Thoracic myelopathy caused by ossification of the yellow ligament in patients with posterior instrumented lumbar fusion

Purpose: The objective of this study was to investigate thoracic myelopathy caused by ossification of the yellow ligament (OYL) in patients with posterior instrumented lumbar fusion. Methods: Seven patients, who had undergone posterior instrumented lumbar fusion, presented with thoracic myelopathy caused by OYL. No patient had a history of thoracic myelopathy at previous surgery. Instrumented fusions were performed from L1-5 in two patients, L2-5 in three patients and L1-S1 and L2-S1 in one patient each, respectively. MRI and CT scans were performed to confirm cord compression by OYL. Of the seven patients, six patients underwent decompressive laminectomy and OYL removal while one was treated conservatively. Results: The average time to presentation after first surgery was 63.4 months. OYL was located at T9-10 in two patients, T11-12 in three patients, and T10-11 and T9-11 in one patient each, respectively. All patients had a myelopathic gait and the average Japanese Orthopaedic Association (JOA) score was 3.9, preoperatively. The average JOA score improved from 3.7 to 8 and the average recovery rate was 58.9 % in the six patients who underwent surgical intervention. However, the JOA score fell from 5 to 4 in the one patient who was treated conservatively. Conclusions: We report seven patients who suffered from thoracic myelopathy after instrumented lumbar fusion. Surgeons must be aware of the possibility of thoracic myelopathy caused by OYL at the thoracolumbar junction, especially in patients with a complaint of gait disturbance after long instrumented lumbar fusion.