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Lateral Mass of C1 Fixation and Ponticulus-Posticus
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
Michael Y. Wang, M.D. Professor, Departments of Neurological Surgery and Rehabilitation Medicine University of Miami Miller School of Medicine
Lateral Mass of C1 Fixation and Ponticulus-Posticus Faiz U. Ahmad and Michael Y. Wang
P
osterior interspinous wiring, with or without halo fixation, was previously the most common method of fusion of C1-2 and is still very popular. With the increasing adaptation of screw instrumentation for more rigid fixation of the spine, other techniques have become popular. Transarticular C1-2 fusions (Magerl method) using a screw to cross the joint supplanted wiring due to improved fusion rates, but carried a higher risk of injuring the vertebral artery (2). In the modern Goel/Harms technique, using screws in lateral mass of C1 and pars or pedicle of C2 has been increasingly applied due to its robust biomechanical properties and rigid stabilization in various planes (1, 3). One of the major advantages of C1 lateral mass screw fixation has been that the generous size of the lateral mass makes the technique relatively safe. The ponticulus posticus, also known as the arcuate foramen or Kimmerle anomaly, is a partial or complete bony arch over the vertebral artery as it crosses the superolateral surface of the posterior arch of the atlas. In the past it has been associated with neck pain, headaches/migraines, and orthodontic symptoms, but has assumed surgical significance mainly after the introduction of C1 lateral mass screw. There are three main methods of inserting the C1 lateral mass screw (Figure 1): 1) directly into the lateral mass after visualizing it lateral to the dura and superior to the C2 root; 2) making a notch in the inferior aspect of the posterior arch and drilling the hole through that notch; and 3) directly through the posterior arch into the lateral mass. There can be
Key words C1 - C1-2 - Arcuate foramen - Atlantoaxial - Atlas - Goel - Harms - Kimmerle -
Abbreviations and Acronyms CT: Computed tomography
WORLD NEUROSURGERY - [-]: ---, MONTH 2014
a significant amount of blood loss during dissection of the epidural and perineural venous plexus in the first method, along with a higher degree of C2 root manipulation. Also this method is sometimes technically not feasible if the C1-2 foramen is very small, not leaving enough room below the C1 posterior arch. As a result, some surgeons chose the entry point directly on the posterior arch (4, 5, 7). This also allows more bony purchase and probably more construct rigidity. Understandably, as the screw entry point moves more superiorly, it moves away from the C2 root but closer to the vertebral artery. This risk is even greater if there is an unidentified arcuate foramen hiding the vertebral artery. A complete arcuate foramen can give a false intraoperative impression of a wide posterior arch and the surgeon can mistakenly drill the hole right through the vertebral artery. Obviously, the identification of this anomaly on preoperative radiographs and, particularly, a high resolution computed tomography (CT) scan cannot be overemphasized. At the University of Miami, we routinely go through the thin cuts of preoperative CT scans to look for the course of the vertebral artery and arcuate foramen. We also have to look for a high riding transverse C2 foramen while inserting the C2 screw (6). In a recent case, we had to carefully drill away the posterior arch of C1 to unroof the vertebral artery and mobilize it upward to make
Departments of Neurological Surgery and Rehabilitation Medicine, University of Miami Miller School of Medicine, Miami, Florida, USA To whom correspondence should be addressed: Michael Y. Wang, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2014). http://dx.doi.org/10.1016/j.wneu.2014.02.011
www.WORLDNEUROSURGERY.org
e1
PERSPECTIVES
Figure 1. (A) Sagittal computed tomography angiogram of 72-year-old woman with chin-on-chest deformity with partial ponticulus posticus on the right side with a very tight C1-2 space for the C1 lateral mass screw. (B) We drilled the bone of the ponticulus posticus to unroof and mobilize the vertebral artery upward to put in the C1 lateral mass screw.
room for the partially threaded C1 lateral mass screw in a tight C1-2 space (Figure 1).
REFERENCES 1. Goel A, Laheri V: Plate and screw fixation for atlanto-axial subluxation. Acta Neurochir (Wien) 129:47-53, 1994. 2. Grob D, Magerl F: [Surgical stabilization of C1 and C2 fractures]. Orthopade 16:46-54, 1987.
