Surgical management of atlantoaxial nonunions

Direct osteosynthesis in the treatment of atlas burst fractures: a systematic review

PURPOSE

The treatment of unstable atlas fractures remains a controversial topic. The study aims at assessing the prognosis and efficacy of osteosynthesis for unstable atlas fractures through a review of the current literature and additionally aims to compare outcomes between the transoral and posterior approaches.

METHODS

A systematic review of databases including PubMed, EMBASE, Cochrane, Web of Science, CNKI, and Wanfang was conducted. Titles and abstracts were screened by two reviewers to identify studies meeting pre-defined inclusion criteria for comprehensive analysis.

RESULTS

The systematic review included 28 articles, 19 employing the posterior approach and 9 utilizing the transoral approach. It covered osteosynthesis in 297 patients with unstable atlas fractures, comprising 169 treated via the posterior approach and 128 via the transoral approach. Analysis revealed high healing rates and clinical improvement in both approaches, evidenced by improvements in the visual analog scale, range of motion, atlantodens interval, and lateral displacement distance post-surgery.

CONCLUSION

Osteosynthesis offers effective treatment for unstable atlas fractures. Both transoral and posterior approaches can achieve good clinical outcomes for fracture, and biomechanical studies have confirmed that osteosynthesis can maintain the stability of the occipitocervical region, preserve the motor function of the atlantoaxial and occipito-atlantoaxial joints, and greatly improve the quality of life of patients. However, variations exist in the indications and surgical risks associated with each method, necessitating their selection based on a thorough clinical evaluation of the patient's condition.

Safety and Feasibility of DTRAX Cervical Cages in the Atlantoaxial Joint for C1/2 Stabilization

BACKGROUND

Pathological changes in the atlantoaxial joint often lead to instability, pain, and neurological deterioration. One treatment option is the surgical stabilization of the atlantoaxial joint. In other areas of the spine, fusion rates have been improved by the introduction of an interbody cage. Our aim was to use cervical interbody spacers, originally designed to augment fusion across subaxial posterior cervical facets, to optimize the conditions for atlantoaxial fusion.

OBJECTIVE

To evaluate the safety and efficacy of implanting cervical cages in the atlantoaxial joint for C1/2 stabilization.

METHODS

Our retrospective study evaluated patients who had undergone C1/2 cervical fusions by the Harms/Goel technique. This technique was modified by implanting a titanium cervical interbody spacer into the joint space. Mean overall pain, as measured by a 0 to 10 visual analog scale (VAS) and neurological outcomes were measured preoperatively and postoperatively. In addition, radiological outcomes were collected using follow-up imaging.

RESULTS

Nine patients were included in this case series. The mean preoperative VAS for overall pain was 5.0 ± 4.0, which changed to a mean VAS of 2.0 ± 3.0 after an average follow-up period of 41.4 ± 20.4 (P = .043). All patients showed a bony fusion in our case series. None of the radiological imaging during follow-up showed screw loosening, hardware breakage, implant migration, or nonunion.

CONCLUSION

The implantation of cervical titanium cages into the atlantoaxial joint in combination with posterior fixation appears to be a safe and effective method for achieving C1/2 fusion.

[Progress in treatment of unstable atlas fracture]

OBJECTIVE

To summarize the progress in treatment of unstable atlas fracture, the existing problems, and the research direction.

METHODS

Related literature at home and abroad was reviewed. The stability evaluation of atlas fracture and treatment methods were introduced, and the selection of surgical approach and fixation instruments in treatment of unstable atlas fracture were summarized and analyzed.

RESULTS

At present, atlas fractures are considered as unstable fractures except single anterior arch fractures with complete transverse ligament or simple posterior arch fractures. The treatment of unstable atlas fracture has been developed from nonsurgical treatment and traditional fusion surgery to single-segment fixation. Nonsurgical treatment is less effective, while traditional fusion surgery has a disadvantage of limited the motion of the upper cervical spine. Single-segment fixation can not only restore and fix the fracture, but also preserve the upper cervical motion function. Single-segment fixation approaches include posterior and transoral approaches, and the fixation instruments are being constantly improved, mainly including screw-rod system, screw-plate system, and plate system.

CONCLUSION

For unstable atlas fracture, single-segment fixation is an ideal surgical method, and has more advantages when compared with nonsurgical treatment and traditional fusion surgery. Single-segment fixation via transoral approach is more direct for atlas anterior arch fracture reduction, but there is a high risk of infection; and single-segment fixation via posterior approach is less effective for the reduction of atlas anterior arch fracture. Therefore, a better reduction method should be explored.

Computed Tomography-Based Feasibility Study of C1 Posterior Arch Crisscrossing Screw Fixation

Study Design

Retrospective radiographic analysis.

Purpose

Posterior fixation of C1 using screws is the most popular technique among the various methods for C1 stabilization, but it places the surrounding neurovascular structures at risk. Approximately 20% of the population has an anomalous groove for the vertebral artery; therefore, salvage methods are necessary. Therefore, we analyzed the feasibility of a newer C1 posterior arch crisscrossing screw fixation technique and studied its feasibility in the Indian population on the basis of the anatomy of the C1 posterior arch.

Overview of Literature

Multiple techniques have been described for C1–C2 fixation, such as wiring techniques, interlaminar clamps, transarticular screws, screw-plate/screw-rod system fixation, and hook-screw system fixation techniques, to provide rigid C1–C2 stability. However, although C1 fixation has evolved with time, it is not complication-free.

Methods

A 100 computed tomography (CT) scans of cervical spines with 1 mm slice thickness in the axial and sagittal sections obtained were randomly selected for the evaluation. Atlantoaxial anomalies due to trauma, deformities, infections, and tumors were excluded. All the images were measured for height of the posterior tubercle, width of the posterior arch, and length of the screw, and the screw projection angle was calculated. Demographic data were collected for all the subjects.

Results

Out of the 88 CT scans analyzed, the mean height of the posterior tubercle was 7.4 mm, wherein 84.09% exceeded 7 mm, and the width of the posterior tubercle was 5.4 mm, wherein 88.6% (n=78) had posterior arch width >3.5 mm. A total of 13.6% (n=12) vertebrae were not suitable for screw placement, whereas 75% (n=66) vertebrae could accommodate 3.5×15 mm or longer screws. The screw projection angles ranged from 11.2° to 35° on the right and from 15.6° to 38.2° on the left.

Conclusions

C1 posterior arch screw fixation is a feasible and safe method because it poses little risk of injury to the surrounding neurovascular structures.

Management and Outcome of Dens Fracture Nonunions in Geriatric Patients

BACKGROUND

Dens fractures are known to have high rates of pseudarthrosis. The aim of this study was to define clinical and radiographic long-term outcomes, specifically in relation to osseous union, cervical spine movement, neurological sequelae, and quality of life, in a geriatric cohort (sixty-five years of age or older) treated operatively or nonoperatively for a dens fracture nonunion.

METHODS

Forty-four patients (twenty-eight women and sixteen men; average age, seventy-two years) met the inclusion criteria and were enrolled in this study. Sixteen patients (36%) underwent operative stabilization with posterior cervical arthrodesis, and twenty-eight (64%) were treated nonoperatively with a predefined protocol. All patients had a post-treatment follow-up period of at least five years.

RESULTS

Radiographic evaluation showed osseous union at the site of the C1-C2 arthrodesis in all sixteen patients who had undergone surgical treatment. Clinical follow-up revealed that fourteen had satisfactory results following postoperative rehabilitation. In contrast, radiographic evaluation of the twenty-eight nonoperatively treated patients showed persistence of the pseudarthrosis of the dens in twenty-six and osseous union of the dens in two. All twenty-eight patients (100%) had a satisfactory clinical outcome.

CONCLUSIONS

C1-C2 arthrodesis was a reliable treatment option for dens fracture nonunions that were unstable, those associated with neurological symptoms, and those causing persistent pain. Clinical and radiographic monitoring was an acceptable nonoperative treatment option but was associated with a very low rate of osseous union of the dens.

Treatment of craniocervical instability using a posterior-only approach

The object of this study was to demonstrate that a posterior-only approach for craniocervical junction pathology is feasible with intraoperative reduction. The authors reviewed 3 cases of craniocervical instability. All patients had craniocervical instability according to radiological imaging and various methods of measurement, with results outside the normal range. Posterior instrumentation aided the intraoperative reduction techniques while maintaining structural integrity and the desired fusion construct. No anterior approach was necessary in any of the patients. Neurological symptoms resolved in two patients and significantly improved in another. Follow-up imaging demonstrated stable constructs.

