Process Uncinatus

It is not a true joint.It is a developmental bone projection from posterior lateral aspect of superior portion of the vertebral bodies,do not appear until the latter part of the first decade.

In general animal that hold their necks in an upright position have this process.There is a small gap between the uncus and the opposite surface of the upper spine.It is called lateral joint by Luschka. But there is no disc formed because uncus belongs to the arch and not to the body and the disc


can only be formed in correspondence to the body
When viewed anteriorly the lateral margin of the superior surface of each subaxial cervical vertebral body extends cranially as a bony process called the uncinate process.It articulates with a reciprocal convex area on the inferolateral aspect of the next cranial vertebral body.
This articulation is called uncovertebral joint or neurocentral joint of Luschka

It serves as

• rail to limit lateral translation or bending and as a guiding mechanism for flexion and extension.
• as a barrier to the direct extrusion of the disc material posterolaterally into the foramen and against the nerve root and vertebral artery
  

Surgically it is important because:

• It is involves in degenerative changes and formation of osteophytes .It can compressed on the vertebral artery when it projects into the interverbral foramen and the artery is which already fixed in the vertebral foramen
• It is a landmark(its medial border) during corpectomy to avoid injuring the vertebral artery and a landmark before operating microscope is positioned.
• It anterior decompressive surgery for OPLL,it is important to exposed widely both uncus to confirm the localization of OPLL to the body
• Pseudofracture of uncinate process is a known radiological phenomenon due to Mach effect

References:
Clinical anatomy of cervical spine: k hayashi -chapter 2 in book"Cervical spondylosis and similar disorders"
Cervical spine 3rd Edition CSRS