Multi-centre Study to Evaluate ACAF Versus Laminoplasty in Treating Cervical Ossification of the Posterior Longitudinal Ligament

Inclusion Criteria: 1. The patient's age is 18-70 years old, regardless of gender; 2. The patient was diagnosed as severe ossification of the posterior longitudinal ligament (X-ray or CT showed ossification of the posterior longitudinal ligament); The imaging findings showed occupied ratio ≥ 60% or involved three or more segments; 3. Symptoms of spinal cord and nerve root compression, or accompanied by spinal cord compression symptoms such as dysfunction of urination and defecation, conservative treatment was ineffective or aggravated gradually; 4. The participant (or his legal guardian) can sign the informed consent. Exclusion Criteria: 1. Congenital malformations (including but not limited to occipitocervical malformations, congenital cervical fusion, cervical related neurovascular malformations), ossification of cervical ligamentum flavum, cervical trauma, cervical cancer, cervical tuberculosis and other inflammatory diseases; 2. Patients with other spinal diseases such as thoracolumbar vertebrae that affect clinical symptoms; Patients with motor neuron diseases such as amyotrophic lateral sclerosis and other nervous system diseases; 3. The symptoms were aggravated due to recent trauma; 4. Patients who participated in other clinical trials in recent 3 months; 5. The participant (or his legal guardian) with mental illness and cognitive impairment can not give full informed consent; 6. Those who are in poor health and can not tolerate surgery; The patients were not suitable for surgical treatment after preoperative examination.