Symptomatic atlantoaxial instability needs stabilization of the atlantoaxial joint. Among the various techniques described in literature for the fixation of atlantoaxial joint, Magerl's technique of transarticular screw fixation remains the gold standard. Traditionally this technique combines placement of transarticular screws and posterior wiring construct. The aim of this study is to evaluate clinical and radiological outcomes in subjects of atlantoaxial instability who were operated using transarticular screws and iliac crest bone graft, without the use of sublaminar wiring (a modification of Magerl's technique).
We evaluated retrospectively 38 subjects with atlantoaxial instability who were operated at our institute using transarticular screw fixation. The subjects were followed up for pain, fusion rates, neurological status and radiographic outcomes. Final outcome was graded both subjectively and objectively, using the scoring system given by Grob et al.
Instability in 34 subjects was secondary to trauma, in 3 due to rheumatoid arthritis and 1 had tuberculosis. Neurological deficit was present in 17 subjects. Most common presenting symptom was neck pain, present in 35 of the 38 subjects.
Postoperatively residual neck and occipital pain was present in 8 subjects. Neurological deficit persisted in only 7 subjects. Vertebral artery injury was seen in 3 subjects. None of these subjects had any sign of neurological deficit or vertebral insufficiency. Three cases had nonunion. At the latest follow up, subjectively, 24 subjects had good result, 6 had fair and 8 had bad result. On objective grading, 24 had good result, 11 had fair and 3 had bad result. The mean follow up duration was 41 months.
Transarticular screw fixation is an excellent technique for fusion of the atlantoaxial complex. It provides highest fusion rates, and is particularly important in subjects at risk for nonunion. Omitting the posterior wiring construct that has been used along with the bone graft in the traditional Magerl' s technique achieves equally good fusion rates and is an important modification, thereby avoiding the complications of sublaminar wire passage.
We present a case of an athetoid cerebral palsy with quadriparesis caused by kyphotic deformity of the cervical spine, severe spinal stenosis at the cervicomedullary junction, and atlantoaxial instability. The patient improved after the first surgery, which included a C1 total laminectomy and C-arm guided righ side unilateral C1-2 transarticular screw fixation. C1-2 fixation was not performed on the other side because of an aberrant and dominant vertebral artery (VA). Eight months after the first operation, the patient required revision surgery for persistent neck pain and screw malposition. We used intraoperative VA angiography with simultaneous fluoroscopy for precise image guidance during bilateral C1-2 transarticular screw fixation. Intraoperative VA angiography allowed the accurate insertion of screws, and can therefore be used to avoid VA injury during C1-2 transarticular screw fixation in comorbid patients with atlantoaxial deformities.
Atlantoaxial instability; Transarticular screw fixation; Vertebral artery; Intraoperative angiography; Athetoid cerebral palsy
Posterior transarticular screw fixation C1-2 with the Magerl technique is a challenging procedure for stabilization of atlantoaxial instabilities. Although its high primary stability favoured it to sublaminar wire-based techniques, the close merging of the vertebral artery (VA) and its violation during screw passage inside the axis emphasizes its potential risk. Also, posterior approach to the upper cervical spine produces extensive, as well as traumatic soft-tissue stripping. In comparison, anterior transarticular screw fixation C1-2 is an atraumatic technique, but has been neglected in the literature, even though promising results are published and lectured to date. In 2004, anterior screw fixation C1-2 was introduced in our department for the treatment of atlantoaxial instabilities. As it showed convincing results, its general anatomic feasibility was worked up. The distance between mid-sagittal line of C2 and medial border of the VA groove resembles the most important anatomic landmark in anterior transarticular screw fixation C1-2. Therefore, CT based measurements on 42 healthy specimens without pathology of the cervical spine were performed. Our data are compiled in an extended collection of anatomic landmarks relevant for anterior transarticular screw fixation C1-2. Based on anatomic findings, the technique and its feasibility in daily clinical work is depicted and discussed on our preliminary results in seven patients.
C1–C2; Atlantoaxial instability; Anatomy; Upper cervical spine; Cervical fusion
Traumatic posterior atlantoaxial dislocation without related fracture of the odontoid process is very rare, and only ten cases have been previously reported. The objective of this paper was to describe a case of traumatic posterior atlantoaxial dislocation without related fracture of the odontoid process, and its management with atlantoaxial transarticular screw fixation and bony fusion through an anterior retropharyngeal approach, and to review the relevant literature. The patient’s medical and radiographic history is reviewed as well as the relevant medical literature. Posterior atlantoaxial dislocation was confirmed in a 48-year-old male struck by an automobile through conventional radiography, computed tomography and magnetic resonance imaging. No related fracture of the odontoid process or neurological deficit was found in this patient. Transarticular screw fixation of the atlantoaxial articulation through anterior retropharyngeal approach was performed after several unsuccessful attempts of closed reduction. At the latest follow-up, the lateral cervical spine radiography in flexion and extension demonstrated no instability of the atlantoaxial complex 21 months after the operation. In conclusion, patients with posterior atlantoaxial dislocation without fracture may survive with few or no-long term neurological deficit. Routine CT and MRI of the cervical spine should be carried out in patients with head or neck trauma to prevent missing of this rare clinical entity. Transarticular screw fixation of the atlantoaxial articulation through anterior retropharyngeal approach is safe and useful in case the management of dislocation is unsuccessful under closed reduction.
