Involvement of the feet in patients with SpA. A. Dactylitis of the third digit in a 12-year-old boy with undifferentiated SpA. B. Diffuse swelling of the tarsal region of a 11- year-old boy with juvenile-onset AS. C. Tarsal swelling, hyperextension of the digits, and keratoderma blenorrhagica spots in a 16-year-old boy with chronic reactive arthritis. D. Diffuse swelling of the posterior aspect of feet including the ankles, Achilles, peroneal and tibial posterior tendons in a 12 year-old-boy with undifferentiated SpA (Modified from Burgos-Vargas R, Vázquez-Mellado J. Reactive arthritides. In: Cassidy JT, Petty RE (eds): Textbook of Pediatric Rheumatology. 5th Edition. Philadelphia. Elsevier Saunders. 2005:604–612 and Burgos-Vargas, R. 2006, The juvenile-onset spondyloarthritides. In: Weisman MH, van der Heijde D, Reveille JD. Ankylosing spondylitis and the Spondyloarthropathies. Mosby. Philadelphia. pp 94–106).