Shenglin Wang

Atlantoaxial transarticular screw fixation with morselized autograft and without additional internal fixation : Technical description and report of 57 cases

Study Design. Retrospective clinical and radiologic evaluation of posterior C1–C2 fusion by transarticular screw (TAS) with morselized autograft and without additional internal fixation. Objective. Description and assessment of a modified Magerl technique. Summary of Background Data. The majority of spine surgeons prefer to supplement the posterior TAS with a posterior cable-secured strut graft and a postoperative rigid cervical orthosis. Our hypotheses are that the 2 posterior TASs alone are enough for stabilization and that morselized cancellous grafts have similar clinical result as the structural graft. Methods. Fifty-seven consecutive patients, including atlantoaxial instability in 52 and atlantoaxial dislocation in 5, were treated by bilateral TAS fixation alone with morselized grafts by the same surgeon. The postoperative external immobilization was abandoned. Results. A total of 114 transarticular screws were placed. Radiographs demonstrated all the screws were placed satisfactorily except two. One screw penetrated into the occipitoatlantal joint, and the other one slightly breached the vertebral artery groove but did not injure vertebral artery. None of these 2 screws was associated with clinical sequelae. There were 2 patients who had postoperative iatrogenic C2–C3 instability on dynamic radiograph, which did not need treatment. These cases had an average follow-up of 47 months (range, 24–76 months). All patients attained solid fusion without screw failure. Conclusions. Bilateral transarticular screws alone and morselized grafts have high fusion rate in atlantoaxial arthrodesis without instrument failure. TAS fixation could provide stability that is clinically equivalent to the standard screws plus tension band construct as described by Magerl. With anatomic reduction and ideal screw position, additional internal fixation and postoperative collar are not necessary.

Anomalous vertebral artery in craniovertebral junction with occipitalization of the atlas.

Study Design. Observational study with 3-dimensional computed tomography angiography analysis. Objective. To examine the course of the vertebral artery (VA) at the craniovertebral junction (CVJ) in individuals with occipitalization of the atlas. Summary of Background Data. The anatomy of the VA at the CVJ should be completely understood to decrease the risk of iatrogenic injury. Although quantitative anatomic studies have focused on the normal VA, the anomalous VA with occipitalization of the atlas has not been fully explored. Methods. A consecutive series of 36 cases with occipitalization of the atlas underwent 3-dimensional computed tomography angiography. Seventy-two vertebral arteries were analyzed. In this setting, the safety of placing lateral mass screws (LMS) was studied. Results. Four different pathways of the VA at the CVJ with occipitalization of the atlas were found. Type I, wherein the VA enters the spinal canal below the C1 posterior arch, and the course of the VA is below the occipitalized C1 lateral mass (8.3% of 72 vertebral arteries); Type II, the VA enters the spinal canal below the C1 posterior arch, and the course of the VA is on the posterior surface of the occipitalized C1 lateral mass, or makes a curve on it (25%); Type III, wherein the VA ascends externally laterally after leaving the axis transverse foramen, enters an osseous foramen created between the atlas and occipital bone, then into the cranium (61.1%); and Type IV, in which the VA is absent (5.6%). Conclusion. Four types of VA with occipitalization of the atlas are confirmed. Type-I and type-IV VA have relatively low risks for C1 LMS perforation. Type-II and type-III anomalies will probably increase the risk of VA injury during C1 LMS placement. Definite caution should also be taken during the procedure on the contralateral side of a type-IV VA.

Radiographic evaluation of the technique for C1 lateral mass and C2 pedicle screw fixation in three hundred nineteen cases.

