A novel computed tomography scoring system for evaluating the risk of dural defects in anterior surgery for cervical ossification of the posterior longitudinal ligament.

OBJECTIVE: To develop and validate a computed tomography (CT)-based scoring system for evaluating the risk of dural defects (DDs) in anterior surgery for cervical ossification of the posterior longitudinal ligament (OPLL). METHODS: We retrospectively analyzed CT imaging features of 114 OPLL patients in our institute who received anterior decompression surgery. Intraoperative DDs were found in 16 patients. A multivariable logistic regression was used to evaluate the predictors. According to the odd ratio of the included risk factors, we developed a CT scoring system for evaluating the risk of DDs in anterior OPLL surgery. The system was further validated in an independent group of 39 OPLL patients. RESULTS: We developed a CT scoring system as follows: hook sign (2 points), K-line (-) (1 point) and broad base (1 point). Thus, the system comprised 4 total points, and patients were at high risks of dural defects when the score ≥3 points. The operating characteristics of a score ≥3 for predicting DDs in the validation group were: sensitivity of 0.83, specificity of 0.94, LR positive of 13.75, LR negative of 0.18 and AUC of 0.886. The discriminatory ability of the proposed score could be demonstrated in the validation cohort. CONCLUSIONS: The relatively simple and easy-to-use scoring system we propose integrates the 3 most reliable spinal CT findings observed in patients with OPLL and a DD. The likelihood to identify the underlying risks of spinal CSF leaks may be useful to triage patients who may benefit from indirect decompression techniques.

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.

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.

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.

Predictors for Development of Symptomatic Myelopathy in Patients with Radiculopathy Caused by Cervical Ossification of Posterior Longitudinal Ligament.

OBJECTIVE: To identify clinical factors predicting the development of myelopathy in cervical ossification of the posterior longitudinal ligament (OPLL) patients with radiculopathy. METHODS: We retrospectively reviewed 83 cervical OPLL patients who presented with radiculopathy. On the basis of the symptoms and physical findings, we divided patients into 2 groups: myelopathy group and nonmyelopathy group. Demographic, clinical, and radiologic characteristics were reviewed and analyzed among the 2 groups. Predictors for the development of myelopathy were assessed via univariate and multivariate analysis. RESULTS: Univariate analysis demonstrated that a high occupying ratio and the presence of an intramedullary high signal were risk factors for development of myelopathy from radiculopathy in OPLL patients. Multivariate analysis further identified that a high occupying ratio was the only independent predictor (odds ratio 1.05, 95% confidence interval 1.003-1.091, P = 0.035). The cervical range of motion and minor trauma were not related to the development of myelopathy in our study. CONCLUSIONS: Nonmyelopathic OPLL patients with radiculopathy and a high occupying ratio were at higher risk of developing myelopathy, and surgical intervention should be recommended in these cases. However, for elderly patients with significant comorbid conditions, the risks and benefits of surgery should be carefully considered.

Carotid Artery-Related Perioperative Stroke Following Anterior Cervical Spine Surgery: A Series of 3 Cases and Literature Review.

BACKGROUND: Vascular complications following anterior cervical spine surgery are rare but potentially devastating. Complications associated with the carotid artery are even more disastrous but largely anecdotal, with no more than 4 reported cases. MATERIALS AND METHODS: We report 3 new cases of carotid artery-related perioperative stroke following anterior cervical spine surgery. All 3 patients had carotid artery atherosclerosis and the time of intraoperative carotid artery retraction was longer than 1 hour. One patient underwent hypotension during surgery. Risk factors as well as prevention and management protocols of carotid artery-related perioperative stroke based on the literature review and our clinical experience are discussed. CONCLUSIONS: Carotid artery-related perioperative stroke following anterior cervical spine surgery is extremely rare. Prolonged traction, carotid artery atherosclerosis, and intraoperative hypotension can produce cerebral hypoperfusion and cause ischemic stroke. Preoperative risk assessment, adequate perioperative manipulation, and postoperative management can minimize overall morbidity and mortality.

Risk Factors and Management of Dural Defects in Anterior Surgery for Cervical Ossification of the Posterior Longitudinal Ligament.

OBJECTIVE: To investigate risk factors and outcomes and to develop a cogent perioperative management algorithm for dural defects (DDs) in anterior surgery for cervical ossification of the posterior longitudinal ligament (OPLL). METHODS: Ninety OPLL patients who had undergone anterior cervical decompression between January 2014 and December 2016 were reviewed. DDs occurred in 12 patients. Demographic, clinical, and radiologic data; intraoperative and postoperative management; and complications were analyzed. Risk factors for DDs were assessed with multivariate analysis. A treatment algorithm was identified based on these findings and our experience. RESULTS: The prevalence of DDs was 13.3% (12/90). Univariate and multivariate analyses showed that the ratio of OPLL base to spinal canal (odds ratio [OR] 1.09, P = 0.012), kyphotic cervical alignment with thick OPLL masses (OR 9.44, P = 0.026), and lateral, curved, and irregular OPLL masses (OR 8.28, P = 0.037) could be risk factors for DDs. DDs were repaired intraoperatively with onlay grafts, and lumbar drains were placed in all DD patients. The treatment was successful in all DD patients, and outcome measures did not differ between the DD and no DD groups. No patient had experienced complications associated with DDs and CSF leaks at the final follow-up visit. CONCLUSIONS: Patients with broad-based OPLL, kyphotic cervical alignment with thick OPLL masses, and lateral, curved, and irregular OPLL masses have a higher risk of DD in anterior surgery for OPLL. Intraoperative primary repair with onlay grafts combined with early lumbar drains is a simple, safe, and effective strategy for DDs. The outlook for the long-term sequelae of DDs is optimistic if they are managed adequately.