A 70-year-old male patient suffered from progressive aggravating numbness and weakness of limbs. The patient’s symptoms started 5 years ago without any trauma or accident. When admitted to our hospital, he could only move using a wheelchair. The patient had no previous relevant medical history. The patient had no previous relevant family history. The results of physical examination revealed that the grip strength in both hands was grade 3, the muscle tension of both lower limbs was high, bilateral Hoffman sign was positive, knee and ankle reflexes were hyperactive, and ankle clonus was positive. Laboratory examinations showed no obvious deficits. Considering that there was no history of trauma, and the borders of the odontoid free body and basis were smooth and rounded, an old PAD combined with OO was diagnosed based on computed tomography (CT) results. The C1 inner sagittal diameter was 22.51 mm which supported the diagnosis of AH[]. The results of magnetic resonance imaging (MRI) showed that the spine cord was constricted by the odontoid process and the signal of the spine had changed at the level of atlantoaxial dislocation.