Abstract and Introduction
Study Design: Retrospective cohort study.
Objective: The aim of this study was to elucidate the progression of ossification of the posterior longitudinal ligament (OPLL) in conservatively managed patients and determine its risk factors
Summary of Background Data: Although several studies have demonstrated how OPLL progresses after laminoplasty or fusion, its progression in conservatively managed patients remains unclear.
Methods: The vertical length of the ossified mass and its thickness at each segment were evaluated on sagittal computed tomography images. Patients with vertical growth >2 mm were included in the vertical progression group. Segments with a thickness progression >1 mm were classified as thickness progressed segments, and patients who had at least one progressed segment were included in the thickness progression group. Based on the characteristics at each disc level, the ossified mass at each segment was classified into four types: type 1, no disc space involvement; type 2, involving the disc space, but not crossing; type 3, crossing the disc space, but not fused; and type 4, completely fused.
Results: The progression of ossified mass was observed in younger patients (P < 0.01) and in C2-C3 involvement (P < 0.01) cases. Moreover, progression in both directions was observed more frequently in the mixed-type OPLL (P < 0.01). Progression occurred most often in type 3 segments (72.0%, P < 0.01). In type 3 segments, thickness progression was found more frequently in segments with segmental range of motion (ROM) ≥5° (55.6% vs. 27.8%, P = 0.04). The proportion of segments whose initial thickness was >5 mm was significantly higher among progressed segments (60.0% vs. 35.2%, P = 0.03).
Conclusion: Young age, C2-C3 involvement, and mixed-type OPLL are risk factors for OPLL progression. Segments with morphology of crossing the segment, but without fusion (type 3), segmental ROM ≥5°, and initial thickness >5 mm need special attention.
Level of Evidence: 3
Ossification of the posterior longitudinal ligament (OPLL) is a condition that involves abnormal calcification of the posterior longitudinal ligament, and can cause cervical myelopathy. Cord compression caused by ossified mass can lead to neurological deficit and often requires surgical management such as laminoplasty.[2–4] However, when cord compression by ossified mass is not prominent, OPLL does not cause neurological symptoms of myelopathy. Patients, who initially present with OPLL, but have no neurological symptoms, have low chance of developing neurological deterioration, which justifies conservative management in such patients.[5–7] However, long-term observation studies demonstrated that although patients with OPLL initially do not have neurologic deficit, symptoms of myelopathy can develop as the ossified mass continuously grows and begins to compress the spinal cord.[7–10] OPLL is known to progress faster in surgically managed patients than in conservatively managed patients, and several risk factors of ossified mass progression have been reported in patients who had undergone laminoplasty.[8,10,11] Whether these risk factors can be applied to patients managed conservatively and what factors can predict ossified mass progression in these patients are not clearly known.
Although progression of OPLL does not always result in myelopathy, clinical observation is needed for such patients, as an enlarged ossified mass carries an increased risk of cervical myelopathy. If surgeons can identify patients with high risk of OPLL progression, the follow-up strategy can be tailored for each patient. This could be helpful for avoiding unnecessary clinic visits and radiation hazards for low-risk patients, and for earlier detection of myelopathy in high-risk patients. The aims of the present study were to describe the prevalence and direction of OPLL progression in conservatively managed patients; evaluate whether known risk factors for post-laminoplasty OPLL progression can be applied to conservatively managed patients; and identify the progression of OPLL in each motion segment according to a new classification system.
Spine. 2020;45(4):234-243. © 2020 Lippincott Williams & Wilkins