Postoperative ossification progression after decompression for thoracic ossification of the ligamentum flavum: associated factors identified by serial CT analysis

Postoperative ossification progression after decompression for thoracic ossification of the ligamentum flavum (T-OLF) has been reported, but factors associated with its progression remain poorly understood. The role of additional instrumentation in preventing postoperative ossification progression also remains controversial. We retrospectively reviewed 65 patients who underwent primary surgery for T-OLF between 2007 and 2024. Clinical characteristics and surgical outcomes were compared between patients treated with decompression alone and those treated with decompression and instrumentation. Detailed CT analysis was performed in 31 patients who underwent serial CT examinations before surgery, immediately after surgery, and at the final follow-up with at least 2 years of radiological follow-up. Residual ossification and postoperative ossification progression were evaluated using CT imaging. Among the 65 patients, postoperative ossification progression occurred in five patients (7.6%), and two patients required revision surgery. No significant differences in postoperative ossification progression or reoperation were observed between the decompression-alone and instrumentation groups. In the detailed CT cohort, postoperative ossification progression was significantly associated with a greater preoperative ossification occupying ratio ( p = 0.02) and residual ossification on immediate postoperative CT ( p < 0.01). Instrumentation was not significantly associated with postoperative ossification progression. Additional instrumentation was not significantly associated with postoperative ossification progression in this cohort. However, detailed CT analysis demonstrated that a greater preoperative ossification occupying ratio and residual ossification were associated with postoperative ossification progression. These findings suggest that minimizing residual ossification during decompression may be important for reducing postoperative ossification progression. Larger multicenter studies are warranted to clarify the role of instrumentation in selected high-risk patients.