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.