The Échancrure of the Uncovertebral Joint: A Forgotten Structure of the C3-C7 Cervical Vertebral Bodies.

Introduction The  (a French term meaning "indentation") of the cervical vertebrae is the poorly defined articular part on the inferolateral aspect of the cervical spine body, which, with the uncinate processes of the associated caudal vertebra, makes up the joints of Luschka (uncovertebral joint). With no known previous studies on the , the present anatomical study aimed to better elucidate this structure, its prevalence, and its relationships to the adjacent intervertebral foramen and uncinate process. Methods We observed 50 adult cervical spines (100 sides) for the presence of an . When an was identified, its morphometry was documented and photographed. Measurements included the width and height of the . The relationship with the adjacent uncinate process was also studied. Any correlation between the size and shape of the adjacent uncinate process and the was recorded. Results An was found at all levels of the cervical vertebrae except at C1 and C7 and was clearly visible on 88% of the sides. The , more or less, conformed to the reciprocal shape of the uncinate process, which was found on all sides. The shapes were roughly arched, ovoid, or linear. These structures were always in an anterolateral position on the body of the vertebra and just outside the apophyseal ring. The mean height of the was 2.1 mm. The length of the uncinate process correlated positively (r=0.8) to the size of the adjacent . The height of the was inversely related to the diameter of the adjacent intervertebral foramen. The mean width was 8.3 mm. These structures tended to be largest at C3 and C4 vertebral levels and were smallest at C5 and C6 levels. The was most in contact with the uncinate process with lateral flexion of the cervical spine and in specimens with a longer uncinate process, e.g., C6. The was also found to be wider in cases of cervical spine degeneration involving the body of the cervical vertebrae. Degeneration of the uncovertebral joint was most often seen at the and not at the adjacent uncinate process. Conclusions We found that the is found in the majority of cervical spines. These structures tended to be largest at C3 and C4 vertebral levels and were smallest at C5 and C6 levels, and they had more prominence when the adjacent uncinate process was enlarged. The should be considered a normal feature of the inferolateral aspect of the cervical vertebrae. Future clinical studies are necessary to better elucidate their functional significance.