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Nerves Are Not Made to Be Cut
Perspectives Commentary on: C2 Nerve Root Sectioning in Posterior Atlantoaxial Instrumented Fusions: A Structured Review of Literature by Elliott et al. pp. 697-708.
Alessandro Ducati, M.D. Professor and Chairman Division of Neurosurgery University of Torino
Nerves Are Not Made to Be Cut Alessandro Ducati
W
“
hen therefore you cut the heart-wood of the nerve, immediately the limb in which the nerve goes is observed to lose all sensation and motion” (4). These were the words of Galen about the function of the peripheral nerves: he stated that the power of the brain passed to the muscles through the internal part of the nerves (the heart wood) and not through the coverings, that are there just to protect, like the dura. According to this principle, before cutting or damaging a nerve, one should know exactly what is its territory of innervation and what are the consequences of its section. The anatomy of the C2 nerve and of its ganglion has been studied in detail (1, 2, 10, 13). Like any spinal nerve, the C2 root gives rise to 2 rami, the ventral and the dorsal. The C2 ventral rami join and mix with the ventral rami of C1, of C3, and of C4 to form the cervical plexus. From the cervical plexus depart 2 different roots to form the ansa cervicalis (a.k.a., ansa hypoglossi): the superior, made up of C1 and C2, and the inferior, made up of C2 and C3. The ansa lies superficial to the jugular vein in the carotid sheath. Three of 4 infrahyoid muscles are innervated by the ansa, whereas the thyrohyoid muscle is innervated by the hypoglossal nerve. The omohyoid muscle as well receives innervation from the ansa, and therefore partially from C2. As seen, many muscles are partly innervated by C2, but no one exclusively by it. A lesion of C2 does not cause significant motor disorders because of the multiple afferents of each single muscle and because its motor function may be covered by the action of nearby muscles. The dorsal rami of C2 are mainly sensitive and may mix with C1 dorsal rami: together they exit the C1-C2 foramen and form the greater and lesser occipital nerve, to the skin of the posterior part
Key words 䡲 Arthrodesis 䡲 Atlantoaxial 䡲 C1-2 䡲 C1-C2 䡲 C2 ganglion 䡲 Fusion 䡲 Neuralgia 䡲 Occipital neuralgia
WORLD NEUROSURGERY 78 [6]: 601-602, DECEMBER 2012
of the scalp up to the vertex. Therefore, the lesion or the section of the C2 nerve or ganglion causes sensitive symptoms only; there is a difference between a simple nerve transection or a partial nerve injury and a neurectomy including a ganglionectomy, because in the first case the sensitive loss is probably milder, but the possibility of resulting in neuropathic symptoms is definitely higher. Another anatomical element is important, and has been studied in detail (1). The C2 ganglion lies in the intervertebral space between C1 and C2, bordered by the posterior arch of the atlas, the lamina of the axis, and the atlantoaxial joint. The height of the C2 ganglion is 5.7 ⫾ 0.8, whereas the height of the foramen is only modestly larger, i.e., 7.7 ⫾ 1.2 mm. The ratio C2 foramen/C2 ganglion is 1:0.76; the ganglion occupies up to three quarters of the foramen. A 4-mm-screw uses up approximately 50% of the foramen, and it is very difficult to avoid conflict between the screw and the ganglion. It is well known in the classic neurological literature that a lesion to the C2 root caused by trauma or by other mechanical conflict due to arthrosis or subluxation of atlanto-occipital joint is the reason for severe and invalidating occipital pain (2, 11, 15), and that the treatment for this is neurectomy-ganglionectomy, or pharmacological block of the nerve (12). All of these considerations must be kept in mind when approaching surgery for C1-C2 fixation using screws with the modified Harms technique (9). The report by Elliott et al., “C2 Nerve Root Sectioning in Posterior Atlantoaxial Instrumented Fusions: A Structured Review of Literature”, appearing in WORLD NEUROSURGERY, discusses the problem of whether C2 nerve section is better or worse than sparing it during placement of the C1
Division of Neurosurgery, University of Torino, Torino, Italy To whom correspondence should be addressed: Alessandro Ducati, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2012) 78, 6:601-602. DOI: 10.1016/j.wneu.2011.12.077
www.WORLDNEUROSURGERY.org
601
PERSPECTIVES
