Introducing the craniocervical Y-ligament.
We examined the accessory atlantoaxial ligaments and found them to be a part of a complex ligamentous structure, which we named craniocervical Y-ligament with respect to its shape. The ligaments of the upper cervical spine were dissected in ten Thiel embalmed human cadavers. Origin and attachment of the Y-ligament were described and a detailed photo and video-documentation was carried out with the head in the neutral position, flexion, extension and rotation to study the ligament during these movements. The Y-ligaments were found to be paired and symmetric in all specimens. The shape of the ligament is similar to an Y, its lateral arm connecting the atlas to the axis, its medial arm connecting the occipital bone to the axis, fusing with the two main ligaments, the alar and transverse ligaments. The lateral arm of the Y-ligament was found to be analogous to the accessory atlantoaxial ligament. During cervical flexion, both arms of the Y-ligament became taut while extension made the Y-ligaments relaxed. During rotation both Y-ligaments became taut, moving in the opposite directions in the sagittal plane while following the gliding movements of the lateral masses of the atlas. The craniocervical Y-ligament is a complex ligamentous structure and has a constant anatomy. Because of its shape and special arrangement, it probably plays a role in limiting both atlantooccipital and atlantoaxial movements. Acknowledgement of this ligamentous structure will help understand upper cervical stability. The present study should serve as a basis for future biomechanical and radiological studies.