Abstract
Basilar invagination with assimilated atlas in adults may be accompanied by degenerative arthropathy, which can worsen instability and lead to neurological deterioration. A 36-year-old woman with a short neck presented wheelchair bound with complaints of chronic neck pain, bilateral hand clumsiness, and urinary urgency. Examination showed spastic quadriparesis, sensory impairment below the neck, and positive hand myelopathic signs (modified Japanese Orthopaedic Association score 9/18). Imaging demonstrated basilar invagination and assimilated atlas with asymmetric C1 to C2 facet joints, with severe cord compression and myelomalacia. Computed tomography and magnetic resonance imaging datasets were combined in a mixed reality (MR) viewer to generate 3-dimensional visualization. Using MR, the patient and family were counseled about the need for surgery. MR also facilitated preoperative surgical planning by improving anatomical understanding, particularly regarding the anatomy of asymmetric facets and screw trajectories. The patient underwent a posterior C1 to C2 joint reconstruction, reduction with facet spacers, and fusion using the Goel technique. At 1-year follow-up, the patient was able to ambulate on her own with improved neurology (modified Japanese Orthopaedic Association score 18/18). Reports describing MR applications in the evaluation and surgical planning of complex craniovertebral junction anomalies remain limited. In this case report, we describe the successful management of a complex craniovertebral junction anomaly and how MR devices supported the preoperative planning and facilitated counseling of an anxious patient.
Introduction
Craniovertebral junction (CVJ) anomalies commonly comprise atlantoaxial dislocation and basilar invagination, frequently associated with assimilation of the C1 arch.1 Basilar invagination may remain asymptomatic and unrecognized until adulthood.2 Goel’s technique, which involves facet joint release, placement of intraarticular spacers, and posterior atlantoaxial fixation, is widely used and consistently effective for management of such cases.3
With advances in spine surgery, virtual reality, augmented reality, and mixed reality (MR) are increasingly being incorporated into spine practice.4,5 MR blends augmented reality and virtual reality by placing virtual objects within the real environment in a way that allows them to respond to and interact with physical surroundings.4 Despite growing interest in immersive visualization technologies, the role of MR in guiding management of CVJ anomalies is not well established.
In this case report, we describe the successful single-stage posterior management of chronic atlantoaxial dislocation (AAD) secondary to basilar invagination (BI) with an assimilated atlas and asymmetric C1 to C2 facet joints using MR-assisted devices. We emphasize the contribution of contemporary technologies like MR-based preoperative planning and patient counseling. We also detail the operative steps and present the clinical and radiological outcomes.
Case Presentation
Written informed consent was obtained from the patient for publication of this case report. Institutional review board approval was not required for a single patient report at our institution. Figure 1 includes an image of the surgeon. Written consent for publication of the image was obtained from the surgeon.
Mixed reality-based data visualization, preoperative planning, and counseling. (A–D) Three-dimensional visualization of patient imaging and screw insertion planning. (E) Magic Leap 2 head-mounted display as demonstrated by the chief surgeon.
Case Description
A 36-year-old woman with chronic neck pain presented wheelchair bound with a 3-month history of progressive quadriparesis and hand clumsiness. She also reported urinary urgency and sensory loss below the neck. On presentation, she required 2-person assistance to stand and walk. Neurological examination revealed spasticity in all 4 limbs, bilateral positive Hoffmann sign, extensor plantar responses, and generalized hyperreflexia. Her modified Japanese Orthopaedic Association score at presentation was 9/18.
Radiographs showed an assimilated atlas and craniocervical kyphosis with normal to increased subaxial sagittal lordosis (Figure 2A). Magnetic resonance imaging showed basilar invagination with severe craniocervical canal stenosis and cord myelomalacia, with C1 assimilated with the base of the skull and altered signal changes at the tip of the odontoid (Figure 2B–D). The vertebral artery course looked normal (Figure 2E). Computed tomography (CT) midsagittal sections showed erosions and cystic changes at the tip of the odontoid process (Figure 3A). The right-sided C1 to C2 joint was more arthritic with a normally inclined joint surface (Figure 3B), whereas the left-sided joint was more vertical with less arthritic changes (Figure 3C). The odontoid tip projected 48 mm above the McGregor line, 38 mm above Chamberlain’s line, and 33 mm above McRae’s line (Figure 3D and E). Her sagittal atlantoaxial joint inclination angle was 173° on the right side and 141° on the left side. Data visualization and surgical planning were performed using the Brainlab Mixed Reality Viewer (Brainlab AG, Munich, Germany), which allows for viewing of patient data in 3 dimensions (3D; Figure 1A–D). We utilized the Magic Leap 2 head-mounted display (Magic Leap, Dania Beach, Florida, USA) for patient counseling and training of spine fellows prior to surgery (Figure 1E).
