dictating surgical access. Normal  left foraminal anatomy L2-S1. Blue:  hubbed needles are inserted into  the disc space in the  foramen accessing the posterolateral  quadrant of  the disk. Note  the furcal nerve  branch at L4-L5.  The epidural space  can be  reached  with  a far lateral  trajectory and/or by  removing the ventral  facet  with trephines, lasers, or endoscopic high-speed diamond burrs. All soft tissue has been stripped  from the transverse processes, including dorsal ramus innervation  of the dorsal column. The intertransverse ligament covering the exiting nerves in the foramen has  been stripped away. B, Facet innervation and the relationship of  the transverse process, the interspinous ligament, and the exiting nerve in the foramen. The right exiting nerve at L3-L4 exhibits a furcal nerve branch traversing the  foramen in the far lateral quadrant of the L3-L4 disc annulus. Furcal nerves are the myelinated branches of normal spinal nerves (usually the exiting nerve), commonly  seen endoscopically in the foramen. When stimulated or cut, these nerves can cause dysesthesia and react like the parent spinal  nerve. It does not respond like the  main nerve because it is usually too small to be  detected by continuous intraoperative electromyography or radicular pain reported by the patient. The endoscopic  surgeon should take care to recognize and not injure these furcal nerves if they  are more than 1 mm in diameter, but they cannot always be avoided. Dysesthesia,  immediately postoperative or delayed, is readily treated by transforaminal epidural blocks combined with sympathetic blocks. Furcal nerves can be responsible  for  sciatica that is seemingly out of proportion to what is suggested by relatively normal MRI appearance, and may be part of the sciatica reported preoperatively. Note  also the proximity of the intermediate and lateral branches of the dorsal ramus on the cephalic edge of the transverse process at L3. The dorsal ramus sends a medial  branch that crosses the transverse process on the way to innervate the facet joint above and below the disc level. Irritation of the lateral branch, when irritated, can  cause muscle spasm and  an involuntary list. C, Dorsal  ramus innovation of L3, L4,  and L5 facets. The dorsal  ramus emanating from the origin  of the spinal nerve  sends off medial, intermediate, and lateral branches to  innervate the facets and the dorsal muscle column. The interspinous ligament has been removed to expose  the dorsal ramus. It is found just ventral to the intertransverse ligament and can irritate the exiting nerve and its dorsal root ganglion. This poorly studied nerve can  be responsible for severe chronic axial back pain associated with a degenerating disc exhibiting grade IV and V far lateral  annular tears. Back pain, not just sciatica,  caused  by  disc  protrusions  and  annular  tears  can  be  explained  by  irritation of the dorsal ramus, not just  the  spinal  nerves.  Selective  endoscopic  diskectomy  and  thermal annuloplasty can reduce axial back pain and sciatica, and Intradiscal Electrothermic Therapy (IDET) cannot reach these nerves! Endoscopic rhizotomy of the  branches of the dorsal ramus has shown to be a very effective means of decreasing chronic severe axial back pain.