Background Surgical treatment of thoracic myelopathy caused by ossification of the posterior longitudinal ligament (OPLL) and ossification of the ligamentum flavum (OLF) is technically demanding,and the results tend to be unfavorable.Various operative approaches and treatment strategies have been attempted,and posterior decompression with transforaminal thoracic interbody fusion (PTTIF) may be the optimal method with which the anterior-posterior compression was removed in one step.It is comparatively less traumatic with fewer serious complications.Methods Sixteen patients with thoracic myelopathy due to concurrent OLF and OPLL at the same level underwent PTTIF.We investigated clinical outcomes and neurological improvements.Magnetic resonance imaging (MRI) was performed on all patients preoperatively and postoperatively,and intramedullary signal changes were evaluated.Results The mean operating time was 275 minutes,and the mean operative bleeding amount was 1031 ml.Cerebrospinal fluid leakage occurred in three patients and healed well after repair.Neurological symptom deterioration occurred in one patient,but the patient recovered to nearly the preoperative level after methylprednisolone treatment.The follow-up period ranged from 28 to 47 months.The mean score on the Japanese Orthopedic Association scale improved from 4.3±1.2 preoperatively to 7.3±1.7 at 3 months postoperatively to 8.5±1.5 at the final follow-up (P ＜0.01),with a recovery rate of (63.6±20.0)％.Postoperative images showed a significant improvement in local kyphosis (P ＜0.01).Eleven patients (68.8％) showed increased signal intensity (ISI) on preoperative T2-weighted MRI.At the final follow-up,the intramedullary ISI totally recovered in five patients.Neurological improvement was worse in patients with persistent ISI than in the other patients (P ＜0.05).Conclusions PTTIF is an effective therapeutic option for combined OPLL and OLF and provides satisfactory neurological recovery and stabilized thoracic fusion through a single posterior approach.Intramedullary signal changes do not always indicate a poor prognosis; only irreversible ISI is correlated with a poor clinical result.