Indirect Ventral Brainstem Decompression by Posterior C1-C2 Distraction and Fixation for Basilar Invagination.

OBJECTIVE: Basilar invagination usually shows a decrease of clivus axis angle (CAA), which could give rise to progressive neural compression. Exploring a safe and effective fixation technique to achieve atlantoaxial stability and neural decompression remains necessary. In this study, we introduce a modified posterior C1-C2 distraction and fixation technique by which we obtained indirect ventral neural decompression and atlantoaxial stability in a series of patients with decreased CAA. METHODS: Thirty patients of basilar invagination were enrolled in our series. All patients underwent thin-slice computed tomography (CT) scan, magnetic resonance imaging, and dynamic plain radiography examinations before surgery, at discharge and during the follow-ups. Posterior C1-C2 facet joint release and intraoperative reduction by fastening rods were performed in all patients. The CAA was measured on midsagittal CT scans. Patients' neurologic status was evaluated by the Japanese Orthopaedic Association score. RESULTS: No neurovascular injury and serious postoperative complication occurred in all patients. Complete ventral brainstem decompression was achieved in 20 patients and partial in 10 patients. The mean postoperative CAA significantly improved to 132.6 degrees compared with the preoperative 123.6 degrees (P < 0.01). The bone fusion was confirmed in all patients on the basis of the last follow-up spine CT scans. CONCLUSIONS: Indirect ventral brainstem decompression by posterior C1-C2 distraction and fixation is a safe and effective technique for treatment of basilar invagination.

Can C1 lateral mass and C3 pedicle screw fixation be used as an option for atlantoaxial reduction and stabilization in Klippel-Feil patients? A study of its morphological feasibility, technical nuances, and clinical efficiency.

In Klippel-Feil patients with atlantoaxial dislocation, narrow C2 pedicles are often encountered preventing pedicle screw placement. Alternative techniques, including translaminar screws, pars screws, and inferior process screws could not achieve 3-column rigid fixation, and have shown inferior biomechanical stability. The present study aimed to evaluate the feasibility, safety, and efficacy of C3 pedicle screws (C3PSs) as an option for atlantoaxial stabilization in Klippel-Feil patients, and to introduce a freehand technique, the "medial sliding technique," for safe and accurate C3PS insertion. Thirty-seven Klippel-Feil patients with congenital C2-3 fusion who have received atlantoaxial fixation were reviewed. Preoperative CT and CT angiography were acquired to evaluate the feasibility of C3PS placement. C1 lateral mass and C3PS constructs were used for atlantoaxial stabilization. The "medial sliding technique" was introduced to facilitate C3PS insertion. Clinical outcomes and complications were evaluated, and screw accuracy was graded on postoperative CT scans. Morphological measurements showed that more than 80% C3 pedicles could accommodate a 3.5-mm screw. Fifty-eight C3PSs were placed in 33/37 patients using the medial sliding technique. Overall, 96.7% screws were considered safe and there was no related neurovascular complications; 27/33 patients exhibited neurological improvement and 30/33 patients had a solid bone fusion at an average 19.3-month follow-up. Therefore, the C3PS was a feasible option for atlantoaxial fixation in Klippel-Feil patients. The clinically efficiency of C3PS was satisfied with high fusion rates and low complications. The medial sliding technique we used could facilitate safe and accurate placement of C3PSs in Klippel-Feil patients with fused C2-3 vertebra.

Treatment of Reducible Atlantoaxial Dislocation and Basilar Invagination Using the Head Frame Reduction Technique and Atlantoaxial Arthrodesis.

