ORIGINAL ARTICLE Microendoscopic posterior decompression for the treatment of thoracic myelopathy caused by ossification of the ligamentum flavum: a technical report Satoshi Baba 1,2,3 • Yasushi Oshima 1,2 • Tomoyuki Iwahori 1 • Yuichi Takano 1 • Hirohiko Inanami 1 • Hisashi Koga 1,4 Received: 10 December 2014 / Revised: 22 July 2015 / Accepted: 22 July 2015 Ó Springer-Verlag Berlin Heidelberg 2015 Abstract Purpose Ossification of the ligamentum flavum (OLF) is a common cause of progressive thoracic myelopathy in East Asia. Good surgical results are expected for patients who already show myelopathy. Surgical decompression using a posterior approach is commonly used to treat OLF. This study investigated the use of microendoscopic poste- rior decompression for the treatment of thoracic OLF. Methods Microendoscopic posterior decompression was performed on 9 patients with myelopathy. Patients had a mean age of 59.8 years and single-level involvement, mostly at the T10–11 and T11–12 vertebrae. Computed tomography and magnetic resonance imaging were used to classify the OLF. A tubular retractor and endoscopic system were used for microendoscopic posterior decompression. Midline and unilateral paramedian approaches were performed in 2 and 7 patients, respectively. Intraoperative motor evoked poten- tials (MEPs) of 7 patients were monitored. Pre- and postoperative neurological status was evaluated using the modified Japanese Orthopaedic Association (mJOA) score. Results Thoracic OLF for all patients were classed as bilateral type with a round morphology. Improvement of MEPs at least one muscle area was recorded in all patients following posterior decompression. A dural tear in one patient was the only observed complication. The mean recovery rate was 44.9 %, as calculated from mJOA scores at a mean follow-up period of 20 months. Conclusions Microendoscopic posterior decompression combined with MEP monitoring can be used to treat patients with thoracic OLF. The optimal surgical indication is OLF at a single vertebral level and of a unilateral or bilateral nature, without comma and tram track signs, and a round morphology. Keywords Ossification of the ligamentum flavum Á Thoracic myelopathy Á Microendoscopic posterior decompression Á Minimally invasive Introduction Ossification of the ligamentum flavum (OLF) is a relatively rare condition in Africa, Europe, and North and South America [1]. In comparison, OLF is a well-known cause of progressive thoracic myelopathy in the countries of East Asia, such as Japan, Korea, and China [2]. OLF usually occurs in the lower thoracic spine (at the T9–12 levels) [3, 4, 5]. The natural course and prognosis of OLF are still unclear, but good surgical results are expected in patients who already show myelopathy [4, 6]. The duration of preoperative symptoms and preoperative severity of myelopathy have been shown to be important factors in the prognosis [3, 6]. Therefore, we should select appropriate timing for surgical treatment against thoracic OLF. Electronic supplementary material The online version of this article (doi:10.1007/s00586-015-4158-9) contains supplementary material, which is available to authorized users. & Hisashi Koga hkoga0808@gmail.com 1 Department of Orthopaedics, Iwai Orthopaedic Medical Hospital, 8-17-2 Minamikoiwa Edogawa-ku, Tokyo 133-0056, Japan 2 Department of Orthopaedic Surgery, The University of Tokyo, 7-3-1 Hongo Bunkyo-ku, Tokyo 113-8655, Japan 3 Department of Orthopaedics, Japan Community Health Care Organization Tokyo Shinjuku Medical Center, 5-1 Tsukudo- cho Shinjuku-ku, Tokyo 162-8543, Japan 4 Department of Minimally Invasive Spinal Surgery, Zhangzhou Zhengxing Hospital, No.1608 North Circle Road State Highway, 363000 Zhangzhou, Fujian Province, China 123 Eur Spine J DOI 10.1007/s00586-015-4158-9