Study design. Patients were blindly randomized on a 1:1 ratio to receive subcutaneous administration every 4 weeks of either canakinumab 300 mg (4 mg/kg for weight ≤40 kg) or placebo. Study visit schedule was as follows: Screening period before randomization for up to 28 days that included recording of daily pain frequency and intensity by eDiary for at least 1 week. On Day 0, patients underwent baseline assessments and dosing. Study visits thereafter occurred every 4 weeks up to the final blinded assessment at Week 24, after which patients had the option to receive open label canakinumab 300 mg subcutaneously every 4 weeks until Week 48, with final study outcome assessments made on Week 52. Patients underwent a safety follow-up visit or telephone call 8 weeks after receiving the last study dose.