- Department of Neurosurgery, National Neuroscience Institute of Singapore, 11 Jalan Tan Tock Seng, 308433, Singapore
Department of Neurosurgery, National Neuroscience Institute of Singapore, 11 Jalan Tan Tock Seng, 308433, Singapore
DOI:10.4103/2152-7806.109454Copyright: © 2013 Ling JM This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
How to cite this article: Ling JM, Tiruchelvarayan R, Seow WT, Ng HB. Surgical treatment of adult and pediatric C1/C2 subluxation with intraoperative computed tomography guidance. Surg Neurol Int 22-Mar-2013;4:
How to cite this URL: Ling JM, Tiruchelvarayan R, Seow WT, Ng HB. Surgical treatment of adult and pediatric C1/C2 subluxation with intraoperative computed tomography guidance. Surg Neurol Int 22-Mar-2013;4:. Available from: http://sni.wpengine.com/surgicalint_articles/surgical-treatment-of-adult-and-pediatric-c1c2-subluxation-with-intraoperative-computed-tomography-guidance/
Background:Surgical treatment of C1/C2 subluxation has evolved significantly over the past 2 decades, from the relatively simpler posterior wiring to more technically demanding instrumentations such as C1 lateral mass screws – C2 pedicle screws, C1/C2 transarticular screws, and occipital cervical fusion. Navigation with fluoroscopy is currently the standard of practice in most centers. However, fluoroscopy at this level carries several major drawbacks, such as blockage by the mandible and inability to produce axial images for assessment of the reduction of rotatory subluxation.
Methods:The authors report a series of 21 patients with C1/C2 subluxation treated surgically with intraoperative computed tomography (ICT) guidance.
Results:There were 7 children and 14 adults. Eight patients underwent C1/C2 fixation with a Harm's construct, and 13 patients underwent occipital cervical fusion. One out of 17 (6%) C1 lateral mass screws has breached the medial wall of lateral mass by 1 mm. Two out of 20 (10%) C2 pedicle screws have breached the foramen transversarium by 1 mm (Neo classification grade 1). The position of all subaxial screws (49 lateral mass screws and 13 pedicle screws) and occipital screws (50 screws) appeared satisfactory. No neurovascular damage occurred in all the patients.
Conclusions:Ninety eight percent of the screws were placed in ideal position with the aid of ICT. Only 2% of the screws deviated from the planned position, but the breaches were not clinically significant and hence no revision was required. This showed that ICT guidance can help to achieve a high accuracy of surgical instrumentation for the treatment of C1/C2 subluxation.
Keywords: Atlanto-axial subluxation, C1/C2, intraoperative computed tomography, navigation, stereotaxy
Among all conditions of spinal instability requiring surgical treatment, atlanto-axial subluxation is a less commonly encountered entity. However, instrumentation at this anatomical region poses a great technical challenge, owing to the proximity of vital neurovascular structures.[
Computed tomography (CT) is the gold standard imaging for preoperative planning of surgical approach. The choice of implants, screw length, trajectory, and the method of instrumentation can be made based on CT anatomy.[
Instrumentation based on landmarks alone is subjected to significant inaccuracy even in experienced hands. Fluoroscopy is available in most neurosurgical/spine centers. Nevertheless, it has several limitations when used for instrumentation at the cranio-cervical junction. Fluoroscopy produces 2-dimensional image. Interpretation of screw trajectory requires constant switching between the lateral and anterior–posterior (AP) view. Moreover, the mandible, maxilla, and overlapping of screws significantly degrade the images of C1 and C2 at various angles. The pursuit for improved accuracy has led to the use of intraoperative CT (ICT) and stereotaxy for fixation of the cranio-cervical junction. The purpose of this study is to determine the accuracy of instrumentation with ICT guidance.
Twenty-one cases of atlanto-axial subluxation with surgical treatment were prospectively recorded from May 2008 to November 2012. All cases were done by single surgeon (RT) and surgical instrumentation in every case was guided by ICT navigation.
Fixation with screws-and-rods construct was performed if both C1 and C2 were suitable for instrumentation. Occipito-cervical (OC) fusion was done for patients with either concurrent atlanto-occipital instability, or if C1 or C2 bone were unhealthy and not amenable to instrumentation. A C2 translaminar screw was inserted instead of C2 pedicle screw if isthmus of C2 pedicle was smaller than 3.5 mm or in the presence of a high riding vertebral artery. All patients in our series were operated in prone position. The head was fixed with a radiolucent Mayfield clamp. CT scan was performed after the patient was appropriately positioned and secured. The scan ensured adequate reduction of the C1/2 subluxation, as well good cranio-cervical alignment in cases where OC fusion would be performed.
