Perspectives Commentary on: The Prevalence of the Ponticulus Posticus (Arcuate Foramen) and Its Importance in the Goel-Harms Procedure: Meta-Analysis and Review of the Literature by Elliott and Tanweer World Neurosurg 2014 http://dx.doi.org/10.1016/j.wneu.2013.09.014
Volker K. H. Sonntag, M.D. Vice Chairman Emeritus, Division of Neurological Surgery Barrow Neurological Institute St. Joseph’s Hospital and Medical Center
Beware of the Arcuate Foramen Volker K. H. Sonntag
T
raditionally, atlantoaxial fixation has been performed using a posterior approach with wires or cables to anchor C1 and C2 together with bone grafts. There are 3 basic wiring techniques: interspinous fusion (Sonntag fusion), Gallie fusion, and Brooks fusion. Wiring techniques provide semirigid fixation of C1 and C2; to improve fusion rates, halo braces have been recommended to stabilize C1 and C2 further until the bone heals. This strategy improves fusion rates from 70% to 90%, especially in patients prone to nonunions, such as patients with rheumatoid arthritis (1, 3, 4, 7). Several screw techniques are available to provide rigid internal fixation of C1-2, avoiding the application of a halo brace. Magerl (6) developed his technique of posterior atlantoaxial transfer set screw fixation to achieve rigid internal fixation of C1-2. However, despite the obvious advantage of rigid internal fixation, it is associated with risk. The primary concern is the chance of vertebral artery injury, especially when the pars of C2 is narrow secondary to prominent looping of the vertebral artery into the pars. Alternatively, the technique of C1-2 fixation using the lateral mass of C1 and pars interarticularis, lamina, or pedicle of C2 with screw-rod fixation is an excellent method of achieving solid fixation. This method was first described by Goel in 1994 (2) and modified by Harms as described in 2001 (5). The advantage of the Goel technique is that the risk of injury to the vertebral artery is decreased. In addition, C1 and C2 can be manipulated and reduced intraoperatively, in contrast to the Magerl technique, which requires normal alignment of C1-2 for appropriate screw positioning.
Key words Arcuate foramen - Atlantoaxial - Atlas - C1 - C1-2 - Goel - Harms - Kimmerle -
WORLD NEUROSURGERY - [-]: ---, MONTH 2014
C1-2 screw-rod fixation requires careful exposure of the C1 lateral mass, which is difficult because of the venous plexus surrounding the C2 ganglion. The venous plexus may be quite extensive and further engorged by the prone patient position required for the procedure. Careful microdissection is often required to dissect the bone free and to allow adequate exposure of the lateral mass. The ideal entry point for the C1 lateral mass screw is inferior to the C1 arch in the middle of the mass. Depending on the patient’s anatomy, it may be impossible to fit the screw below the arch without penetrating the C1-2 joint space when the posterior arch is very thick in the craniocaudal plane. In these cases, very cautiously drilling away the caudal lip of the posterior arch can create enough room for the screw. An alternative to placing a screw in the lateral mass is placing a screw in the posterior atlantal arch as a starting point for the C1 lateral mass screw. Advantages to this technique include longer bone purchase, increased rigidity, less C2 ganglion manipulation, and possibly less intraoperative blood loss owing to disruption of the perineural venous plexus. Nevertheless, the vertebral artery is still at risk because it lies immediately cranial to the arch. As with any surgical procedure, a detailed analysis of the preoperative diagnostic studies is mandatory, especially when placing C1-2 screws. Detailed analysis of the computed tomography scan and possibly computed tomography angiography is mandatory to rule out a thin pars, a large vertebral foramen, and the possibility of a ponticulus posticus (arcuate foramen), which may give the surgeon a false impression of a thick, tall posterior
Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona, USA To whom correspondence should be addressed: Volker K. H. Sonntag, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2014). http://dx.doi.org/10.1016/j.wneu.2013.10.042
www.WORLDNEUROSURGERY.org
1
PERSPECTIVES
arch that would adequately accommodate a 3.5-mm to 4.0-mm screw. In their article, Elliott and Tanweer have provided a great service to surgeons by systemically reviewing and analyzing radiographic, cadaveric, and surgical data and reporting on the prevalence of ponticulus posticus. They found that the overall prevalence of ponticulus posticus was 16.7%; 18.8% were identified in cadaver studies, 17.2% were identified in computed tomography studies, and 16.6% were identified in x-ray studies. The presence of bilateral versus unilateral ponticulus posticus and the laterality often cannot be determined on standard radiographs. They also found that this anomaly constituted the
REFERENCES 1. Dickman CA, Sonntag VK, Papadopoulos SM, Hadley MN: The interspinous method of posterior atlantoaxial arthrodesis. J Neurosurg 74:190-198, 1991. 2. Goel A, Laheri V: Plate and screw fixation for atlanto-axial subluxation. Acta Neurochir (Wien) 129:47-53, 1994. 3. Grob D, Crisco JJ III, Panjabi MM, Wang P, Dvorak J: Biomechanical evaluation of four different posterior atlantoaxial fixation techniques. Spine (Phila Pa 1976) 17:480-490, 1992.
