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STUDY DESIGN A retrospective study. OBJECTIVE To describe a novel posterior approach, circumspinal decompression technique "IV+V+VI" for ossification of the posterior longitudinal ligament (OPLL) or hard disc herniation (HDH) in thoracic spine and assess its safety and efficacy. SUMMARY OF BACKGROUND DATA Thoracic myelopathy caused by OPLL or HDH is a rare but intractable disorder that can only be effectively treated with surgery. Nevertheless, few studies have reported on a detailed resection of OPLL or HDH using a single posterior approach and no consistent procedures have been established. METHODS Fifteen consecutive patients with single-level OPLL or HDH who were treated with this novel technique at our center between January 2016 and June 2017 were recruited. The perioperative complications, operation time, blood loss, pre-and post-operative neurological statuses were recorded and analyzed. Neurological status was evaluated with a modified Japanese Orthopaedic Association (JOA) scale and the neurological recovery rate was calculated using the Hirabayashi's Method. RESULTS All the included patients underwent one-stage posterior circumferential decompression. The average age at surgery was 43.3 ± 12.8 years. Eight cases were diagnosed with HDH, four with OPLL, and three with OPLL+OLF (ossification of the ligamentum flavum). The mean operation time was 109.9 ± 25.3 minutes with an average blood loss of 433.3 ± 221.8 ml. The mean follow-up period was 33.1 ± 7.5 months. Five patients experienced a dural tear, while another case experienced a transient numbness in the right lower limb. All these patients were treated conservatively and their neurological function recovered well at the final follow-up. The average JOA score increased from 5.8 ± 1.9 before surgery to 10.2 ± 1.0 postoperatively, and the average recovery rate was 87.2%. CONCLUSION The "IV+V+VI" technique is a safe and effective method for thoracic OPLL and HDH resection. It can be used as a standard surgical procedure for thoracic spinal circumferential decompression. LEVEL OF EVIDENCE 4.