Cervical Epidural Depth: Correlation Between Cervical MRI Measurements of the Skin- toCervical Epidural Space and the Actual Needle Depth During Interlaminar Cervical Epidural Injections

Objective. The purpose of this study was to assess the correlation between skin-to-epidural space depth, as measured on cervical magnetic resonance imaging (MRI), and actual needle depth, as measured by Tuohy needle markings during cervical epidural steroid injections. Methods. We conducted a retrospective review of cervical MRI images to determine estimated depth from skin to epidural space. Of the 121 reviewed patients who underwent cervical epidural steroid injections, 81 met inclusion criteria and were retained for data analysis. Results. At the C6-C7 level, the estimated needle depth according to MRI images was 6.0361.15 cm (mean6SD) and the actual needle depth was 5.6260.77 cm. At the C7-T1 level, the estimated needle depth based on MRI images was 5.9061.05cm and the actual needle depth was 5.7360.98cm. At both C6-C7 and C7-T1, MRI depth (P<0.009, P<0.001) and body mass index (P<0.001, P<0.002) were significantly associated with actual depth. Conclusions. Estimates of needle depth made with MRI were consistently slightly deeper than the actual loss-of-resistance needle depth, indicating that the provider should employ caution when using MRI predictive depths. Information garnered from preprocedure MRIs can be used to improve the safety of cervical epidural steroid injection procedures.