screws. This topic has received an increasing amount of attention recently, as more and more cases of complications after this procedure are appearing in the literature. Through an exhaustive review of the literature, the authors conclude that deliberate section of the C2 nerve and ganglion is a reasonable choice because it allows a series of facilitations of the surgical act: a better visualization of the entry point, a better preparation of the joint to achieve fusion, a reduction of blood loss (because the root is encased in a rich venous plexus), a reduction of operation time, and a highly reduced risk of postoperative neuropathic pain. On the other hand, they agree that the loss of sensation in the posterior part of the scalp may be not easily be accepted by everyone in our countries, particularly among young people. It has been noted that elderly patients tolerate better hypoesthesia (14, 15); not so the pain (8). As noted in the title, nerves are not made to be cut: this simple and self-evident sentence is possibly ascribed to Lazorthes, but I could not find the exact quotation. I agree with it of course in general terms, but there are several reasons why in my opinion Elliott et al. are correct in suggesting a deliberate section of the C2 root. Aside from the fact that the original technique described by Goel and Laheri (5) and Goel et al. (6), who used plates and screws, had the necessity to cut the nerve, and no significant consequences have been described in their rich series, there is a basic anatomical consideration. In the majority of cases, the anatomy is such that it is not possible to accommodate without conflict the nerve and the screw in the same narrow space, as described earlier. Moreover, it is necessary to visualize completely the joint, to allow synovectomy and decortication, and this requires downward mobilization and traction on the nerve. The coagulation or the compression of the venous plexus around the root is another dangerous maneuver that becomes necessary when bleeding occurs due to plexus lesion during mobilization of
REFERENCES 1. Bilge O: An anatomic and morphometric study of C2 nerve root ganglion and its corresponding foramen. Spine 29:495-499, 2004. 2. Bogduk N: An anatomical basis for the neck-tongue syndrome. J Neurol Neurosurg Psychiatry 44:202208, 1981. 3. Conroy E, Laing A, Keneally R, Poyton A: C1 lateral mass screw-induced occipital neuralgia: a report of two cases. Eur Spine J 19:474-476, 2010.
the nerve. At the end of the procedure, the nerve is not intact in most cases, but it is partially damaged. When not present at the end of the procedure, the neuropathy ascribed to the conflict between the nerve and the screw may appear some time after surgery, and a progressively more nagging pain develops: in some cases, it is not enough to remove the screw to obtain control of the pain; Conroy et al. (3) did not observe remission even after removal of the screw in 2 patients. The point is, therefore, that the nerve should not be injured in the surgical procedure. This is certainly possible in some anatomical situations. Gunnarsson et al. (7) (although not favoring the deliberate section of C2) studied this problem and identified the anatomy that is compatible with a placement of the screw without root conflict: the data that can be derived from the preoperative thin-cut computed tomography of the atlas are relative to the height of the posterior arch of C2. When the arch is sufficiently thick, it is possible to place a screw through it with minimal manipulation and dissection of the C2 nerve root, and with no risk for the vertebral artery (see Figure 1 in Gunnarsson et al. [7]). The trajectory of the screw should obviously be modified according to the change of the entry point, resulting in the screw being more horizontal. Unfortunately, this favorable anatomy is not the more common one, and in most cases the arch cannot be used. To conclude, neuropathic pain is possible with significant incidence after procedures with preservation of C2 root, whereas it is not observed when C2 neurectomy is carried out, and sensory disturbances due to C2 neurectomy-ganglionectomy are much better tolerated than neuropathic pain caused by C2 nerve injury, particularly in elderly patients. To rephrase the title, nerves are not made to be cut, but better a neurectomy-ganglionectomy than a partial nerve injury.
7. Gunnarsson T, Massicotte EM, Govender PV, Raja Rampersaud Y, Fehlings MG: The use of C1 lateral mass screws in complex cervical spine surgery: indications, techniques, and outcome in a prospective consecutive series of 25 cases. J Spinal Disord Tech 20:308-316, 2007. 8. Hamilton K, Smith J, Sansur C, Dumont A, Shaffley C: C-2 neurectomy during atlantoaxial instrumented fusion in the elderly: patient satisfaction and surgical outcome. J Neurosurg Spine 15:3-8, 2011.
