 The purpose of this study is to assess the safety and efficacy of brodalumab compared with placebo in participants with axial spondyloarthritis. Subjects will be randomized in a 1:1 ratio to brodalumab or placebo for the first part of the study. Subjects will then receive open label brodalumab for the remainder of the study. The entire study will be 312 weeks in duration for each subject. 