Virtual placement of posterior C1-C2 transarticular screw fixation

Improving C1-C2 Complex Fusion Rates: An Alternate Approach

The surgical repair of atlantoaxial instabilities (AAI) presents complex and unique challenges, originating from abnormalities and/or trauma within the junction regions of the C1-C2 atlas-axis, to surgeons. When this region is destabilized, surgical fusion becomes of key importance in order to prevent spinal cord injury. Several techniques can be utilized to provide for the adequate fusion of the atlantoaxial construct. Nevertheless, many individuals have less than ideal rates of fusion, below 35%-40%, which also involves the C2 nerve root being sacrificed. This suboptimal and unavoidable iatrogenic complication results in the elevated probability of complications typically composed of vertebral artery injury. This review is a retrospective analysis of 87 patients from Cedars Sinai Medical Center in Los Angeles, California, who had the C1-C2 surgical fusion procedure performed within the time frame from 2001 to 2008, with a mean follow-up period of three years. These patients had presented with typical AAI symptoms of fatigability, limited mobility, and clumsiness. Diagnosis of C1-C2 instability was documented via radiographic studies, typically utilizing computed tomography (CT) scans or x-rays. All patients had bilateral C1 lateral masses and C2 pedicle screws. In addition, the C1-C2 joint was accessed by retracting the C2 nerve root superiorly and exposing the joint by utilizing a high-speed burr. The cavity that is developed within the joint is packed with local autologous bone from the cephalad resection of the C2 laminae. Fusion of the C1-C2 joint was achieved in all patients and a final follow-up was conducted approximately three years postoperative. Of the 87 patients, two presented with occipital headaches resulting from the C1 screws impinging on the C2 nerve root. The issue was rectified by removing instrumentation in both patients after documenting complete fusion via radiographic studies, with complete resolution of symptoms. No vertebral artery or spinal cord injuries were reported as a result of the minor complication. Overall, we aim to describe a safe and reliable alternative technique to fuse C1-C2 instability by focusing on intra-articular arthrodesis complementing instrumentation fixation. This methodology is advantageous from a biomechanical standpoint secondary to axial loading, as well as the large surface area available for arthrodesis. Additionally, this technique does not involve the resection of the C2 nerve root, resulting in low risk for vertebral artery or spinal cord injury.

Comparison of fusion rates between rod-based laminar claw hook and posterior cervical screw constructs in Type II odontoid fractures

BACKGROUND

This study was aimed (i) to compare the fusion rates of rod-based laminar claw hook constructs to that of posterior C1/C2 screw constructs in odontoid fractures, and (ii) to evaluate any complications associated with claw hook/rod constructs. To our knowledge, no study in contemporary literature has presented the effects of using modern rod-based laminar claw hooks for treating odontoid fractures. Unlike laminar clamps from the 1980s, contemporary laminar hook-rod instrumentation systems provide better immobilisation of the cervical spine and allows for building reliable frame-like constructs similar to cervical screw-rod systems.

METHODS

A retrospective review of a series of 167 consecutive odontoid fractures from a single-institution was conducted. 30 cases from the series were treated using posterior atlantoaxial fusion, 12 using C1/C2 posterior screws (control group), and 18 with rod-based laminar claw hooks (study group). Hooks were mounted bilaterally in a claw manner on each individual lamina and were rigidly fixed to perpendicular rods with a transverse connector whenever feasible. The minimum follow-up period was one year. Bony union was determined using computed tomography (CT) scan, while stability at the fusion site was assessed using dynamic radiograms.

RESULTS

The study group had an overall fusion rate of 89% (non-geriatric 93% while geriatric subgroup 75%) with a 100% stability rate at the fusion site in all cases. In the control group fusion rate was 100%. There were no major complications in both control and study groups. Four minor complications, three in the control and one in the study group, were noted in 3 patients.

CONCLUSION

Preliminary results of this study suggest that laminar claw hook-rod systems are useful alternatives to posterior screw techniques. Moreover, the fusion rate in non-geriatric patients is comparable to that of posterior screws. Importantly, they are devoid of the disadvantages and complications posed by screw constructs. Further studies are necessary to confirm these promising results.