Atlantoaxial dislocation; Anterior retropharyngeal approach; Transarticular screw; Neurological deficit
A retrospective analysis of 7 patients with traumatic rotatory atlanto-axial subluxation.
Overview of Literature
Cases of traumatic rotatory atlantoaxial subluxation in children are difficult to be stabilized. Surgical challenges include: narrow pedicles, medial vertebral arteries, vertebral artery anomalies, fractured pedicles or lateral masses, and fixed subluxation. The use of O-arm and computer-assisted navigation are still tested as aiding tools in such operative modalities.
Report of clinical series for evaluation of the safety of use of the O-arm and computed assisted-navigation in screw fixation in children with traumatic rotatory atlantoaxial subluxation.
In the present study, 7 cases of rotatory atlantoaxial traumatic subluxation were operated between December 2009 and March 2011. All patient-cases had undergone open reduction and instrumentation using atlas lateral mass and axis pedicle screws with intraoperative O-arm with computer-assisted navigation.
All hardware was safely placed in the planned trajectories in all the 7 cases. Intraoperative O-arm and computer assisted-navigation were useful in securing neural and vascular tissues safety with tough-bony purchases of the hardware from the first and only trial of application with sufficient reduction of the subluxation.
Successful surgery is possible with using the intraoperative O-arm and computer-assisted navigation in safe and proper placement of difficult atlas lateral mass and axis pedicle screws for rotatory atlantoaxial subluxation in children.
Atlantoaxial joint fusion; Intraoperative computer-assisted 3D navigation; Computer-assisted three-dimensional imaging
There are several treatment options for rigid fixation at C1–C2 including Brooks and Gallie type wired fusions and C1–2 transarticular screws. The use of a Goel–Harms type fusion, a construct with C1 lateral mass screws and C2 pedicle screws, has not been extensively described in pediatric patients. Here, we describe its relatively safe and effective use for treating pediatric patients by retrospective chart review of patients treated by the senior author for atlantoaxial instability with a Goel–Harms-type constructs during a 3-year period (2005–2007). Six patients were treated using Goel–Harms-type constructs. Five patients were treated utilizing a construct containing C1 lateral mass screws and C2 pedicle screws; one patient was treated using construct containing C1 lateral mass screws and C2 trans-laminar screws. The patients ranged in age from 7 to 17 years old (mean 12.7). All patients had findings of an os odontoideum on CT scans and three of the six patients had T2 hyperintensity on MRI. Three of the six patients presented with transient neurologic deficits: quadraplegia in two patients and paresthesias in two patients. In each patient C1 lateral mass and C2 screws were placed and the subluxation was reduced to attain an anatomical alignment. No bone grafts were harvested from the iliac crest or rib. Local morsalized bone and sub-occipital skull graft was used. All patients tolerated the procedure well and were discharged home on post-operative day 3–4. The patients wore a hard cervical collar and no halo-vests were needed. All patients had solid fusion constructs and normal alignment on post-operative imaging studies performed on average 14 months post-operatively (range: 7–29). The results demonstrated that Goel–Harms fusions are a relatively safe and effective method of treating pediatric patients with atlantoaxial instability and are not dependent on vertebral anatomy or an intact ring of C1. Follow-up visits and studies in this limited series of patients demonstrated solid fusion constructs and anatomical alignment in all patients treated.
Atlantoaxial instability; Os odontoideum; Goel–Harms fusion; Pediatrics; Cervical spine
To investigate the feasibility of C1 lateral mass screw and C2 pedicle screw with polyaxial screw and rod system supplemented with miniplate for interlaminar fusion to treat various atlantoaxial instabilities.
After posterior atlantoaxial fixation with lateral mass screw in the atlas and pedicle screw in the axis, we used 2 miniplates to fixate interlaminar iliac bone graft instead of sublaminar wiring. We performed this procedure in thirteen patients who had atlantoaxial instabilities and retrospectively evaluated the bone fusion rate and complications.
By using this method, we have achieved excellent bone fusion comparing with the result of other methods without any complications related to this procedure.
C1 lateral mass screw and C2 pedicle screw with polyaxial screw and rod system supplemented with miniplate for interlaminar fusion may be an efficient alternative method to treat various atlantoaxial instabilities.