In this issue of WORLD NEUROSURGERY, Elliott and Tanweer have done a commendable job summarizing the published data on ponticulus posticus. They have reviewed the cadaveric, radiographic, and CT scan literature in detail (including 44 studies and more than 20,000 patients) and found a 16%e 19% prevalence of this anomaly. Although there was an impressive range (4%e52%) in its prevalence across various studies, the overall rate was surprising similar in the 16%e 18% range when averages were compared within each cohort based on methodology (cadaveric, radiographic, and CT). It is also interesting that despite the narrow range, due to the large number of patients in the study, the cadaveric direct inspection group had a statistically higher prevalence (P < 0.01). There were a similar number of complete and partial/incomplete foramina. The anomaly was present bilaterally in 5.6% of patients and slightly more common on the left side. There was also no gender difference in prevalence. Elliott and Tanweer also discussed the study limitations in some detail, but overall, this study is a very useful addition to the spine literature, particularly to surgeons treating the pathology of upper cervical spine as iatrogenic injuries to the vertebral artery can be devastating.
trajectory, and length for safe fixation with C2 pars interarticularis screws. J Neurosurg: Spine 12: 602-612, 2010. 5. Wang MY, Samudrala S: Cadaveric morphometric analysis for atlantal lateral mass screw placement. Neurosurgery 54:1436-1440, 2004.
3. Harms J, Melcher RP: Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine (Phila Pa 1976) 26:2467-2471, 2001.
6. Yeom JS, Buchowski JM, Kim HJ, Chang BS, Lee CK, Riew KD: Risk of vertebral artery injury: comparison between C1-C2 transarticular and C2 pedicle screws. Spine J 13:775-785, 2013.
4. Hoh DJ, Liu CY, Wang MY: A radiographic CTbased study to determine the ideal entry point,
7. Yeom JS, Kafle D, Nguyen NQ, Noh W, Park KW, Chang BS, Lee CK, Riew KD: Routine insertion of
e2
www.SCIENCEDIRECT.com
the lateral mass screw via the posterior arch for C1 fixation: feasibility and related complications. Spine J 12:476-483, 2012.
Citation: World Neurosurg. (2014). http://dx.doi.org/10.1016/j.wneu.2014.02.011 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2014 Elsevier Inc. All rights reserved.
WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2014.02.011
Michael Y. Wang, M.D. Professor, Departments of Neurological Surgery and Rehabilitation Medicine University of Miami Miller School of Medicine
Lateral Mass of C1 Fixation and Ponticulus-Posticus Faiz U. Ahmad and Michael Y. Wang
P
osterior interspinous wiring, with or without halo fixation, was previously the most common method of fusion of C1-2 and is still very popular. With the increasing adaptation of screw instrumentation for more rigid fixation of the spine, other techniques have become popular. Transarticular C1-2 fusions (Magerl method) using a screw to cross the joint supplanted wiring due to improved fusion rates, but carried a higher risk of injuring the vertebral artery (2). In the modern Goel/Harms technique, using screws in lateral mass of C1 and pars or pedicle of C2 has been increasingly applied due to its robust biomechanical properties and rigid stabilization in various planes (1, 3). One of the major advantages of C1 lateral mass screw fixation has been that the generous size of the lateral mass makes the technique relatively safe. The ponticulus posticus, also known as the arcuate foramen or Kimmerle anomaly, is a partial or complete bony arch over the vertebral artery as it crosses the superolateral surface of the posterior arch of the atlas. In the past it has been associated with neck pain, headaches/migraines, and orthodontic symptoms, but has assumed surgical significance mainly after the introduction of C1 lateral mass screw. There are three main methods of inserting the C1 lateral mass screw (Figure 1): 1) directly into the lateral mass after visualizing it lateral to the dura and superior to the C2 root; 2) making a notch in the inferior aspect of the posterior arch and drilling the hole through that notch; and 3) directly through the posterior arch into the lateral mass. There can be
Key words C1 - C1-2 - Arcuate foramen - Atlantoaxial - Atlas - Goel - Harms - Kimmerle -
Abbreviations and Acronyms CT: Computed tomography
WORLD NEUROSURGERY - [-]: ---, MONTH 2014