4. Galen: On the doctrines of Hyppocrates and Plato. Phillip de Lacy, translator. Book VIII 1. Berlin: Akademie Verlag; 1996.
9. Harms J, Melcher RP: Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine 26:24672471, 2001.
5. Goel A, Laheri V: Plate and screw fixation for atlanto-axial subluxation. Acta Neurochir (Wien) 129: 47-53, 1994.
10. Lu J, Ebraheim NA: Anatomic considerations of C2 nerve root ganglion. Spine 23:649-652, 1998.
6. Goel A, Desai KI, Muzumdar DP: Atlantoaxial fixation using plate and screw method: a report of 160 treated patients. Neurosurgery 51:1351-1357, 2002.
11. Lozano A, Vanderlinden G, Bachoo R, Rothbart P: Microsurgical C2 ganglionectomy for chronic intractable pain. J.Neurosurg 89:359-365, 1998.
12. Rhee WT, You SH, Kim SK, Lee SY: Troublesome occipital neuralgia developed by C1-C2 Harms construct. J Korean Neurosurg Soc 43:111-113, 2008. 13. Rosse C, Gaddum-Rose P: The neck. Philadelphia: Hollinshead, 1997. 14. Squires J, Molinari R: C1 lateral mass screw placement with intentional sacrifice of the C2 ganglion: functional outcomes and morbidity in elderly patients. Eur Spine J 19:1318-1324, 2010. 15. Vanederen P, Lataster A, Levy R, Mekail N, van Kleef M, van Zundert J: Occipital neuralgia. Pain Pract 10:137-144, 2010. Citation: World Neurosurg. (2012) 78, 6:601-602. DOI: 10.1016/j.wneu.2011.12.077 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com
602
www.SCIENCEDIRECT.com
1878-8750/$ - see front matter © 2012 Elsevier Inc. All rights reserved.
WORLD NEUROSURGERY, DOI:10.1016/j.wneu.2011.12.077
Alessandro Ducati, M.D. Professor and Chairman Division of Neurosurgery University of Torino
Nerves Are Not Made to Be Cut Alessandro Ducati
W
“
hen therefore you cut the heart-wood of the nerve, immediately the limb in which the nerve goes is observed to lose all sensation and motion” (4). These were the words of Galen about the function of the peripheral nerves: he stated that the power of the brain passed to the muscles through the internal part of the nerves (the heart wood) and not through the coverings, that are there just to protect, like the dura. According to this principle, before cutting or damaging a nerve, one should know exactly what is its territory of innervation and what are the consequences of its section. The anatomy of the C2 nerve and of its ganglion has been studied in detail (1, 2, 10, 13). Like any spinal nerve, the C2 root gives rise to 2 rami, the ventral and the dorsal. The C2 ventral rami join and mix with the ventral rami of C1, of C3, and of C4 to form the cervical plexus. From the cervical plexus depart 2 different roots to form the ansa cervicalis (a.k.a., ansa hypoglossi): the superior, made up of C1 and C2, and the inferior, made up of C2 and C3. The ansa lies superficial to the jugular vein in the carotid sheath. Three of 4 infrahyoid muscles are innervated by the ansa, whereas the thyrohyoid muscle is innervated by the hypoglossal nerve. The omohyoid muscle as well receives innervation from the ansa, and therefore partially from C2. As seen, many muscles are partly innervated by C2, but no one exclusively by it. A lesion of C2 does not cause significant motor disorders because of the multiple afferents of each single muscle and because its motor function may be covered by the action of nearby muscles. The dorsal rami of C2 are mainly sensitive and may mix with C1 dorsal rami: together they exit the C1-C2 foramen and form the greater and lesser occipital nerve, to the skin of the posterior part
Key words 䡲 Arthrodesis 䡲 Atlantoaxial 䡲 C1-2 䡲 C1-C2 䡲 C2 ganglion 䡲 Fusion 䡲 Neuralgia 䡲 Occipital neuralgia
WORLD NEUROSURGERY 78 [6]: 601-602, DECEMBER 2012
