Comment to the article: Contributing factors affecting the prognosis surgical outcome for thoracic OLF (S. U. Kuh et al.).

Dear sir, Kuh et al. [1] treated 19 thoracic OLF patients from 1998 to 2002, and retrospectively reviewed the patients age, sex, symptom duration, involved disease level, preoperative clinical features, neurological findings, radiological findings, the other combined spinal diseases and the surgical outcomes. The authors classified the OLF into three types: unilateral, bilateral and bridge type. In their series, there was no relationship between OLF type and the surgical outcome statistically, but the unilateral types and the single lesion of thoracic OLF was thought to be a relatively favorable factor to the surgical outcome. In the past 12 years, 74 cases of OLF underwent en-bloc decompression in our hospital. We performed CT scan in every case. However, we found the CT shape of the ossified ligaments changing according to the different scan planes. We found different types on different planes in one patient (Fig. 1). We think that this may be the reason for no relationship between OLF type and the surgical outcome. We wonder whether the authors also found these phenomena, and how they classified the patients in those cases. Fig. 1 Different CT scan plane showed different type of ossification in one patient. According to the authors typing system, a the plane through pedicle showed bilateral type ossification, b the plane through the intervertebral disc showed bridge type ossification ...