Atalantoaxial stabilization; Cervical spine; Interlaminar fusion
Prophylactic or therapeutic arthrodesis is recommended for atlantoaxial instability in Morquio syndrome. Occipitocervical fusion, the common approach for upper cervical fusion in Morquio syndrome sacrifices the movements at the occipitoatlantal joints. The use of C1-C2 transarticular screws for achieving C1-C2 arthrodesis, without compromising mobility at the occipitoatlantal joint in Morquio syndrome has not been reported. We report a case of Morquio syndrome with atlantoaxial instability and odontoid hypoplasia, where we successfully achieved C1-C2 arthrodesis using transarticular screws and bone graft. The advantages of this method over other methods of atlantoaxial arthrodesis in Morquio syndrome have also been discussed.
Atlantoaxial arthrodesis; Morquio syndrome; occipitocervical fusion; transarticular screw
To reconstruct highly destructed unstable rheumatoid arthritis (RA) cervical lesions, the authors have been using C1/2 transarticular and cervical pedicle screw fixations. Pedicle screw fixation and C1/2 transarticular screw fixation are biomechanically superior to other fixation techniques for RA patients. However, due to severe spinal deformity and small anatomical size of the vertebra, including the lateral mass and pedicle, in the most RA cervical lesions, these screw fixation procedures are technically demanding and pose the potential risk of neurovascular injuries. The purpose of this study was to evaluate the accuracy and safety of cervical pedicle screw insertion to the deformed, fragile, and small RA spine lesions using computer-assisted image-guidance systems. A frameless, stereotactic image-guidance system that is CT-based, and optoelectronic was used for correct screw placement. A total of 21 patients (16 females, 5 males) with cervical disorders due to RA were surgically treated using the image-guidance system. Postoperative computerized tomography and plane X-ray was used to determine the accuracy of the screw placement. Neural and vascular complications associated with screw insertion and postoperative neural recovery were evaluated. Postoperative radiological evaluations revealed that only 1 (2.1%; C4) of 48 screws inserted into the cervical pedicle had perforated the vertebral artery canal more than 25% (critical breach). However, no neurovascular complications were observed. According to Ranawat’s classification, 9 patients remained the same, and 12 patients showed improvement. Instrumentation failure, loss of reduction, or nonunion was not observed at the final follow-up (average 49.5 months; range 24–96 months). In this study, the authors demonstrated that image-guidance systems could be applied safely to the cervical lesions caused by RA. Image-guidance systems are useful tools in preoperative planning and in transarticular or transpedicular screw placement in the cervical spine of RA patients.
Cervical spine; Image guidance; Rheumatoid arthritis; Cervical pedicle screw; Transarticular screw
The most common cervical abnormality associated with rheumatoid arthritis (RA) is atlantoaxial subluxation, and atlantoaxial transarticular screw fixation has proved to be one of the most reliable, stable fixation techniques for treating atlantoaxial subluxation. Following C1–C2 fixation, however, subaxial subluxation reportedly can bring about neurological deterioration and require secondary operative interventions. Rheumatoid patients appear to have a higher risk, but there has been no systematic comparison between rheumatoid and non-rheumatoid patients. Contributing radiological factors to the subluxation have also not been evaluated. The objective of this study was to evaluate subaxial subluxation after atlantoaxial transarticular screw fixation in patients with and without RA and to find contributing factors. Forty-three patients who submitted to atlantoaxial transarticular screw fixation without any concomitant operation were followed up for more than 1 year. Subaxial subluxation and related radiological factors were evaluated by functional X-ray measurements. Statistical analyses showed that aggravations of subluxation of 2.5 mm or greater were more likely to occur in RA patients than in non-RA patients over an average of 4.2 years of follow-up, and postoperative subluxation occurred in the anterior direction in the upper cervical spine. X-ray evaluations revealed that such patients had a significantly smaller postoperative C2–C7 angle, and that the postoperative AA angle correlated negatively with this. Furthermore, anterior subluxation aggravation was significantly correlated with the perioperative atlantoaxial and C2–C7 angle changes, and these two changes were strongly correlated to each other. In conclusion, after atlantoaxial transarticular screw fixation, rheumatoid patients have a greater risk of developing subaxial subluxations. The increase of the atlantoaxial angel at the operation can lead to a decrease in the C2–C7 angle, followed by anterior subluxation of the upper cervical spine and possibly neurological deterioration.
Atlantoaxial transarticular screw fixation; Atlantoaxial subluxation; Subaxial subluxation; Rheumatoid arthritis; Operative complications
C2 laminar screw fixation is considered as an excellent alternative to Magerl's transfacetal approach or Harms construct for the atlantoaxial stabilization. However, to our knowledge, there is no report on the feasibility of the new approach to Korean population. We investigated morphometric parameters of the dorsal arch of the C2 to provide the quantitative data for the feasibility of laminar screw fixation.
