaging for elucidating this clinical finding.
Methods
604 cases of lumbar interlaminar epidural injections were performed in 2020. Cases in which suspected facet joint injection on x-ray image were identified by two different pain physicians. Contrast spread patterns on x-ray image, pre-procedural MRI findings, and the patients’ medical records were reviewed. Micro-CT images of the space of Okada were acquired after PTA preparation at L4-5 region of embalmed cadavers. The space of Okada and its adjacent tissues were examined meticulously based on its 3D topography and histologic evaluation.
Results
We have identified a total of 36 cases (6.0%) in 33 patients who had been injected lumbar facet joint unintentionally. In 32 cases (88.9%), the appropriate location of the needle tip indicating posterior epidural space was documented on x-ray image. In 8 cases (22.2%), the simultaneous epidural space and facet joint injections occurred. Among the 36 cases, 33 (91.7%) showed central stenosis and 26 (72.2%) showed ligamentum flavum hypertrophy on MRI findings. Also, lumbar spine surgeries were performed before epidural injections in 4 cases (11.1%). Micro-CT images clearly showed the serial topography of the space of Okada and its adjacent structures. The retrodural space of Okada between ligamentum flavum and vertebral lamina was observed and this space was communicated with both facet joint space in all cases. Ligamentum flavum seems to be a robust barrier distinguishing the space of Okada and epidural space, but midline gap filled with interspinous ligamentous tissue was observed. Also, the boundary and connectivity of this Okada space were changed in some pathologic and degenerative conditions of lumbar spine.
Conclusions
Contrast spread to facet joint space has a characteristic pattern and can be distinguished from true epidural injection, but this event can simulate the appearance of a successful epidural injection. A non-destructive, multi-sectional approach using 3D micro-CT comprehensively demonstrated the real topography of the retrodural space of Okada. A precise anatomical understanding and recognizing the fluoroscopic imaging features of injection into this space permits pain physician to further manipulate the needle tip for true epidural injection.
A clinical information and an anatomical understanding of the retrodural space of Okada are essential to understand how this space cause a false-positive loss of resistance during interlaminar epidural approach. The purpose of this study was to analyze retrospectively the characteristics of patients with contrast spreading into the space of Okada during fluoroscopically guided lumbar interlaminar epidural injection. Also, we sought to anatomically clarify the 3D structures of this space and adjacent tissues using micro-CT imaging for elucidating this clinical finding.
Methods
604 cases of lumbar interlaminar epidural injections were performed in 2020. Cases in which suspected facet joint injection on x-ray image were identified by two different pain physicians. Contrast spread patterns on x-ray image, pre-procedural MRI findings, and the patients’ medical records were reviewed. Micro-CT images of the space of Okada were acquired after PTA preparation at L4-5 region of embalmed cadavers. The space of Okada and its adjacent tissues were examined meticulously based on its 3D topography and histologic evaluation.
Results
We have identified a total of 36 cases (6.0%) in 33 patients who had been injected lumbar facet joint unintentionally. In 32 cases (88.9%), the appropriate location of the needle tip indicating posterior epidural space was documented on x-ray image. In 8 cases (22.2%), the simultaneous epidural space and facet joint injections occurred. Among the 36 cases, 33 (91.7%) showed central stenosis and 26 (72.2%) showed ligamentum flavum hypertrophy on MRI findings. Also, lumbar spine surgeries were performed before epidural injections in 4 cases (11.1%). Micro-CT images clearly showed the serial topography of the space of Okada and its adjacent structures. The retrodural space of Okada between ligamentum flavum and vertebral lamina was observed and this space was communicated with both facet joint space in all cases. Ligamentum flavum seems to be a robust barrier distinguishing the space of Okada and epidural space, but midline gap filled with interspinous ligamentous tissue was observed. Also, the boundary and connectivity of this Okada space were changed in some pathologic and degenerative conditions of lumbar spine.
Conclusions
Contrast spread to facet joint space has a characteristic pattern and can be distinguished from true epidural injection, but this event can simulate the appearance of a successful epidural injection. A non-destructive, multi-sectional approach using 3D micro-CT comprehensively demonstrated the real topography of the retrodural space of Okada. A precise anatomical understanding and recognizing the fluoroscopic imaging features of injection into this space permits pain physician to further manipulate the needle tip for true epidural injection.
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