STUDY DESIGN: Retrospective case series. OBJECT: To evaluate the outcomes of a head frame reduction and atlantoaxial arthrodesis technique for the treatment of reducible basilar invagination (BI) and atlantoaxial dislocation (AAD). METHODS: Seventy-two reducible BI and AAD cases who were treated with the head frame reduction and atlantoaxial arthrodesis technique from June 2015 to December 2018 were retrospectively analyzed. Radiological measurements including the atlantodental interval (ADI), the height of odontoid process above Chamberlain line, Wackenheim line, clivus-canal angle (CCA) and JOA score were evaluated. RESULTS: There was no death in this series. The follow-up period ranged from 6 to 32 months (mean: 21.2 months). Radiological, complete or 90% reduction was attained and complete decompression was demonstrated in all patients. The CCA increased from 123.22 ± 8.36 preoperatively to 143.05 ± 8.79 postoperatively (P < 0.01). There was no patient found postoperative dysphagia. Neurological improvement was observed in all patients, with the JOA scores increasing from 12.53 ± 1.93 preoperatively to 16.13 ± 1.23 postoperatively (P < 0.01). Solid bony fusion was demonstrated in 69 patients at follow-up (95.8%). CONCLUSION: Head frame reduction technique is a simple and effective treatment which could relief neurologic compression and adjust the CCA in patients with reducible AAD and BI with lower potential risks. Atlantoaxial fixation with short segmental fixation, strong purchase and low shearing force could maintain superior stabilization. The safety and long-term efficacy of such fixation and reduction technique were favorable, which illustrated that it could be a promising treatment algorithm for such kind of disease.

A novel surgical protocol for safe and accurate placement of C1 lateral mass screws in patients with atlas assimilation, basilar invagination and atlantoaxial instability: technical details, accuracy assessment and perioperative complications.

PURPOSE: To introduce a novel surgical protocol for safe and accurate placement of C1 lateral mass screws in patients with atlas assimilation, basilar invagination and atlantoaxial instability, and to categorize the screw accuracy and perioperative complications regarding this technique in a large case series. METHODS: Between January 2015 and January 2020, patients who had atlas assimilation, basilar invagination and atlantoaxial instability, and underwent atlantoaxial fixation using C1 lateral mass screws were reviewed. C1 lateral mass screws were placed with a novel surgical protocol following a series key steps, including posterior para-odontoid ligament release, panoramic exposure of the invaginated lateral mass, and diligent protection of the abnormal VA. Screw accuracy and related complications were specifically evaluated. RESULTS: A total of 434 C1 lateral mass screws were placed. Fifteen screws (3.5%) were classified as unacceptable, 54 screws (12.4%) were classified as acceptable, and 365 screws (84.1%) were classified as ideal. Overall, 96.5% of screws were deemed safe. There were no cases of vascular injury or permanent neurological defects. One patient with an unacceptable screw presented with hypoglossal nerve paralysis and recovered after an immediate revision surgery. Thirty-seven patients complained about occipital neuralgia and were successfully managed with medication. CONCLUSION: Placement of C1 lateral mass screws in patients with atlas assimilation, basilar invagination and atlantoaxial instability following this surgical protocol is safe and accurate. Thorough para-odontoid ligamental release, wide exposure of the invaginated lateral mass, and diligent protection of the vertebral artery are critical to maximize the chances of successful screw placement.

Feasibility of occipital condyle screw placement in patients with Chiari malformation type I: a computed tomography-based morphometric study.

BACKGROUND: The occipital condyle (OC) screw is an alternative technique for occipitocervical fixation that is especially suitable for revision surgery in patients with Chiari malformation type I (CMI). This study aimed to investigate the feasibility and safety of this technique in patients with CMI. METHODS: The CT data of 73 CMI patients and 73 healthy controls were retrospectively analyzed. The dimensions of OCs, including length, width, height, sagittal angle, and screw length, were measured in the axial, sagittal, and coronal planes using CT images. The OC available height was measured in the reconstructed oblique parasagittal plane of the trajectory. RESULTS: The mean length, width, and height of OCs in CMI patients were 17.79 ± 2.31 mm, 11.20 ± 1.28 mm, and 5.87 ± 1.29 mm, respectively. All OC dimensions were significantly smaller in CMI patients compared with healthy controls. The mean screw length and sagittal angle were 19.13 ± 1.97 mm and 33.94° ± 5.43°, respectively. The mean OC available height was 6.36 ± 1.59 mm. According to criteria based on OC available height and width, 52.1% (76/146) of OCs in CMI patients could safely accommodate a 3.5-mm-diameter screw. CONCLUSIONS: The OC screw is feasible in approximately half of OCs in CMI patients. Careful morphometric analyses and personalized surgical plans are necessary for the success of this operation in CMI patients.

C2 medial pedicle screw: a novel "in-out-in" technique as an alternative option for posterior C2 fixation in cases with a narrow C2 isthmus.

