Transforaminal epidural sleeve injection
Position and anatomical landmarks
The patient lies in the prone position on the operating table with a pillow under the abdomen to flatten the lumbar lordosis. In a transforaminal approach, the C-arm is adjusted in such a way that the X-rays run parallel to the cover plates of the relevant level. Thereafter, the C-arm is rotated until the spinal process projects over the contralateral facet column. With the C-arm in this projection, the injection point is found by projecting a metal ruler over the medial part of the intervertebral foramen. If there is superposition of the superior articular process of the underlying joint, the C-arm must be rotated cranially. If no superposition of the superior articular process of the underlying joint is acquired, the C-arm should be rotated cranially.
A 10-cm long, 25-G or 22-G needle with connection tubing that is first flushed with contrast medium is inserted locally in the direction of the radiation beam. Thereafter, the direction is corrected such that the needle is projected as a point on the screen (Figure 1). Then, in a lateral view, the depth of the needle tip is checked. A classical approach is in the dorsal cranial quadrant, care should be taken that no arterial/venous flow is noted during real-time imaging of contrast injection.
Figure 1. Lumbar transforaminal epidural injection: injection point (oblique view).
We recommend avoiding that the needle elicits paresthesia in the patient. Paresthesia is considered unpleasant by the patient and, in addition, segmental medullar blood vessels may be hit. Therefore, the 'safe triangle' should be taken into account (Figure 2). This triangle is formed cranially by the underside of the upper pedicle, laterally by a line between the lateral edges of the upper and lower pedicle, and medially by the spinal nerve root (as the tangential base of the triangle).
Figure 2. 'Safe triangle' for insertion of the needle in transforaminal epidural injection
This is considered to be a safe zone; if a radiating pain still occurs during the procedure, the needle must be pulled back several millimetres. The direction of the radiation beam is now modified to anterior-posterior. As a result, the point of the needle should be located between the lateral edge and the middle of the facet column. After injection of a small quantity of contrast agent during real-time imaging, the course of the anterior branch of the spinal nerve, in an epidural or anterior caudal direction becomes visible (Figure 2).
Figure 3. Lumbar spinal ganglion: Spreading of contrast along the nerve root.
If this image is not acquired, due to the position being too lateral, the needle must be inserted more deeply towards the spinal ganglion. The execution of this procedure during real-time imaging allows a distinction to be made between an accidental intrathecal, intra-arterial or intravenous injection.
After correct visualisation of the anterior branch of the spinal nerve, a test block is carried out with 1 ml bupivacaine 0.5% or xylocaine. One to two minutes thereafter, the patient is asked to move his legs in order to rule out sudden paresthesia based on medullar ischemia. Then the corticosteroid (40 mg) can be injected.
Procedure transforaminal of S1 nerve root
Position and anatomical landmarks
The patient lies in the prone position on the operating table with a pillow under the abdomen to flatten the lumbar lordosis.
The technique used at the S1 level is analogous with that used for the lumbar levels. However, this time the needle is positioned through the dorsal sacral foramen of S1 on the S1 pedicle (Figure 4). For this, the target lies at the caudal edge of the pedicle of S1 at a location homologous to the site of the lumbar transforaminal infiltrations.
With fluoroscopy, this foramen cannot be clearly distinguished, but by reorienting the C-arm cranially caudally and rotating it ipsilaterally, the foramen ventral sacral and the dorsal sacral foramen of S1 will overlap. The insertion point is chosen at the level of the lateral edge of the dorsal sacral foramen of S1. In an optimal position and in lateral view, the needle tip is positioned 5 mm from the floor of the sacral canal.
Figure 4. Needle position at level S1: AP view.
It is recommended that transforaminal infiltrations should only be performed under the L3 level and that the injection fluid should always be administered during real-time imaging. The additional use of digital subtraction angiography may be of value.
- Neurological deficit due to puncture of an aberrant course of Adamkiewicz's artery.
- Retroperitoneal hematoma.
- Infection and epidural abscess.