2
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complete foramen in 9.3% of patients and a partial or incomplete foramen in 8.7%. It was present bilaterally in 5.4% of cases and unilaterally in 7.6% of cases. There was no difference between males and females. There has been a dramatic increase in the number of patients treated with C1 lateral mass screws through the posterior arch. It is important to recognize ponticulus posticus before performing the Goel procedure. Consequently, it behooves the surgeon, as mentioned before, to be aware of the possibility of an arcuate foramen or ponticulus posticus and then proceed with lateral mass placement of the screw rather than through the arch.
4. Hanley EN Jr, Harvell JC Jr: Immediate postoperative stability of the atlantoaxial articulation: a biomechanical study comparing simple midline wiring, and the Gallie and Brooks procedures. J Spinal Disord 5:306-310, 1992. 5. Harms J, Melcher RP: Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine (Phila Pa 1976) 26:2467-2471, 2001. 6. Magerl F, Seemann PS: Stable posterior fusion of the atlas and axis by transarticular screw fixation. In: Kehr P, Weidner A, eds. Cervical Spine. New York: Springer-Verlag; 1987:322-327.
spine internal fixation. Spine (Phila Pa 1976) 16: S10-S16, 1991.
Citation: World Neurosurg. (2014). http://dx.doi.org/10.1016/j.wneu.2013.10.042 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2014 Elsevier Inc. All rights reserved.
7. Montesano PX, Juach EC, Anderson PA, Benson DR, Hanson PB: Biomechanics of cervical
WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2013.10.042
Volker K. H. Sonntag, M.D. Vice Chairman Emeritus, Division of Neurological Surgery Barrow Neurological Institute St. Joseph’s Hospital and Medical Center
Beware of the Arcuate Foramen Volker K. H. Sonntag
T
raditionally, atlantoaxial fixation has been performed using a posterior approach with wires or cables to anchor C1 and C2 together with bone grafts. There are 3 basic wiring techniques: interspinous fusion (Sonntag fusion), Gallie fusion, and Brooks fusion. Wiring techniques provide semirigid fixation of C1 and C2; to improve fusion rates, halo braces have been recommended to stabilize C1 and C2 further until the bone heals. This strategy improves fusion rates from 70% to 90%, especially in patients prone to nonunions, such as patients with rheumatoid arthritis (1, 3, 4, 7). Several screw techniques are available to provide rigid internal fixation of C1-2, avoiding the application of a halo brace. Magerl (6) developed his technique of posterior atlantoaxial transfer set screw fixation to achieve rigid internal fixation of C1-2. However, despite the obvious advantage of rigid internal fixation, it is associated with risk. The primary concern is the chance of vertebral artery injury, especially when the pars of C2 is narrow secondary to prominent looping of the vertebral artery into the pars. Alternatively, the technique of C1-2 fixation using the lateral mass of C1 and pars interarticularis, lamina, or pedicle of C2 with screw-rod fixation is an excellent method of achieving solid fixation. This method was first described by Goel in 1994 (2) and modified by Harms as described in 2001 (5). The advantage of the Goel technique is that the risk of injury to the vertebral artery is decreased. In addition, C1 and C2 can be manipulated and reduced intraoperatively, in contrast to the Magerl technique, which requires normal alignment of C1-2 for appropriate screw positioning.