The posterior elements of the cervical vertebrae and suboccipital skull were exposed with subperiosteal dissection. A reference array was clamped to a spinous process nearest to the levels to be operated on (usually on C2). An intraoperative CT was then performed, followed by auto-registration. The accuracy of the navigation was verified by placing the pointers on prominent landmarks such as the superior and inferior edges of the spinous process of C2, as well as pins on the reference array.
Entry points of screws were selected based on navigation, and prepared with awl/drill. A reference array was attached to the pedicle probe and registered. The “navigated” pedicle probe was used to find the pedicle track. The position of the probe was tracked by the navigation system throughout the course of insertion. The track was then tapped, followed by insertion of screws based on the same trajectory. For lateral mass screws, the entry points were similarly selected based on navigation. The trajectory was planned using the navigation probe. Drilling, tapping and screws insertion were executed based on the planned trajectory. The site of insertion of the occipital plate was planned with particular attention paid to the anatomy of the dural venous sinuses as they appear on CT. The screw lengths were planned based on the measured thickness of the skull bone, with midline keel fixation being the priority.
Upon completion of instrumentation, a CT scan was done to ascertain satisfactory position of all instruments, as well as excluding an epidural hematoma at the suboccipital area. Revision of screws was done when necessary.
Twenty-one patients with C1/C2 subluxation were included in the study. Age of patients ranged from 6 to 83 years (average 43 years). There were 12 males and 9 females. There were 7 pediatric patients (defined as being under the age of 16 years) and 14 adults. Etiologies of C1/C2 subluxation included congenital, trauma, autoimmune (arthritis), degenerative, infection, and radionecrosis.
Seven patients underwent C1/C2 fixation with a screw-and-rod construct. Thirteen patients underwent occipital cervical fusion. One patient underwent C1 to C5 instrumented fusion (ossification of the posterior longitudinal ligament with concurrent atlanto-axial instability). A total of 153 screws were inserted (103 cervical screws and 50 occipital screws). The type of screws inserted for each levels are shown in
Example case 1: C1/C2 fixation
A 25-year-old man was involved in a road traffic accident. He was a motorcyclist who skidded and fell from motorbike. He sustained severe head injury requiring intensive care for intracranial pressure (ICP) control. CT of cervical spine showed a rotatory subluxation of C1/C2. He was taken to operating theatre for fixation of the C1/C2 instability after the ICP was under control. As shown in
Example case 2: Occipito-cervical fusion
A 9-year-old girl presented with stiff neck and development of right torticollis over 3 months. Examination showed right hypoglossal neuropathy. CT of the cervical spine showed rotatory subluxation of C1/C2. She was treated with halo vest immobilization for 2 months, which resulted in symptom improvement and resolution of the hypoglossal neuropathy. However, the degree of her torticollis worsened after the removal of the halo vest. Repeat CT scan 6 months later [
Stereotaxy in instrumentation
The advent of stereotaxy is beginning to revolutionize the practice of spinal instrumentation. There is a growing amount of evidences showing that navigated spinal instrumentation is highly accurate.[
The restoration of atlantoaxial rotational alignment with intraoperative computed tomography
Restoration of rotational alignment of the C1-C2 junction is important prior to fusion. Spinal alignment is conventionally assessed with fluoroscopy after patient is placed in the final surgical position. Fluoroscopy is usually adequate for the assessment of sagittal and coronal alignment, but its ability to ascertain rotational alignment is limited. In our experience, the assessment of the axis of C1-C2 rotation may not be reliable based on the head position, because a malrotated C1-C2 junction may be compensated by counter-rotation of C0-C1 or the subaxial spine. ICT allows accurate reduction of the rotational angle based on axial images with reconstructed sagittal/coronal views. This is important because failure to fuse the C1-C2 in the neutral axial alignment can lead to permanent torticollis – a significant compromise of function, comfort, and cosmesis.