OBJECTIVE: The authors describe a novel "in-out-in" technique as an alternative option for posterior C2 screw fixation in cases that involve narrow C2 isthmus. Here, they report the preliminary radiological and clinical outcomes in 12 patients who had a minimum 12-month follow-up period. METHODS: Twelve patients with basilar invagination and atlantoaxial dislocation underwent atlantoaxial reduction and fixation. All patients had unilateral hypoplasia of the C2 isthmus that prohibited insertion of pedicle screws. A new method, the C2 medial pedicle screw (C2MPS) fixation, was used as an alternative. In this technique, the inner cortex of the narrow C2 isthmus was drilled to obtain space for screw insertion, such that the lateral cortex could be well preserved and the risk of vertebral artery injury could be largely reduced. The C2MPS traveled along the drilled inner cortex into the anterior vertebral body, achieving a 3-column fixation of the axis with multicortical purchase. RESULTS: Satisfactory C2MPS placement and reduction were achieved in all 12 patients. No instance of C2MPS related vertebral artery injury or dural laceration was observed. There were no cases of implant failure, and solid fusion was demonstrated in all patients. CONCLUSIONS: This novel in-out-in technique can provide 3-column rigid fixation of the axis with multicortical purchase. Excellent clinical outcomes with low complication rates were achieved with this technique. When placement of a C2 pedicle screw is not possible due to anatomical constraints, the C2MPS can be considered as an efficient alternative.

The Role of Transverse Connectors in C1-C2 fixation for Atlantoaxial Instability: Is It Necessary? A Biomechanical Study.

OBJECTIVE: To investigate the biomechanical effect of C1 lateral mass-C2 pedicle screw-rod (C1LM-C2PS) fixation with and without transverse connectors (TC) in an atlantoaxial instability (AAI) model. METHODS: Ten freshly frozen cadaveric specimens were tested using an industrial robot under the following conditions: intact model, AAI model, C1-C2 model, C1-C2 with one TC model, and C1-C2 with two TCs model. Three types of motion, flexion-extension (FE), lateral bending (LB), and axial rotation (AR), were applied (1.5 Nm) to the specimens. The range of motion (ROM) and neutral zone (NZ) between C1 and C2 in all directions were measured. RESULTS: Compared with those of the intact and AAI models, the C1-C2 ROM and NZ of all instrumented groups were decreased significantly in each direction of loading motion (P < 0.05). The mean FE ROM in the no TC, 1 TC, and 2 TC groups was 2.12° ± 0.41°, 2.29° ± 0.42°, and 2.04° ± 0.69°, respectively (P = 0.840, 0.981, 0.628, respectively); the mean LB ROM in the 3 intervention groups was 1.26° ± 0.67°, 1.02° ± 0.51° and 1.03° ± 0.57°, respectively (P = 0.489, 0.501, 1.000, respectively). During AR, the ROM and NZ of the no TC group (3.19° ± 0.89° and 1.51° ± 0.42°) were significantly reduced by more than 60% compared with those in the 1 (0.98° ± 0.28° and 0.40° ± 0.11°) and 2 TC groups (1.17° ± 1.69° and 0.42° ± 0.61°) (P < 0.001). Two TCs were equivalent for all loading motions to 1 TC (P > 0.05). CONCLUSIONS: Adding TCs to C1LM-C2PS can effectively decrease the axial rotation ROM and enhance the stability of C1-C2 segment. Therefore, it is necessary to use TC-strengthened C1 lateral mass -C2 pedicle screw-rod fixation in patients with instability of C1-C2.

Posterior atlantoaxial facet joint reduction, fixation and fusion as revision surgery for failed suboccipital decompression in patients with basilar invagination and atlantoaxial dislocation: Operative nuances, challenges and outcomes.

