Characteristics of highly impaired children with severe chronic pain: a 5-year retrospective study on 2249 pediatric pain patients - Zernikow, B; Wager, J; Hechler, T; Hasan, C; Rohr, U; Dobe, M; Meyer, A; Hübner-Möhler, B; Wamsler, C; Blankenburg, M (BMC Pediatr, 2012)