Comparison of Rigid and Non-Rigid Interbody Fusion Device for Cervical Degenerative Disc Disease in Adults

Inclusion Criteria: 1. Age 20 - 69 years; 2. Symptomatic cervical degenerative disc disease in one or two levels between C3-7 with radiculopathy or myeloradiculopathy and/or decrease muscle strength and/or abnormal sensation and/or abnormal reflexes; 3. Deficit confirmed by CT, MRI, or X-ray; 4. NDI Score of ≥ 30/100; 5. Unresponsive to non-operative treatment of at least 6 weeks or presence of progressive symptoms or signs of nerve root/spinal cord compression despite continued non-operative treatment; 6. No prior surgical procedures at the operative level and non-prior fusions at any cervical level; 7. Physically and mentally able and willing to comply with the protocol; 8. Signed informed consent; Exclusion Criteria: 1. Patient does not meet the indication of Anterior Cervical Discectomy and Fusion (ACDF), which is under the surveillance. (Surgical indication of ACDF is approved by National Health Insurance Administration Ministry of Health and Welfare, a blinded third-party authority). 2. More than two vertebral levels required surgery; 3. Immobile levels between C1 and C7 from any cause; 4. Any prior surgery at the operative level or any prior fusion at any cervical level; 5. T-score less than -1.5 (osteoporosis evaluation) 6. Paget's disease, osteomalacia, or any other metabolic bone disease other than osteoporosis; 7. Active infection of surgical site or history of anticipated treatment for systemic infection including HIV 8. Active malignancy: a history of any invasive malignancy (except carcinoma in situ and non-melanoma skin cancer), unless treated with curative intent with no clinical signs or symptoms of malignancy in the past 5 years; 9. Marked instability of the cervical spine on resting lateral or flexion-extension radiographs; 10. Known allergy to device materials including titanium or polyetheretherketone (PEEK); 11. Segmental kyphosis of greater than 11 degrees at treatment or adjacent levels 12. Rheumatoid arthritis, lupus, or other autoimmune disease; 13. Any diseases or conditions that would preclude accurate clinical evaluation; 14. Daily, high-dose oral and/or inhaled steroid or a history of chronic use of high dose steroids; 15. Body Mass Index (BMI) \> 35 16. Smoking more than one pack of cigarettes per day;