This is a prospective study reporting on the efficacy of a modified technique of Concave Rib Osteotomy (CRO) in conjunction with posterior instrumented fusion in the treatment of severe and rigid curves in patients with adolescent idiopathic scoliosis. The mean post-operative frontal plane correction was 68%. The incidence of pulmonary complications was 11.5%. The modified technique of CRO is a safe alternative to anterior release in treatment of severe and rigid curves.