Release, reduction, and fixation of one-stage posterior approach for basilar invagination with irreducible atlantoaxial dislocation

Novel MRI signs of the atlantodental space in patients with atlantoaxial dislocation

OBJECTIVES

The type of atlantodental space tissue in patients with atlantoaxial dislocation (AAD) can help doctors understand the possibility of reduction before surgery. However, relevant research on this topic is lacking. In this study, we aimed to summarise the atlantodental space classification of patients with AAD using magnetic resonance imaging (MRI) and explore their clinical characteristics.

MATERIALS AND METHODS

Preoperative 3T cervical MR images of patients who underwent posterior reduction and fixation surgery for non-traumatic AAD between 1 September 2012 and 31 July 2023 were collected. Two radiologists read and recorded the MRI results based on the standard protocol. The kappa value was used to evaluate intra- and inter-observer agreements. The patient's age, sex, body mass index, clinical symptoms, Japanese Orthopaedic Association (JOA) score, and visual analogue scale information were obtained from medical records.

RESULTS

A total of 135 patients with AAD (mean age, 51.3 ± 14.0 years, 52 men) were included in the analysis. The inter-observer agreement between the two readers was 0.818 (P < 0.0001). The intra-observer consistencies were 0.882 (P < 0.0001) and 0.896 (P < 0.0001). Patients with inflexible tissue signs exhibit more irreducible in hyperextension position, and their range of motion of ADI is smaller. These patients were older and had a higher incidence of abnormal spinal cord signals and JOA scores.

CONCLUSIONS

Novel MRI signs exhibited high inter- and intra-observer consistency and were associated with patient age, abnormal spinal cord signals, reducibility, range of motion of ADI, and symptoms.

The development of posterior reduction forceps for atlantoaxial dislocation and its preliminary application in irreducible atlantoaxial dislocation

OBJECTIVE

To develop posterior reduction forceps for atlantoaxial dislocation and evaluate the preliminary clinical application of this forceps in assisting simple posterior screw-rod system reduction and fixation in the treatment of irreducible atlantoaxial dislocation.

METHODS

Based on the posterior atlantoaxial screw-rod system, posterior reduction forceps was developed to assist simple posterior screw-rod system for the treatment of irreducible atlantoaxial dislocation. From January 2021 to October 2022, 10 cases with irreducible atlantoaxial dislocation were treated with this technique. The Japanese Orthopaedic Association (JOA) score was applied before and after surgery to evaluate the neurological status of the patient, and the Atlanto-dental interval (ADI) was measured before and after surgery to evaluate the atlantoaxial reduction. X-ray and CT were performed to evaluate internal fixation, atlantoaxial sequence and bone graft fusion during regular follow-up. MRI was performed to evaluate the status of atlantoaxial reduction and spinal cord compression after surgery.

RESULTS

All 10 patients were successfully operated, and there were no complications such as spinal nerve and vascular injury. Postoperative clinical symptoms were significantly relieved in all patients, and postoperative JOA score and ADI were significantly improved compared with those before surgery (P < 0.05).

CONCLUSIONS

The developed posterior reduction forceps for atlantoaxial dislocation can assist the simple posterior screw-rod system in the treatment of irreducible atlantoaxial dislocation to avoid the release in anterior or posterior approach and reduce the difficulty of surgery. The preliminary results of this technique are satisfactory and it has a good application prospect.

Sagittal slope angle of lateral atlantoaxial articulation is associated with the severity of basilar invagination with atlantoaxial dislocation and predicts reduction degree after surgery

OBJECTIVE

To investigate (1) lateral atlantoaxial articulation (LAA) morphology in patients with basilar invagination (BI) with atlantoaxial dislocation (AAD) and healthy individuals and its relationship with the severity of dislocation and (2) the effect of the LAA morphology on reduction degree (RD) after surgery.

METHODS

In this retrospective propensity score matching case-control study, imaging and baseline data of 62 patients with BI and AAD from 2011 to 2022 were collected. Six hundred thirteen  participants without occipitocervical junctional deformity served as controls. Logistic regression and receiver operating characteristic (ROC) curve were used for analysis.

RESULTS

The age, BMI and sex did not differ significantly between the two groups after propensity score matching. Sagittal slope angle (SSA) and coronal slope angle (CSA) was lower and greater, respectively, in the patient group than in the control group. A negative SSA value usually indicates anteverted LAA. Regression analysis revealed a significant negative correlation between SSA and severity of dislocation. However, no relationship was found between CSA and the severity of dislocation. The multivariate logistic regression analysis revealed that minimum-SSA emerged as an independent predictor of satisfactory reduction (RD ≥ 90%). The ROC curve demonstrated an area under the curve of 0.844, with a cut-off value set at -40.2.