Anterior pedicle screw fixation of C2: an anatomic analysis of axis morphology and simulated surgical fixation

STUDY DESIGN

Human cadaveric study measuring the morphology of C2 vertebra, description of anterior placement of pedicle screw with post-fixation computed tomography (CT) analysis.

OBJECTIVE

To assess the potential feasibility and safety anterior placement of C2 pedicle screws.

SUMMARY OF BACKGROUND DATA

Posterior pedicle screw fixation has become an established technique for upper cervical reconstruction. To our knowledge few reports in the previous literature have described the placement of or anatomy related to anteriorly approach C2 pedicle screws.

METHODS

The morphology of 60 human C2 vertebrae was measured directly to assess the size, position, and relative approach angle of the pedicles from an anterior perspective. In an additional 20 cadaveric cervical spines, bilateral 3.5 mm titanium C2 pedicle screws were placed and analyzed for pedicle morphology and placement accuracy with thin cut, 1 mm axial CT.

RESULTS

The mean C2 pedicle width measured directly and by CT scan was 7.8 and 6.6 mm, and the average length of the right and left pedicle was 26.4 and 25 mm, respectively. The mean transverse angle (α) was 17.6° and 21.4°, whereas declination angle (β) anterior to posterior was 13.8° and 10.6°, respectively.

CONCLUSIONS

Quantitative data regarding C2 pedicle shape and location with respect to the anterior placement of pedicle screws have not been previously reported. This study indicates that anterior placement of 3.5 mm C2 pedicle screws through a transoral approach may be both feasible and safe and also provides an important anatomic analysis that may guide clinical application.

C1-C2 posterior fixation: are 4 screws better than 2?

BACKGROUND

Several types of C1-C2 fixation techniques have been described over the years in order to treat atlantoaxial instability.

OBJECTIVE

To compare the pros and cons of the most popular C1-C2 posterior fixation used today: C1 lateral mass-C2 pedicle screw and rods (Harms) and transarticular screw (Magerl) fixations.

METHODS

Retrospective review of 122 patients who underwent Harms or Magerl fixation for atlantoaxial instability. Surgical, clinical, and radiological outcomes were compared in the 2 groups.

RESULTS

123 operations were performed, of which 47 were by the Harms technique (group H) and 76 by the Magerl technique (group M). No significant differences were found in duration of surgery, blood loss, postoperative pain, and length of hospitalization. Postoperatively, neck pain, C2-radiculopathy, and hand function improved in both groups, with better, but not statistically significant, results for group H. The intraoperative complication rate was 2.1% in group H and 21% in group M (P < .05); postoperative complication rate was 10.6% in group H and 21% in group M (P > .05). The major complications were vertebral artery injury (2.1% in group H, 13.1% in group M, P = .05) and screw fracture (2.1% in group H, 9.2% in group M, P > .05). Fusion rate at the end of follow-up was not significantly higher in group H. C1-C2 range of movements in flexion/extension at the end of follow-up was lower in group H (P = .017).

CONCLUSION

Magerl with posterior wiring and Harms techniques are both effective options for stabilizing the atlantoaxial complex. However, the Harms technique appears to be safer, to have fewer complications, and to demonstrate a more robust long-term fixation.

Treatment algorithm for dens fractures: non-halo immobilization, anterior screw fixation, or posterior transarticular C1-C2 fixation

BACKGROUND

The appropriate treatment of dens fractures is unclear. We established a staged treatment protocol for dens fractures and conducted a prospective study to evaluate the outcome of treatment based on this protocol.