OBJECTIVE: To report the technical nuances and clinical outcomes of posterior atlantoaxial facet joint reduction, fixation and fusion (AFRF) technique as a revision procedure for BI and AAD patients with failed suboccipital decompression and large occipital bone defect. PATIENTS AND METHODS: We reviewed 32 patients with BI and AAD who were misdiagnosed as a simple Chiari malformation and received a suboccipital decompression surgery before admission. All patients underwent AFRF as a revision surgery. The separating, fusing, opacifying and false-coloring-volume rendering (SFOF-VR) technique was used to identify the course of the VA. Clinical and radiological outcomes were assessed after revision surgeries. RESULTS: Clinical symptoms improved in all patients. The postoperative atlantodens interval, Wackenheim line and clivus-canal angle significantly improved (all P < 0.01). Intraoperative dural tear and cerebrospinal fluid leakage occurred in 3 patients and were managed by suture repair and lumbar drain. Abnormal VA was identified in 7 patients and no VA injury occurred with the aid of SFOF-VR technique. The average follow-up was 19.1 months and atlantoaxial bone fusion was confirmed in 31 patients. CONCLUSION: For BI and AAD patients with failed suboccipital decompression, revision surgery is challenging. Occipitocervical fixation and posterior midline bone grafting are rather difficult due to the large occipital bone defect. The current study demonstrated that the posterior AFRF is a simple, safe and highly effective technique in revision surgery for such cases. For VA variations, the SFOF-VR technique is an effective tool to delineate the course VA.

Biomechanical evaluation of two alternative techniques to the Goel-Harms technique for atlantoaxial fixation: C1 lateral mass-C2 bicortical translaminar screw fixation and C1 lateral mass-C2/3 transarticular screw fixation.

OBJECTIVE: The authors conducted a study to investigate the biomechanical feasibility and stability of C1 lateral mass-C2 bicortical translaminar screw (C1LM-C2TL) fixation, C1 lateral mass-C2/3 transarticular screw (C1LM-C2/3TA) fixation, and C1LM-C2/3TA fixation with transverse cross-links (C1LM-C2/3TACL) as alternative techniques to the Goel-Harms technique (C1 lateral mass-C2 pedicle screw [C1LM-C2PS] fixation) for atlantoaxial fixation. METHODS: Eight human cadaveric cervical spines (occiput-C7) were tested using an industrial robot. Pure moments that were a maximum of 1.5 Nm were applied in flexion-extension (FE), lateral bending (LB), and axial rotation (AR). The specimens were first tested in the intact state and followed by destabilization (a type II odontoid fracture) and fixation as follows: C1LM-C2PS, C1LM-C2TL, C1LM-C2/3TA, and C1LM-C2/3TACL. For each condition, the authors evaluated the range of motion and neutral zone across C1 and C2 in all directions. RESULTS: Compared with the intact spine, each instrumented spine significantly increased in stability at the C1-2 segment. C1LM-C2TL fixation demonstrated similar stability in FE and LB and greater stability in AR than C1LM-C2PS fixation. C1LM-C2/3TA fixation was equivalent in LB and superior in FE to those of C1LM-C2PS and C1LM-C2TL fixation. During AR, the C1LM-C2/3TA-instrumented spine failed to maintain segmental stability. After adding a cross-link, the rotational stability was significantly increased in the C1LM-C2/3TACL-instrumented spine compared with the C1LM-C2/3TA-instrumented spine. Although inferior to C1LM-C2TL fixation, the C1LM-C2/3TACL-instrumented spine showed equivalent rotational stability to the C1LM-C2PS-instrumented spine. CONCLUSIONS: On the basis of our biomechanical study, C1LM-C2TL and C1LM-C2/3TACL fixation resulted in satisfactory atlantoaxial stabilization compared with C1LM-C2PS. Therefore, the authors believe that the C1LM-C2TL and C1LM-C2/3TACL fixation may serve as alternative procedures when the Goel-Harms technique (C1LM-C2PS) is not feasible due to anatomical constraints.

Can Posterior Reduction Replace Odontoidectomy as Treatment for Patients With Congenital Posterior Atlantoaxial Dislocation and Basilar Invagination?