There are many approaches to anterior cervical pathology at the craniocervical junction. Posterior instrumented reduction and stabilization of the occipitocervical spine can be safely achieved, obviating the need for a transoral approach in the setting of craniocervical junction settling.

C1 posterior arch crossing screw fixation for atlantoaxial joint instability

STUDY DESIGN

Anatomical measurements and in vitro biomechanical testing were performed to evaluate a new method for posterior C1 fixation.

OBJECTIVE

This study sought to assess C1 posterior arch crossing screw fixation for posterior C1-C2 fixation, using anatomical measurements and biomechanical testing with traditional C1 pedicle screws (PS) in a cadaveric model.

SUMMARY OF BACKGROUND DATA

Atlantoaxial instability often requires surgery, and the current methods for atlas fixation incur some risk to the vascular and neurological tissues. Thus, new, effective, and safe methods are needed for salvage operations.

METHODS

Morphometric analysis of the C1 posterior arch was performed using 3-dimensional computed tomography. Six fresh ligamentous human cervical spines (C0-C4) were evaluated for their biomechanics. The specimens were tested in their intact condition and after stabilization (C1-C2 PS, C1 posterior arch screws [PAS] with C2 PS) and injury due to 1.5 N·m of pure moment in flexion, extension, lateral bending, and axial rotation. During testing, 3-dimensional angular motion was measured with a motion capture platform (Vicon Nexus). Data for all scenarios were recorded, and statistical analysis was performed.

RESULTS

Anatomical assessment indicated that 91.51% of C1 posterior tubercles exceeded 7 mm in thickness, 93.40% had a width of the posterior arch of greater than 3.5 mm, and 65.57% had a unilateral screw length of greater than 15 mm, indicating that the posterior arch fixation could be achieved by two 3.5 × 15-mm screws placed in a crossed manner. Twenty-two cases (11%) were not suitable for crossing screw placement because the posterior arch was flat and the entry point was present on the same side. Biomechanical testing showed that the PS and PAS rod-screw systems significantly reduced flexibility in flexion, extension, and rotation compared with the intact position. For lateral bending, there was a trend for the C1 PS and PAS systems toward decreased flexibility in comparison with the intact position. At the same time, C1 PAS decreased C1-C2 movement by 33.0% in left bending (P = 0.171) and 24.4% in right bending (P = 0.095); however, no significant difference was observed for left bending with C1 PAS compared with C1 PS, and the C1 PS and PAS systems significantly reduced the flexibility more than destabilization.

CONCLUSION

Crossing screw fixation of the C1 posterior arch is straightforward and imposes little risk of injury to the neural and vascular structures as long as the implants remain intraosseous. According to the results of our anatomical and biomechanical study, C1 posterior arch crossing screw fixation may constitute an alternative method for posterior atlantoaxial fixation.

LEVEL OF EVIDENCE

3.

Upper cervical spine injuries: a management of a series of 70 cases

Traumatic injuries of the upper cervical spine are often encountered, and may be associated to severe neurological outcome. This is a retrospective study of 70 patients, admitted over a 14 years period (1996 to 2010), for management of upper cervical spine injuries. Data concerning epidemiology, radiopathology and treatment was reviewed, and clinical and radiological evaluation was conducted. Men are more affected than women, with traffic accidents being the major traumatic cause. A cervical spine syndrome of varied intensity was found in about 90% of patients; neurological deficit was noted in 10 patients (21%). Radiological analysis discovered varied and many combined lesions: C1-C2 dislocation (7 cases), C2-C3 dislocation (9 cases), C1 fracture (10 cases) and C2 fracture (44 cases) including 28 odontoid fractures. Orthopedic treatment was carried out exclusively for 31 patients, and surgical treatment for 38 patients. One patient died before surgery because of a polytraumatisme. Posterior approach was performed in 29 cases including hooks and rods in 18 patients, wiring in 9 cases, and 2 transarticular screw fixations. In 9 cases anterior approach was performed: 5 odontoid screwing and 4 cases of C2-C3 discectomy with bone graft. Nearly all patients were improved in post-operative. Elsewhere, the operating results were marked by a persistent neurological deficit in 2 cases, and infection in 2 cases controlled by medical treatment. Mean follow-up was 23 months and showed good clinical and radiological improvement. Early management of cervical spine injuries can optimize outcome. Treatment modalities are well codified; however controversy remains especially with type II odontoid fractures.

C1-C2 posterior fixation: indications, technique, and results

The atlantoaxial motion segment, which is responsible for half of the rotational motion in the cervical spine, is a complex junction of the first (C1) and second (C2) cervical vertebrae. Destabilization of this joint is multifactorial and can lead to pathologic motion with neurologic sequelae. Posterior spinal fixation of the C1-C2 articulation in the presence of instability has been well described in the literature. Early reports of interspinous/interlaminar wiring have evolved into modern-day pedicle screw/translaminar constructs, with excellent results. The success of a C1-C2 posterior fusion rests on appropriate indications and surgical techniques.

Clinical outcome of posterior fixation of the C1 lateral mass and C2 pedicle by polyaxial screw and rod

OBJECTIVE

Because of atlantoaxial complex has a unique and complicated anatomy and instability of this complex is very dangerous. We investigated the clinical results of posterior C1-C2 fixation with a polyaxial screw-rod system.

METHODS

Between July 2001 and December 2007, the authors treated 17 patients suffering from atlantoaxial deformity and instability. Atlantoaxial fusion was employed in 9 patients with upper cervical fracture and dislocation, in 6 patients with atlantoaxial subluxation, in 1 patient with pure transverse ligament injury, and in 1 patient with basilar invagination. The mean age at the time of surgery was 40.4 years (range, 15-68 years).

RESULTS

Operative times ranged from 165 to 420 min (average 306 min), and the postoperative mean VAS score was 2.4. The mean follow-up period was 26 months. Solid fusion was achieved in 15 patients at the last follow up; no injury of the vertebral artery or spinal cord and no operative mortality occurred in these cases.

CONCLUSIONS

We suggest that posterior atlantoaxial fixation using the polyaxial screw-rod system is an effective and relatively safe technique. The navigation guidance system employed during the surgical procedure was helpful methods. Future studies of the feasibility of navigation system-guided surgical procedures will be required.

Combination of skull traction with posterior C1-2 fusion for old C1-2 dislocations

Between January 2003 and December 2009, 23 patients who had suffered old C1-2 dislocations, were surgically treated in our orthopedics department. Fifteen patients underwent direct posterior C1-2 fusion following pre-operative reduction by skull traction. In eight patients, reduction was achieved only by skull traction under general anesthesia, facilitated by manual hyperextension of the cervical spine and maintained by simultaneous posterior C1-2 fusion. Intra-operative traction was monitored using C-arm fluoroscopy and cortical somatosensory-evoked potentials. Posterior C1-2 fixation was achieved in nine patients using C1-2 laminar hooks and in 14 patients using C1 laminar hooks with C2 pedicle screws. During the follow-up of 5 to 72 months (mean: 42.8 months), solid bony fusion was accomplished in all patients. Using Di Lorenzo's grades and Japanese Orthopedics Association scores, there was significant improvement (p<0.05). The cervical medullary angle exhibited a significant improvement of 31.7°, from 121.6° to 153.3° (p<0.05). There were no complications, including dural tears, spinal cord damage, vertebral artery damage, or breakage or loosening of implants.

Bilateral atlantoaxial transarticular screws and atlas laminar hooks fixation for pediatric atlantoaxial instability

STUDY DESIGN

An atlantoaxial fixation using bilateral C1-C2 transarticular screws and C1 laminar hooks was used in 5 pediatric patients, who were then followed up for 12 to 17 months to evaluate the technique.

OBJECTIVE

To describe a modified posterior C1-C2 fixation technique and preliminary clinical and radiographic results in 5 pediatric patients.

SUMMARY OF BACKGROUND DATA

Conventional posterior atlantoaxial fixations, such as Gallie and Brooks techniques, are frequently associated with high rates of pseudarthrosis and implant failure. The C1-C2 transarticular screw fixation has been shown to be effective in treatment of pediatric atlantoaxial instability, as well as adult atlantoaxial instability; however, this 2-point fixation merely stabilizes the atlantoaxial motion segment laterally. A 3-point fixation, composed with bilateral C1-C2 transarticular screws and C1 laminar hooks, has been developed.

METHODS

Five patients with atlantoaxial instability, including 4 males and 1 female, aged 6 to 17 (average 10) years, underwent atlantoaxial fixation using bilateral C1-C2 transarticular screws and C1 laminar hooks during a 2-year period. The surgical technique and treatment procedures were intensively reviewed, and clinical symptoms and imaging appearance were retrospectively evaluated.

