Cranio-vertebral instability - Dislocation in multiple planes and multiplanar realignment

Introduction: The C1-2 can translate and/or rotate in axial, coronal and sagittal planes. The joint can dislocate in any of these planes. Abnormal disposition of facets due to deformed C1-2 joints (congenital anomalies) and incompetent ligaments makes the Craniovertebral Junciton unstable, giving rise to progressive C1-2 dislocation. The deformed joints can be corrected by comprehensively drilling the C1-2 facets (wedge osteotomies). The posterior approach releases the joints and these can be further manipulated to achieve realignment in multiple planes. This study evaluates the C1-2 dislocation in various planes explained by the underlying C1-2 joint deformity. Furthermore, outcomes after C1-2 joint deformity correction and multiplanar realignment have been described.

Methods: This study consisted of 426 patients of congenital AAD/ Basilar-invagination operated on with the posterior approach alone. Preoperative and postoperative CT imaging was studied in axial, coronal, and sagittal planes. The relationship of C1-C2 along with C1-C2 joint inclination was studied in each plane. The extent and type of dislocation was objectively assessed in each plane and compared with follow-up imaging for correction. The preoperative and postoperative modified Japenese orthopaedics association scores (mJOAS) were compared.

Results: Anteroposterior (AP) with vertical C1-C2 dislocation (traditionally Basilar invagination type 1) was seen in 305 patients. Twenty-five patients had predominant AP, 16 vertical, 14 axial rotational, 34 lateral angular tilt, and 5 had lateral translational. Twenty-seven patients had a combination of dislocations in all planes. Sagittal and coronal inclination of C1-C2 joints were associated with antero-posterior and vertical dislocation. Asymmetry in the joint's sagittal inclination added to a rotational component, whereas asymmetry in the coronal angulation caused lateral angular tilt. Patients with rotational dislocation had near normal C1-C2 orientation. Only AP or lateral translation was seen with os-odontoideum with normal orientation of C1-2 joints. Preoperative mJOAS was worst in the lateral translation and lateral angular dislocation. Multiplanar realignment was achieved in all patients. There was a significant improvement in post operative mJOAS.

Conclusion : The orientation of facets decides the plane of dislocation. Wedge osteotomies to correct the C1-2 deformity in all planes, releases the joints and helps in multiplanar realignment providing good clinical and radiological outcomes.