In this phase 3 , multicentre , placebo-controlled trial , 312 adults with active PsA were randomised ( stratified by site , weight ( 100 kg / > 100 kg ) , methotrexate use ) to ustekinumab 45 mg or 90 mg at week 0 , week 4 , q12 weeks or placebo at week 0 , week 4 , week 16 and crossover to ustekinumab 45 mg at week 24 , week 28 and week 40 .