of the scalp up to the vertex. Therefore, the lesion or the section of the C2 nerve or ganglion causes sensitive symptoms only; there is a difference between a simple nerve transection or a partial nerve injury and a neurectomy including a ganglionectomy, because in the first case the sensitive loss is probably milder, but the possibility of resulting in neuropathic symptoms is definitely higher. Another anatomical element is important, and has been studied in detail (1). The C2 ganglion lies in the intervertebral space between C1 and C2, bordered by the posterior arch of the atlas, the lamina of the axis, and the atlantoaxial joint. The height of the C2 ganglion is 5.7 ⫾ 0.8, whereas the height of the foramen is only modestly larger, i.e., 7.7 ⫾ 1.2 mm. The ratio C2 foramen/C2 ganglion is 1:0.76; the ganglion occupies up to three quarters of the foramen. A 4-mm-screw uses up approximately 50% of the foramen, and it is very difficult to avoid conflict between the screw and the ganglion. It is well known in the classic neurological literature that a lesion to the C2 root caused by trauma or by other mechanical conflict due to arthrosis or subluxation of atlanto-occipital joint is the reason for severe and invalidating occipital pain (2, 11, 15), and that the treatment for this is neurectomy-ganglionectomy, or pharmacological block of the nerve (12). All of these considerations must be kept in mind when approaching surgery for C1-C2 fixation using screws with the modified Harms technique (9). The report by Elliott et al., “C2 Nerve Root Sectioning in Posterior Atlantoaxial Instrumented Fusions: A Structured Review of Literature”, appearing in WORLD NEUROSURGERY, discusses the problem of whether C2 nerve section is better or worse than sparing it during placement of the C1
Division of Neurosurgery, University of Torino, Torino, Italy To whom correspondence should be addressed: Alessandro Ducati, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2012) 78, 6:601-602. DOI: 10.1016/j.wneu.2011.12.077
www.WORLDNEUROSURGERY.org
601
PERSPECTIVES
screws. This topic has received an increasing amount of attention recently, as more and more cases of complications after this procedure are appearing in the literature. Through an exhaustive review of the literature, the authors conclude that deliberate section of the C2 nerve and ganglion is a reasonable choice because it allows a series of facilitations of the surgical act: a better visualization of the entry point, a better preparation of the joint to achieve fusion, a reduction of blood loss (because the root is encased in a rich venous plexus), a reduction of operation time, and a highly reduced risk of postoperative neuropathic pain. On the other hand, they agree that the loss of sensation in the posterior part of the scalp may be not easily be accepted by everyone in our countries, particularly among young people. It has been noted that elderly patients tolerate better hypoesthesia (14, 15); not so the pain (8). As noted in the title, nerves are not made to be cut: this simple and self-evident sentence is possibly ascribed to Lazorthes, but I could not find the exact quotation. I agree with it of course in general terms, but there are several reasons why in my opinion Elliott et al. are correct in suggesting a deliberate section of the C2 root. Aside from the fact that the original technique described by Goel and Laheri (5) and Goel et al. (6), who used plates and screws, had the necessity to cut the nerve, and no significant consequences have been described in their rich series, there is a basic anatomical consideration. In the majority of cases, the anatomy is such that it is not possible to accommodate without conflict the nerve and the screw in the same narrow space, as described earlier. Moreover, it is necessary to visualize completely the joint, to allow synovectomy and decortication, and this requires downward mobilization and traction on the nerve. The coagulation or the compression of the venous plexus around the root is another dangerous maneuver that becomes necessary when bleeding occurs due to plexus lesion during mobilization of
REFERENCES 1. Bilge O: An anatomic and morphometric study of C2 nerve root ganglion and its corresponding foramen. Spine 29:495-499, 2004. 2. Bogduk N: An anatomical basis for the neck-tongue syndrome. J Neurol Neurosurg Psychiatry 44:202208, 1981. 3. Conroy E, Laing A, Keneally R, Poyton A: C1 lateral mass screw-induced occipital neuralgia: a report of two cases. Eur Spine J 19:474-476, 2010.