Preoperative radiographs and magnetic resonance imaging (MRI) of the craniovertebral junction. (A) Lateral cervical radiograph demonstrating assimilation of the atlas and craniocervical kyphosis (yellow arrow). (B–D) MRI showing basilar invagination with severe craniocervical canal stenosis and cervical cord myelomalacia (red arrow), with signal alteration at the tip of the odontoid process. (E) Normal course of vertebral artery on computed tomography angiography.
Preoperative computed tomography findings at the craniovertebral junction. (A) Midsagittal section demonstrating erosions and cystic changes at the odontoid tip (yellow arrow). (B) Parasagittal image showing arthritic changes in the right C1–C2 facet joint with a relatively normal joint inclination (red arrow). (C) Corresponding image of the left C1–C2 facet joint demonstrating a more vertical orientation with comparatively less degeneration (blue arrow). (D and E) Superior migration of the odontoid into the foramen magnum, confirmed by violation of Chamberlain’s and McRae’s lines.
Surgical Technique
The patient was managed preoperatively with skull traction up to 15 kg in the supine position with slight extension to reduce the basilar invagination (Figure 4A). X-ray images in traction after 12 hours showed no significant change (Figure 4B). She underwent posterior C1 to C2 joint manipulation, reconstruction, reduction, and fixation with iliac graft fusion.
(A) Preoperative skull traction up to 15 kg in the supine position with slight neck extension to facilitate reduction of basilar invagination. (B) Cervical radiograph obtained after 12 h of traction. (C and D) Postoperative radiographs demonstrating satisfactory alignment and instrumentation.
The patient underwent fiberoptic intubation and awake prone positioning. A preinduction neurological assessment was documented, after which general anesthesia was induced. The head was secured in Sugita 4-pin construct and was positioned in a slight reverse Trendelenburg position. A standard posterior C1 to C2 exposure was performed subperiosteally to avoid bleeding from the venous plexuses over C2 ganglia and C1 to C2 joint. On both sides, C2 ganglia were sacrificed to have better and wider visualization of the joint space.
The atlantoaxial joint on the left side was more vertical, and it was reconstructed using the ultrasonic bone scalpel (Sonopet, Stryker) into a horizontal joint, especially the C2 side of the joint. The right side joint was more oblique coronally, and it was prepared by denuding the cartilage to facilitate fusion. Joint spacers of appropriate sizes (right cage larger than left), along with bone grafts, were inserted for distraction and caudal translation of dens. The head at this stage was manipulated using the Sugita frame to reduce the C1 to C2 horizontal translation and the craniocervical kyphosis.
C2 pedicle screws were placed under navigation guidance (Loop X, Brainlab, Munich, Germany), followed by C1 lateral mass screws. The C1 screws were inserted in a subarticular, bicortical manner to optimize screw purchase and to facilitate further reduction of the anterior slip. A 2-hole plate of appropriate length was fastened with screws across the C1 to C2 joint to provide immediate joint stabilization and maintain the achieved reduction.
Creation of a clear space between the spinal cord and the C1 arch and visible cord pulsations intraoperatively confirmed adequate reduction and decompression. Therefore, foramen magnum decompression was not performed. Iliac grafts were harvested from the posterior iliac area and were used as onlay bone grafts over the C1 to C2 posterior surface for fusion. Postoperative radiographs looked satisfactory (Figure 4C and D). Neuromonitoring signals remained the same throughout the procedure.
No intraoperative complications occurred, and the patient tolerated the procedure well. She was monitored in the intensive care unit on postoperative day 1 and mobilized with support with a rigid cervical collar, which was continued for 6 weeks. A structured rehabilitation program was initiated, consisting of supervised in-hospital physiotherapy followed by home-based physiotherapy. At 1-year follow-up, she demonstrated marked neurological recovery and was able to ambulate independently, with an improvement in modified Japanese Orthopaedic Association score to 18/18 postoperatively and with radiographs demonstrating maintained reduction and stable instrumentation with evidence of fusion (Figure 5A and B). She had mild hypoesthesia in C2 dermatome, which was not bothersome to her.