RESULTS

Clinical follow-ups were obtained for an average of 14.4 (range: 12-17) months. The clinical and radiologic follow-up indicated a stable arthrodesis and offered clinical relief from symptoms for all patients. No neural or vascular impairment related to this technique was observed.

CONCLUSION

Fixation of the atlantoaxial articulation using bilateral C1-C2 transarticular screws and C1 laminar hooks appears to be a reliable technique for treatment of pediatric atlantoaxial instability.

C1 lateral mass screw insertion with protection of C1-C2 venous sinus: technical note and review of the literature

STUDY DESIGN

This is a technical note and review of the literature.

OBJECTIVE

We propose to describe a revised surgical technique of C1 lateral mass screw insertion with protection of C1-C2 venous sinus surrounding the C2 nerve root.

SUMMARY OF BACKGROUND DATA

During C1 lateral mass screw insertion and in posterior C1-C2 fixation, iatrogenic injury of C1-C2 venous sinus results in bleeding, which is troublesome. Appropriate management of the venous sinus in this region is critical to successful surgery in this complex anatomic region.

METHODS

We reviewed 48 patients who underwent posterior C1-C2 fixation at our institution between September 2001 and October 2008. Twenty-four atlas screws were inserted by the originally described C1 lateral mass screw technique (group A), and 28 through a revised posterior arch and lateral mass screw technique (C1 transpedicular screw) (group B). The final group of 44 atlas screws was placed with our newly revised technique (group C).

RESULTS

Bleeding of venous sinus was encountered in 3 group A, 2 group B, and 1 group C atlas screw insertions. The incidence rate was 12.50% (A), 7.14% (B), and 2.27% (C). Statistical comparison showed no significant difference between the groups. All the cases were followed for a mean period of 28.1 month. Four patients in group A complained of postoperative numbness in occipitocervical region. No patients in group B or group C voiced this complaint. A high fusion rate was found in all 3 groups with no signs of implant failure.

CONCLUSION

Bleeding of C1-C2 venous sinus is vigorous and frustrating. The revised technique we describe provides theoretical and practical protection of venous sinus. In addition, the firm bony purchase of screws afforded by this technique contributes to achieving stabilization of the upper cervical spine and a high fusion rate.

Biomechanical evaluation of an atlantoaxial lateral mass fusion cage with C1-C2 pedicle fixation

STUDY DESIGN

A biomechanical testing protocol was used to evaluate atlantoaxial fixation techniques in a human cadaveric model.

OBJECTIVE

To compare in vitro biomechanics of atlantoaxial lateral mass fusion cage combined with C1-C2 pedicle screw technique with those of C1-C2 pedicle screw technique alone and C1-C2 transarticular screws combined with Gallie wires.

SUMMARY OF BACKGROUND DATA

An atlantoaxial lateral mass fusion cage was designed, knowing that the cage, when rigidly combined with C1-C2 pedicle screws, could offer other fusion spots for atlantoaxial stabilization in cases when the posterior arch of the atlas is absent or removed for decompression and a Gallie fixation is impossible. No comparative in vitro biomechanical test has been conducted previously to evaluate the feasibility of this method.

METHODS

Anatomic measurements of the atlantoaxial lateral masses were taken using computed tomography in normal human subjects. Six fresh-frozen human cadaveric cervical spines (C0-C4) were used in the biomechanical study. Specimens were tested in their intact condition, after destabilization via transverse-alar-apical ligament disruption, and after implantation of 3 fixation constructs: (1) transarticular screws combined with Gallie wires, (2) C1-C2 pedicle screws, and (3) atlantoaxial lateral mass fusion cage combined with C1-C2 pedicle screws. Pure moment loading up to 1.5 Nm in flexion/extension, right-left lateral bending, and right-left axial rotation was applied to the occiput, and relative intervertebral rotations were determined using stereophotogrammetry. Range of motion for the intact, destabilized, and 3 fixation scenarios were determined.

RESULTS

The anatomic data indicated that feasible cage design were in 3 sizes: 11/8, 12/9, and 13/10 mm for length/width, and 3.5, 4, and 4.5 mm for height. The biomechanical data indicated that transverse-alar-apical ligament disruption significantly increased C1-C2 motion for all directions. All the 3 fixation techniques significantly reduced motion compared with the intact and destabilized cases. There were no statistically significant differences among the 3 fixation techniques.

CONCLUSION

The biomechanical study indicated that, contrary to expectation, addition of a cage did not increase the stability compared with C1-C2 pedicle screw alone. However, the C1 + C2 + Cage technique may be a viable alternative for atlantoaxial stabilization when the posterior arch of the atlas is absent or removed for decompression and a Gallie fixation is impossible.

Axis fractures

BACKGROUND

Traumatic fractures of the second cervical vertebra are common, representing nearly 20% of all acute cervical spinal fracture-dislocation injuries. They are divided into 3 distinct injury patterns: odontoid fractures, hangman's fracture injuries, and fractures of the axis body, involving all other fracture injuries to the C2 vertebra.

OBJECTIVE

An evidence-based overview of the medical and surgical treatment strategies for each axis fracture injury sub-type.

RESULTS

Current medical and surgical management of traumatic fractures of the axis.

Treatment of atlantoaxial rotatory fixation with botulinum toxin muscle block and manipulation

Slippage after reduction of atlantoaxial rotatory fixation (AARF) is usually treated with repeated cervical traction and brace immobilization. To date, no data have been published on the management of muscle spasm during treatment. Here, we describe the case of a 7-year-old girl with AARF for 1 month who visited our hospital for treatment. During physical examination, spasm of the sternocleidomastoid muscle was noted. The patient was treated with manipulative reduction, and slippage after reduction was managed with botulinum spasticity block of the sternocleidomastoid and splenius capitis muscles, and repeated manipulation. Cervical orthosis immobilization with a rehabilitation program of isometric contract-relax exercise for the neck was conducted for 3 months. The subject had full recovery from AARF at 1-year follow-up. This report demonstrates that, in selected cases of slippage after reduction from AARF, conservative management with manipulation under anesthesia is a good method, and the muscle components may play a crucial role in AARF.

Biomechanical assessment of bilateral C1 laminar hook and C1-2 transarticular screws and bone graft for atlantoaxial instability

STUDYDESIGN: In vitro biomechanical test was conducted to compare the stability of 5 different atlantoaxial posterior fusion techniques.

OBJECTIVE

To evaluate the biomechanical stability of an atlas laminar hook combined with transarticular (TA) screws relative to 4 different conventional fusion techniques.

SUMMARY OF BACKGROUND DATA

The atlantoaxial instability caused by fractures, rheumatoid arthritis, congenital deformity, or traumatic lesions of the transverse ligament often result in acute or chronic spinal cord compression, a possible threat to a patient's life. Posterior atlantoaxial fixations are used to reconstruct the stability of atlantoaxial articulation. Conventional posterior atlantoaxial fixations are associated with high rates of pseudoarthrosis and carry the potential risk of neurologic complication. TA screw fixation can provide an excellent biomechanical stability. As a modified 3-point fixation technique, the bilateral C1-2 TA screws have been combined with C1 laminar hook and bone grafts. This modified technique had carried good clinical outcomes.

METHODS

Eight human specimens (C0-C4) were loaded nondestructively with pure moments and the range of motion at the level of C1-C2 was measured. Eight specimens were implanted with each of the following techniques, respectively: Gallie fixation, C1-2 TA screw fixation combined with Gallie fixation, C1-2 TA screw fixation, C1 laminar hook combined with C1-2 TA screw fixation plus bone grafts, and the C1 lateral mass screws in the atlas combined with C2 isthmic screws in axis.

RESULTS

Although the C1-2 TA screws best restricted lateral bending and axial rotation, the modified 3-point fixation technique additionally restricted flexion-extension and provided the excellent stability. Differences in axial rotation and lateral bending (with + or - 1.5 Nm load) were observed when the 3-point fixation techniques (TA + Gallie and TA + hook) were compared with atlas lateral mass screws in the atlas combined with isthmic screws in axis.

CONCLUSIONS

The modified C1 laminar hook combined with C1-2 TA screws and bone graft fixation provided the best biomechanical stability. The C1 lateral mass screws in the atlas combined with isthmic screws in axis fixation is a sound alternative when the C1-2 TA screw fixation is not feasible.

Efficacy and durability of the titanium mesh cage spacer combined with transarticular screw fixation for atlantoaxial instability in rheumatoid arthritis patients

STUDY DESIGN

A retrospective study.