the nerve. At the end of the procedure, the nerve is not intact in most cases, but it is partially damaged. When not present at the end of the procedure, the neuropathy ascribed to the conflict between the nerve and the screw may appear some time after surgery, and a progressively more nagging pain develops: in some cases, it is not enough to remove the screw to obtain control of the pain; Conroy et al. (3) did not observe remission even after removal of the screw in 2 patients. The point is, therefore, that the nerve should not be injured in the surgical procedure. This is certainly possible in some anatomical situations. Gunnarsson et al. (7) (although not favoring the deliberate section of C2) studied this problem and identified the anatomy that is compatible with a placement of the screw without root conflict: the data that can be derived from the preoperative thin-cut computed tomography of the atlas are relative to the height of the posterior arch of C2. When the arch is sufficiently thick, it is possible to place a screw through it with minimal manipulation and dissection of the C2 nerve root, and with no risk for the vertebral artery (see Figure 1 in Gunnarsson et al. [7]). The trajectory of the screw should obviously be modified according to the change of the entry point, resulting in the screw being more horizontal. Unfortunately, this favorable anatomy is not the more common one, and in most cases the arch cannot be used. To conclude, neuropathic pain is possible with significant incidence after procedures with preservation of C2 root, whereas it is not observed when C2 neurectomy is carried out, and sensory disturbances due to C2 neurectomy-ganglionectomy are much better tolerated than neuropathic pain caused by C2 nerve injury, particularly in elderly patients. To rephrase the title, nerves are not made to be cut, but better a neurectomy-ganglionectomy than a partial nerve injury.
7. Gunnarsson T, Massicotte EM, Govender PV, Raja Rampersaud Y, Fehlings MG: The use of C1 lateral mass screws in complex cervical spine surgery: indications, techniques, and outcome in a prospective consecutive series of 25 cases. J Spinal Disord Tech 20:308-316, 2007. 8. Hamilton K, Smith J, Sansur C, Dumont A, Shaffley C: C-2 neurectomy during atlantoaxial instrumented fusion in the elderly: patient satisfaction and surgical outcome. J Neurosurg Spine 15:3-8, 2011.
4. Galen: On the doctrines of Hyppocrates and Plato. Phillip de Lacy, translator. Book VIII 1. Berlin: Akademie Verlag; 1996.
9. Harms J, Melcher RP: Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine 26:24672471, 2001.
5. Goel A, Laheri V: Plate and screw fixation for atlanto-axial subluxation. Acta Neurochir (Wien) 129: 47-53, 1994.
10. Lu J, Ebraheim NA: Anatomic considerations of C2 nerve root ganglion. Spine 23:649-652, 1998.
6. Goel A, Desai KI, Muzumdar DP: Atlantoaxial fixation using plate and screw method: a report of 160 treated patients. Neurosurgery 51:1351-1357, 2002.
11. Lozano A, Vanderlinden G, Bachoo R, Rothbart P: Microsurgical C2 ganglionectomy for chronic intractable pain. J.Neurosurg 89:359-365, 1998.
12. Rhee WT, You SH, Kim SK, Lee SY: Troublesome occipital neuralgia developed by C1-C2 Harms construct. J Korean Neurosurg Soc 43:111-113, 2008. 13. Rosse C, Gaddum-Rose P: The neck. Philadelphia: Hollinshead, 1997. 14. Squires J, Molinari R: C1 lateral mass screw placement with intentional sacrifice of the C2 ganglion: functional outcomes and morbidity in elderly patients. Eur Spine J 19:1318-1324, 2010. 15. Vanederen P, Lataster A, Levy R, Mekail N, van Kleef M, van Zundert J: Occipital neuralgia. Pain Pract 10:137-144, 2010. Citation: World Neurosurg. (2012) 78, 6:601-602. DOI: 10.1016/j.wneu.2011.12.077 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com
602
www.SCIENCEDIRECT.com
1878-8750/$ - see front matter © 2012 Elsevier Inc. All rights reserved.
WORLD NEUROSURGERY, DOI:10.1016/j.wneu.2011.12.077