Study Design. Retrospective radiographic study of the technique for C1 lateral mass screw (C1LMS) and C2 pedicle screw (C2PS) fixation. Objective. To evaluate (1) the accuracy of the C1LMS and C2PS placement; (2) the fusion rate between C1 and C2; (3) the risk for vertebral artery (VA) injury. Summary of Background Data. C1LMS and C2PS fixation is widely used when treating atlantoaxial instability. Several authors have reported their experience focusing on the technical outcomes, with many reporting fusion rates near 100%. However, most of them are relatively small series, and many have applied only plain postoperative radiographs instead of computed tomography (CT). Thus, we feel that the accuracy of C1LMS and C2PS placement has not been fully analyzed, as well as the anatomic relationship between the VA and the screws. Methods. Between December 2000 and September 2008, the fusion status and accuracy of the screws were evaluated on the postoperative reconstructive CT of 319 patients with atlantoaxial instability. Cases with malpositioned screws underwent CT angiography or magnetic resonance angiography after surgery, to evaluate potential VA injury. Results. C1LMS of 95.5% and C2PS of 92.8% were found to be in a “good” position. After 2007, six cases had malpositioned screws, which were all in the “out” or “down” area of the C2 pedicle. Five cases underwent CT angiography and 1 had magnetic resonance angiography to evaluate potential VA injury. No occlusion, associated aneurysm or fistula of the VA was found. All cases (100%) achieved solid fusion between C1 and C2. Conclusion. C1LMS of 95.5% and C2PS of 92.8% were confirmed to be in good position. None of the screws including the malpositioned caused VA injury, clinically or radiographically. The technique for C1LMS and C2PS fixation appears to be safe and effective.

A Review of the Diagnosis and Treatment of Atlantoaxial Dislocations

Study Design Literature review. Objective Atlantoaxial dislocation (AAD) is a rare and potentially fatal disturbance to the normal occipital-cervical anatomy that affects some populations disproportionately, which may cause permanent neurologic deficits or sagittal deformity if not treated in a timely and appropriate manner. Currently, there is a lack of consensus among surgeons on the best approach to diagnose, characterize, and treat this condition. The objective of this review is to provide a comprehensive review of the literature to identify timely and effective diagnostic techniques and treatment modalities of AAD. Methods This review examined all articles published concerning “atlantoaxial dislocation” or “atlantoaxial subluxation” on the PubMed database. We included 112 articles published between 1966 and 2014. Results Results of these studies are summarized primarily as defining AAD, the normal anatomy, etiology of dislocation, clinical presentation, diagnostic techniques, classification, and recommendations for timely treatment modalities. Conclusions The Wang Classification System provides a practical means to diagnose and treat AAD. However, future research is required to identify the most salient intervention component or combination of components that lead to the best outcomes.

Novel surgical classification and treatment strategy for atlantoaxial dislocations.

Study Design. Retrospective study of 904 patients with a diagnosis of atlantoaxial dislocation (AAD), using a novel surgical classification and treatment strategy. Objective. To describe a novel surgical classification and treatment strategy for AADs. Summary of Background Data. AADs can result from a variety of etiologies, yet no comprehensive classification has been accepted that guides treatment. Because of the rarity of the cases, however, the treatment strategy has also been debated. Methods. During a period of 12 years, a total of 904 patients with a diagnosis of AAD were recruited from a single academic institution. According to the treatment algorithm that included preoperative evaluation using dynamic radiograph, reconstructive computed tomography, and skeletal traction test, the cases were classified into 4 types: I to IV. Types I and II were fused in the reduced position from a posterior approach. Type III, which were irreducible dislocations, were converted to reducible dislocations using a transoral atlantoaxial release, followed by a posterior fusion. Type IV presented with bony dislocations and required transoral osseous decompressions prior to posterior fusion. Results. Four hundred seventy-two cases were classified as type I, 160 as type II, 268 as type III, and 4 cases as type IV. Follow-up was in the range of 2 to 12 years (average: 60.5 mo). Eight hundred and ninety-nine cases (99.4%) achieved a solid atlantoaxial fusion. Anatomic atlantoaxial reduction was achieved in 892 cases (98.7%), whereas 12 cases had a partial reduction. Neurological improvement was seen in 84.1% (512/609) of the patients with myelopathy. The overall complication rate was 9.1% (82/949). Conclusion. Our surgical classification and treatment strategy for AADs was applied in those 904 cases and associated with excellent clinical results with a minimal risk of complications. Level of Evidence: 4

Relationship between the alignment of the occipitoaxial and subaxial cervical spine in patients with congenital atlantoxial dislocations.

