MISCELLANEOUS

Pain during spinal canal puncture and its relationship with ligamentum flavum, dura-mater and posterior longitudinal ligament innervation^*

El dolor durante la punción del canal vertebral y su relación con la inervación del ligamento amarillo, de la dura-máter y del ligamento longitudinal posterior

Edmundo Zarzur, TSA, M.D.

Co-responsável do CET em Anestesiologia da Santa Casa de Misericórdia de São Paulo

Correspondence

SUMMARY

BACKGROUND AND OBJECTIVES: Pain during spinal puncture is a warning that needle tip has touched a nervous structure. If patients refer pain during puncture, it is mandatory to interrupt the technique. Anesthetic solution should not be injected to prevent potential nervous root or spinal cord injury. Needle should be drawn back and have its direction changed before a new advance is attempted. Pain complain is totally impossible if patients are asleep under the influence of general anesthesia and that is why blockade with conscious patients is advisable. Pain is only referred when needle or catheter tip bypass the medium sagital plane to reach the antero-lateral epidural compartment, thus being able to touch nervous rootlets close to intervertebral foramina. Except for studies on skin, subcutaneous tissue and interspinous ligament innervation, this study aimed at reviewing the innervation of some spinal canal structures, namely, ligamentum flavum, posterior longitudinal ligament, dura-mater and intervertebral disk.
CONTENTS: Studies on spinal canal innervation are presented in this literature review, aiming at understanding pain during spinal puncture.
CONCLUSIONS: Ligamentum flavum is not innervated, thus explaining lack of pain during puncture. Other pains during puncture may be attributed to Luschka's nerve, which innervates posterior longitudinal ligament and dural ventral portion.

Key Words: ANESTHETIC TECHNIQUES, Regional: epidural, spinal block

RESUMEN

JUSTIFICATIVA Y OBJETIVOS: El dolor durante la punción raquidiana es un señal de alarma, indicando que la punta de la aguja tocó en una estructura nerviosa. Por este motivo, si el paciente acusa dolor durante la punción, es obligatoria la interrupción de la técnica. La solución anestésica no deberá ser inyectada para evitar una posible lesión de la raíz nerviosa o de la médula espinal. Se debe retroceder la aguja y alterar su dirección antes de nuevo avance. El relato de dolor es totalmente imposible si el paciente está adormecido bajo influencia de la anestesia general y, por este motivo, es recomendable que bloqueos sean realizados con el paciente consciente. El dolor solamente es referido cuando la punta de la aguja o la punta del catéter se desvían del plano medio sagital para alcanzar el compartimiento peridural antero-lateral, pudiendo, de esta forma tocar las radículas nerviosas situadas próximas a los forames intervertebrales. Excluyéndose los estudios sobre la inervación de la piel, del tejido celular subcutáneo y del ligamento interespinoso, el objetivo de este trabajo es el de rever la inervación de algunas estructuras del canal vertebral: del ligamento amarillo, del ligamento longitudinal posterior, de la dura-máter y del disco intervertebral.
CONTENIDO: Estudios sobre la inervación del canal vertebral serán presentados en esta revisión de la literatura, con la intención de querer entender la razón del origen del dolor durante la punción del canal raquidiano.
CONCLUSIONES: El ligamento amarillo es desprovisto de inervación, explicando la ausencia de dolor durante su punción. Otros dolores, durante la punción, pueden ser atribuidos al nervio de Luschka que inerva el ligamento longitudinal posterior y la porción ventral de la dura-máter.

INTRODUCTION

In addition to CSF, spinal space has nervous roots and the spinal cord. Ventral or motor root has its neurons in the gray matter of anterior funiculus medullae spinalis. These motor neurons form four or five rootlets in each spinal segment, which get together to form the anterior root, which after crossing the subarachnoid space perforates the dural sac and, involved by the dura, travels along dorsal root ganglion. Dorsal or sensory root has its neurons in the dorsal root ganglion, crosses the dura and the subarachnoid space to be divided, close to the spinal cord, into six rootlets before penetrating posterior funiculus medullae spinalis.

The conclusion is that these ventral and dorsal roots only travel in the subarachnoid space thus not being responsible for spinal canal structures innervation.

This study aimed at reviewing the innervation of structures involved in epidural and/or spinal puncture, calling the attention for potential complications when patients refer pain during the procedure.

HISTORY

Several investigators have studied spinal canal innervation. Ligamentum flavum is not innervated, explaining the lack of pain during its puncture ¹. Luschka, in 1850, has described for the first time a recurrent meningeal branch currently known as being responsible for the innervation of several vertebral column structures ².

