Letter to the Editor: “Axial superior facet slope may determine anterior or posterior atlantoaxial displacement secondary to os odontoideum and compensatory mechanisms of the atlantooccipital joint and subaxial cervical spine” - Ma, Fei; Liao, Yehui; Tang, Qiang; Tang, Chao; Wang, Qing; Zhong, Dejun (European radiology, 2024)