Contralateral surgical exploration during inguinal hernia repair in infants (HERNIIA trial): study protocol for a multi-centre, randomised controlled trial oleh Kelly M. A. Dreuning, Maurits W. van Tulder, Jasper V. Been, Maroeska M. Rovers, Jurgen C. de Graaff, Markus F. Stevens, Johannes R. Anema, Jos W. R. Twisk, L. W. Ernest van Heurn, Joep P. M. Derikx, on behalf of the HERNIIA study group