A multicenter, randomized, open-label, parallel-group trial.To investigate interbody bone fusion rates in titanium-coated polyetheretherketone (TiPEEK) and polyetheretherketone (PEEK) cages after posterior lumbar interbody fusion (PLIF) surgery.Previous clinical studies have not revealed any significant difference in bone fusion rates between TiPEEK and PEEK cages.During one-level PLIF surgery, 149 patients (84 men, 65 women, mean age 67 years) were randomly allocated to use either a TiPEEK cage (n = 69) or PEEK cage (n = 80). Blinded radiographic evaluations were performed using computed tomography (CT) and assessed by modified intention-to-treat (mITT) analysis in 149 cases and per-protocol (PP) analysis in 143 cases who were followed for 12 months. Clinical outcomes were assessed using the Japanese Orthopaedic Association Back Pain Evaluation Questionnaire (JOABPEQ) and the Oswestry Disability Index (ODI).The interbody union rate at 12 months after surgery was 45% owing to a very strict definition of bone fusion. The rates of bone fusion were significantly higher at 4 and 6 months after surgery in the TiPEEK group than in the PEEK group in the unadjusted mITT analysis and were significantly higher at 6 months in the unadjusted PP analysis. Binary logistic regression analysis adjusted for sex, age, body mass index, bone mineral density, and surgical level showed that using a TiPEEK cage (odds ratio, 2.27; 95% confidence interval: 1.09-4.74; p = 0.03) was independently associated with bone fusion at 6 months after surgery. JOABPEQ and ODI results improved postoperatively in both groups.Using the TiPEEK cage for PLIF enabled the maintenance of better bone fusion to the endplate than using the PEEK cage at 6 months after the surgery. Our findings suggest the possibility of an earlier return to rigorous work or sports by the use of TiPEEK cage.1.