One-year follow-up radiographs. (A) Anteroposterior open-mouth radiograph and (B) lateral cervical radiograph demonstrating maintained C1–C2 alignment with satisfactory implant position and stable fixation.
Discussion
In basilar invagination with assimilation of the atlas, the normal formation of the ligament complex that stabilizes C1 to C2 is altered.6 The primary pathology here is instability, and management rests on stabilization.7 The goals of surgery are multiplanar reduction (addressing anteroposterior translation, vertical odontoid migration, and associated kyphosis), decompression, and stabilization.
Our case was technically challenging because of the patient’s short neck and arthritic changes superimposed on a dysplastic C1 to C2 complex with assimilated atlas. Accessing the C1 to C2 joint in the setting of atlas assimilation is technically challenging, particularly with an incurved occiput. The joints are often deformed and markedly oblique, which can make adequate exposure and soft joint release difficult. In addition, significant preoperative anxiety of the patient added an important counseling challenge.
The use of an MR viewer helped us with preoperative planning of this complex CVJ anomaly case. By enabling an interactive 3D reconstruction from fused CT-magnetic resonance imaging datasets, MR improved our anatomical understanding of the asymmetric C1 to C2 complex. It also supported patient and family education by providing a clear, intuitive visualization of the deformity and thereby aided counseling and informed decision-making. Previous studies have demonstrated that XR (extended reality) platforms are effective adjuncts for spine fellowship training, facilitating clearer comprehension of complex CVJ anatomy and improving 3-dimensional understanding.8 Moreover, it gave us a 3D visualization of CVJ, which helped in preoperative rehearsal of the surgery in the surgeon’s mind. The Table summarizes the reported applications of XR, including virtual, augmented, and MR in CVJ surgery.
Reported XR (VR/AR/MR) applications in CVJ.
Reduction strategies include preoperative traction; Goel C1- to C2 joint release and distraction; constructs based on distraction, compression, extension, and reduction (DCER); and transoral approaches.12–14 Preoperative skeletal traction did not achieve meaningful reduction; hence, Magerl transarticular screw fixation was not considered suitable. We planned for a posterior C1 to C2 joint manipulation with interfacetal spacers, aiming for reduction using the Goel technique followed by definitive fixation.
A key anatomic issue was the markedly vertical left C1 to C2 facet orientation, which was visualized on the MR device. This made joint reconstruction mandatory to achieve reduction and stable alignment. The left facet joint was carefully opened using osteotomes to create space and was additionally burred to facilitate a more favorable, horizontalized joint surface for spacer placement. In such scenarios, a DCER technique can be avoided. The DCER technique requires occipital screw placement, which carries a risk of inadvertent dural tears and cerebrospinal fluid leak.1
We used a fulcrum maneuver in which bilateral joints were distracted with spacers and provided a controlled pivot to reduce the slip and translate the invaginated dens caudally away from the foramen magnum. After achieving reduction with spacer-assisted distraction, fixation was completed using a 2-hole plate construct to maintain the reduction and stability, with C2 anchored first, followed by C1 to facilitate stepwise, controlled correction. Implanted C1 to C2 instruments function as a lever mechanism, drawing C1 posteriorly while pushing C2 inferiorly and forward.15 Using intraoperative navigation, we were able to insert subarticular and bicortical screws at C1 to have better purchase over the plate, which can avoid the loosening of implants.
Conclusion
This case report is strengthened by the use of MR to visualize and communicate patient-specific anatomy to an anxious patient to understand the rationale for surgery and to train spine fellows. Surgically, we employed a single-stage posterior strategy comprising unilateral joint reconstruction, spacer-assisted reduction using a fulcrum maneuver, and definitive Goel-type fixation, achieving an excellent clinical recovery at 1-year follow-up. Nevertheless, this report remains a single-patient experience. Another limitation is the absence of postoperative follow-up CT assessment; therefore, radiological evaluation was based only on radiographs. Generalizability may be constrained by case-to-case variability, cost, and access to MR platforms, as well as the associated learning curve. Larger prospective series with standardized clinical and radiological endpoints are needed to clarify where MR adds value and to establish reproducible workflows for CVJ deformity surgery.
Acknowledgments
The authors thank the operating room, nursing, and physiotherapy teams at Aster Whitefield Hospital, Bengaluru, for their support in managing this complicated case.
Footnotes
Funding The authors received no financial support for the research, authorship, and/or publication of this article.