METHODS

We prospectively evaluated sixty-nine consecutive patients who presented to our institution with a dens fracture. The mean duration of follow-up was 9.7 months (range, six to fifty-eight months). Fractures were categorized as stable or unstable. Stable fractures were treated by immobilization in a rigid collar. Patients seventy-five years or older with unstable fractures, patients with a neurological deficit, and patients with Anderson and D'Alonzo type-III fractures underwent posterior transarticular C1-C2 stabilization. Unstable fractures in patients younger than seventy-five years were stabilized with direct anterior screw fixation. Thirty-one patients were treated with a Philadelphia collar, twenty-five with posterior transarticular fixation, and thirteen with direct anterior screw fixation.

RESULTS

Fracture-healing or solid fusion of C1-C2 was documented in sixty-eight of sixty-nine treated patients at final follow-up. The remaining patient had a stable nonunion of the dens. Secondary procedures were performed in five patients.

CONCLUSIONS

Our treatment algorithm based on dens fracture type, fracture stability, and patient age was associated with a high success rate. Evaluating fracture stability is crucial when considering nonoperative treatment. External stabilization with a rigid cervical collar was adequate for stable fractures of the dens and was associated with a high healing rate. Posterior transarticular screw fixation of C1-C2 was associated with a high success rate, including in elderly patients.

LEVEL OF EVIDENCE

Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Biomechanical investigation of a novel integrated device for intra-articular stabilization of the C1-C2 (atlantoaxial) joint

BACKGROUND CONTEXT

The anatomy of the atlantoaxial joint makes stabilization at this level challenging. Current techniques that use transarticular screw fixation (Magerl) or segmental screw fixation (Harms) give dramatically improved stability but risk damage to the vertebral artery. A novel integrated device was designed and developed to obtain intra-articular stabilization via primary interference fixation within the C1-C2 lateral mass articulation.

PURPOSE

To assess the atlantoaxial stability achieved with a novel integrated device when compared with the intact, destabilized, and stabilized state using the Harms technique.

STUDY DESIGN

A biomechanical study of implants in human cadaveric cervical spines.

METHODS

Six human cadaveric specimens were used. Biomechanical testing was performed with moment control in flexion-extension, lateral bending, and axial rotation. Range of motion (ROM) was measured in the intact state, after both destabilization by creation of a Type II odontoid peg fracture and sequential stabilization using the integrated device and the Harms technique.

RESULTS

Mean flexion-extension ROM of the intact specimens at C1-C2 was 14.1°±2.9°. Destabilization increased the ROM to 31.6°±4.6°. Instrumentation with the Harms technique reduced flexion-extension motion to 4.0°±1.4° (p<.01). The integrated device reduced flexion-extension motion to 3.6°±1.8° (p<.01). In lateral bending, the respective mean angular motions were 1.8°±1.1°, 14.1°±5.8°, 1.4°±0.7°, and 0.4°±0.3° for the intact destabilized Harms technique and integrated device. For axial rotation, the respective mean values were 67.3°±13.8°, 74.2°±16.1°, 1.4°±0.7° and 0.9°±0.7°. Both the Harms technique and integrated device significantly reduced motion compared with the destabilized spine in flexion-extension, lateral bending, and axial rotation (p<.05). Direct comparison of the Harms technique and the integrated device revealed no significant difference (p>.10).

CONCLUSIONS

The integrated device resulted in interference fixation at the C1-C2 lateral mass joints with comparable stability to the Harms technique. Perceived advantages with the integrated device include avoidance of fixation below the C2 lateral mass where the vertebral artery is susceptible to injury, and access to the C1 screw entry point through the blade of the integrated device avoiding extended dissection superior to the C2 nerve root and its surrounding venous plexus.

A novel patient-specific navigational template for cervical pedicle screw placement