OBJECTIVE

This retrospective investigation was conducted to determine efficacy and endurance of titanium mesh cage as a strut for interlaminar wiring by comparing with autologous iliac bone graft (AIBG). For patients with atlantoaxial instability (AAI), allograft bone was harvested on an interlaminar mesh cage and transarticular fixation (TAF) was performed.

SUMMARY OF BACKGROUND DATA

There have been few studies about atlantoaxial fusion rate and advantages for titanium mesh cage from comparison with AIBG in rheumatoid arthritis (RA) patients.

METHODS

Between January 1998 and October 2007, 55 RA patients were surgically treated for AAI. Among them, 34 patients who underwent surgical treatment with TAF and interlaminar wiring using mesh cage packed with allograft, enrolled in this study (group I). For evaluation of bone fusion about mesh cage group, 21 RA patients who underwent TAF and interlaminar wiring with AIBG were also selected (group II). In both groups, radiologic evidence of bone fusion was assessed with measuring atlantodental interval. Patients were strongly encouraged to mobilize by postoperative 1 day with external cervical bracing. The mean follow-up period was 12.3 months (6-36 months).

RESULTS

Overall, bone fusion was achieved in 33 patients (97%) in group I. And, this was comparable with 100% of group II. There was no statistical difference in bone fusion rate. During the study period, there were 2 instrument-related complications of screw malposition and cable loosening.

CONCLUSION

The results of this study in which mesh cage was used as an interlaminar spacer, showed immediate rigid fixation and successful bone union. We also could prevent donor site morbidities frequently seen in patients with surgical treatment for AAI.

Anatomic determination of optimal entry point and direction for C1 lateral mass screw placement

STUDY DESIGN

Anatomic study of C1 osteology using computerized tomography.

OBJECTIVES

To define the anatomy of the C1 lateral mass and make recommendations for optimal entry point and screw placement at C1.

SUMMARY OF BACKGROUND DATA

C1 lateral mass screw fixation is a reliable biomechanical technique that gives equivalent stability to that of Magerl transarticular screw fixation combined with posterior wiring for C1-C2 fusion. Use of a lateral mass screw allows alternative stabilization constructs to the transarticular technique when C2 vertebral artery anatomy is unfavorable. Because the vertebral artery travels lateral to the lateral mass, then crosses medially over the C1 neural arch, it is at risk during instrumentation. Medially, the cord and canal contents are at risk. While the anatomy of the C1 vertebra and lateral mass is well known, specific definition of ideal entry points, screw pathway direction, and dimensions of screws requires further clarification to enable a clinically safe surgical technique.

METHODS

Fifty consecutive patients underwent computerized tomography scans of their cervical spine. Using calibrated scans, measurements were taken to give the average dimensions of the C1 vertebra with a view for insertion of lateral mass screws beneath the posterior arch. The range of anatomic dimensions was examined to assess risk of vertebral artery damage in this population.

RESULTS

The average length of screw within the lateral mass is 17.9 mm with 21.5 mm of screw posterior to the lateral mass, necessary to allow rod placement posteriorly. The safest entry point was directly beneath the medial edge of the posterior arch/lamina where it joins the lateral mass. The ideal direction of screw angulation in the sagittal plane was parallel to the posterior arch of C1. In the medial lateral plane, direct anterior placement could be used, but the lateral mass will tolerate 20 degrees of medial angulation from this starting point. The average distance between the vertebral artery foramen laterally and the screw pathway was 8.8 mm using these landmarks, and 5.8 mm from the medial aspect of the lateral mass. The range of anatomic variation was such that 9 lateral masses had a vertebral artery foramen to screw distance of only 3 mm. The vertebral artery was not at risk when these anatomic landmarks were used.

CONCLUSIONS

C1 lateral mass screws are best placed beneath the posterior arch, parallel with the arch in the sagittal plan. The entry point is the medial border of the neural arch at its junction with the lateral mass. Straight ahead screw direction is safe in the axial plane, but up to 20 degrees of medial angulation will increase the safety margin from the vertebral artery foramen, and this technique avoids vertebral artery damage and optimizes lateral mass screw purchase. We suggest that this is the preferred method of entry into the lateral mass of C1.

C1 pedicle screws versus C1 lateral mass screws: comparisons of pullout strengths and biomechanical stabilities

STUDY DESIGN

In vitro biomechanical study.

OBJECTIVE

To compare the pullout strengths and the biomechanical stabilities afforded by C1 lateral mass screws and C1 pedicle screws using bicortical and unicortical fixation techniques.

SUMMARY OF BACKGROUND DATA

Posterior screw fixation techniques in the atlas including C1 lateral mass screw and C1 pedicle screw. The shortcomings of C1 lateral mass screw technique and potential risks of bicortical fixation method were recently described; C1 pedicle screw technique with unicortical fixation might overcome these anatomic and clinical drawbacks. However, it is unknown whether the biomechanical characteristics of unicortical C1 pedicle screw are comparable with that of bicortical C1 lateral mass screw. METHODS.: Bicortical or unicortical C1 pedicle screws and C1 lateral mass screws were inserted into 12 adult fresh human C1 specimens. Pullout strength was evaluated using a material testing machine. The construct's stability of bicortical C1 lateral mass screws or unicortical C1 pedicle screws incorporating unicortical C2 pedicle screws was compared with bilateral transarticular screws using another 6 fresh cervical cadaver spines. Pullout strength and biomechanical stability differences were compared statistically.

RESULTS

Bicortical C1 pedicle screws provided the biggest pullout strength (1757.0 +/- 318.7 N) of all 4 methods, whereas unicortical C1 lateral mass screws provided the weakest(794.5 +/- 314.8 N). However, there were no statistically significant differences between bicortical C1 lateral mass screws (1243.8 +/- 350.0 N) and unicortical C1 pedicle screws (1192.5 +/- 172.6 N). Furthermore, there was no statistically significant difference of biomechanical construct stability between unicortical C1 pedicle screw-rod constructs and bicortical C1 lateral mass screw-rod constructs.

CONCLUSION

C1 pedicle screws are stiffer than C1 lateral mass screws. Unicortical C1 pedicle screw provided the same pullout resistance and three-dimensional stability as bicortical C1 lateral mass fixation. Although lateral mass screw placement into C1 requires bicortical purchase, pedicle screw insertion into the atlas only requires unicortical fixation.

Posterior atlanto-axial arthrodesis for fixation of odontoid nonunions

STUDY DESIGN

A retrospective case series.

OBJECTIVE

To determine the clinical and radiographic long-term results after posterior atlanto-axial arthrodesis of odontoid nonunions.

SUMMARY OF BACKGROUND DATA

Nonunion of odontoid fractures is a relatively common and dreaded complication after surgical and nonoperative treatment of these injuries. Although there might be a significant rate, which require surgical stabilization due to atlanto-axial instability, only few publications have covered this issue and presented reliable long-term results.

METHODS

We retrospectively analyzed the clinical and radiographic records of 9 (4 women and 5 men) patients with an average age of 68 (42-78) years at the time of injury who had undergone posterior atlanto-axial arthrodesis for surgical treatment of odontoid nonunions between 1988 and 2004. For posterior atlanto-axial arthrodesis, we performed either C1-C2 transarticular screw fixation, or posterior wiring and bone grafting, or a combination of these 2 techniques.

RESULTS

Eight patients achieved a satisfactory clinical outcome and returned to their preinjury activity level. The Smiley-Webster scale showed an overall functional outcome score of 2.2, which was 0.9 points superior to the outcome score before surgery. Neurologic deficits after operative treatment of the odontoid nonunion were evaluated in 2 patients. In all the other patients with primary neurologic deficits or delayed neurologic sequelae we saw a full recovery. Solid bony fusion of the cervical arthrodesis was achieved in all of the patients. Failures of reduction or fixation were noted in 2 patients, but no reoperations were necessary.

CONCLUSION

In summary, we had a satisfactory outcome after surgical treatment of odontoid nonunions in patients with atlanto-axial instability and severe motion pain at the cervical spine. With a bony union rate of 100% and a noticeable improvement of clinical results and neurologic function, posterior atlanto-axial arthrodesis seems to be an appropriate option for nonunited odontoid fractures that require surgical stabilization.

