Original articleCharacteristics of ossification of the spinal ligament; incidence of ossification of the ligamentum flavum in patients with cervical ossification of the posterior longitudinal ligament – Analysis of the whole spine using multidetector CT
Introduction
Ossified lesions in the spinal canal have a risk of spinal cord and nerve roots compression. Diseases, such as ossification of the posterior longitudinal ligament (OPLL) and ossification of the ligamentum flavum (OLF), are in the category of ossified lesions in the spinal canal. OPLL and OLF are characterized by replacement of ligamentous tissue by ectopic new bone formation [1], [2], [3]. Although the background of both diseases might be similar, there are some differences between two diseases. OPLL mainly affects the cervical spine, and often results in cervical myelopathy [4]. In contrast, OLF is predominantly observed at the upper or lower third of the thoracic spine and may cause thoracic myelopathy due to narrowing of the spinal canal [5], [6]. The etiology of OPLL and OLF is still unknown. Some studies have found that genetic background is strongly related to OPLL [7]. Several candidate genes for cervical OPLL were identified to date [8], [9], [10]. But, no significant candidate genes were found for OLF. In the clinical practice, we sometimes encounter the cases who have OPLL in the cervical spine and OLF in the thoracic spine [11], [12], [13], [14]. Some cases have spinal cord compression by both OPLL and OLF at the same spinal level, especially in the thoracic spine. These cases were very difficult to treat. However, the precise lesions of OPLL and OLF are still unclear. Recently, we performed the study to evaluate the coexisting OPLL in patients with cervical OPLL using multi-detector CT of the whole spine [15]. The study demonstrated that more than half of the patients with cervical OPLL had coexistent OPLL in the thoracic and/or lumbar spine. Our study regarding OPLL lesions of the whole spine by CT can also be used for the detection of OLF in the spinal canal. This information should be very beneficial to consider the therapeutic strategy in patients with ossified lesions in the spinal canal. The purpose of this study was to evaluate OLF of the whole spine in patients with cervical OPLL and to analyze the relationship of the ossified lesions between OLF and OPLL.
Section snippets
Materials and methods
This study included 178 patients who were diagnosed as cervical OPLL by plain radiographs. All of the patients were treated in our university hospital. There were 108 men and 70 women, with an average age of 67.0 years old (range, 36–86 years). Informed consent was obtained from each patient before enrollment in the study, and the study was approved by the institutional review board of our university hospital. Regarding medical history, 79 patients had a history of cervical laminoplasty which
Inter-rater and intra-rater reliability and agreement
Averaged Fleiss' Kappa coefficient of inter-rater agreement of OLF was 0.61 ± 0.11 in three observers. The intra-rater reliability for the existence of OPLL was 94.6% (95% CI 94.4–94.8), 93.5% (95% CI 93.2–93.7) and 94.5% (95% CI 94.2–94.7), respectively.
Incidence of spinal level of OPLL and OLF
OPLL was seen both at vertebral and intervertebral levels (Fig. 1). The most frequent level of OPLL was at C5 vertebral level where 82% of the patients had OPLL. Subsequently, C4 and C6 vertebral level was frequent. At the thoracic and lumbar
Discussion
Our previous study revealed the precise ossified lesion of OPLL at the whole spine using CT images [15]. As for the evaluation for OPLL, the averaged Fleiss Kappa coefficient of inter-rater agreement was 0.83 ± 0.008. The intra-rater reliability for the existence of OPLL was 81.5% (95%confidence interval, 77.7–84.7), 98.1% (95% confidence interval, 96.5–99.0), and 92.7% (95% confidence interval, 90.0–94.7). The current study focused on OLF using the same CT images. Similarly to the previous
Conflict of interest
The authors declare that they have no conflict of interest.
Acknowledgment
The work reported in this article was supported by grants from the Ministry of Health, Labour and Welfare of Japan: Committee for Study of Ossification of Spinal Ligament and Committee for Research and Development of Therapies for Ossification of Posterior Longitudinal Ligament.
The authors thank Mika Kigawa, for her effort in statistical analysis.
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2022, NeurochirurgieCitation Excerpt :This major finding coexists with calcified cartilage areas and already ossified zones of lamellar or trabecular bone with or without continuity with laminae [6,8,16] (Fig. 5). At other hand, calcification is characterized by foci of calcium hydroxyapatite depositions into already degenerated ligament, with no mature bone forming within the ligament itself [3,6,8,16]. Ossification of ligamentum flavum is an uncommon condition at all spinal level in Caucasians [3,17].