[1] Rigshosp Glostrup, Ctr Rheumatol & Spine Dis, Copenhagen Spine Res Unit CSRU, Sect Spine Surg, Valdemar Hansens Vej 17, DK-2600 Glostrup, Denmark
[2] Statens Serum Inst, Dept Epidemiol Res, Artillerivej 5, DK-2300 Copenhagen, Denmark
[3] Copenhagen Univ Hosp, Dept Orthoped Surg, Spine Unit, Rigshosp, Blegdamsvej 9, DK-2100 Copenhagen, Denmark
[4] Univ Copenhagen, Dept Clin Med, Copenhagen, Denmark
[5] Texas Childrens Hosp, Dept Orthoped & Scoliosis Surg, 6621 Fannin St, Houston, TX 77030 USA
[6] Baylor Coll Med, 6621 Fannin St, Houston, TX 77030 USA