Known and potential factors affecting radiographic progression were included while the formulation of the linear regression model: sex, age at diagnosis, disease duration, body mass index (BMI), HLA-B27, peripheral involvement, uveitis, enthesitis, inflammatory bowel disease, psoriasis, smoking, baseline CRP level, baseline ASDAS-CRP, grade of sacroiliitis, grade of hip joint involvement, and baseline mSASSS. Here, CRP is linked to enthesitis.