BACKGROUND: For patients with odontoid process protrusion and basilar invagination, posterior screw-rod fixation can usually achieve satisfactory horizontal reduction, but in some cases satisfactory reduction in the vertical direction cannot be achieved at the same time. OBJECTIVE: To propose a method for calculation of the theoretical maximum vertical reduction possible in individual patients. METHODS: The computed tomography imaging data of patients with occipitalization and basilar invagination who were treated at our institute between January 2013 and June 2016 were retrospectively analyzed. The direction of odontoid reduction was decided by the inclination of the lateral joint. The atlanto-dental distance was assumed to be the maximum possible reduction in the horizontal direction. The maximum vertical reduction possible was calculated based on these values. RESULTS: A total of 82 patients (34 males and 48 females) were included. The theoretical vertical reduction value was 4.2 ± 3.0 mm, which was significantly smaller than that of the dental protrusion (14.5 ± 3.8 mm, P = .000). Analysis of follow-up data (29 cases) showed that, the difference between the theoretical vertical reduction value H (4.7 ± 3.5 mm) and the actual vertical reduction value Ha (5.6 ± 3.5 mm) was not significant (P = .139). CONCLUSION: The theoretical calculation method we proposed can well predict the actual degree of vertical reduction. The theoretical vertical reduction value is significantly lower than the odontoid protrusion value, indicating that satisfactory reduction in the vertical direction is difficult with a posterior approach alone.

Usefulness of 3D Printed Models in the Management of Complex Craniovertebral Junction Anomalies: Choice of Treatment Strategy, Design of Screw Trajectory, and Protection of Vertebral Artery.

OBJECTIVE: To evaluate the usefulness of 3-dimensional (3D) printed models as an aid for the treatment of complex CVJ anomalies. METHODS: 3D printed models were fabricated for 21 patients with complex CVJ anomalies, including vertebral artery anomaly, thin C2 pedicle, vertical atlantoaxial facet joint, or rotational dislocation combined with atlantoaxial dislocation and basilar invagination. Preoperative planning, surgical simulation, and intraoperative reference were achieved using the 3D model during the surgical treatment. The usefulness of 3D printed models, and postoperative clinical and radiological outcomes were assessed. RESULTS: Direct posterior reduction and atlantoaxial fixation were achieved in 19 patients. Transoral odontoidectomy followed by posterior fixation was implemented for 2 patients with vertical facet joint and rotational dislocation. All screws were safely inserted with no complication, and 90% patients achieved a >60% reduction of both horizontal and vertical dislocation. Clinical symptoms improved in all patients, with the averaged Japanese Orthopedic Association scores increasing from 11.14 to 14.43 (P < 0.01). CONCLUSIONS: The patient-specific 3D printed model would be an effective tool for evaluation of the reducibility of the atlantoaxial dislocation and basilar invagination, decision making in choosing the optimal surgical approach and way of fixation, and precise placement of the screw while protecting the vertebral artery and spinal cord. The risk of neurovascular injury was minimized, and encouraging outcomes were achieved with the aid of this technique.

Effects of transverse connector on reduction and fixation of atlantoaxial dislocation and basilar invagination using posterior C1-C2 screw-rod technique.

BACKGROUND CONTEXT: The mechanical strength provided by internal fixation is crucial for maintaining reduction and facilitating bony fusion. Though satisfactory results with the C1-C2 technique have been acquired in most clinical reports, the related problems of fusion delay and pseudarthrosis still exist. To increase the chance of bony fusion, a transverse connector (TC) is frequently used to augment torsional stiffness of thoracolumbar screw/rod constructs. Nevertheless, the clinical implication of TC in the management of atlantoaxial dislocation (AAD) and basilar invagination (BI) remains largely unknown. PURPOSE: To evaluate the effects of TC application on C1-C2 screw-rod constructs based on consecutive adult patients with AAD and BI in a single institution over a 10-year period. STUDY DESIGN: A retrospective study. PATIENT SAMPLE: Patients with AAD and BI, who were treated with posterior C1-C2 screw-rod technique with or without TC usage from June 2007 to June 2017 at a single institution. OUTCOME MEASURES: The radiological measurements included the anterior atlantodental interval (AADI), posterior atlantodental interval (PADI), height of odontoid process above Chamberlain line, and cervicomedullary angle (CMA). Patients' neurologic status was evaluated with the Japanese Orthopaedic Association (JOA) score. Fusion status was evaluated at different follow-up periods. METHODS: We compared the difference of clinical, radiological, and surgical outcomes between the TC and NTC groups postoperatively. RESULTS: In total, there were 149 consecutive patients in the TC group and 168 patients in the NTC group. On average, 1.2 TCs per patient were used in the TC group. No significant differences were identified for operative time and blood loss between groups. There was also no statistical difference in the radiological measurements of AADI, PADI, Chamberlain line, and CMA between the TC and NTC groups preoperatively and postoperatively. A significantly higher JOA score was obtained in the TC group than that in the NTC group postoperatively. The fusion rates were higher in the TC group than those in the NCT group at the early stage postoperatively (3 and 6 months; p<.01). CONCLUSIONS: Use of TCs seems to improve bony fusion and neurologic outcomes in the treatment of AAD and BI with C1-C2 screw-rod technique.

