Nerve Supply of the Lumbar Facet Joints
The lumbar facet joints are innervated by the medial branches of the dorsal rami, with each joint receiving dual innervation from the medial branch at the same segmental level and the level above. 1, 2
Anatomical Distribution by Spinal Level
L1-L4 Segments
- Each dorsal ramus divides into medial, lateral, and intermediate branches 2
- The medial branch emerges from the intertransverse ligament and crosses the superior margin of the transverse process, passing through the root of the superior articular process 3
- Each medial branch provides innervation to two adjacent facet joints: the joint at its own level and the joint immediately below 1, 2
- The medial branch also supplies the multifidus muscle, specifically those fascicles arising from the spinous process with the same segmental number 2
L5 Segment
- The L5 dorsal ramus has a distinctly different anatomy compared to the upper lumbar levels and is considerably longer 3, 2
- It emerges dorsally and inferiorly on top of the sacral ala, traveling in a bony groove at the junction between the sacral wing and the posterior region of the sacral articular process 3
- Near the inferior portion of the articular process, the L5 dorsal ramus divides into only medial and intermediate branches (no lateral branch) 2
- The medial branch curves around the inferior portion of the L5-S1 facet joint, which it innervates 3
Clinical Implications for Interventional Procedures
Target Points for Medial Branch Blocks
- For L1-L4 levels: the medial branch lies at the junction of the superior articular process and transverse process 3
- For L5 level: the dorsal ramus is located in the groove between the sacral ala and superior articular process of the sacrum 3
- The needle approach should contact the transverse process and feel the resistance of the articular joint to achieve precise denervation 3
Diagnostic Confirmation
- The dual innervation pattern means that blocking a single medial branch will not completely denervate a facet joint 1
- This anatomical arrangement explains why the double-injection technique with an 80% pain relief threshold is recommended for diagnostic confirmation of facet-mediated pain 4
Common Pitfalls
- Failure to account for the unique L5 anatomy when performing procedures at the lumbosacral junction, as the L5 dorsal ramus has a different course and branching pattern than L1-L4 3, 2
- Targeting only one level when attempting to denervate a specific facet joint, given the dual innervation pattern 1
- Not recognizing that the intertransversarii mediales receive separate innervation from a branch near the origin of the medial branch 2