Stabilization of the atlantoaxial complex via C-1 lateral mass and C-2 pedicle screw fixation in a multicenter clinical experience in 102 patients: modification of the Harms and Goel techniques

Object

Stabilization of the atlantoaxial complex has proven to be very challenging. Because of the high mobility of the C1–2 motion segment, fusion rates at this level have been substantially lower than those at the subaxial spine. The set of potential surgical interventions is limited by the anatomy of this region. In 2001 Jürgen Harms described a novel technique for individual fixation of the C-1 lateral mass and the C-2 pedicle by using polyaxial screws and rods. This method has been shown to confer excellent stability in biomechanical studies. Cadaveric and radiographic analyses have indicated that it is safe with respect to osseous and vascular anatomy. Clinical outcome studies and fusion rates have been limited to small case series thus far. The authors reviewed the multicenter experience with 102 patients undergoing C1–2 fusion via the polyaxial screw/rod technique. They also describe a modification to the Harms technique.

Methods

One hundred two patients (60 female and 42 male) with an average age of 62 years were included in this analysis. The average follow-up was 16.4 months. Indications for surgery were instability at the C1–2 level, and a chronic Type II odontoid fracture was the most frequent underlying cause. All patients had evidence of instability on flexion and extension studies. All underwent posterior C-1 lateral mass to C-2 pedicle or pars screw fixation, according to the method of Harms. Thirty-nine patients also underwent distraction and placement of an allograft spacer into the C1–2 joint, the authors' modification of the Harms technique. None of the patients had supplemental sublaminar wiring.

Results

All but 2 patients with at least a 12-month follow-up had radiographic evidence of fusion or lack of motion on flexion and extension films. All patients with an allograft spacer demonstrated bridging bone across the joint space on plain x-ray films and computed tomography. The C-2 root was sacrificed bilaterally in all patients. A postoperative wound infection developed in 4 patients and was treated conservatively with antibiotics and local wound care. One patient required surgical debridement of the wound. No patient suffered a neurological injury. Unfavorable anatomy precluded the use of C-2 pedicle screws in 23 patients, and thus, they underwent placement of pars screws instead.

Conclusions

Fusion of C1–2 according to the Harms technique is a safe and effective treatment modality. It is suitable for a wide variety of fracture patterns, congenital abnormalities, or other causes of atlantoaxial instability. Modification of the Harms technique with distraction and placement of an allograft spacer in the joint space may restore C1–2 height and enhance radiographic detection of fusion by demonstrating a graft–bone interface on plain x-ray films, which is easier to visualize than the C1–2 joint.

The lasso technique for posterior C1-C2 fusion

OBJECTIVE

Posterior atlantoaxial arthrodesis requires placement of a bone graft in a properly prepared environment that includes decorticated bony surfaces, compressive forces between graft and native bone, and limited motion. To achieve posterior atlantoaxial arthrodesis, various cable-and-graft constructs have been used, all of which require an intact posterior arch of C1. For patients who lack an intact arch owing to congenital, iatrogenic, or traumatic causes, we have devised the "lasso technique," which uses the remnants of the posterior arch of C1 for placement of the graft to achieve fusion isolated to C1-C2 or to be part of an occipitocervical construct.

METHODS

A retrospective record review was conducted of all patients who underwent the lasso technique. Clinical and radiographic history, perioperative course, and time to fusion were recorded. We describe the technique in detail.

RESULTS

During the last 13 years, we have used this technique successfully in five female and four male patients. The absent or incompetent posterior arch was a congenital defect in one patient, a result of prior surgical removal in four patients, and caused by fracture associated with prior failed fusion attempts in four other patients. All patients experienced successful fusion after an average of 6.8 months.

CONCLUSION

Securing a bone graft in the absence of an intact C1 lamina is a challenge when a patient presents with atlantoaxial instability. We have devised the lasso technique to secure an interpositional C1-C2 graft using the remnants of the posterior atlantal arch. Although this technique has been required relatively infrequently, we have found it to be valuable and effective in our practice.

Transarticular screws in the management of C1-C2 instability in children

C1-C2 instability is a challenging problem in the pediatric population. Small patient size and poor healing potential in the at-risk groups, such as patients with Down syndrome and os odontoideum, make fixation difficult. Instability in patients with Down syndrome is a common problem, and traditional methods of fixation have a high complication rate and are a challenge given the frequent anatomic abnormalities such as an incomplete or hypoplastic arch, os odontoideum, and incomplete passive reduction. The purpose of this study was to review our experience of transarticular screw use in pediatric patients and to define the potential applications of this technique in pediatric C1-C2 instability. Twelve patients, with C1-C2 instability managed with transarticular screws at the authors' institution, were reviewed. The youngest patient treated was 5 years old with a mean age for the group of 11.5 years. The group consisted of 3 patients with Down syndrome and 9 patients with os odontoideum. Three of the patients with os odontoideum failed previous posterior wiring. Two patients presented with an acute spinal cord injury in the setting of chronic instability. Preoperative computed tomography or magnetic resonance imaging was used in all patients to define the vascular and bony anatomy. No further surgery has been required at a mean follow-up of 5.1 years in all patients. Although vertebral size and congenital anomalies may make screw positioning challenging, the technique allows fixation in the absence of a complete posterior arch of C1 and eliminates the need for instrumentation in the canal. This technique also provides a high fusion rate in a complicated patient population.

C1 lateral mass screws for posterior segmental stabilization of the upper cervical spine and a new method of three-point rigid fixation of the C1-C2 complex

OBJECTIVE: To describe our experience with C1 lateral mass screws as part of a construct for C1-2 stabilization and report an alternate method of C1-C2 complex three-point fixation. METHOD: All patients that had at least one screw placed in the lateral mass of C1 as part of a construct for stabilization of the C1-C2 complex entered this study. In selected patients who had a higher chance of nonunion an alternate construct was used: transarticular C1-C2 screws combined with C1 lateral mass screws. RESULTS: Twenty-one C1 lateral mass screws were placed in 11 patients. In three patients the alternate construct was used. All patients had a demonstrable solid and stable fusion on follow-up. CONCLUSION: C1 lateral mass screws are safe and provide immediate stability. The use of C1-C2 transarticular screws combined with C1 lateral mass screws is a feasible and also an excellent alternative for a three-point fixation of the C1-C2 complex.

Clinical experience with rigid occipitocervical fusion in the management of traumatic upper cervical spinal instability

Traumatic injuries of the craniovertebral junction or the upper cervical spine may result in occipitocervical (OC) or upper cervical spinal instability. Internal fixation can provide immediate stability to this region. Over a 6-year period, 16 patients with traumatic upper cervical spinal instability underwent a posterior approach OC fusion, using a plate and screw system, at the neurosurgical department of our institution. One patient died. The postoperative course of all the other patients was uncomplicated. At the most recent follow-up examination, all patients had satisfactory fusion. OC fusion with a plate and screw system is a safe and effective method for the treatment of traumatic craniovertebral and high cervical spine instability. Accurate imaging diagnosis and strict patient selection are the keys to a successful outcome.

Radiographic assessment of segmental motion at the atlantoaxial junction in the Klippel-Feil patient

STUDY DESIGN

A retrospective review of 33 consecutive Klippel-Feil syndrome (KFS) patients at a single institution.

OBJECTIVES

To assess in KFS patients the presence and degree of radiographic segmental motion at the atlantoaxial junction, factors contributing to such motion, and associated clinical manifestations.

SUMMARY OF BACKGROUND DATA

Studies suggest that abnormal segmentation in KFS patients may result in cervical hypermobility, increasing the risk of developing neurologic compromise and the need for surgical intervention. The use of the anterior and posterior atlantodens interval (AADI/PADI) has gained interest as a method for assessing atlantoaxial instability and for space available for the cord. Although helpful for identifying instability after trauma, these measurements are not understood in KFS patients. In addition, the effects of the fusion process associated with KFS on atlantoaxial motion and associated clinical findings have not been properly addressed.

METHODS

Radiographs were analyzed for the presence of occipitalization, number/location of congenitally fused segments, and the AADI and PADI.

RESULTS

There were 15 males and 18 females (mean age, 13.9 years). Occipitalization occurred in 48.5% of patients. A fused C2-C3 segment was noted in 72.7% of cases. More motion with respect to AADI was evident on O-C1 and C2-C3 fusion only patients, which were all asymptomatic. Overall, 24.2% of patients were symptomatic. Mean AADI and PADI difference was 2.0 mm (symptomatic: mean, 1.5 mm; asymptomatic: mean, 2.1 mm) and -1.7 mm (symptomatic: mean, -1.0 mm; asymptomatic: mean, -2.0 mm), respectively (P > 0.05).

