Ossification of Posterior Longitudinal Ligament Growth in the C1/2 Segment and its Clinical Significance

STUDY DESIGN: A retrospective analysis at a single institution. OBJECTIVE: This study aimed to determine whether ossification of posterior longitudinal ligament (OPLL) growth in the C1/2 area remains clinically uneventful despite visible radiologic enlargement. BACKGROUND: In cervical decompressive surgery for OPLL, preserving the C2 lamina is preferred for stability, and the larger spinal canal space above C2 tends to mitigate clinical issues caused by OPLL growth. However, the effects of OPLL progression in the C1/2 segment, which often remains untreated, on patients' clinical outcomes are unclear. PATIENTS AND METHODS: We enrolled 144 patients with cervical OPLL who underwent decompression surgery between January 2011 and December 2018. The patients were categorized based on whether they underwent a C2 sparing procedure or C2 laminectomy. The primary outcome was radiologic progression of OPLL, defined as a 2 mm increase in sagittal thickness or longitudinal elongation, and its correlation with clinical symptoms. RESULTS: Of the 144 patients, 35 were in the C2 sparing group, and 109 were in the C2 laminectomy group, with an average follow-up period of 5.2 to 5.6 years. The rate of radiologic progression of OPLL in the C1/2 segment was comparable between the two groups (54.3% vs. 51.4%, P = 0.916). However, diagnosis of C1/2 stenosis at the final follow-up was still lower in the C2 sparing group than in the C2 laminectomy group (2.9% vs. 10.1%, P = 0.294), and there were no new cases of symptoms caused by cord compression in the C1/2 segment in either group. CONCLUSION: OPLL in the C1/2 segment was clinically silent despite radiologic growth. For patients who do not present with significant canal stenosis or cord compression due to OPLL above the C2 upper lamina, C2 lamina-sparing decompressive surgery is preferred. LEVEL OF EVIDENCE: Level III.