Luschka's nerve is the first branch originated from the spinal nerve. Soon after leaving intervertebral foramen, the spinal nerve supplies a first branch which crosses the intervertebral foramen and, returning to the canal, together with a communicating gray branch of the sympathetic nerve, is distributed through very thin filaments throughout the intervetebral disk, into anterior and posterior longitudinal ligaments and throughout the dural ventral portion.

Groen et al. have dissected vertebral column of different fetuses aiming at studying dural innervation. After removing thoracic meninges, nervous plexuses were stained and photographed by a transilumination process ³.

They have observed that Luschka's recurrent nerve forms an extensive nervous plexus over posterior longitudinal ligament and over dural ventral portion, remaining the dorsal face of the dural sac without innervation. So, only ventral dura, dura involving nervous roots after leaving the dural sac and posterior longitudinal ligament receive sensory fibers supplied by Luschka's nerve (Figure 1).

Dural dorsal face remains without innervation, thus explaining lack of pain during puncture. Raoul et al. ⁴ have also studied the recurrent meningeal nerve of six fresh cadavers and three kept in formalin. Their observations however were directed to the lumbar region They have observed that Luschka's nerve together with a sympathetic communicating branch, would return to the canal to innervate intervertebral disk, dural ventral face and anterior and posterior longitudinal ligaments. They have concluded that back pain might be related to this innervation, and that epidural space infiltrations with anesthetic solutions could be used to relieve such pain.

Because ventral dura is innervated, Cyriax admits that its compression by a herniated disk may cause acute low back pain ⁵. In this case, treatment with epidural anesthesia has a dramatic effect, relieving pain in few minutes.

It is clear that after dural perforation there might be low back pain caused by nervous roots injury, as well as thoracic pain, caused by direct spinal cord injury.

The conclusion is that pain referred during spinal puncture should be attributed to shift in the direction (medium sagital plane) the needle should follow. Pain may also appear during epidural block with single dose. Aiming at proving this thesis, Mondadore injected distilled water to confirm the exact location of the needle in the epidural space ⁶. The injection of 3 to 4 ml distilled water in the epidural space would cause pain. This was the "Pain Test" considered by him more frequent than hanging-drop aspiration sign. This practice has been abandoned for causing very severe pain not tolerated by patients. However, distilled water injected in the subarachnoid space would not cause any pain or sensation. Mondadore has not found anatomic reasons for epidural space pain.

Zarzur et al. have observed that the "test dose", when performed with anesthetic solution with epinephrine, promotes perfectly tolerable pain ⁷. This pain would be a confirmation of needle tip location in the epidural space. A second test dose would not cause pain. They have also observed that test-dose, when performed with epinephrine-free anesthetic solution would not cause pain. Pain could be possibly attributed to special dural sensitivity due to low pH of the anesthetic solution with epinephrine. By the time when the study about test-dose pain was published, we had no idea of the reason for the lack of pain during the second test-dose. With current knowledge, one may conclude that the first test-dose blocks nervous terminations justifying lack of pain during the second test-dose.

It should be reminded that paresthesias or pain during catheter introduction, by continuous epidural block technique, are evidences of poor catheter tip location, which may be touching nervous roots located in the antero-lateral epidural compartment, thus close to intervertebral foramina. Since current catheters do not perforate dura ⁸ and, when introduced in the epidural space for 2 or more centimeters, they advance following dural sac curvature, they may reach the dorsal root located in the antero-lateral epidural compartment. In these cases, there might be a high incidence of failures or unilateral and unsatisfactory block. Hehre et al. ⁹ have mentioned that 7 of 16 epidural block failures were preceded by paresthesias. For Sanches et al. ¹⁰ when the catheter tip is close to the intervertebral foramen causing paresthesias, it may also result in unilateral anesthesia.

In conclusion, pain during spinal puncture or epidural catheter introduction is a warning. It may indicate poorly positioned needle or catheter deviation, with risk for nervous structure injury or unsatisfactory block.

REFERENCES

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02. Luschka H von - Die nerven des menschlichen wirbelkanales. Tübingen: Laupp & Siebeck, 1850:346-356.        [ Links ]

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Correspondence to
Dr. Edmundo Zarzur
Address: Rua Ziembinski, 314
ZIP: 05086-020 City: São Paulo, Brazil

Submitted for publication February 4, 2004
Accepted for publication May 18, 2004

* Received from CET em Anestesiologia da Santa Casa de Misericórdia de São Paulo