STUDY DESIGN.: Prospective trial. OBJECTIVE.: To develop and validate a novel, patient-specific navigational template for cervical pedicle placement. SUMMARY OF BACKGROUND DATA.: Owing to the narrow bony anatomy and the proximity to the vertebral artery and the spinal cord, cervical instrumentation procedures demand the need for a precise technique for screw placement. PATIENT.: Specific drill template with preplanned trajectory has been thought as a promising solution for cervical pedicle screw placement. METHODS.: Patients with cervical spinal pathology (n = 25) requiring instrumentation were recruited. Volumetric CT scan was performed on each desired cervical vertebra and a 3-dimensional reconstruction model was generated from the scan data. Using reverse engineering technique, the optimal screw size and orientation were determined and a drill template was designed with a surface that is the inverse of the posterior vertebral surface. The drill template and its corresponding vertebra were manufactured using rapid prototyping technique and tested for violations. The navigational template was sterilized and used intraoperatively to assist with the placement of cervical screws. In total, 88 screws were inserted into levels C2-C7 with 2 to 6 screw in each patient. After surgery, the positions of the pedicle screws were evaluated using CT scan and graded for validation. RESULTS.: This method showed its ability to customize the placement and the size of each screw based on the unique morphology of the cervical vertebra. In all the cases, it was relatively very easy to manually place the drill template on the lamina of the vertebral body during the surgery. The required time between fixation of the template to the lamina and insertion of the pedicle screws was about 80 seconds. Of the 88 screws, 71 screws had no deviation and 14 screws had deviation <2 mm, 1 screw had a deviation between 2 to 4 mm and there were no misplacements. Fluoroscopy was used only once for every patient after the insertion of all the pedicle screws. CONCLUSION.: The authors have developed a novel patient-specific navigational template for cervical pedicle screw placement with good applicability and high accuracy. This method significantly reduces the operation time and radiation exposure for the members of the surgical team. The potential use of such a navigational template to insert cervical pedicle screws is promising. This technique has been clinically validated to provide an accurate trajectory for pedicle screw placement in the cervical spine.

Radiographic and clinical evaluation of free-hand placement of C-2 pedicle screws

Object

Stabilization of the cervical spine can be challenging when instrumentation involves the axis. Fixation with C1–2 transarticular screws combined with posterior wiring and bone graft placement has yielded excellent fusion rates, but the technique is technically demanding and places the vertebral arteries (VAs) at risk. Placement of screws in the pars interarticularis of C-2 as described by Harms and Melcher has allowed rigid fixation with greater ease and theoretically decreases the risk to the VA. However, fluoroscopy is suggested to avoid penetration laterally, medially, and superiorly to avoid damage to the VA, spinal cord, and C1–2 joint, respectively. The authors describe how, after meticulous dissection of the C-2 pars interarticularis, such screws can be placed accurately and safely without the use of fluoroscopy.

Methods

Prospective follow-up was performed in 55 consecutive patients who underwent instrumented fusion of C-2 by a single surgeon. The causes of spinal instability and type and extent of instrumentation were documented. All patients underwent preoperative CT or MR imaging scans to determine the suitability of C-2 screw placement. Intraoperatively, screws were placed following dissection of the posterior pars interarticularis. Postoperative CT scans were performed to determine the extent of cortical breach. Patients underwent clinical follow-up, and complications were recorded as vascular or neurological. A CT-based grading system was created to characterize such breaches objectively by location and magnitude via percentage of screw diameter beyond the cortical edge (0 = none; I = < 25% of screw diameter; II = 26–50%; III = 51–75%; IV = 76–100%).

Results

One-hundred consecutive screws were placed in the pedicle of the axis by a single surgeon using external landmarks only. In 10 cases, only 1 screw was placed because of a preexisting VA anatomy or bone abnormality noted preoperatively. In no case was screw placement aborted because of complications noted during drilling. Early complications occurred in 2 patients and were limited to 1 wound infection and 1 transient C-2 radiculopathy. There were 15 total breaches (15%), 2 of which occurred in the same patient. Twelve breaches were lateral (80%), and 3 were superior (20%). There were no medial breaches. The magnitude of the breach was classified as I in 10 cases (66.7% of breaches), II in 3 cases (20% of breaches), III in 1 case (6.7%), and IV in 1 case (6.7%).

Conclusions

Free-hand placement of screws in the C-2 pedicle can be done safely and effectively without the use of intraoperative fluoroscopy or navigation when the pars interarticularis/pedicle is assessed preoperatively with CT or MR imaging and found to be suitable for screw placement. When breaches do occur, they are overwhelmingly lateral in location, breach < 50% of the screw diameter, and in the authors' experience, are not clinically significant.