Three-Dimensional Evaluation and Classification of the Anatomy Variations of Vertebral Artery at the Craniovertebral Junction in 120 Patients of Basilar Invagination and Atlas Occipitalization.

BACKGROUND: Patients with basilar invagination and atlas occipitalization usually present abnormal anatomy of the vertebral arteries (VAs) at the craniovertebral junction (CVJ). OBJECTIVE: To describe and further classify different types of VA variations at the CVJ with 3D visualization technology. METHODS: One hundred twenty patients with basilar invagination and atlas occipitalization who had undergone 3-dimensional computed tomographic angiography (3D-CTA) were retrospectively studied. Imaging data were processed via the separating, fusing, opacifying, and false-coloring-volume rendering technique. Abnormal anatomy of the VA at the CVJ was categorized and related anatomic parameters were measured. RESULTS: Seven different types were classified. Type I, VAs enter the cranium after leaving VA groove on the posterior arch of atlas (26.7% of 240 sides); Type II, VAs enter an extraosseous canal created in the assimilated atlas lateral mass-occipital condyle complex before reaching the cranium (53.3%); Type III, VA courses above the axis facet or curves below the atlas lateral mass then enter the cranium (11.7%); Type IV, VAs enter the spinal canal under the axis lamina (1.3%); Type V, high-riding VA (31.3%); Type VI, fenestrated VA (2.9%); Type VII, absent VA (4.2%). Distance from the canal of Type II VA to the posterior facet surface of atlas lateral mass (5.51 ± 2.17 mm) means a 3.5-mm screw can be safely inserted usually. Shorter distance from the midline (13.50 ± 4.35) illustrates potential Type III VA injury during exposure. Decreased height and width of axis isthmus in Type V indicate increased VA injury risks. CONCLUSION: Seven types of VA variations were described, together with valuable information helpful to minimize VA injury risk intraoperatively.

Morphometric Measurements of the C1 Lateral Mass with Congenital Occipitalization of the Atlas.

OBJECTIVE: Unfamiliarity with the morphometry of the assimilated C1 lateral mass (C1LM) could make screw placement dangerous. In the present study, we defined the morphometric dimensions of the occipitalized C1LM to provide surgeons with valuable information for preoperative planning. METHODS: Thin-slice computed tomography scanning data from 131 patients with occipitalization of the atlas (OA) and 50 control cases were imported into Mimics software for analysis. The widths and heights of the C1LM were fully measured in the different planes. The ideal inward angulation and the safe maximum cephalic angulation of C1 screw trajectory were evaluated. RESULTS: Except for the medial height, all the widths and heights of C1LM were significantly shorter in the OA group than those in the control group. The ideal inward angle (α) was significantly larger in the OA group (23.8° ± 8.3°) than that (15.3° ± 3.8°) in the control group; the corresponding screw length was also significantly longer in the OA group (20.9 ± 2.9 mm). The safe maximum cephalic angles (ß) of the screw trajectory did not reach a significant difference between the 2 groups. All the widths and heights were shorter in the females than those in the males. The α angle also did not reach a significant difference between the sexes; however, the ß angles in the males (35.9° ± 10.4°) was significantly larger than that in the females (32.0° ± 9.4°). CONCLUSIONS: Although the hypoplastic C1LM brings limitations to screw insertion to some extent, it is still broad enough to accommodate a screw safely in both female and male patients. Considering the irregularity of the C1LM in patients with OA, the preoperative imaging assessment is critical, and C1LM screw placement should be performed individually.

Surgical Treatment of Occipitocervical Dislocation with Atlas Assimilation and Klippel-Feil Syndrome Using Occipitalized C1 Lateral Mass and C2 Fixation and Reduction Technique.