CONCLUSION

SSA in patients group was significantly smaller and more asymmetric than that in the control group. Dislocation severity was related to SSA but not to CSA. Minimum-SSA can be used as a predictor of horizontal RD after surgery.

The Classification of Axial Deformity in Patients with Basilar Invagination

OBJECTIVE

To summarize the variation types of the axis in patients with basilar invagination (BI), then propose a classification scheme of the axis deformity.

METHODS

From December 2013 to September 2020, 92 patients (male 42, female 50) who were diagnosed with BI were studied retrospectively. Based on the imaging data of CT, the width and height of the axis pedicle and the sagittal diameter of the lateral mass were measured in each patient. According to the development of axis pedicle and lateral mass, the types of axis variation were summarized, and then the classification scheme of axis deformity was put forward.

RESULTS

All cases were analyzed and axis deformities were divided into four types. Type I: the axis is basically normal (53 cases, 57.6%). Type II: axis lateral mass is dysplasia (eight cases, 8.7%), which includes two subtypes: type IIA, the axis unilateral lateral mass is dysplasia (three cases); type IIB, the axis bilateral lateral masses are all dysplasia (five cases). Type III: axis pedicle is dysplasia (11 cases, 12%), which is subdivided into two subtypes: type IIIA, the axis unilateral pedicle is dysplasia (six cases); type IIIB, the axis bilateral pedicles are all dysplasia (five cases). Type IV: axis pedicle and lateral mass are all dysplasia (20 cases, 21.7%), this type contains the following four subtypes: type IVA, the unilateral axis pedicle and unilateral lateral mass (contralateral or ipsilateral) are all hypoplasia (four cases); type IVB, the unilateral axis pedicle and bilateral lateral masses are all hypoplasia (five cases); type IVC, the bilateral axis pedicles and unilateral lateral mass are all dysplasia (seven cases); type IVD, the bilateral axis pedicles and bilateral lateral masses are all dysplasia (four cases). The left and right abnormal lateral mass sagittal diameter (Type II) was (7.23 ± 1.39) mm and (5.96 ± 1.37) mm, respectively, the left and right abnormal pedicle width (Type III) was (2.61 ± 1.01) mm and (3.23 ± 0.66) mm, respectively, left and right abnormal pedicle height (Type III) was (5.43 ± 2.19) mm and (4.92 ± 1.76) mm, respectively. Moreover, the classification scheme has good repeatability and credibility.

CONCLUSIONS

The classification about axis deformity could provide personalized guidance for axis screw placement in the BI and other upper cervical surgery, and axis screw placement errors would be effectively avoided.

Retropharyngeal Reduction Plate for Atlantoaxial Dislocation: A Cadaveric Test and Morphometric Trajectory Analysis

Objective

To evaluate the placement feasibility and safety of the newly designed retropharyngeal reduction plate by cadaveric test and to perform morphometric trajectory analysis.

Methods

The five cadaveric specimens with intact atlantoaxial joint were enrolled in this study. They were used for simulating the placement process and evaluating the placement feasibility of the retropharyngeal reduction plate. The atlantoaxial dislocation (AAD) of five cadaveric specimens were obtained by proper external force after dissecting ligaments. The retropharyngeal reduction plate was placed on atlantoaxial joint of cadaveric specimens. The X‐ray and three‐dimensional (3D) spiral CT were used for evaluating the placement safety of retropharyngeal reduction plate. The DICOM data was obtained after 3D spiral CT scanning for the morphometric trajectory analysis.

Results

The reduction plates were successfully placed on the atlantoaxial joint of five cadaveric specimens through the retropharyngeal approach, respectively. The X‐ray and 3D spiral CT showed the accurate screw implantation and satisfying plate placement. The length of the left/right atlas screw trajectory (L/RAT) was, respectively, 1.73 ± 0.01 cm (LAT) and 1.71 ± 0.02 cm (RAT). The length of odontoid screw trajectory (OST) was 1.38 ± 0.02 cm. The length of the left/right axis screw trajectory (L/RAXT) was, respectively, 1.67 ± 0.02 cm (LAXT) and 1.67 ± 0.01 cm (RAXT). There was no statistical significance between left side and right side in terms of AT and AXT (P > 0.05). The angles of atlas screw trajectory angle (ASTA), axis screw trajectory angle (AXSTA), and odontoid screw trajectory angle (OSTA) were 38.04° ± 2.03°, 56.92° ± 2.66°, and 34.78° ± 2.87°, respectively.

Conclusion

The cadaveric test showed that the retropharyngeal reduction plate is feasible to place on the atlantoaxial joint, which is also a safe treatment choice for atlantoaxial dislocation. The meticulous preoperative planning of screw trajectory based on individual differences was also vital to using this technique.