CONCLUSIONS

Hypermobility of the atlantoaxial junction, as indicated by increased AADI on flexion-extension radiographs, is not necessarily associated with an increased risk for the development of symptoms or neurologic signs in the KFS patient. Occipitalization plays an integral role in the degree of motion at the atlantoaxial region. Greatest AADI values were in patients with occipitalization and a fused C2-C3 segment. The presence of symptoms was not related to the degree of AADI change. Evaluation of the PADI provides additional information for identifying patients at risk for developing symptoms. Nonetheless, KFS patients remain largely asymptomatic.

Frameless Stereotactic Image-Guided C1-C2 Transarticular Screw Fixation for Atlantoaxial Instability

OBJECTIVE

We retrospectively studied 20 adults who underwent C1-C2 transarticular screw (TAS) fixation utilizing frameless stereotaxy.

METHODS

The study group comprised 13 men and 7 women, with a mean age of 63 years (range 12-87 years). All patients demonstrated clinical and radiographic evidence of C1-C2 instability. The cause of the instability was trauma in 11 patients, rheumatoid arthritis in 6 patients, failed prior surgery in 2 patients, and congenital malformation in 1 patient. All patients underwent stabilization with C1-C2 TASs using image-guided frameless stereotaxy.

RESULTS

There were no new or worsening neurologic symptoms reported at 18-month follow-up. Motor weakness improved in seven of nine patients, myelopathy in seven of seven, and gait in three of six patients in whom these deficits were present preoperatively. Postoperative complications included one surgical site abscess, one cutaneous pressure ulcer, and one iliac crest donor site infection. Of 36 screws placed, 33 (92%) were well positioned. Normal C1-C2 alignment was achieved in 17 of 20 (85%) patients. In 4 of 20 cases, screw implant, which was thought to be anatomically difficult, if not impossible, on the basis of routine magnetic resonance or computed tomography imaging, was actually accomplished successfully using surgical navigation.

CONCLUSIONS

C1-C2 TAS placement is a safe and accurate surgical technique that may improve neurologic function. Use of intraoperative navigation can facilitate achieving difficult surgical trajectories that match the patient's anatomy, thus allowing TAS implant in patients who otherwise would not be candidates for this type of internal fixation.

A safe screw trajectory for atlantoaxial transarticular fixation achieved using an aiming device

STUDY DESIGN

A retrospective evaluation and characterization of the trajectory of atlantoaxial transarticular screws inserted using an aiming device.

OBJECTIVES

To confirm that the screws were inserted through the safest trajectory, which is through the most dorsal and medial part of the isthmus of C2, and to characterize the trajectory on lateral radiograms by comparison with historical controls.

SUMMARY OF BACKGROUND DATA

Posterior atlantoaxial transarticular screw fixation entails the potential risk of vertebral artery (VA) injury, which may be lethal. Although much literature recommends that the screws should be inserted aiming at the anterior arch of C1, the authors considered that the safest screw path is via the most dorsal and medial part of the isthmus regardless of the C1 anterior arch, and have used an original aiming device to achieve this trajectory.

METHODS

Forty-three consecutive patients who submitted to atlantoaxial transarticular screw fixation using the aiming device were evaluated for screw position using computed tomography (CT) and lateral radiogram. The medialization index (the distance between the screw and the cortex of the spinal canal of C2 on axial CT) and the dorsalization index (the thickness of the bone remaining dorsal to the screw at the isthmus of C2 on sagittal reconstruction CT) were measured. Further, three parameters on the lateral radiograms of these patients were compared with those in the literature and those of our previous cases performed without the aiming device.

RESULTS

Neither VA injury nor violation of the spinal canal was encountered, although 12 high-riding VAs were included in this series. The mean medialization index was 0.21 mm, and the indexes of 86.3% of the screws were zero. The mean dorsalization index was 0.36 mm, and the indexes of 76.8% of the screws were zero. These results demonstrated that most of the screws were inserted as aimed, proving the usefulness of the aiming device. The trajectory of these screws on lateral radiograms was characterized by significantly less bone thickness dorsal to the screw at the isthmus compared with the two control groups. As a result, more screws were pointed above the anterior arch of C1.

CONCLUSIONS

The atlantoaxial transarticular screw was inserted safely as aimed by using the aiming device. The trajectory was characterized by less bone thickness dorsal to the screw on lateral radiogram, which should be a new intraoperative landmark for screw insertion, in place of the anterior arch of C1.

Posterior atlantoaxial transpedicular screw and plate fixation

✓ The authors describe a modified posterior atlantoaxial fixation technique for the treatment of reducible atlantoaxial instability, which can be performed simply and easily, and can decrease the risk of vessel and/or neural damage.

During an 18-month period, this technique was undertaken in 11 patients with atlantoaxial instability. There was no procedure-related morbidity. The follow-up period ranged from 8 to 18 months (mean 13.2 months). Fusion was documented in all 11 patients, and there was no progression of spinal deformity.

This technique can be considered an effective alternative in the treatment of atlantoaxial subluxation.

Stereotactic atlantoaxial transarticular screw fixation

Atlantoaxial stabilisation can be performed using a variety of surgical techniques. Developments in spinal instrumentation and stereotactic technology have been incorporated into these procedures. We have recently adopted frameless stereotaxy to assist in such operations. A retrospective study of patients treated by the authors and using frameless stereotaxy from 2001 to 2002 was performed. Each patient underwent pre-operative fine-cut CT in the position of fixation. Using these images, screw trajectory was planned. Stereotaxis and fluoroscopy was utilised during fixation. A post-operative CT was performed. There were nine patients. Bilateral screw placement was achieved in eight. In the remaining case stereotactic planning predicted the single screw fixation. There were no post-operative complications. Post-operative CT showed screw placement corresponding to the planned trajectory in all 17 screws. Stabilisation was achieved in all. Stereotactic atlantoaxial screw fixation is an accessible, safe and accurate method for the management of C1-2 instability.

Implantable direct current stimulation in para-axial cervical arthrodesis

This retrospective, case-controlled pilot study was designed to examine the efficacy and safety of an implantable direct current bone growth stimulator (IDCBGS) as an adjunct to cervical arthrodesis in patients at high risk for nonunion after undergoing cervical fusion in region from the occiput to C3. Twenty patients underwent para-axial cervical arthrodesis (involving posterior spine fusion and instrumentation using standard surgical techniques) for the correction of instability. All were at high risk for nonunion due to advanced age, rheumatoid arthritis, prior failed fusion attempts, infection, or immunosuppressive drug use. An IDCBGS was used to augment the surgical procedure. The mean follow-up period was 19 months, and 16 patients were available for follow-up. Radiographic evidence of fusion was demonstrated in 15 of 16 patients (94%). After surgery, all patients demonstrated clinical stabilization, a resolution of symptoms in combination with an improvement in neurologic status, or both. The mean elapsed time before fusion occurred was 4.6 months. No neurologic complications related to cathode or generator placement were observed. The use of the stimulator as an adjunct to instrument- or non-instrument-assisted surgical fusion of the para-axial region in these high-risk patients appeared both safe and efficacious. Further investigation is warranted to define the possible role and clinical utility of the IDCBGS in selected patients requiring cervical fusion, particularly those at high risk for nonunion.

Biomechanical comparison of anterior and posterior stabilization methods in atlantoaxial instability

OBJECT

The authors compared the biomechanical stability of two anterior fixation procedures--anterior C1-2 Harms plate/screw (AHPS) fixation and the anterior C1-2 transarticular screw (ATS) fixation; and two posterior fixation procedures--the posterior C-1 lateral mass combined with C-2 pedicle screw/rod (PLM/APSR) fixation and the posterior C1-2 transarticular screw (PTS) fixation after destabilization.

METHODS

Sixteen human cervical spine specimens (Oc-C3) were tested in three-dimensional flexion-extension, axial rotation, and lateral bending motions after destabilization by using an atlantoaxial C1-2 instability model. In each loading mode, moments were applied to a maximum of 1.5 Nm, and the range of motion (ROM), neutral zone (NZ), and elastic zone (EZ) were determined and values compared using the intact spine, the destabilized spine, and the postfixation spine. The AHPS method produced inferior biomechanical results in flexion-extension and lateral bending modes compared with the intact spine. The lateral bending NZ and ROM for this method differed significantly from the other three fixation techniques (p < 0.05), although statistically significant differences were not obtained for all other values of ROM and NZ for the other three procedures. The remaining three methods restored biomechanical stability and improved it over that of the intact spine.

CONCLUSIONS

The PLM/APSR fixation method was found to have the highest biomechanical stiffness followed by PTS, ATS, and AHPS fixation. The PLM/APSR fixation and AATS methods can be considered good procedures for stabilizing the atlantoaxial joints, although specific fixation methods are determined by the proper clinical and radiological characteristics in each patient.