One-hundred-and-two patients' cervical computed tomography had been reconstructed and investigated on the anatomical parameters related with C2 laminar screw placement. Sixty patients were male and forty-two patients were female. Measurements included the laminar thickness and slope, spino-laminar angle, and maximal screw length.
Ages ranged from 20 to 81 and the mean age was 48.4. Mean laminar thickness was 5.7 mm (±1.0) (5.8 mm in male and 5.4 mm in female). Fifty-one patients (50%) had a laminar thickness smaller than 5.5 mm at least unilaterally, therefore the patients were considered as inappropriate candidates for the laminar screw fixation in the smaller side of the laminae. Mean value of maximal length of screw was 33.3 mm (34.3 mm in male and 31.9 mm in female). Mean spino-laminar angle was 43.2° and mean slope angle was 32.9°.
Half of patients had inappropriate laminar profiles to accommodate a 3.5 mm screw in at least one side of the axis. The three-dimensional computed tomography reconstruction is mandatory for the preoperative assessment for the feasibility of the C2 lamina.
Axis; Laminar screw
The aim of this study is to evaluate the first results of the atlantoaxial fixation using polyaxial screw–rod system. Twenty-eight patients followed-up 12–29 months (average 17.1 months) were included in this study. The average age was 59.5 years (range 23–89 years). The atlantoaxial fusion was employed in 20 patients for an acute injury to the upper cervical spine, in 1 patient with rheumatoid arthritis for atlantoaxial vertical instability, in 1 patient for C1–C2 osteoarthritis, in 2 patients for malunion of the fractured dens. Temporary fixation was applied in two patients for type III displaced fractures of the dens and in two patients for the atlantoaxial rotatory dislocation. Retrospectively, we evaluated operative time, intraoperative bleeding and the interval of X-ray exposure. The resulting condition was subjectively evaluated by patients. We evaluated also the placement, direction and length of the screws. Fusion or stability in the temporary fixation was evaluated on radiographs taken at 3, 6, 12 weeks and 6 and 12 months after the surgery. As concerns complications, intraoperatively we monitored injury of the nerve structures and the vertebral artery. Monitoring of postoperative complications was focused on delayed healing of the wound, breaking or loosening of screws and development of malunion. Operative time ranged from 35 to 155 min, (average 83 min). Intraoperative blood loss ranged from 50 to 1,500 ml (average 540 ml). The image intensifier was used for a period of 24 s to 2 min 36 s (average 1 min 6 s). Within the postoperative evaluation, four patients complained of paresthesia in the region innervated by the greater occipital nerve. A total of 56 screws were inserted into C1, their length ranged from 26 to 34 mm (average, 30.8 mm). All screws were positioned correctly in the C1 lateral mass. Another 56 screws were inserted into C2. Their length ranged from 28 to 36 mm (average 31.4 mm). Three screws were malpositioned: one screw perforated the spinal canal and two screws protruded into the vertebral artery canal. C1–C2 stability was achieved in all patients 12 weeks after the surgery. No clinically manifested injury of the vertebral artery or nerve structures was observed in any of these cases. As for postoperative complications, we recorded wound dehiscence in one patient. The Harms C1–C2 fixation is a very effective method of stabilizing the atlantoaxial complex. The possibility of a temporary fixation without damage to the atlantoaxial joints and of reduction after the screws and rods had been inserted is quite unique.
Atlantoaxial fixation; Spine surgery; Atlantoaxial instability
Objective: The purpose of this comparison case study is to show a potential complication associated with atlantoaxial fusion, and the preoperative evaluation that could help to avoid it.
Background data: The use of lateral mass screw fixation in atlantoaxial fusion has provided surgeons the ability to create rigid fixation, with a high success rate of fusion. While the use of screws for fixation is relatively easy to adopt, the risk of causing neurological damage to the patient is ever present. Many major structures, such as the vertebral artery, carotid artery, and spinal cord, must all be considered during surgery.
Methods: A comparison of two patients who underwent the same procedure was reviewed—the first had no complications from surgery and the second underwent revision surgery because of the C1 screw impinging on the C1 nerve exiting the foramen.
Results: After removal of the C1 screw and converting to a cable technique, the patient made a full recovery and neurological function was restored.
Conclusions: When considering C1-C2 lateral mass screw fixation for atlantoaxial fusion, the size of the foramen should be considered. If the foramen is significantly narrowed, alternate fixation should be selected.
