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 diagnostic block, the C-arm is positioned in such a way that the X-rays run parallel to the end 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 position, the injection point is found by projecting a metal ruler over the lateral part of the intervertebral foramen.
A 10-cm long, 22-G needle is inserted 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).
Figure 1. Lumbar DRG test block: oblique view.
The direction of the radiation beam is now modified to a profile (lateral) view, and the needle inserted until the point is located in the cranial dorsal part of the intervertebral foramen (Figure 2).
Figure 2. Lumbar DRG test block: lateral view.
In AP view, the course of a small amount of contrast agent is monitored with 'real-time imaging'. The contrast spreads laterally caudally along the spinal nerve root (Figure 3).
Figure 3. Lumbar DRG test block: spreading of contrast along the nerve root in AP view.
Finally, a maximum of 1 ml lidocaine 2% or bupivacaine 0.5% is injected.
A test block is considered positive if there is a 50% reduction in symptoms 20-30 minutes after the procedure. The level with the largest pain reduction > 50% is chosen for subsequent PRF treatment.
- Infection and epidural abscess.