OBJECTIVE: To introduce and assess a surgical treatment of occipitocervical (OC) dislocation with atlas assimilation and Klippel-Feil syndrome (KFS) using occipitalized C1 lateral mass and C2 fixation and reduction technique. METHODS: From January 2007 to August 2013, 58 symptomatic patients with OC dislocation and KFS of C2-3 congenital fusion and atlas assimilation were surgically treated in our institution via this technique. After opening the C1-2 facet joints via a posterior approach, OC reduction was conducted by intraoperative manipulation and C1 lateral mass and C2 pedicle screw and rod fixation. The instrument position, fusion status, and clinical outcome were analyzed. RESULTS: The average follow-up was 36 months (range, 18-52 months). Radiologically, effective reduction was achieved in 56 patients (96.6%) and <50% reduction in 2 (3.4%) who had additional transoral decompression. Neurologic improvement and solid bone fusion were achieved in all patients. The clinical symptoms improved for all patients, with the averaged Japanese Orthopedic Association myelopathy scores increasing from 11.5 to 15.6 (P < 0.01). CONCLUSIONS: In patients with OC dislocation and KFS of C2-3 fusion and atlas assimilation, posterior manipulative reduction combined with occipitalized C1 lateral mass and C2 fixation provides a reliable and effective treatment.

Posterior Reduction of Fixed Atlantoaxial Dislocation and Basilar Invagination by Atlantoaxial Facet Joint Release and Fixation: A Modified Technique With 174 Cases.

BACKGROUND: Treatment of fixed atlantoaxial dislocation (AAD) with basilar invagination (BI) is challenging. OBJECTIVE: To introduce a modified technique to reduce fixed AAD and BI through a posterior approach. METHODS: From 2007 to 2013, 174 patients with fixed AAD and BI underwent surgical reduction by posterior atlantoaxial facet joint release and fixation technique. RESULTS: There was 1 death in the series, and 3 patients were lost to follow-up. The follow-up period ranged from 12 to 52 months (mean: 35.2 months) for the remaining 170 patients. Neurological improvement was observed in 168 of 170 patients (98.8%), and was stable in 1 (0.06%) and exacerbated in 1 (0.06%), with the Japanese Orthopedic Association scores increasing from 11.4 preoperatively to 15.8 postoperatively (P < .01). Radiologically, complete or >90% reduction was attained in 107 patients (62.9%), 60% to 90% reduction was attained in 51 patients (30%), and <50% reduction was attained in 12 patients (7.1%), who underwent additional transoral decompression. Complete decompression was demonstrated in all 170 patients. Solid bony fusion was demonstrated in 167 patients at follow-up (98.2%). CONCLUSION: This series showed the safety and efficacy of the posterior C1-2 facet joint release and reduction technique for the treatment of AAD and BI. Most fixed AAD and BI cases are reducible via this method. In most cases, this method avoids transoral odontoidectomy and cervical traction. Compared with the occiput-C2 screw method, this short-segment C1-2 technique exerts less antireduction shearing force, guarantees longer bone purchase, and provides more immediate stabilization.

C1 lateral mass screw placement in occipitalization with atlantoaxial dislocation and basilar invagination: a report of 146 cases.

STUDY DESIGN: Retrospective study of 146 patients with the diagnosis of occipitalization, atlantoaxial dislocation (AAD) and basilar invagination, using a novel surgical treatment strategy. OBJECTIVE: To introduce a novel fixation and reduction technique. SUMMARY OF BACKGROUND DATA: Atlas occipitalization associated with basilar invagination often result in fixed AAD that need reduction and occipitocervical fixation. The widely used occipitocervical fixation with suboccipital screws has several limitations such as the poor screw purchase in maldevelopment of the occipital bone, limited area available for implants in previous suboccipital craniectomy. The placement of occipitalized C1 lateral mass screw is an alternative option. METHODS: From June 2007 to June 2013, 146 patients of occipitalized atlas with fixed AAD and basilar invagination, underwent fixation and reduction via C1 lateral mass and C2 pars/pedicle screw. RESULTS: A total of 143 patients achieved the follow-up in the range from 6 months to 4 years (average, 30 mo). Neurological improvement was seen in all the 143 patients, with the averaged Japanese Orthopedic Association scores increasing from 11.6 to 15.5. Radiographical evaluation showed that solid bony fusion was achieved in all patients, and complete reduction was attained in 95 patients, and partial reduction (>60%) in 40 patients, and no effective reduction in 8 patients who had additional transoral decompression. Magnetic resonance imaging demonstrated that the ventral cervicomedullary compression was relieved in all patients. CONCLUSION: Although technically demanding, the C1 lateral mass placement in occipitalization is very useful in the rescue situation where more conventional stabilization alternatives are not technically possible, or as routine occipitocervical stabilization. It provides firm stabilization offering an optimum situation for bony fusion, and meanwhile the effective reduction of fixed AAD and basilar invagination. An extremely high fusion rate can be expected with minimal complications and minimal postoperative immobilization with this technique.

