Using Patient-Specific 3D-Printed C1-C2 Interfacet Spacers for the Treatment of Type 1 Basilar Invagination: A Clinical Case Report

Abstract

Background: Type 1 basilar invagination (BI) is caused by a structural instability at the craniovertebral junction (CVJ) and has been historically treated with distraction and stabilization through fusion of the C1-C2 vertebrae. Recent advances in 3D printed custom implants (3DPIs) have improved the array of available options for reaching distraction and alignment goals. Case Presentation: We report the case of a 15-year-old male who presented with early signs of cervical myelopathy. Radiographic evaluation revealed type 1 BI with a widened atlantodental interval (ADI) of 3.7 mm and a 9 mm McRae's line violation (MLV) of the dens, resulting in severe narrowing at the CVJ and brainstem/spinal cord impingement. Of note, the patient had bilateral dysplastic C1 and C2 anatomy, thus requiring a patient-specific 3DPI to conform to this anatomy and enable sufficient distraction and fusion. Custom 3D printed C1-C2 interfacet spacers were created and implemented within 14 days to achieve sufficient distraction, osteoconduction, and stabilization of the C1-C2 joint. Outcome: Postoperatively, the patient remained neurologically intact with myelopathic symptom improvement before discharge on postoperative day 4. Postoperative imaging demonstrated the resolution of BI from successful C1-C2 joint distraction and confirmed intended implant placement with resolution of canal stenosis. During his 6-week follow-up, the patient remained neurologically stable with intact hardware and preserved alignment. Conclusions: This case is the first in the United States demonstrating the use of custom 3D printed interfacet spacers to achieve successful distraction, decompression, and stabilization of type 1 BI. These patient-specific 3DPIs were designed and created in a streamlined manner and serve as proof-of-concept of pragmatic implant design and manufacturing. Future optimization of the workflow and characterization of long-term patient outcomes should be explored for these types of 3DPI.

Keywords: atlantoaxial instability; basilar invagination; cervical spine; craniovertebral junction; custom implant; pediatric spine; three-dimensional printing.

Figure 1

Preoperative mid-sagittal cervical spine CT (left) and X-ray (right) demonstrate superior and posterior translation of the dens consistent with BI (9 mm McRae’s line violation, 3.7 mm ADI, and CXA of 119°).

Figure 2

Preoperative sagittal (left) and coronal (right) CT demonstrating irregular anatomy of cervical spine, including malformed clivus, hypoplastic posterior C1 arch, hypoplastic inferior C1 lateral masses, and dysplastic C2 superior articulating facets.

Figure 3

Preoperative mid-sagittal T2 MRI of caudal brain and cervical spine in neutral (left) and extension (right) demonstrating severe canal stenosis and T2/STIR hyperintensity of the upper cervical cord.

Figure 4

Schematics demonstrating coronal (A) and sagittal (B) views of the custom 3D-printed titanium implants at various stages of insertion using a fixation pin driver (C) and insertion adapter (D). A 3D rendering of the implant (E) is also shown.

Figure 5

Sagittal (left) and axial (right) postoperative CT demonstrating successful implant insertion with corresponding rods and screws.

Figure 6

Mid-sagittal cervical CT pre- (A) and postoperatively (B) demonstrate decreased basilar invagination (preop 5 mm, postop 2 mm), decreased ADI (preop 3.7 mm, postop 3 mm), and increased CXA (preop 119°, postop 134°). Lateral radiographs pre- (C) and postoperatively (D) demonstrated proper positioning and decompression from 3DPI insertion.

Figure 7

Postoperative sagittal and coronal 3D renderings of the cervical spine demonstrating implant location and surrounding bony anatomy.

Figure 8

Six-week follow-up lateral radiograph demonstrating spacer placement and intact instrumentation with preserved spinal alignment.

Figure 9

Bullet shaped custom 3DPI cage used by Jian et al. (top) with a relatively narrow base compared to our own custom implant (bottom). The bullet implant’s small footprint may increase subsidence risks. Image adapted from Jian et al. with permission per the Creative Commons CC BY license [12].