Ankylosing spondylitis with thoracic OPLL and OYL requiring multiple surgeries: A case report.

Introduction: We encountered a rare and complex case of severe kyphosis resulting from ankylosing spondylitis (AS) in conjunction with ossification of the posterior longitudinal ligament (OPLL) and the yellow ligament (OYL), which necessitated multiple surgical interventions. Presentation of case: The patient was a 45-year-old male with a high body mass index and severe thoracolumbar rigid kyphosis caused by AS. Given the significant degree of the pelvic incidence minus lumbar lordosis (PI-LL) mismatch, a two-stage L2 and L4 pedicle subtraction osteotomy (PSO) was planned, extending from T8 to the pelvis. At that juncture, although concomitant OPLL and OYL at the thoracic spine were observed, these were excluded from the surgical plan, as there were no neurological symptoms before surgery. On the fifth postoperative day following a two-stage surgery, motor weakness and paresthesia in the lower extremities manifested. Based on the neurological findings, a diagnosis of compressive thoracic myelopathy caused by OPLL/OYL at T4-8 level was made, and extensive laminectomy with extended thoracic fusion up to T3 was successfully performed. Discussion: In retrospect, considering the risks associated with frequent surgery, a single-stage double-level PSO might have been preferable alternative. Furthermore, preparations could have been made for additional thoracic decompression and fusion on a standby basis in case thoracic myelopathy developed due to OPLL/OYL. Conclusion: The rapid development of thoracic myelopathy following a double-level PSO at the lumbar spine, in the presence of AS and concomitant thoracic OPLL/OYL, despite the presence of ankylosing spine and apparent loss of mobility, was not predicted.