Concept of Transforaminal Injection
To treat radicular syndrome (e.g., C6 radiculopathy), CT-guided transforaminal periradicular injection is frequently used.
- The needle is advanced posterior to the nerve trunk, contacting the anterior surface of the facet joint.
- The injected contrast medium diffuses around the nerve root, enters the dorsal epidural space, and spreads along the affected spinal nerve.
Note: For axial neck pain associated with cervical spondylosis or osteoarthritis, intra-articular steroid injections, medial branch blocks, and radiofrequency ablation (RFA) may also be used.
Intervertebral Disc Anatomy and Discogenic Pain
The healthy intervertebral disc is avascular (has no blood vessels) but has a complex innervation:
- The dorsal circumference of the annulus fibrosus (annulus fibrosus) and the posterior longitudinal ligament are innervated by the sinuvertebral nerve, which branches off the ramus communicans (ramus communicans).
- The anterolateral part of the annulus and the anterior longitudinal ligament are innervated by the lateral branches of the ramus communicans and direct branches of the sympathetic trunk.
This extensive nerve plexus accounts for significant crossover of pain signals from adjacent levels.
Pathogenesis of Herniation and Pain: Herniation occurs when the cartilaginous annulus fibrosus ruptures, accompanied by local extrusion of the nucleus pulposus (nucleus pulposus). Pain is caused by physical compression of the nerve root and local release of pro-inflammatory cytokines. Discogenic pain is typically localized medially in the back, worsens with coughing, is provoked by pressure on the spinous processes, and can mimic lumbosacral radicular pain.
Percutaneous Disc Decompression (Discectomy)
The intervertebral disc is a closed hydraulic space. The goal of the procedure is to remove a small volume of the nucleus pulposus to decrease pressure and relieve nerve compression.
Indications:
- Failure of conservative treatment (including epidural injections) for 6–12 weeks.
- Symptomatic protrusions or herniations with an intact annulus fibrosus.
Contraindications:
- Disc extrusion and free fragments (sequestration).
- Presence of red flags and acute neurological deficit (urgent neurosurgical consultation required).
Types of Nucleotomy:
- Chemical (chemonucleolysis): injection of ethanol gel or an oxygen-ozone mixture. This method dehydrates the nucleus and accelerates disc degeneration.
- Mechanical: automated discectomy, which reduces pressure by tissue extraction.
- Thermal: laser or radiofrequency denervation. Causes shrinkage of peripheral collagen fibers, but carries a risk of thermal injury to the endplates (end plates) and nerves.
- Radiofrequency coblation: uses a low-temperature plasma field. Causes cavitation (destruction of molecular bonds) without the risk of thermal burn, creating channels within the nucleus pulposus.
Technique (Fluoroscopically Guided)
The procedure requires strict asepsis and fluoroscopic control.
Cervical spine:
- The patient is placed in the supine position (supine).
- An anterolateral approach is used.
- During manual palpation, the carotid artery and internal jugular vein are displaced laterally.
- The needle (16–19 G) is advanced toward the intervertebral space between the vessels (laterally) and the esophagus (medially).
- Device insertion is always performed from the unaffected (healthy) side of the disc.
Lumbar spine:
- The patient lies prone (prone).
- The C-arm is set to the "scotty dog" oblique projection (scotty dog).
- The needle target is the junction of the pedicle (pedicle) and the transverse process ("eye of the dog"). The needle enters the disc at the inferior aspect of the neural foramen to avoid puncturing the spinal nerve.
Briefly: answers to topical questions
What are the anatomical boundaries of the safe zone during the anterolateral cervical approach?
During the anterolateral approach to the cervical spine, the anatomical corridor for safe needle advancement is the space between the major vessels and the esophagus.
- Lateral boundary: carotid artery and jugular vein (displaced laterally during manual palpation).
- Medial boundary: esophagus.
An appropriately sized needle is inserted from the healthy side of the disc, advancing toward the intervertebral space strictly between the specified anatomical structures to minimize the risk of neurovascular bundle injury.
What major complications can occur during a cervical transforaminal injection?
Major complications of cervical transforaminal injection are rare but severe neurological complications:
- tetraplegia;
- death.
To reduce the risk of complications, the procedure is performed under imaging guidance; incorrect needle placement, including intravascular injection, must be ruled out with a test dose of contrast medium prior to medication administration.
What are the main indications for selective transforaminal injection?
Main indications and applications of selective transforaminal injection:
- foraminal and extraforaminal disc herniations;
- radicular pain / radiculopathy: the source cites an example of a CT-guided transforaminal periradicular injection at the C6 root level for radiculopathy;
- diagnostic selective segmental block: ultrasound- or CT-guided transforaminal lidocaine injection; a negative result helps rule out the suspected level of pathology.
Class and exam questions
What is the patient's positioning during a cervical spine injection?
The procedure is performed in the supine position (supine). An anterolateral approach is used, with the carotid artery and internal jugular vein manually displaced laterally.
What are the absolute contraindications for percutaneous disc decompression?
Disc extrusion, presence of free fragments (sequestration), acute neurological deficit, and the presence of red flags. In these cases, the patient is referred to a neurosurgeon immediately.
How does radiofrequency coblation differ from thermal denervation?
Coblation nucleotomy uses a low-temperature ionic plasma field to break down molecular bonds of the nucleus. This avoids the risk of thermal injury to surrounding structures (nerves and endplates).
What else to study on this topic
- Scotty dog oblique projection technique for lumbar access
- Mechanisms of action of the oxygen-ozone mixture in chemonucleolysis
- Differential diagnosis of discogenic and radicular pain
- Radiofrequency ablation methods for the treatment of axial neck pain
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