Posterior C1-C2 screw and rod instrument for reduction and fixation of basilar invagination with atlantoaxial dislocation.

PURPOSE: To report the surgical technique and preliminary clinical results for the treatment of basilar invagination (BI) with atlantoaxial dislocation (AAD) by posterior C1-C2 pedicle screw and rod instrument. METHODS: Between July 2012 and August 2013, 33 patients who had BI with AAD underwent surgery at our institution. Pre and postoperative three-dimensional computed tomographic (CT) scans were performed to assess the degree of dislocation. Magnetic resonance (MR) imaging was used to evaluate the compression of the medulla oblongata. For all patients, reduction of the AAD was conducted by two steps: fastening nuts and rods was performed to achieve the horizontal reduction. Distraction between C1 and C2 screws was performed to obtain the vertical reduction. RESULTS: No neurovascular injury occurred during surgery. Follow-up ranged from 6 to 15 months (mean 10.38 months) in 32 patients. Post-operative three-dimensional CT showed that complete horizontal reduction was obtained in 30/33 (90.9%), and complete vertical reduction was obtained in 31/33 (93.9%). The repeated three-dimensional CT and MR image demonstrated that bony fusion and the decompression of the medulla oblongata were obtained in all patients. Clinical symptoms improved significantly 3 months after surgery. CONCLUSIONS: This C1-C2 pedicle screw and rod instrument is a promising technique for the treatment of BI with AAD.

Posterior realignment of irreducible atlantoaxial dislocation with C1-C2 screw and rod system: a technique of direct reduction and fixation.

BACKGROUND CONTEXT: Treatment of chronic and irreducible atlantoaxial dislocation (AAD) with ventral compression is challenging for surgeons. The main procedures are occipitocervical/C1-C2 fusion after transoral odontoidectomy or release of the periodontoid tissues. These surgical procedures, which are performed simultaneously or intermittently, have many disadvantages that may discount their effectiveness. Therefore, a more effective way to achieve surgical reduction and to keep solid stability with only a single procedure is needed. PURPOSE: We describe a technique to reduce chronic and irreducible AAD with C1 lateral mass and C2 pedicle screw and rod system. STUDY DESIGN: This was a retrospective case series. PATIENT SAMPLE: Our sample comprised 26 patients (9 men and 17 women) with irreducible AAD who ranged in age from 15 to 54 years (mean, 35 years). OUTCOME MEASURES: Patients' neurologic status was evaluated with the Japanese Orthopedic Association (JOA) scale. METHODS: Twenty-six symptomatic patients underwent posterior realignment and reduction through the C1 lateral mass and C2 pedicle screw and rod system. The proposed mechanism of reduction is that the implanted screws and rods between C1 and C2 acting as a lever system drew C1 backward and pushed C2 downward and forward after removing circumambient obstruction and scars and thoroughly releasing the facet joints. The preoperative and postoperative JOA score, the extent of reduction, and the conditions of C1-C2 bony fusion were examined. RESULTS: No neurovascular injury occurred during surgery. Follow-up ranged from 6 to 40 months (mean 20.7 months). Radiographic evaluation showed that solid bony fusion was achieved in all patients, and that complete reduction was attained in 18 patients and partial reduction (>60% reduction) in 8 patients. The mean postoperative JOA score at last follow-up was 15.7, compared with the preoperative score of 12.1 (p<.01). CONCLUSIONS: This C1-C2 screw and rod system provides reliable stability and sufficient reduction of the anatomic malalignment at the craniovertebral junction and meanwhile retains the mobility of atlanto-occipital joints in the treatment of chronic and irreducible AAD. Sophisticated skills, thorough release of the facet joints, and intraoperative protection of the vertebral artery are key points to accomplish this technique.