Declaration of Conflicting Interests The authors report no conflicts of interest in this work.
Research Ethics The procedure and reporting complied with the Declaration of Helsinki. Written informed consent for publication was obtained from the patient. IRB approval was not required for this single case technical note.
- This manuscript is generously published free of charge by ISASS, the International Society for the Advancement of Spine Surgery. Copyright © 2026 ISASS. To see more or order reprints or permissions, see http://ijssurgery.com.
References
- 1.↵Sarat Chandra P, Bajaj J, Singh PK, Garg K, Agarwal D. Basilar invagination and atlantoaxial dislocation: reduction, deformity correction and realignment using the DCER (distraction, compression, extension, and reduction) technique with customized instrumentation and implants. Neurospine. 2019;16(2):231–250. 10.14245/ns.1938194.097
- 2.↵Smith JS, Shaffrey CI, Abel MF, Menezes AH. Basilar invagination. Neurosurgery. 2010;66(3 Suppl):39–47. 10.1227/01.NEU.0000365770.10690.6F
- 3.↵Li T, Du YQ, Yin YH, Xing SL, Qiao GY. Treatment of reducible atlantoaxial dislocation and basilar invagination using the head frame reduction technique and atlantoaxial arthrodesis. Global Spine J. 2022;12(5):909–915. 10.1177/2192568220970164
- 4.↵Bui T, Ruiz-Cardozo MA, Dave HS, et al. Virtual, augmented, and mixed reality applications for surgical rehearsal, operative execution, and patient education in spine surgery: a scoping review. Medicina (Kaunas). 2024;60(2):332. 10.3390/medicina60020332
- 5.↵Morimoto T, Kobayashi T, Hirata H, et al. XR (extended reality: virtual reality, augmented reality, mixed reality) technology in spine medicine: status quo and quo vadis. J Clin Med. 2022;11(2):470. 10.3390/jcm11020470
- 6.↵Botelho RV, Ferreira JA, Zandonadi Ferreira ED. Basilar invagination: a craniocervical kyphosis. World Neurosurg. 2018;117:e180–e186. 10.1016/j.wneu.2018.05.233
- 7.↵Goel A. Basilar invagination: instability is the cause and stabilization is the treatment. Neurospine. 2020;17(3):585–587. 10.14245/ns.2040522.261
- 8.↵Cai S, He Y, Cui H, et al. Effectiveness of three-dimensional printed and virtual reality models in learning the morphology of craniovertebral junction deformities: a multicentre, randomised controlled study. BMJ Open. 2020;10(9):e036853. 10.1136/bmjopen-2020-036853
- 9.↵Ganeshkumar A, Katiyar V, Singh P, et al. Innovations in craniovertebral junction training: harnessing the power of mixed reality and head-mounted displays. Neurosurg Focus. 2024;56(1):E13. 10.3171/2023.10.FOCUS23613
- 10.↵Sanker V, Nordin EOR, Badary A, et al. Extended reality in skull base surgery: a systematic literature review. Front Surg. 2025;12:1642033. 10.3389/fsurg.2025.1642033
- 11.↵Zhang P, Sun Z, Zhang K, Guo J, Yang X. Augmented reality navigation technology in atlantoaxial pedicle screw fixation for atlantoaxial dislocation treatment. Front Surg. 2025;12:1574741. 10.3389/fsurg.2025.1574741
- 12.↵Duan W, Chou D, Jian F, Chen Z. Navigated transoral odontoidectomy to treat congenital basilar invagination after failed posterior reduction and fusion. Neurosurg Focus. 2020;3(1):V8. 10.3171/2020.4.FocusVid.20158
- 13.↵Goel A. Treatment of basilar invagination by atlantoaxial joint distraction and direct lateral mass fixation. J Neurosurg Spine. 2004;1(3):281–286. 10.3171/spi.2004.1.3.0281
- 14.↵Peng X, Chen L, Wan Y, Zou X. Treatment of primary basilar invagination by cervical traction and posterior instrumented reduction together with occipitocervical fusion. Spine. 2011;36(19):1528–1531. 10.1097/BRS.0b013e3181f804ff
- 15.↵Yin Y-H, Qiao G-Y, Yu X-G, Tong H-Y, Zhang Y-Z. Posterior realignment of irreducible atlantoaxial dislocation with C1-C2 screw and rod system: a technique of direct reduction and fixation. Spine J. 2013;13(12):1864–1871. 10.1016/j.spinee.2013.08.014