Insertion of percutaneous iliosacral screws with fluoroscopic guidance is associated with a relatively high screw malposition rate and long radiation exposure. We asked whether radiation exposure was reduced and screw position improved in patients having percutaneous iliosacral screw insertion using computer-assisted navigation compared with patients having conventional fluoroscopic screw placement. We inserted 26 screws in 24 patients using the navigation system and 35 screws in 32 patients using the conventional fluoroscopic technique. Two subgroups were analyzed, one in which only one iliosacral screw was placed and another with additional use of an external fixator. We determined screw positions by computed tomography and compared operation time, radiation exposure, and screw position. We observed no difference in operative times. Radiation exposure was reduced for the patients and operating room personnel with computer assistance. The postoperative computed tomography scan showed better screw position and fewer malpositioned screws in the three-dimensional navigated groups. Computer navigation reduced malposition rate and radiation exposure.
Level of Evidence: Level II, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.
Bilateral C1-2 transarticular screw fixation (TAF) with interspinous wiring has been the best treatment for atlantoaxial instability (AAI). However, several factors may disturb satisfactory placement of bilateral screws. This study evaluates the usefulness of unilateral TAF when bilateral TAF is not available.
Between January 2003 and December 2007, TAF was performed in 54 patients with AAI. Preoperative studies including cervical x-ray, three dimensional computed tomogram, CT angiogram, and magnetic resonance image were checked. The atlanto-dental interval (ADI) was measured in preoperative period, immediate postoperatively, and postoperative 1, 3 and 6 months.
Unilateral TAF was performed in 27 patients (50%). The causes of unilateral TAF were anomalous course of vertebral artery in 20 patients (74%), severe degenerative arthritis in 3 (11%), fracture of C1 in 2, hemangioblastoma in one, and screw malposition in one. The mean ADI in unilateral group was measured as 2.63 mm in immediate postoperatively, 2.61 mm in 1 month, 2.64 mm in 3 months and 2.61 mm in 6 months postoperatively. The mean ADI of bilateral group was also measured as following; 2.76 mm in immediate postoperative, 2.71 mm in 1 month, 2.73 mm in 3 months, 2.73 mm in 6 months postoperatively. Comparison of ADI measurement showed no significant difference in both groups, and moreover fusion rate was 100% in bilateral and 96.3% in unilateral group (p=0.317).
Even though bilateral TAF is best option for AAI in biomechanical perspectives, unilateral screw fixation also can be a useful alternative in otherwise dangerous or infeasible cases through bilateral screw placement.
Atlatoaxial instability (AAI); Atlantodental interval (ADI); Transarticular screw fixation (TAF); Unilateral; Vertebral artery
C2 laminar screws have become an increasingly used alternative method to C2 pedicle screw fixation. However, the outcome of this technique has not been thoroughly investigated. A total of 35 cases with upper cervical spinal instability undergoing C2 laminar screw fixation were reviewed. All cases had symptoms of atlantoaxial instability, such as craniocervical junction pain, and were fixed with the Vertex cervical internal fixation system. A total of 68 screws were placed and hybrid constructs (a C2 translaminar screw combined with a C2 pars screw) were incorporated in two patients. In this series, there were no intraoperative complications and no cases of neurological worsening or vascular injury from hardware placement. Computed tomographic scans demonstrated a partial dorsal laminar breach in ten patients. None of these resulted in neurological symptoms. None of the patients was found to have a breach of the ventral laminar cortex. All the C2 laminar screws fixations were performed successfully. There was no instability seen on the films with no evidence of hardware failure or screw loosening during the follow-up period in all patients. In conclusion, C2 laminar screw technique is straightforward and easily adopted; it can efficiently and reliably restore upper cervical stability. It is an alternative method to C2 pedicle screw fixation, especially in patients with unilateral occlusion of vertebral artery and pedicle deformity of C2.
C2 translaminar screws; Atlantoaxial stabilization; Cervical fusion; Screw fixation; Posterior instrumentation
The management of odontoid fracture has evolved but controversy persists as to the best method for Type II odontoid fractures with or without atlantoaxial (AA) instability. The anterior odontoid screw fixation can be associated with significant morbidity while delayed odontoid screw fixation has shown to be associated with reasonable good fusion rates. We conducted a retrospective analysis to evaluate the outcome of a trial of conservative management in type II odontoid fractures without atlantoaxial instability (Group A) followed by delayed odontoid screw fixation in cases in which fusion was not achieved by conservative treatment. The outcome of type II odontoid fracture with AA subluxation (Group B) was also analysed where closed reduction on traction could be achieved and in those atlantoaxial subluxations that were irreducible an intraoperative reduction was done.
Materials and Methods:
A retrospective evaluation of 53 cases of odontoid fractures treated over a 9-year period is being reported. All odontoid fractures without AA instability (n=29) were initially managed conservatively. Three patients who did not achieve union with conservative management were treated with delayed anterior screw fixation. Twenty-four cases of odontoid fractures were associated with AA instability; 17 of them could be reduced with skeletal traction and were managed with posterior fusion and fixation. Of the seven cases that were irreducible, the initial three cases were treated by odontoid excision followed by posterior fusion and fixation; however, in the later four cases, intra operative reduction was achieved by a manipulation procedure, and posterior fusion and fixation was performed.