Acute atlanto-axial post-operative subluxation following posterior C1/2 fusion

Two cases referred with acute post-operative C1/2 subluxation following posterior fusion are reported. Both cases had initial treatment for atlanto-axial instability with posterior cable (Brooks and interspinous) and graft techniques, and placed immediately in a Philadelphia collar. One case was found to have subluxed immediately post-operatively when failing to breathe following reversal of anaesthetic agents, and despite immediate realignment and reoperation was left with a significant quadriparesis. The other patient was noted to have subluxed on routine X-ray on day 4, and had no neurological deficit before or after reoperation. Risk factors for this dangerous complication are discussed and the techniques of C1/2 posterior fusion and stabilization are reviewed in detail. Surgeons performing atlanto-axial stabilization procedures should be familiar with and have expertize in the complete range of techniques described and choose the one most appropriate for the patient's individual requirements.

Interlaminar Fixation Using the Atlantoaxial Posterior Fixation System (3XS System) for Atlantoaxial Instability: Surgical Results and Biomechanical Evaluation

This study evaluated the surgical results for patients with atlantoaxial instability due to various lesions treated using the atlantoaxial posterior fixation system (3XS system; Kisco DIR, Paris, France), together with a biomechanical study of this system. The strength of the 3XS system during torsion was examined using a biomechanical simulation model. The 3XS system consists of a transverse unit, hooks, and rods. The lower part of the biomechanical simulation machine was rigidly fixed and the upper part was movable, allowing torsion to be applied until the point of failure. The test was started at 1.5 newton-meters, thought to be the maximum load on the upper cervical spine. The 3XS system tolerated torsion of up to 20 newton-meters, but became deformed. The instrument was fractured at 30 newton-meters. Fifteen patients, four with atlantoaxial instability, seven with os odontoideum, and four with odontoid fractures, underwent surgery using the 3XS system and an iliac bone fragment inserted between the C-1 and C-2 laminae. Postoperative rigid fixation of the lesion and optimal cervical alignment was obtained in all patients, and the patients were discharged within 2 weeks after surgery. Follow-up radiography showed bony fusion between C-1 and C-2 in all patients. Posterior fixations between C-1 and C-2 using the 3XS system were easy to perform and no surgical complications were encountered. The biomechanical study showed the 3XS system can tolerate torsions unlikely to occur during rotation movements in the atlantoaxial region in humans. The surgical use of the 3XS system for the treatment of atlantoaxial instability has several advantages.

Anatomic relationship of the internal carotid artery to the C1 vertebra: A case report of cervical reconstruction for chordoma and pilot study to assess the risk of screw fixation of the atlas

STUDY DESIGN

A case of internal carotid artery impingement by the tip of a well-positioned C1-C2 transarticular screw is presented along with a pilot study involving radiologic and anatomic evaluation of human cadaveric specimens.

OBJECTIVE

To raise awareness that the internal carotid artery may be in close proximity to the anterior aspect of the atlas and at risk of injury during placement of C1-C2 transarticular screws or C1 lateral mass screws.

SUMMARY OF BACKGROUND DATA

To our knowledge, no cases of internal carotid artery injury or impingement have been reported with screw fixation of the atlas.

METHODS

A case of internal carotid artery impingement by a C1-C2 transarticular screw is presented. The C1-C2 rotation appeared to place the internal carotid artery in the path of the screw, prompting a pilot study. Three fresh-frozen human cadaveric head and neck specimens were fixed in different degrees of rotation. Thin-section computed tomography of the specimens was obtained in the plane of the atlas. The frozen specimens were sectioned in the same plane as the computed tomography images. Measurements were taken to assess the location of the internal carotid artery relative to the anterior aspect of the atlas.

RESULTS

Cervical rotation does not have a predictable effect on the location of the internal carotid artery. Medial angulation of a screw placed in the lateral mass of C1 appears to increase the margin of safety for the internal carotid artery. The internal carotid artery varies in location and may be within 1 mm of the ideal exit point of a bicortical transarticular screw or a C1 lateral mass screw.

CONCLUSIONS

The internal carotid artery is at risk during bicortical screw fixation of the atlas. We recommend a contrast-enhanced computed tomography to assess the location of the internal carotid artery before screw fixation of the atlas.

Atlantoaxial stabilization: clinical comparison of posterior cervical wiring technique with transarticular screw fixation

Symptomatic atlantoaxial instability requires atlantoaxial stabilization. In this study the authors compared clinical, radiographic, and cervical outcome questionnaire results in 67 such patients who underwent 71 separate procedures. Thirty-eight patients had traditional posterior C1-C2 cervical wiring and halo-vest immobilization (group 1), whereas 33 were alternatively managed with transarticular screw fixation without rigid external immobilization (group 2). Mean follow-up in group 1 was 53.2 months and mean follow-up in group 2 was 41.0 months. Radiographic evaluation demonstrated seven pseudoarthroses and four fibrous unions in group 1, with six patients subsequently undergoing reoperation. There were no pseudoarthroses and two fibrous unions in the transarticular screw group (p = 0.015). In those that fused, >2-mm displacement occurred in six of the group 1 patients (p = 0.027). There was a trend toward fewer complications in group 2 patients (p = 0.085) with four complications, as compared with 12 complications in group 1, including a 21% incidence of halo-vest-related complications. These results demonstrate the significant benefits of transarticular screw fixation over posterior cervical wiring techniques in the management of atlantoaxial instability.

C1-C2 posterior fusion in growing patients: long-term follow-up

STUDY DESIGN

A retrospective review of patients undergoing C1-C2 posterior fusion during childhood was undertaken.

OBJECTIVES

The aim of this study was to investigate the change in the sagittal curvature of the cervical spine in children after C1-C2 posterior fusion.

SUMMARY OF BACKGROUND DATA

There have been only a few reports on postoperative changes in the sagittal curvature of the cervical spine after C1-C2 posterior fusion in children. However, they have all described the onset of sagittal postoperative cervical deformities.

METHODS

Between January 1977 and December 1992, a total of 12 children underwent C1-C2 posterior fusion for atlantoaxial instability resulting from congenital malformation in eight, juvenile rheumatoid arthritis in one, and rotatory subluxation in three. The average age at the time of surgery was 10.9 years (range 7-12 years). All children underwent a similar treatment program with gradual preoperative reduction in halo cast, followed by C1-C2 posterior fusion with Mersilene loops in two cases, wiring in eight (Gallie's or Brooks' techniques), and interlaminar clamps in the remaining two. The halo cast made it possible to avoid a hyperextended or hyperflexed C1-C2 position while performing the atlantoaxial fusion, thus ensuring a more anatomic position during C1-C2 fusion. In the postoperative period, the halo cast was maintained for 7 to 9 weeks. RESULTS Follow-up ranged from 7 years to 13 years. Preoperative alignment of the cervical spine was classified into two groups: lordosis (eight patients) and straight (four patients). Postoperative subaxial malalignment (kyphosis) occurred in four cases (33%): these patients showed evidence of spontaneous and gradual sagittal improvement and presented either a straight (two cases) or a lordotic (two cases) cervical spine at follow-up. Immediately after surgery, the cervical spine was normally aligned in the remaining eight patients (lordosis and straight alignment in six and two cases, respectively) and was unchanged at follow-up. At follow-up, none of the 12 patients had a cervical deformity on sagittal plane.

CONCLUSION

In children, a spontaneous realignment of the subaxial kyphosis observed after C1-C2 posterior fusion can be noted at follow-up, when a postoperative deformity occurs (33% in the present series). According to the present findings, it is not always mandatory to perform occipitocervical fusion in children with atlantoaxial instability just to prevent subaxial deformity in the cervical spine.

Biomechanical testing of posterior atlantoaxial fixation techniques

STUDY DESIGN

An in vitro biomechanical study of C1-C2 posterior fusion techniques was conducted using a cadaveric model.

OBJECTIVE

To investigate and compare the acute stability afforded by a novel rod-based construct that uses direct polyaxial screw fixation to C1 and C2 with contemporary transarticular screw and wire techniques.

SUMMARY AND BACKGROUND DATA

Acute stability of the atlantoaxial complex is required to achieve bony consolidation. Various forms of posterior wiring were the first standardized procedures advocated to achieve C1-C2 fixation, but because of insufficient construct stability, these techniques have been coupled with transarticular screw fixation. Significant technical difficulties, however, including the possibility of neurovascular compromise during implantation are associated with transarticular screw placement. A novel technique that uses direct polyaxial screw fixation to C1 and C2 and bilateral longitudinal rods was developed recently. However, there are no published reports detailing the biomechanical characteristics of this new construct.

