- Lumbar plexus
The lumbar plexus consists of five nerves on each side. It is formed by the ventral divisions of the first four lumbar nerves (L1-L4) and contribution from the subcostal nerve, the anterior branch of the last thoracic nerve (T12). The L2, L3, and L4 roots of the lumbar plexus become embedded in the psoas major muscle, plitting into anterior and posterior divisions, and eventually reuniting to form the individual branches of the plexus, including the genitofemoral, lateral femoral cutaneous, femoral, and obturator nerves.
Determining which nerve trunk is involved and localizing area for injection requires:
- Examination of peripheral areas of pain and tenderness
- Location of paravertebral tenderness at points corresponding to peripheral tenderness using deep palpation
The spinous processes and last ribs on affected side can be used to gauge position of the lumbar vertebrae.
Injection Technique For Lumbar Nerves
For the 1st lumbar nerve, the needle is inserted to contact the transverse process of the 2nd lumbar vertebra, then passed over the upper edge, employing the technique described above.
1. The 2nd, 3rd and 4th lumbar nerves are reached similarly. In each case, the needle is slid over the upper edge of the next lower process
2. The 5th lumbar nerve is reached by striking the 5th transverse process, then passing the needle point below