Study Design: Prospective radiographic analysis. Objective: This study aimed to characterize the relationship between the alignment of the occipitoaxial (OA) and the subaxial spine, establish normal parameters, and to determine the influence of upper cervical spine alignment on subaxial degenerative disc disease (DDD) and clinical outcomes in this population. Summary of Background Data: Previous studies reported that the alignments of the upper and lower cervical spine are closely interrelated in patients with atlantoaxial dislocations of a rheumatoid etiology. None have focused on congenital etiologies or included patients with OA kyphosis. The influence of the upper cervical alignment on subaxial (DDD) and outcomes is also unclear. Methods: Fifty-eight patients with congenital AAD undergoing surgical reduction and fusion were included. C0-C2 and C2-C7 angles were measured and DDD was assessed using plain radiographs. The relationship between the alignment of the OA joint and the subaxial cervical spine was evaluated, as well as the relationships between the cervical alignment, outcomes, and cervical DDD. Results: C0-2 improved from a mean of 1.59±17.3 degrees preoperatively to a mean of 15±9.8 degrees postoperatively (P<0.001). C2-7 changed from a mean of 25.55±19.6 degrees to a mean of 14.2±14.4 degrees postoperatively (P<0.001). The OA and subaxial alignment were negatively correlated in this population both before (r=−0.84; P<0.001) and after (r=−0.64; P<0.001) surgical treatment. There was an increased incidence of DDD postoperatively (P<0.01), which was positively correlated with the postoperative C0-2 angle (r=0.54; P<0.001), but negatively correlated with the postoperative C2-7 angle (r=−0.79; P<0.001). Conclusions: Changes in OA alignment before and after surgery are associated with changes in the subaxial spine. There is a high incidence of postoperative DDD in the subaxial spine that seems to be related to sagittal alignment after surgery.

Cable-strengthened C2 pedicle screw fixation in the treatment of congenital C2-3 fusion, atlas occipitalization, and atlantoaxial dislocation.

BACKGROUND Atlas occipitalization and congenital C2-3 fusion often result in atlantoaxial dislocation (AAD) and superior odontoid migration that requires occipitocervical fixation. The widely used technique is posterior occiput-C2 fixation with pedicle screws. However, congenital C2-3 fusion cases tend to have thinner C2 pedicles that are inadequate for normal-sized pedicle screw fixation. With the presence of AAD, the strength of the fixation is further compromised as the C2 pedicle screws (C2PS) sustain considerable cephalic shearing force during the reduction procedure. Therefore, a novel technique has been developed to augment the C2 pedicle screw fixation with a strengthening cable. OBJECTIVE To introduce and assess this new technique. METHODS Seventy-six patients who underwent this procedure were reviewed. The position of the instrument and resultant fusion were examined retrospectively. In the biomechanical test, 6 fresh specimens were subjected to 2 types of fixation in the order of Oc-C2 screw-plate fixation followed by additional use of strengthening cable. Under 3 loading modes (extension-flexion, lateral bending, and axial rotation), the relative movement between the occiput and C2 was measured and compared in the form of range of motion. RESULTS The average follow-up time was 26 months. Solid fusion was achieved in 75 patients (98.7%) as assessed radiologically. The only patient who experienced hardware failure eventually obtained solid fusion between the occiput and C2 after revision. Biomechanically, there was significant difference between the occiput and C2 fixation and cable-strengthened fixation in range of motion for all modes. CONCLUSION This technique is a promising option for the treatment of AAD with congenital C2-3 fusion and occipitalization. Biomechanically, this technique can reduce the occipital-axial motion significantly compared with occiput-C2 fixation.

The reversibility of swan neck deformity in chronic atlantoaxial dislocations.