C1/C2 fixation with ICT
The historical breach rate of C1 lateral mass and C2 pedicle screw ranges from 5% to 21% based on findings of postoperative CT scan.[
When navigated with fluoroscopy, frequent switching between AP and lateral views was required, especially during the critical step of screw insertion. The surgeon could not see both views at the same time. Importantly, a screw that was angulated too medially could only be detected by the AP view of fluoroscopy after it is advanced, and sometimes only after insertion of the entire length of the screw. Neurovascular injury, if any, would have occurred by the time the AP view showed the undesired angulations. If the screw needed to be revised, exchange for a larger rescue screw may not be possible due to limitation of the size of the C1 lateral mass or the C2 pedicle isthmus. Therefore, we found ICT to be superior to fluoroscopy because it allowed navigation based on simultaneous guidance by axial, sagittal, and coronal views. The positions of the screws, or any instruments, were updated in a real-time manner as they were advanced into the vertebrae. In our series, ICT afforded the precision to insert all C1 and C2 screws in a single pass, which technically also translated into greater bony purchase and pullout strength.
Traditionally, a wide exposure of posterior C1, including the lateral mass and sulcus arteriosus, is usually required to delineate the entry point. This process may frequently be hindered by bleeding from the surrounding venous plexuses, and sometimes from the vertebral arteries (VA) at unsuspected locations. We used ICT to define the estimated entry points before exposure of the soft tissue; as such only a limited exposure around the entry point is required. This has resulted in reduced time of exploration, minimal dissection, and reduced blood loss.
A recent study by Yamazaki et al. showed a 10% incidence of extraosseous VA anomalies, namely fenestration and persistent intersegmental artery among 100 patients who underwent craniovertebral junction instrumentation.[
Subaxial cervical pedicle screws with ICT guidance
It has been demonstrated that cervical pedicle screws, when compared with lateral mass screws, have a significantly lower rate of loosening at the bone–screw interface, as well as higher strength after fatigue testing.[
Role of ICT in occipital plates and screws insertion
The transverse sinus and the torcula mark the superior limit of the occipital fixation. Their location can be accurately determined with ICT, by looking for the posterior edge of the tentorium on sagittal images. We favored occipital plates with a configuration of 2-3 midline screws, and 1 paramedian screw on each side. The midline fixation allows longer screws to be inserted at the thicker midline keel, thus increasing bony purchase. By obtaining good midline keel screw fixation, the OC construct can achieve a better biomechanical strength.[
Surgical stabilization of the craniovertebral junction in children poses additional challenges compared with adults. Small bony and ligamentous structures, as well as the unusual configuration of vertebral components, and sometimes the presence of congenital malformations have made instrumentation of the craniovertebral junction in children more difficult. In the past, fixations of C1/C2 in children were mainly limited to wiring with a bone graft, because placement of screws at this location was considered too high risk. The fusion rate of wiring is low. Although strong in limiting flexion, wiring has poor strength in limiting extension, rotation and lateral bending. Wineger et al. reported in their systemic review of various techniques for occipital cervical fusion, that a screw-rod fixation had the highest fusion rate, with bony fusions occurring in less than 4 months.[
Placement of C1 lateral mass screws in pediatric patients is more difficult owing to smaller lateral mass.[
In OC fusion, the thinner occipital bones in children often necessitate multiple screws with bicortical purchase in order to achieve adequate construct rigidity. The recent study of Hwang, et al. showed a 20% complication rate arising from occipital screws insertion among 20 children.[
When compared with fluoroscopy, ICT significantly reduced radiation exposure to operating theatre staffs, including the surgeon.[
Pitfalls of ICT navigation
The surgeon is responsible for the reliability of the stereotaxy system during the entire course of operation. With even a few millimeter of deviation, stereotaxy may end up misleading the surgeon. In our series, there were no cases where the reference array was displaced accidentally. Verification should always be done after registration. The infrared camera should be placed in a position such that it could detect all the fiducials on the reference array and instruments. Care should be taken not to knock the reference array out of position. If this happen, a CT scan needs to be repeated after repositioning and re-tightening the reference array.
Instrumentation of C1/C2 instability is challenging owing to the proximity of vital neurovascular structures. Fluoroscopic navigation, which is the current standard practice, has many limitations. In our series, navigation with intraoperative CT has been employed in 21 cases of fixation of atlanto-axial instability. All screws (103 cervical screws and 50 occipital screws) were placed in a single attempt without the need for revision. Ninety eight percent of the screws were shown to be in ideal/planned position on intraoperative CT. Only 2% of the screws deviated from the planned position, but their positions were deemed acceptable and hence not revised intraoperatively. There was no incidence of extradural hemorrhage, cerebrospinal fluid leak or vertebral artery injury. This showed that ICT guidance can help to obtain a high accuracy of surgical instrumentation for the treatment of C1-2 subluxation.
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