Objective: The purpose of this study was to elucidate the significance of the signs of dural ossification applied to the thoracic ossification of the posterior longitudinal ligament (OPLL), as originally described for cervical OPLL by Hida et al.
Methods: Twenty patients with thoracic OPLL who underwent anterior decompression were retrospectively studied through examination of preoperative computed tomographic scans and medical records. The types of OPLL, single- and double-layer signs, as well as actual dural penetration were evaluated.
Results: Signs of dural ossification were found in 80.0% of the patients. There were 10 (71.4%) cases of a dural ossification sign among the 14 patients with segmental OPLL and six (100%) cases of a dural ossification sign among the six patients with non-segmental OPLL. Dural defects were present in six (60.0%) out of 10 patients with a double-layer sign and three (50.0%) out of six patients with a single-layer sign.
Conclusion: There are several differences between thoracic and cervical OPLL in regard to dural ossification signs. The incidence of these signs with thoracic OPLL was higher than that with cervical OPLL, and these signs can develop in a segmental OPLL as frequently as in a non-segmental OPLL. Dural defects were present in 60% of the patients with a double-layer sign and in 50% of the patients with a single-layer sign. Therefore, surgeons should be alert for the high possibility of a dural defect when these signs are present in thoracic OPLL, although, a dural defect can develop even in the absence of the signs.