Biomechanical evaluation of the craniovertebral junction after inferior-third clivectomy and intradural exposure of the foramen magnum: implications for endoscopic endonasal approaches to the cranial base

Abstract

Endoscopic endonasal approaches to the craniovertebral junction (CVJ) and clivus are increasingly performed for ventral skull-base pathology, but the biomechanical implications of these approaches have not been studied. The aim of this study was to investigate the spinal biomechanics of the CVJ after an inferior-third clivectomy and anterior intradural exposure of the foramen magnum as would be performed in an endonasal endoscopic surgical strategy. Seven upper-cervical human cadaveric specimens (occiput [Oc]-C2) underwent nondestructive biomechanical flexibility testing during flexion-extension, axial rotation, and lateral bending at Oc-C1 and C1-2. Each specimen was tested intact, after an inferior-third clivectomy, and after ligamentous complex dissection simulating a wide intradural exposure using an anterior approach. Angular range of motion (ROM), lax zone, and stiff zone were determined and compared with the intact state. Modest, but statistically significant, hypermobility was observed after inferior-third clivectomy and intradural exposure during flexion-extension and axial rotation at Oc-C1. Angular ROM increased incrementally between 6% and 12% in flexion-extension and axial rotation. These increases were primarily the result of changes in the lax zone. No significant changes were noted at C1-2. Inferior-third clivectomy and an intradural exposure to the ventral CVJ and foramen magnum resulted in hypermobility at Oc-C1 during flexion-extension and axial rotation. Although the results were statistically significant, the modest degree of hypermobility observed compared with other well-characterized CVJ injuries suggests that occipitocervical stabilization may be unnecessary for most patients.