Twenty-six of 29 cases of odontoid fracture without AA instability achieved fracture union with conservative management whereas the remaining three patients achieved union following delayed anterior odontoid screw fixation. 17 out of 24 odontoid fracture with atlantoaxial dislocation could be reduced on traction and these patients underwent posterior fusion and fixation. Optimal or near optimal reduction was achieved by on table manipulation in four cases which were irreducible with skeletal traction. Atlantoaxial stability was achieved in all cases. All cases were noted to be stable on evaluation with x-rays at six months.
The initial conservative management and use of odontoid screw fixation only in cases where conservative management for 6–12 weeks has failed to provide fracture union have shown good outcome in type II odontoid fracture without AA instability rates. Intraoperative manipulation and reduction in patients where AA subluxation failed to reduce on skeletal traction followed by posterior fusion obviates the need for transoral odontoid excision.
Atlantoaxial dislocation; cervical spine injuries; odontoid fractures
The objective of this study was to determine atlanto-axial bone morphometric measurements related to screw transarticular fixation technique. One hundred helical computerized tomography (helical CT) scans with volumetric acquisition, including the first and the second cervical vertebrae, were studied. The screw insertion axis according to the Magerl technique for C1–C2 transarticular fixation was the referential to select the correct oblique axial and oblique parasagittal planes obtained with multiplanar reconstruction (MPR) on helical CT. The selected measured parameters on each side of the vertebrae were C2 interarticular isthmus height and width, optimal screw length, optimal screw trajectory sagittal and axial angles, and the distance between the ideal screw trajectory and the vertebral artery groove. C2 interarticular isthmus height measured 7.75±1.27 mm, C2 interarticular isthmus width 7.94±1.72 mm, optimal screw length 39.03±2.81 mm, optimal screw trajectory sagittal angle 57.54±5.28°, optimal screw trajectory medial angle 7.90±4.05°. Isthmus narrowing under 5 mm (height and/or width) was seen in 5% of cases. In 30% of cases reconstructed parasagittal images showed the vertebral artery groove. In those cases, the distance between the vertebral artery groove and the ideal screw path was measured. This distance measured under 2.5 mm in 7% of C2 articular masses. A classification of C2 articular mass morfology was proposed. The C2 articular masses without anatomic variations predisposing to vertebral artery injury were considered type I. The C2 articular masses potentially associated with vascular injury (12%) were classified as type II. Potential risk was identified at the C2 isthmus only (3%), at the anterior portion of C2 articular mass only (7%) or at both regions (2%). According to selected criteria 18% of patients would have at least one side C2 articular mass with potential risk for the vertebral artery. In 6% of patients the potential risk was identified bilaterally. There is a great variation in the maximum and minimum values of the anatomic measurements. Therefore preoperative CT scans are very important to identify type II cases, such that the surgeon may preoperatively define the bony anatomy trough which the screws will pass.
Atlanto-axial joint; Arthrodesis; Helical computed tomography; Uupper cervical spine
This study is an attempt to describe a new technique for anterior transarticular screw fixation of the atlantoaxial joints, and to compare the stability of this construct to posterior transarticular screw fixation with and without laminar cerclage wiring. Nine human cadaveric specimens were included in this study. The C1–C2 motion segment was instrumented using either anterior transarticular screws (group 1), posterior transarticular screws alone (group 2), or posterior screws with interlaminar cerclage wires (group 3). Using an unconstrained mechanical testing machine, the specimens were tested in rotation, lateral bending, and flexion-extension using nondestructive loads of ±2 N m. The specimens were also tested in translation using nondestructive loads of ±100 N. All values for the three groups with regards to anterior-posterior displacement, rotation, and lateral bending were similar as determined using a Kruskal–Wallis rank sum test with a significance level of p<0.05. The only significant difference was registered in flexion-extension where the cerclage wire added some strength to the construct. Anterior transarticular screw fixation of the atlantoaxial spine has several advantages over posterior fixation techniques, and is as stable as posterior transarticular fixation in all clinically significant planes of motion. The addition of posterior interlaminar cerclage wiring further improves resistance to flexion-extension forces. Anterior transarticular screw fixation of the atlantoaxial joint is a useful technique for achieving C1–C2 stabilization.
