C2 Body as "Keystone" in Management of C1-C2-C3 Dislocation Secondary to Congenital Absence of C2 Posterior Elements.

BACKGROUND: Congenital absence of C2 posterior arch may present with C2-C3 dislocation. Previously these cases were managed by fusing occiput-C1-C4 without including C2 in the construct. Such constructs are likely to immobilize the long segment of the cervical spine, and exclusion of C2 may not yield the best result.

CASE DESCRIPTION: We report a case with congenital absence of posterior arch of axis with C2-3 and C1-C2 dislocation who presented with progressive spastic quadriparesis. The inferior facets of C2 were rudimentary. In our patient the C1-C2-C3 dislocations were stabilized with C1 and C3 lateral mass along with C2 pedicle screws. Clinical improvement with radiologic realignment occurred.

CONCLUSION: Absence of the posterior arch of axis may be associated with adjacent C1-C2 along with C2-C3 dislocation, so both levels need to be addressed. The radiology should be critically evaluated for other structures developing from the C2 neural arch. It is important to include C2 to achieve a stable construct without compromising adjacent-level mobility.