Study Design. Prospective case series and radiographical analysis. Objective. This study aimed to characterize the changes in subaxial alignment after surgical correction of occipitoaxial kyphosis, establish normal parameters, and report on clinical outcomes in a population of patients with chronic atlantoaxial dislocation patients presenting with swan neck deformities. Summary of Background Data. Swan neck deformity of the cervical spine is a term used to describe the simultaneous development of both abnormal kyphosis and hyperlordosis malalignments. Currently, there are no published series that discuss their outcomes after treatment and, more specifically, the subsequent changes that occur in the subaxial spine after the correction of the primary deformity in cases of chronic hyperkyphosis at the occipitoaxial segment. Methods. This was a prospective clinical and radiographical study in a population of patients with chronic atlantoaxial dislocation presenting with swan neck deformities. C0–C2 and C2–C7 angles were measured using plain radiographs pre- and postsurgery. The relationship between the alignment of the occipitoaxial joint and the subaxial cervical spine was evaluated. Japanese Orthopaedic Society scores were used to assess functional outcomes. Results. C0–C2 improved from a mean of −14.4° (SD, 9.5°) preoperatively to a mean of 7.8° (SD, 1.0°) postoperatively (P = 0.02). C2–C7 changed from a mean of 43° (SD, 2.8°) to a mean of 18.6° (SD, 11.2°) postoperatively (P = 0.02). A significant correlation was detected between the changes that occurred in the upper and lower cervical alignments (R2 = 0.133; P < 0.01). Clinically, the Japanese Orthopaedic Society preoperative scores improved significantly to postoperative (P < 0.01). Conclusion. This study reports the novel auto-correction of subaxial abnormalities after treatment of the primary upper cervical deformity and delineates the relationship between these 2 occurrences, thus demonstrating the reversibility of such complex abnormalities. Furthermore, the clinical outcomes after surgical treatment of swan neck deformities secondary to atlantoaxial dislocation are favorable and associated with a low complication rate. Level of Evidence: 2

Does atlantoaxial dislocation influence the subaxial cervical spine

IntroductionPrevious studies have reported that the alignments of the occipital-cervical and subaxial spine were closely interrelated in asymptomatic individuals; however, none have focused on a population with atlantoaxial dislocation.Material and methodsFrom 2007 to 2011, 298 patients with atlantoaxial dislocation and atlas occipitalization were studied. Angles formed between Occiput-C2 and C2–C7 were measured. The relationship between the alignment of the occipital-cervical junction and the subaxial cervical spine was evaluated.ResultsThe range of values for the angles measured was as followed: the Occiput-C2 angles were −35.2° to 44.8°, and the C2–C7 angles were −17.4° to 77.8°. Statistically significant negative correlations were observed between the Occiput-C2 and C2–C7 angles.ConclusionAnterior dislocations of the atlas are associated with diminished lordosis or even kyphosis of the occipital-cervical junction, and result in compensatory hyperlordosis of the subaxial cervical spine, collectively presenting as a “swan neck” deformity. Atlantoaxial dislocation may influence the global cervical alignment.

Atlantoaxial Rotatory Fixed Dislocation: Report on a Series of 32 Pediatric Cases.

Study Design. Retrospective case series of atlantoaxial rotatory fixed dislocation (AARFD). Objective. To describe clinical features and the surgical treatment of AARFD. Summary of Background Data. The classification and treatment strategy for atlantoaxial rotatory fixation (AARF) were previously described and remained controversial. AARF concomitant with atlantoaxial dislocation has different clinical features and treatment strategy with the most AARF. Due to deficiency of the transverse ligament or odontoid, the atlantoaxial remains unstable even after the torticollis relieved or cured. Because of the rarity, treatment strategy for this special condition has not been specialized and fully explored in the literatures. Methods. Thirty-two children with AARFD (sustained torticollis more than 6 weeks and atlanto-dental internal more than 5 mm) were retrospectively reviewed. Treatment methodology, pearls, and pitfalls of the treatment were discussed. Results. Thirty-two cases had sustained torticollis for an average of 5.7 months. ADI of them ranged from 8 to 22 mm, with a mean of 11.3 mm. Eight cases presented with signs and symptoms of spinal cord dysfunction. All 32 cases underwent surgery and had no spinal cord or vertebral artery injury. The surgery included posterior reduction and fusion (reducible dislocation and torticollis, 16 cases), and transoral release followed by posterior reduction and fusion (irreducible dislocation and torticollis, 16 cases). The average follow-up time was 42 months. Solid fusion and torticollis healing were achieved in 31 patients (96.9%) as detected radiologically. Two cases (6.3%, 2/32) suffered complications (cerebrospinal fluid leakage and recurred torticollis followed by revision). Conclusion. AARFD had distinct clinical features relative to common presentations of AARF. Because of deficiency of the transverse ligament or odontoid and subsequent atlantoaxial dislocation, surgical treatments are applied for this condition, including transoral release and posterior C1–2 reduction and fusion. AARFD cases were successfully managed surgically without preoperative traction, with few complications seen. Level of Evidence: 4