Atlas; Axis; Fracture; Spinal instability; Transarticular fixation
Posterior instrumentation of the cervical spine has become increasingly popular in recent years. Dissatisfaction with lateral mass fixation, especially at the cervico-thoracic junction, has led spine surgeons to use pedicle screws. The improved biomechanical stability of pedicle screws and transarticular C1/2 screws allows for shorter instrumentations and improves the repositioning possibilities. Nevertheless, there are potential risks of iatrogenic damage to the spinal cord, nerve roots or the vertebral artery with both techniques. Therefore, the aim of this study was to evaluate whether C1/2 transarticular screws and transpedicular screws can be applied safely and with high accuracy in the cervical spine and the cervico-thoracic junction using a computer-assisted surgery system (CAS system). Posterior instrumentation was performed using the Brainlab VectorVision System (BrainLAB , Heimstetten, Germany) in 19 patients. Surface matching was used for registration. We placed 22 transarticular screws C1/2, 31 cervical pedicle screws, 10 high thoracic pedicle screws and one lateral mass screw C1. The screw position was evaluated postoperatively using CT with multiplanar reconstruction in the screw axis of each screw. None of the transarticular screws or pedicle screws was significantly (>2 mm) misplaced and no screw-related injury to vascular, neurogenic or bony structures was observed. No screw revision was necessary. The mean operation time was 144 min (90–240 min) and the mean blood loss was 234 ml (50–800 ml). C1/2 transarticular screws, as well as transpedicular screws in the cervical spine and the cervico-thoracic junction, can be applied safely and with high accuracy using a CAS system. Computer-assisted instrumentation is recommended especially for pedicle screws at C3–C6.
Computer-assisted surgery; Cervical spine; Posterior instrumentation; Pedicle screws; Transarticular screws; In vivo
Our purpose of this study is to compare insertion angles and screw lengths from Roy-Camille, Magerl, and our designed method for cervical lateral mass screw fixation in the Korean population by quantitative measurement of reformatted two dimensional (2D) computed tomography (CT) images.
We selected thirty Korean patients who were evaluated with thin section CT scans and reconstruction program to obtain reformatted 2D-CT images of the transversal plane passing the cranio-caudal angle using three different techniques. We measured the minimum angle to avoid vertebral artery (VA) injury, the ideal angle and depth for bicortical screwing of cervical lateral mass. Morphometric measurements of the lateral masses from C3-C7 were also taken.
In all three techniques, the mean safety angles from the VA were less than 8 degrees and the necessary depth of the screw was about 14 mm for safety to the VA and for the bicortical purchase. In our designed technique, the mean β angles of each level from C3 to C7 were 29.0, 29.8, 29.5, 26.3, and 23.9 degrees, respectively.
Results of this study and data from the literature indicate that differences may exist between the Korean and Western people in the length and angle for ideal lateral mass screw fixation. In addition, our technique needs further cadaveric and clinical study for safety and efficacy for being performed as alternative method for cervical lateral mass fixation.
Cervical vertebrae; Lateral mass screw; Roy-Camille technique; Magerl technique
Transpedicular screws are commonly and successfully used for posterior fixation in spinal instability, but their insertion remains challenging. Even using navigation techniques, there is a misplacement rate of up to 11%. The aim of this study was to assess the accuracy of a novel pedicle screw system.
Thoracic and lumbar fusions were performed on 67 consecutive patients for tumor, trauma, degenerative disease or infection. A total of 326 pedicular screws were placed using a novel wire-guided, cannulated, polyaxial screw system (XIA Precision®, Stryker). The accuracy of placement was assessed postoperatively by CT scan, and the patients were followed-up clinically for a mean of 16 months.
The total medio-caudal pedicle wall perforation rate was 9.2% (30/326). In 19 of these 30 cases a cortical breakthrough of less than 2 mm occurred. The misplacement rate (defined as a perforation of 2 mm or more) was 3.37% (11/326). Three of these 11 screws needed surgical revision due to neurological symptoms or CSF leakage. There have been no screw breakages or dislocations over the follow up-period.
We conclude that the use of this cannulated screw system for the placement of pedicle screws in the thoracic and lumbar spine is accurate and safe. The advantages of this technique include easy handling without a time-consuming set up. Considering the incidence of long-term screw breakage, further investigation with a longer follow-up period is necessary.
spinal instrumentation; pedicle screws; misplacement; pedicle wall perforation
The objective of this study is to investigate the safety, surgical efficacy, and advantages of a polyaxial screw-rod system for posterior occipitocervicothoracic arthrodesis.
Charts and radiographs of 32 patients who underwent posterior cervical fixation between October 2004 and February 2006 were retrospectively reviewed. Posterior cervical polyaxial screw-rod fixation was applied on the cervical spine and/or upper thoracic spine. The surgical indication was fracture or dislocation in 18, C1-2 ligamentous injury with trauma in 5, atlantoaxial instability by rheumatoid arthritis (RA) or diffuse idiopathic skeletal hyperostosis (DISH) in 4, cervical spondylosis with myelopathy in 4, and spinal metastatic tumor in 1. The patients were followed up and evaluated based on their clinical status and radiographs at 1, 3, 6 months and 1 year after surgery.
