The notched articular process of C7 (dorsalization of C7).
The frequency of variation from the standard in the articular processes of C7 is very high (43.9 percent). These variations are: (1) A notch on the back of the superior articular facet. (2) Elongation the the "articular pillary" so that the posterior edge of the inferior articular process of C7 lies backward in relation to the posterior edges of the other cervical articular process. (3) A combination of both. Item 1 should not be mistaken for a fracture and item 2 should not be mistaken for a dislocation. These variants represent a partial dorsalization of C7.
D000367:Age Factors; D002574:Cervical Vertebrae / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D002648:Child; D002675:Child, Preschool; D003937:Diagnosis, Differential; D006801:Humans; D011859:Radiography; D013124:Spinal Injuries / Q000000981:diagnostic imaging