Joint Distraction with a New Expandable Device for the Treatment of Basilar Invagination with Preservation of the C2 Nerve Root: A Cadaveric Anatomical Study

Fig. 1

(a) Cadaveric specimen, craniocervical junction, posterior view. Atlantoaxial joints and C2 nerve roots are exposed bilaterally. (b) The drilling of the C1-C2 joint to create an appropriate cavity for the expandable device, protecting the C2 nerve root with a blunt dissector

A Vertebral Body Stent (VBS^®; DePuy Synthes Spine, Zuchwil – Switzerland), a balloon-expandable metal stent mounted on a balloon-catheter for kyphoplasty, was shortened in order to fit into the atlantoaxial joint. The modified device was inserted within the joint cavity—with the C2 ganglion being preserved with a dissector—and expanded along with dilatation of the balloon. Once the distraction was visually accomplished, the balloon was pulled out, and the correct positioning of the stent within the joints bilaterally was checked visually (Fig. 2a).

Fig. 2

(a) The insertion of the device is feasible with preservation of the C2 ganglion. (b) At the end of the procedure there was no conflict between the device and the C2 nerve root

Results

In all five cadaveric specimens, the device was inserted without difficulty and with a gentle mobilization of the C2 root, avoiding any stretching of the nerve. Visual inspection of the atlantoaxial joint revealed no conflict between the C2 nerve root and the device (Fig. 2b).

Control CT scans showed the correct positioning of the devices bilaterally and the symmetrical distraction of the C1-C2 joint (Fig. 3a).

Fig. 3

(a) Computed tomography (CT) scan of the anatomical specimen. Axial, coronal, and sagittal planes and maximum intensity projection (device in red) images showing the correct positioning of the device and the symmetrical distraction of the atlantoaxial joint bilaterally. (b) Cervical computed tomography (CT) scan, sagittal plane, showing the unfavorable sagittal inclination of the C1-C2 joint in a patient affected by basilar invagination

Discussion

Basilar invagination is a relatively rare developmental anomaly of the craniovertebral junction, in which the odontoid abnormally prolapses into the foramen magnum. It can be associated with other osseous anomalies of the craniovertebral junction, including atlanto-occipital assimilation, incomplete C1 ring, and hypoplasia of the atlas, basiocciput, and occipital condyles. It is also associated with other malformations, including Chiari malformation, hydrocephalus, and syringomyelia. Patients often present with neurologic deficits and need surgical treatment to prevent progression [11].

Despite recent improvements in the surgical technique [14], the transoral approach for odontoid process removal still carries important surgical risks and entails the need for performing surgery in two steps [9, 12].

In order to avoid the risks of transoral surgery and to accomplish brainstem decompression in a single surgical stage, in 2004 Goel [5] proposed distraction of the atlantoaxial joint for the treatment of type A BI, using a fixed atlantoaxial dislocation with the tip of the odontoid process above the Chamberlain line, the McRae foramen magnum line, and the Wackenheim clival line. This innovative surgical strategy allows the reduction of the atlantoaxial dislocation, pulling the axis downwards with its dens, decompressing the brainstem and improving clinical symptoms, thus avoiding the complications related to the transoral approach.

The introduction of two spacers/cages in the C1-C2 joint requires the section of the C2 ganglions and of their periradicular venous plexuses, followed by a C1-C2 lateral mass fixation [5].

The postoperative QoL of patients who underwent C2 root section was investigated recently in a small group of patients. In that study the C2 nerve root resection was associated with increased occipital numbness but had no effect on the patients’ QoL [3]. Interestingly, this C-2 neurectomy group showed no cases of new-onset postoperative C-2 neuralgia, in contrast to the reporting of new-onset C-2 neuralgia with C-2 ganglion preservation in a growing number of articles in the literature. Moreover, in 80 % of patients in a different series who had preoperative occipital neuralgia, this neuralgia was relieved following C1–2 instrumented arthrodesis with C-2 neurectomy in all of these patients [8].

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