Alvarez DA, Suárez Escudero JC. Undifferentiated Spondyl Arthropathy, Ankylosing Spondylitis and Psoriatic Arthropathy. Clinical, diagnostic and radiological description. Med UPB. 2006;25(2):171-183. Accessed August 2, 2026. https://revistas.upb.edu.co/index.php/medicina/article/view/2348