Erratum to 'Bilateral gluteal advancement flap for treatment of recurrent sacrococcygeal pilonidal disease: A prospective cohort study' [Int. J. Surg. 29 (2016) 1–8]. (August 2016) - Elalfy, Khaled; Emile, Sameh; Lotfy, Ahmed; Youssef, Mohamed; Elfeki, Hossam