Unilateral posterior atlantoaxial transarticular screw fixation in patients with atlantoaxial instability : comparison with bilateral method

OBJECTIVE

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.

METHODS

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.

RESULTS

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).

CONCLUSION

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.

Computer-assisted surgical planning and image-guided surgical navigation in refractory adult scoliosis surgery: case report and review of the literature

STUDY DESIGN

Case report and literature review.

OBJECTIVE

In this case report, we present the utility of computer-assisted surgical planning and image-guided surgical navigation in the planning and execution of a major osteotomy to correct severe kyphoscoliosis.

SUMMARY OF BACKGROUND DATA

Computer-assisted surgical planning is useful to appreciate the three-dimensional nature of scoliotic deformities and allows for operative maneuvers to be simulated on a computer before their implementation in the operating room. Image-guided surgical navigation improves surgical accuracy and can help translate a virtual surgical plan to the operative setting.

METHODS

We report the case of a 38-year-old woman with severe, congenital kyphoscoliosis refractory to many previous surgeries, who presents with moderate progressive myelopathy and severe pain attributable to a sharp angular deformity at T12. Three-dimensional computed tomography reconstruction and computer-assisted surgical planning were used to determine the optimal corrective osteotomy. The surgical plan was translated to the operating room where a posterior vertebrectomy and instrumented correction were executed with the aid of image-guided surgical navigation.

RESULTS

The osteotomy was safely performed resulting in improved sagittal and coronal alignments, as well as, correction of the sharp kyphoscoliotic deformity at the thoracolumbar junction. At 6-month follow-up, the patient's myelopathy and pain had largely resolved and she expressed high satisfaction with the procedure.

CONCLUSION

We advocate this novel application of virtual surgical planning and intraoperative surgical navigation to improve the safety and efficacy of complex spinal deformity corrections.

Laminar screw fixation of the axis

Object

Laminar fixation of the axis with crossing bilateral screws has been shown to provide rigid fixation with a theoretically decreased risk of vertebral artery damage compared with C1–2 transarticular screw fixation and C-2 pedicle screw fixation. Some studies, however, have shown restricted rigidity of such screws compared with C-2 pedicle screws, and others note that anatomical variability exists within the posterior elements of the axis that may have an impact on successful placement. To elucidate the clinical impact of such screws, the authors report their experience in placing C-2 laminar screws in adult patients over a 2-year period, with emphasis on clinical outcome and technical placement.

Methods

Sixteen adult patients with cervical instability underwent posterior cervical and cervicothoracic fusion procedures at our institution with constructs involving C-2 laminar screws. Eleven patients were men and 5 were women, and they ranged in age from 28 to 84 years (mean 57 years). The reasons for fusion were degenerative disease (9 patients) and treatment of trauma (7 patients). In 14 patients (87.5%) standard translaminar screws were placed, and in 2 (12.5%) an ipsilateral trajectory was used. All patients underwent preoperative radiological evaluation of the cervical spine, including computed tomography scanning with multiplanar reconstruction to assess the posterior anatomy of C-2. Anatomical restrictions for placement of standard translaminar screws included a deeply furrowed spinous process and/or an underdeveloped midline posterior ring of the axis. In these cases, screws were placed into the corresponding lamina from the ipsilateral side, allowing bilateral screws to be oriented in a more parallel, as opposed to perpendicular, plane. All patients were followed for > 2 years to record rates of fusion, instrumentation failure, and other complications.

Results

Thirty-two screws were placed without neurological or vascular complications. The mean follow-up duration was 27.3 months. Complications included 2 revisions, one for pseudarthrosis and the other for screw pullout, and 3 postoperative infections.

Conclusions

Placement of laminar screws into the axis from the standard crossing approach or via an ipsilateral trajectory may allow a safe, effective, and durable means of including the axis in posterior cervical and cervicothoracic fusion procedures.