## 2 Material and Methods
### Clinical Presentations
**(b)** CT showed no fracture, and MRI showed compression of the cervical spinal cord due to thickening of the ligamentum flavum and suspected damage to the intervertebral disc and anterior longitudinal ligament. MRI showed stenosis at the level of the pharynx due to 16.3 mm OALL at C3/4 and spinal cord compression. **(c)** Figures from left to right show an O-C2 angle of 25\({}^{\circ}\) and a pharyngeal inlet angle (PIA) of 76\({}^{\circ}\), and the S-line was negative. **(d)** The patient was immobilized in the middle position, and video endoscopy (VE) revealed protrusion of the pharynx due to ossification (arrow), but swallowing was normal. Case 2: A 62-year-old man noted a slight difficulty in swallowing 6 years ago. He was referred to the otorhinolaryngology department. He had no difficulty in passing food but had findings of pharyngeal compression. He was seen by an orthopedic surgeon, who noted C-OALL; he had difficulty eating solid foods and decreased appetite since 1 year ago. X-ray findings revealed increased ossification and were referred to us. Evaluation on admission: there were no symptoms of nerve disturbance. There were no complaints other than dysphagia. The oral function was expected, and the jaw opened to a width of 3 fingers. The tooth was intact. Tongue movement did not differ between the left and right sides, and coughing was possible. On the 30 mL water swallowing test, he was drinking water successfully without interruption or coughing (LEVEL I). His swallowing function was as follows: Food Intake LEVEL Scale: 8, and dysphagia severity scale: 6. Radiological evaluation: the extent of ossification increased from 6.1 mm (Figure 4a) to 11.6 mm over 6 years at C3/4, and the shape was globular type. Intervertebral mobility was noted at C3/4, with a total of 3\({}^{\circ}\) of intervertebral mobility in C3/4 with 2\({}^{\circ}\) of kyphosis in retroflection and \(-1^{\circ}\) of forwarding flexion. The O-C2 angle was 30\({}^{\circ}\), the PIA angle was 80\({}^{\circ}\), the S-line was negative, and the C2-7 angle was 12\({}^{\circ}\) (Figure 4b). Otorhinolaryngological findings: VE and VF demonstrated that the pharyngeal cavity was compressed and narrowed anteriorly due to ossification, which was further exacerbated by flexion of the cervical spine (Figure 4d). Posthospitalization course: C3/4 OALL was resected under general anesthesia. The ossification below C4 persisted and limited cervical mobility, but no dissection was performed without evidence of pharyngeal compression. Postoperatively, C3/4 OALL improved to 1 mm (Figure 5). The patient was able to get out of bed the day after surgery, and the ST intervened. The patient had an inducible swallowing reflex, and an ice massage was performed with no swelling or wet hoarseness. Postoperative day 3: he was able to eat 80% (compared with preoperative days) of main meals and side dishes in 15 min. He continued oral intake after that. On the 5 th postoperative day, he was able to eat regular food without discomfort in the pharynx. He was discharged on the 10 th postoperative day. Food-type-based dysphagia disappeared after 1 month postoperatively. The 30 mL water swallowing test was LEVEL I. His swallowing function was as follows: Food Intake LEVEL Scale: 10, and dysphagia severity scale: 7. Figure 3: Posterior decompression fixation of the 3 rd–6 th cervical vertebrae was performed in case 1. Figure 4: Cont.