Introduction: In cases of irreducible brainstem compression secondary to basilar invagination,
ventral decompression with odontoidectomy is required. As odontoidectomy often results
in C1–C2 and/or O–C1 instability, empiric separate-stage occipitocervical fusion is
performed at many institutions at/near the time of decompression. We thus sought to
investigate the feasibility of design of C1–C2 prosthetic (delivered through the endonasal
cavity) to maintain physiologic stability and motion preservation of the craniocervical
junction following odontoidectomy.
Methods: In four cadaveric heads, we performed inferior U-shaped nasopharyngeal flap exposure
through the endonasal corridor followed by removal of anterior C1 ring and odontoid.
In the 4 specimens, 4 different degrees of odontoidectomy were performed (partial
<50%, subtotal >50%, total ~100%, and supratotal >100%) to recapitulate all clinical
scenarios. Postprocedure CT imaging was obtained in each specimen. 3D segmentation
and subtraction algorithms were subsequently utilized to obtain measurements essential
for prosthetic design.
Results: The average length, height, and depth of the anterior arch of C1 removal was 17.8,
14.3, and 8.7 mm, respectively. The average odontoid depth, width and height was 16.9,
11.7, and 11.6 mm. The average screw length for bicortical fixation of the anterior
C1 arch prosthesis was 13.4 mm. The average screw length required for bicortical fixation
of the odontoid tip at the base was 16.9 mm. Co-axial screw stabilization requires
a 45 degree angled drill and screw driver. On average, length of this single co-axial
screw measured 18.7 mm.
Conclusion: The index study represents the first feasibility analysis for C1–C2 joint prosthetic
designed for delivery through the endonasal corridor. Prosthetic manufacturing followed
by rigorous biomechanical analysis should be the next steps in advancement of this
technology.
