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Influence of needle tip position on injectate spread in 406 interlaminar lumbar epidural steroid injections 2007

Interventional Spine

Elizabeth L Whitlock, B.A.
Keith H Bridwell, M.D., Non ASSR Member
Louis A Gilula, M.D., ASSR Member

Scientific Paper

Purpose

To retrospectively evaluate the relationship of needle tip placement to flow patterns and injectate dispersion in central (interlaminar) lumbar epidural steroid injections (LESIs).

Methods & Materials

This study was approved by our Institutional Review Board, which waived the requirement for informed consent, and it was compliant with Health Insurance Portability and Accountability Act guidelines. Fluoroscopic images from 701 consecutive interlaminar LESIs in 485 patients were reviewed. Vertebral level, needle placement, and flow patterns of an injectate mixture containing radioopaque contrast were determined from procedural fluoroscopic images. History of previous spinal operations was determined from procedural records. A subset of patients with three or more injections at the same site was also examined. Patterns in the data were evaluated with chi-squared tests and t -tests.

Results

Images from 406 LESIs, one per patient (214 female, 192 male, average age 59.8) were used for statistical analysis. To ensure data independence, only the earliest adequately imaged LESI within the series for each patient was used. Also, a number of studies lacked imaging features or views necessary to glean the required data. These two conditions resulted in the exclusion of 295 cases from analysis. There were no statistically significant differences between the included and excluded groups in distribution of sex, age, vertebral level injected, needle placement, or predominance of flow patterns. Among the included cases, midline needle placement was less likely to result in unilateral injectate flow than a more lateral approach ( p = 0.0002). Injectate that was not observed to enter the anterior epidural space was also more likely to remain unilateral ( p = 0.0006). Patients with previous spinal operations were considerably more likely to have injectate flow of less than one vertebral level either cephalad or caudad to the site of injection than patients with no history of spinal operations ( p < 0.0001). Even within a single patient, the flow of injectate from LESIs performed at the same cephalad/caudad, medial/lateral location could vary from injection to injection.

Conclusion

Epidural injectate flow is highly variable, both among patients and between injections in a single patient. A limited extent of flow was noted particularly in patients with previous spinal operations, an important population in the context of pain relief. Verifying epidural placement with a test dose of contrast without adding contrast to the final injectate is inadequate to demonstrate the full extent of flow of the injected medication. Because of the highly variable nature of epidural injectate flow, we recommend fluoroscopic monitoring and administration of radioopaque contrast mixed with medication to permit visualization of the full extent of medication flow and ensure coverage at the target area.

References

Financial disclosures: None.

This work has been accepted for publication by the journal RADIOLOGY, although we have not been given an anticipated date of publication.