a significant amount of blood loss during dissection of the epidural and perineural venous plexus in the first method, along with a higher degree of C2 root manipulation. Also this method is sometimes technically not feasible if the C1-2 foramen is very small, not leaving enough room below the C1 posterior arch. As a result, some surgeons chose the entry point directly on the posterior arch (4, 5, 7). This also allows more bony purchase and probably more construct rigidity. Understandably, as the screw entry point moves more superiorly, it moves away from the C2 root but closer to the vertebral artery. This risk is even greater if there is an unidentified arcuate foramen hiding the vertebral artery. A complete arcuate foramen can give a false intraoperative impression of a wide posterior arch and the surgeon can mistakenly drill the hole right through the vertebral artery. Obviously, the identification of this anomaly on preoperative radiographs and, particularly, a high resolution computed tomography (CT) scan cannot be overemphasized. At the University of Miami, we routinely go through the thin cuts of preoperative CT scans to look for the course of the vertebral artery and arcuate foramen. We also have to look for a high riding transverse C2 foramen while inserting the C2 screw (6). In a recent case, we had to carefully drill away the posterior arch of C1 to unroof the vertebral artery and mobilize it upward to make
Departments of Neurological Surgery and Rehabilitation Medicine, University of Miami Miller School of Medicine, Miami, Florida, USA To whom correspondence should be addressed: Michael Y. Wang, M.D. [E-mail: [email protected]] Citation: World Neurosurg. (2014). http://dx.doi.org/10.1016/j.wneu.2014.02.011
www.WORLDNEUROSURGERY.org
e1
PERSPECTIVES
Figure 1. (A) Sagittal computed tomography angiogram of 72-year-old woman with chin-on-chest deformity with partial ponticulus posticus on the right side with a very tight C1-2 space for the C1 lateral mass screw. (B) We drilled the bone of the ponticulus posticus to unroof and mobilize the vertebral artery upward to put in the C1 lateral mass screw.
room for the partially threaded C1 lateral mass screw in a tight C1-2 space (Figure 1).
REFERENCES 1. Goel A, Laheri V: Plate and screw fixation for atlanto-axial subluxation. Acta Neurochir (Wien) 129:47-53, 1994. 2. Grob D, Magerl F: [Surgical stabilization of C1 and C2 fractures]. Orthopade 16:46-54, 1987.
In this issue of WORLD NEUROSURGERY, Elliott and Tanweer have done a commendable job summarizing the published data on ponticulus posticus. They have reviewed the cadaveric, radiographic, and CT scan literature in detail (including 44 studies and more than 20,000 patients) and found a 16%e 19% prevalence of this anomaly. Although there was an impressive range (4%e52%) in its prevalence across various studies, the overall rate was surprising similar in the 16%e 18% range when averages were compared within each cohort based on methodology (cadaveric, radiographic, and CT). It is also interesting that despite the narrow range, due to the large number of patients in the study, the cadaveric direct inspection group had a statistically higher prevalence (P < 0.01). There were a similar number of complete and partial/incomplete foramina. The anomaly was present bilaterally in 5.6% of patients and slightly more common on the left side. There was also no gender difference in prevalence. Elliott and Tanweer also discussed the study limitations in some detail, but overall, this study is a very useful addition to the spine literature, particularly to surgeons treating the pathology of upper cervical spine as iatrogenic injuries to the vertebral artery can be devastating.
trajectory, and length for safe fixation with C2 pars interarticularis screws. J Neurosurg: Spine 12: 602-612, 2010. 5. Wang MY, Samudrala S: Cadaveric morphometric analysis for atlantal lateral mass screw placement. Neurosurgery 54:1436-1440, 2004.
3. Harms J, Melcher RP: Posterior C1-C2 fusion with polyaxial screw and rod fixation. Spine (Phila Pa 1976) 26:2467-2471, 2001.
6. Yeom JS, Buchowski JM, Kim HJ, Chang BS, Lee CK, Riew KD: Risk of vertebral artery injury: comparison between C1-C2 transarticular and C2 pedicle screws. Spine J 13:775-785, 2013.
4. Hoh DJ, Liu CY, Wang MY: A radiographic CTbased study to determine the ideal entry point,
7. Yeom JS, Kafle D, Nguyen NQ, Noh W, Park KW, Chang BS, Lee CK, Riew KD: Routine insertion of
e2
www.SCIENCEDIRECT.com
the lateral mass screw via the posterior arch for C1 fixation: feasibility and related complications. Spine J 12:476-483, 2012.
Citation: World Neurosurg. (2014). http://dx.doi.org/10.1016/j.wneu.2014.02.011 Journal homepage: www.WORLDNEUROSURGERY.org Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2014 Elsevier Inc. All rights reserved.
WORLD NEUROSURGERY, http://dx.doi.org/10.1016/j.wneu.2014.02.011