A total of 189 screws were implanted in 32 patients. Fixation was carried out over an average of 3.3 spinal segment (range, 2 to 7). The mean follow-up interval was 20.2 months. This system allowed for screw placement in the occiput, C1 lateral mass, C2 pars, C3-7 lateral masses, as well as the lower cervical and upper thoracic pedicles. Satisfactory bony fusion and reduction were achieved and confirmed in postoperative flexion-extension lateral radiographs and computed tomography (CT) scans in all cases. Revision surgery was required in two cases due to deep wound infection. One case needed a skin graft due to necrotic change. There was one case of kyphotic change due to adjacent segmental degeneration. There were no other complications, such as cord or vertebral artery injury, cerebrospinal fluid leak, screw malposition or back-out, or implant failure, and there were no cases of postoperative radiculopathy due to foraminal stenosis.
Posterior cervical stabilization with a polyaxial screw-rod system is a safe and reliable technique that appears to offer several advantages over existing methods. Further biomechanical testings and clinical experiences are needed in order to determine the true benefits of this procedure.
Cervical spine; Lateral mass; Polyaxial screw-rod
Various lateral mass screw fixation methods have been described in the literature with various levels of safety in relation to the anterior neurovascular structures. This study was designed to radiologically determine the minimum lateral angulations of the screw to avoid penetration of the vertebral artery canalusing three of the most common techniques: Roy-Camille, An, and Magerl.
Materials and Methods:
Sixty normal cervical CT scans were reviewed. A minimum lateral angulation of a 3.5 mm lateral mass screw which was required to avoid penetration of the vertebral artery canal at each level of vertebra were measured.
The mean lateral angulations of the lateral mass screws (with 95% confidence interval) to avoid vertebral artery canal penetration, in relation to the starting point at the midpoint (Roy-Camille), 1 mm medial (An), and 2 mm medial (Magerl) to the midpoint of lateral mass were 6.8° (range, 6.3–7.4°), 10.3° (range, 9.8–10.8°), and 14.1° (range, 13.6–14.6°) at C3 vertebrae; 6.8° (range, 6.2–7.5°), 10.7° (range, 10.0–11.5°), and 14.1° (range, 13.4–14.8°) at C4 vertebrae; 6.6° (range, 6.0–7.2°), 10.1° (range, 9.3–10.8°), and 13.5° (range, 12.8–14.3°) at C5 vertebrae and 7.6° (range, 6.9–8.3°), 10.9° (range, 10.3–11.6°), and 14.3° (range, 13.7–15.0°) at C6 vertebrae. The recommended lateral angulations for Roy-Camille, Magerl, and An are 10°, 25°,and 30°, respectively. Statistically, there is a higher risk of vertebral foramen violation with the Roy-Camille technique at C3, C4 and C6 levels, P < 0.05.
Magerl and An techniques have a wide margin of safety. Caution should be practised with Roy-Camille's technique at C3, C4, and C6 levels to avoid vertebral vessels injury in Asian population.
Asians; cervical spine; lateral mass screw; angulation
Patients with os odontoideum always present instability in atlantoaxial joint and need atlantoaxial fixation. C2 pedicle or laminar screws fixation has proven to be efficient and reliable for atlantoaxial instability. However, os odontoideum is a congenital or developmental disease, featured with anomalous bony anatomies. The anatomic measurements and guidelines for C2 pedicle screw placement in general population tends to differ with those of os odontoideum patients, for whom C2 pedicle screws are often needed. The option and techniques of C2 fixation are still challenging and yet to be fully explored.
Material and methods
We recruited 29 adult patients with os odontoideum and measured the dimension of C2 pedicle and lamina for each patient to examine how well do they match with the screws anatomically. In order to access the intra-observer reliability and inter-observer repeatability of the measurements, the intraclass correlation coefficient (ICC) was also calculated.
The results for reliability of the CT measurements showed excellent intraobserver (ICC = 0.95 and 0.96) and interobserver correlation coefficient (ICC = 0.93). The diameter and length of C2 pedicle were found to be 6.06 ± 1.37 and 24.05 ± 2.54 mm, while the corresponding figures of C2 laminar were 6.95 ± 0.82 and 25.60 ± 2.18 mm, respectively. In the measurements, all 29 cases had suitable diameter (larger than 5.5 mm) for C2 laminar screw (the laminar diameters ranged from 5.52 to 8.82 mm). In C2 pedicle measurements, the diameters of the 29 cases were from 3.50 to 9.86 mm, while 20 pedicles (34.5%) in 14 cases were less than 5.5 mm in diameter. Six had bilateral small pedicles where the diameter was less than 5.5 mm.
Anatomically, we found laminar screw is a better match in comparison with pedicle screw for C2 fixation in os odontoideum. The options for C2 fixation should be made based on careful preoperative imaging and thorough consideration. Preoperative reconstructive CT scan can offer great assistance for the choice of fixation in os odontoideum by revealing the anatomy of the C2 pedicles in detail.
Os odontoideum pedicle screw; Laminar screw; C2 fixation