Key words Arcuate foramen - Atlantoaxial - Atlas - C1 - C1-2 - Goel - Harms - Kimmerle -
WORLD NEUROSURGERY - [-]: ---, MONTH 2014
C1-2 screw-rod fixation requires careful exposure of the C1 lateral mass, which is difficult because of the venous plexus surrounding the C2 ganglion. The venous plexus may be quite extensive and further engorged by the prone patient position required for the procedure. Careful microdissection is often required to dissect the bone free and to allow adequate exposure of the lateral mass. The ideal entry point for the C1 lateral mass screw is inferior to the C1 arch in the middle of the mass. Depending on the patient’s anatomy, it may be impossible to fit the screw below the arch without penetrating the C1-2 joint space when the posterior arch is very thick in the craniocaudal plane. In these cases, very cautiously drilling away the caudal lip of the posterior arch can create enough room for the screw. An alternative to placing a screw in the lateral mass is placing a screw in the posterior atlantal arch as a starting point for the C1 lateral mass screw. Advantages to this technique include longer bone purchase, increased rigidity, less C2 ganglion manipulation, and possibly less intraoperative blood loss owing to disruption of the perineural venous plexus. Nevertheless, the vertebral artery is still at risk because it lies immediately cranial to the arch. As with any surgical procedure, a detailed analysis of the preoperative diagnostic studies is mandatory, especially when placing C1-2 screws. Detailed analysis of the computed tomography scan and possibly computed tomography angiography is mandatory to rule out a thin pars, a large vertebral foramen, and the possibility of a ponticulus posticus (arcuate foramen), which may give the surgeon a false impression of a thick, tall posterior
Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph’s Hospital and Medical Center, Phoenix, Arizona, USA To whom correspondence should be addressed: Volker K. H. Sonntag, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2014). http://dx.doi.org/10.1016/j.wneu.2013.10.042
www.WORLDNEUROSURGERY.org
1
PERSPECTIVES
arch that would adequately accommodate a 3.5-mm to 4.0-mm screw. In their article, Elliott and Tanweer have provided a great service to surgeons by systemically reviewing and analyzing radiographic, cadaveric, and surgical data and reporting on the prevalence of ponticulus posticus. They found that the overall prevalence of ponticulus posticus was 16.7%; 18.8% were identified in cadaver studies, 17.2% were identified in computed tomography studies, and 16.6% were identified in x-ray studies. The presence of bilateral versus unilateral ponticulus posticus and the laterality often cannot be determined on standard radiographs. They also found that this anomaly constituted the
REFERENCES 1. Dickman CA, Sonntag VK, Papadopoulos SM, Hadley MN: The interspinous method of posterior atlantoaxial arthrodesis. J Neurosurg 74:190-198, 1991. 2. Goel A, Laheri V: Plate and screw fixation for atlanto-axial subluxation. Acta Neurochir (Wien) 129:47-53, 1994. 3. Grob D, Crisco JJ III, Panjabi MM, Wang P, Dvorak J: Biomechanical evaluation of four different posterior atlantoaxial fixation techniques. Spine (Phila Pa 1976) 17:480-490, 1992.
2
www.SCIENCEDIRECT.com
complete foramen in 9.3% of patients and a partial or incomplete foramen in 8.7%. It was present bilaterally in 5.4% of cases and unilaterally in 7.6% of cases. There was no difference between males and females. There has been a dramatic increase in the number of patients treated with C1 lateral mass screws through the posterior arch. It is important to recognize ponticulus posticus before performing the Goel procedure. Consequently, it behooves the surgeon, as mentioned before, to be aware of the possibility of an arcuate foramen or ponticulus posticus and then proceed with lateral mass placement of the screw rather than through the arch.
4. Hanley EN Jr, Harvell JC Jr: Immediate postoperative stability of the atlantoaxial articulation: a biomechanical study comparing simple midline wiring, and the Gallie and Brooks procedures. J Spinal Disord 5:306-310, 1992. 5. Harms J, Melcher RP: Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine (Phila Pa 1976) 26:2467-2471, 2001. 6. Magerl F, Seemann PS: Stable posterior fusion of the atlas and axis by transarticular screw fixation. In: Kehr P, Weidner A, eds. Cervical Spine. New York: Springer-Verlag; 1987:322-327.
spine internal fixation. Spine (Phila Pa 1976) 16: S10-S16, 1991.
Citation: World Neurosurg. (2014). http://dx.doi.org/10.1016/j.wneu.2013.10.042 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2014 Elsevier Inc. All rights reserved.
7. Montesano PX, Juach EC, Anderson PA, Benson DR, Hanson PB: Biomechanics of cervical
WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2013.10.042