METHODS

In this study, 10 fresh-frozen human cadaveric cervical spines with occiput (C0-C4) were used. Osteoligamentous specimens were tested in their intact condition after destabilization via odontoidectomy, and after two different Gallie wiring techniques. Each specimen was assigned to one of the two screw fixation groups. Five specimens were implanted with the polyaxial screw-rod construct and tested. The remaining five specimens were tested after application of bilateral C1-C2 transarticular screws with Gallie wiring (Magerl-Gallie technique). Pure-moment loading, up to 1.5 Nm in flexion and extension, right and left lateral bending and right and left axial rotation, was applied to the occiput, and relative intervertebral rotations were determined using stereophotogrammetry (motion analysis system). Range of motion data for all fixation scenarios were normalized to the destabilized case, and statistical analysis was performed using one-way analysis of variance with Fisher's least significant difference PLSD post hoc test for multiple comparisons.

RESULTS

The data indicate that destabilization via odontoidectomy significantly increased C1-C2 motion. Both screw techniques significantly decreased motion, as compared with both Gallie wiring methods in lateral bending and axial rotation (P < 0.02 for all) and tended toward reduced motion in flexion-extension. There was no statistically significant difference between the two screw techniques.

CONCLUSIONS

The results clearly indicate the screw-rod system's equivalence in reducing relative atlantoaxial motion in a severely destabilized upper cervical spine, as compared with the transarticular screw-wiring construct. These findings mirror the previously reported clinical results attained using this new screw-rod construct. Thus, the decision to use either screw construct should be based on safety considerations rather than acute stability.

Posterior atlantoaxial fixation: biomechanical in vitro comparison of six different techniques

STUDY DESIGN

Six different techniques for atlantoaxial fixation were biomechanically compared in vitro by nondestructive testing.

OBJECTIVE

To evaluate the immediate three-dimensional stability of a new atlas claw combined with transarticular screws and alternative techniques for transarticular screw fixation in comparison with established techniques.

SUMMARY OF BACKGROUND DATA

Posterior transarticular screw fixation in combination with wire-bone graft constructs is frequently used for C1-C2 fixation. Sublaminar wire passage carries the potential risk of neurologic complication. Transarticular screw fixation is technically demanding and, for anatomic reasons, not always feasible.

METHODS

Six human cervical specimens were loaded nondestructively with pure moments, and unconstrained motion at C1-C2 was measured. The six specimens were instrumented with each of the following fixation techniques: Gallie fixation, transarticular screws and Gallie fixation, transarticular screws, transarticular screws and a new atlas claw, isthmic screws in the axis and the atlas claw, and lateral mass screws in the atlas and isthmic screws in the axis connected with rods.

RESULTS

The transarticular screws restricted lateral bending and axial rotation best. The three-point fixations (transarticular + Gallie and transarticular + claw) additionally restricted flexion-extension, with lowest values for transarticular screws and the atlas claw. The alternative techniques were not as stable as the three-point fixations, but more stable than the Gallie fixation.

CONCLUSIONS

Biomechanically, the three-point fixation with transarticular screws and the atlas claw provides a rigid internal fixation that is not dependent on bone graft and sublaminar wiring. In cases wherein transarticular screws are not feasible, the isthmic screws and claw or the lateral mass screws and isthmic screws are biomechanical alternatives with less immediate stability.

Isolated fractures of the axis in adults

FRACTURES OF THE ODONTOID:

STANDARDS

There is insufficient evidence to support treatment standards.

GUIDELINES

Type II odontoid fractures in patients 50 years and older should be considered for surgical stabilization and fusion.

OPTIONS

Type I, Type II, and Type III fractures may be managed initially with external cervical immobilization. Type II and Type III odontoid fractures should be considered for surgical fixation in cases of dens displacement of 5 mm or more, comminution of the odontoid fracture (Type IIA), and/or inability to achieve or maintain fracture alignment with external immobilization. TRAUMATIC SPONDYLOLISTHESIS OF THE AXIS (HANGMAN'S FRACTURE):

STANDARDS

There is insufficient evidence to support treatment standards.

GUIDELINES

There is insufficient evidence to support treatment guidelines.

OPTIONS

Traumatic spondylolisthesis of the axis may be managed initially with external immobilization in most cases. Surgical stabilization should be considered in cases of severe angulation of C2 on C3 (Francis Grade II and IV, Effendi Type II), disruption of the C2--C3 disc space (Francis Grade V, Effendi Type III), or inability to establish or maintain alignment with external immobilization. FRACTURES OF THE AXIS BODY (MISCELLANEOUS FRACTURES):

STANDARDS

There is insufficient evidence to support treatment standards.

GUIDELINES

There is insufficient evidence to support treatment guidelines.

OPTIONS

External immobilization is recommended for treatment of isolated fractures of the axis body.

Posterior C1-C2 fusion with polyaxial screw and rod fixation

STUDY DESIGN

A novel technique of atlantoaxial stabilization using individual fixation of the C1 lateral mass and the C2 pedicle with minipolyaxial screws and rods is described. In addition, the initial results of this technique on 37 patients are described.

OBJECTIVES

To describe the technique and the initial clinical and radiographic results for posterior C1-C2 fixation with a new implant system.

SUMMARY OF BACKGROUND DATA

Stabilization of the atlantoaxial complex is a challenging procedure because of the unique anatomy of this region. Fixation by transarticular screws combined with posterior wiring and structural bone grafting leads to excellent fusion rates. The technique is technically demanding and has a potential risk of injury to the vertebral artery. In addition, this procedure cannot be used in the presence of fixed subluxation of C1 on C2 and in the case of an aberrant path of the vertebral artery. To address these limitations, a new technique of C1-C2 fixation has been developed: bilateral insertion of polyaxial-head screws in the lateral mass of C1 and through the pars interarticularis into the pedicle of C2, followed by a fluoroscopically controlled reduction maneuver and rod fixation.

METHODS

After posterior exposure of the C1-C2 complex, the 3.5-mm polyaxial screws are inserted in the lateral masses of C1. Two polyaxial screws are then inserted into the pars interarticularis of C2. Drilling is guided by anatomic landmarks and fluoroscopy. If necessary, reduction of C1 onto C2 can be accomplished by manipulation of the implants, followed by fixation to the 3-mm rod. For definitive fusion, cancellous bone can be added. No structural bone graft or wiring is required. In selected cases, e.g., C1-C2 subluxation or fractures in young patients in whom only temporary fixation is necessary, the instrumentation can be removed after an appropriate time. Because the joint surfaces stay intact, the patient can regain motion in the C1-C2 joints.

RESULTS

Thirty-seven patients underwent this procedure. No neural or vascular damage related to this technique has been observed. The early clinical and radiologic follow-up data indicate solid fusion in all patients.

CONCLUSION

Fixation of the atlantoaxial complex using polyaxial-head screws and rods seems to be a reliable technique and should be considered an efficient alternative to the previously reported techniques.

Biomechanical comparison of five different atlantoaxial posterior fixation techniques

STUDY DESIGN

Five different reconstructions of the atlantoaxial complex were biomechanically compared in vitro in a nondestructive test.

OBJECTIVES

To determine whether non-bone graft-dependent one-point fixation affords stability levels equivalent to three-point reconstructions.

SUMMARY OF BACKGROUND DATA

Previous investigations have demonstrated that three-point fixation, using bilateral transarticular screws in combination with posterior wiring, provide the most effective resistance to minimize motion around C1-C2. However, placement of transarticular screws is technically demanding. Posterior wiring techniques affording one-point fixation have failure rates of approximately 15%, with failure considered to be secondary to structural bone graft failures. One-point, non-bone graft-dependent fixations have not been tested.

METHODS

Eight human cervical specimens, C0-C3 were loaded nondestructively. Unconstrained three-dimensional segmental motion was measured. The reconstructions tested were two one-point fixations, one two-point fixation, and two three-point fixations.

RESULTS

Under axial rotation two and three-point reconstructions provided better stiffness than the one-point reconstructions (P < 0.05). During flexion-extension, higher stiffness levels were observed in one- and three-point fixations when compared with the intact spine (P < 0.05). In lateral bending no significant differences were observed among the six groups, although the trend was that reconstructions including transarticular screws provided greater stability than one-point fixations.

CONCLUSION

The current findings substantiate the use of three-point fixation as the treatment of choice for C1-C2 instability. [l: atlantoaxial fixation, biomechanics, cervical spine, instability, spinal instrumentation, transarticular screws]