Procedural Safety Guidelines for Cervical Epidural Steroid Injections: Appendix 1: Part A
Appendix 1: Procedural Safety Guidelines for Cervical Epidural Steroid Injections
Spinal cord injury is undoubtedly the major complication that can occur during, or following, a interlaminar cervical epidural block. The possibility for both immediate and delayed injury exists. Cord damage occurs usually as a result of direct trauma to the cord by either contact with the needle, direct injection into the cord, or a combination of both. Delayed injury can occur due to compression of the spinal cord caused by bleeding or infection. Indirect injury of the cord could occur by injecting a deposteroid solution into the CSF. It is the authors’ opinion that adherence to the following guidelines would serve to mitigate the chance of both direct and indirect spinal cord injury, while enhancing the success rate of cervical epidural steroid injection procedures and decreasing both the risk-to-benefit ratio and the chance of medical misadventure.
(1) Interlaminal cervical epidural blocks should not be performed at any level when the midline sagittal diameter is less than 8mm. If the midline sagittal diameter is between 8mm and 10mm, the procedure should be avoided if possible. If proceeding, extreme caution must be exercised.
Rationale: The cervical epidural space is surrounded and cushioned by an extensive network of venous plexus. Consequently, needle entry into or through a vein is not uncommon. Post-block hematomas therefore can not be prevented and an already compromised canal diameter is placed at further risk from compromise by the possibility of epidural hematoma.
(2) Patients must not take aspirin or aspirin-based products for 7-10 days pre-procedure. Non-steroidal anti-inflammatory drugs (NSAIDs) must also be halted for 3-5 days prior to the block.
(3) An interlaminar epidural block should not be performed at a level where a disk protrusion or spondylolisthetic narrows the midline spinal canal diameter. (Having typically been visualized by a pre-procedure MRI or CT myelography- See guideline #6 below).
(4) A cervical epidural should rarely be performed above the level of C7-T1.
Rationale: Guideline #4 may raise some controversy. An examination of the midline sagittal T1 weighted MRI images, reveals 1 to 2 mm of dorsal epidural fat which can be visualized in the dorsal epidural space at the C7-T1 interspace. However it is rare that such fat is noted in the levels above. The epidural space at higher levels is therefore either very narrow or it is a potential space. Thus, at the moment when the epidural needle is on the verge of penetrating the ligamentum flavum, the needle’s bevel may potentially press the ligamentum flavum against the dura, which in turn may become indented to press directly against the spinal cord. (This situation may further be aggravated by the existence of an anterior disc protrusion displacing the spinal cord posteriorly.) Consequently the injectionist experiences what amounts to a perceptual "absence" of epidural space and hence, the expected telltale "loss of resistance" sensation, indicating penetration into the epidural space, is not encountered. (Under normal circumstances, aspiration of CSF is the primary indication of sub-dural tap, and the procedure can be discontinued immediately, as per guideline #11, with no negative sequelae. However, due the atypical circumstance that finds the ligamentum flavum, the dural sleeve and the spinal cord pressed closely together, CSF may not be aspirated. ) Accordingly, believing the epidural space is yet to be encountered, the injectionist may initiate further advancement of the epidural needle, resulting in inadvertent spinal cord puncture. Needless to say, this represents a highly undesirable procedural outcome.
Although 5 ml of solution injected at the C7-T1 interspace will often fill the entire space to the C2 level, if the structural pathology is at the C5-6 interspace or higher, one can perform a C7-T1 or a T1-T2 puncture and advance a catheter to the desired level.
(5) Fluoroscopy should be utilized to select & identify the level, the midline, and to help locate the depth.
Rationale: As with guideline #4, this guideline is also apt to generate a polemic, and adherence to it will not it itself guarantee needle misplacement. However correctly utilized, fluoroscopic imaging is an invaluable tool for aiding in the prevention of inadvertent dural or cord punctures. The patient is placed in a prone position with the interspace visualized and pinpointed in the AP projection. Using a paramedian approach, with the epidural needle approximately 1cm from the midline and approximately 2 cm below the border of the lamina, (i.e. in the case of a C7-T1 puncture, the needle will be advanced over the lamina of T1), the needle is advanced to the edge of the lower lamina. Since the advancing needle is always over bone, unintentional advancement into the spinal canal is prevented. Once the needle contacts the lamina it is advanced cephlad and toward the midline until the resistance of the ligamentum flavum is felt. If the ligamentum flavum is not felt within 5mm then the needle is withdrawn again to the lamina to reestablish correct positioning and recheck depth. Entry into the epidural space is identified by a loss of resistance to fluid or a "hanging drop technique". Because of poor penetration through the shoulders, and/or rotational misalignments, one should not rely entirely on the lateral fluoroscopic image to identify a space that has a depth of less than 5mm.