VOL. 99-B, No. 12, DECEMBER 2017 1651  SPINE Minimally invasive surgery for adolescent idiopathic scoliosis CORRECTION OF DEFORMITY AND PERI-OPERATIVE MORBIDITY IN 70 CONSECUTIVE PATIENTS C. de Bodman, F. Miyanji, B. Borner, P-Y. Zambelli, G. Racloz, R. Dayer From Lausanne University Hospital, Lausanne, Switzerland  C. de Bodman, MD, Research Assistant, Pediatric Orthopedics and Traumatology Unit  P-Y. Zambelli, Professor, MD, Pediatric Orthopedics and Traumatology Unit Lausanne University Hospital, Rue du Bugnon 46, 1011 Lausanne, Switzerland.  F. Miyanji, MD, Professor, Department of Pediatric Orthopedics British Columbia’s Children’s Hospital, 4480 Oak Street, Vancouver V6H 3N1, British Columbia, Canada.  B. Borner, MD, Research Assistant, Division of Paediatric Orthopaedics  G. Racloz, MD, Research Assistant, Division of Orthopaedics and Trauma Surgery Geneva University Hospitals, Faculty of Medicine, Rue Gabrielle-Perret-Gentil 4, 1205 Geneva, Switzerland.  R. Dayer, MD, Professor, Pediatric Orthopedics and Traumatology Unit, Lausanne University Hospital, Rue du Bugnon 46, 1011 Lausanne, Switzerland and Division of Paediatric Orthopaedics, Faculty of Medicine Geneva University Hospitals, Geneva, Switzerland. Correspondence should be sent to C. de Bodman; email: charlotte.launay@chuv.ch ©2017 The British Editorial Society of Bone & Joint Surgery doi:10.1302/0301-620X.99B12. BJJ-2017-0022.R2 $2.00 Bone Joint J 2017;99-B:1651–7. Received 10 January 2017; Accepted after revision 20 July 2017 Aims The aim of this study was to report a retrospective, consecutive series of patients with adolescent idiopathic scoliosis (AIS) who were treated with posterior minimally invasive surgery (MIS) with a mean follow-up of two years (SD 1.4; 0.9 to 0 3.7). Our objectives were to measure the correction of the deformity and record the peri-operative morbidity. Special attention was paid to the operating time (ORT), estimated blood loss (EBL), length of stay (LOS) and further complications. Patients and Methods We prospectively collected the data of 70 consecutive patients with AIS treated with MIS using three incisions and a muscle-splitting approach by a single surgeon between June 2013 and February 2016 and these were retrospectively reviewed. There were eight male and 62 female patients with a mean age of 15 years (SD 4.5 ) with a mean body mass index of 19.8 kg/m 2 (SD 5.4). The curves were classified according to Lenke; 40 curves were type 1, 15 were type 2, three were type 3, two were type 4, eight were type 5 and two were type 6. Results The mean primary Cobb angle was corrected from 58.9° (SD 12.6°) pre-operatively to 17.7° (SD 10.2°) post-operatively with a mean correction of 69% (SD 20%, p < 0.001). The mean kyphosis at T5 to T12 increased from 24.2° (SD 12.2°) pre-operatively to 30.1° (SD 9.6°, p < 0.001) post-operatively. Peri-operative (30 days) complications occurred in three patients(4.2%): one subcutaneous haematoma, one deep venous thrombosis and one pulmonary complication. Five additional complications occurred in five patients (7.1%): one superficial wound infection, one suture granuloma and three delayed deep surgical site infections. The mean ORT was 337.1 mins (SD 121.3); the mean EBL was 345.7 ml (SD 175.1) and the mean LOS was 4.6 days (SD 0.8). Conclusion The use of MIS for patients with AIS results in a significant correction of spinal deformity in both the frontal and sagittal planes, with a low EBL and a short LOS. The rate of peri- operative complications compares well with that following a routine open technique. The longer term safety and benefit of MIS in these patients needs to be evaluated with further follow-up of a larger cohort of patients. Cite this article: Bone Joint J 2017;99-B:1651–7. Spinal surgery in adults using a posterior open approach has been associated with scarring, muscle morbidity (denervation, leading to atro- phy and reduced extension of the trunk), 1-3 loss of blood and post-operative pain related to a prolonged stay in hospital which may lead to chronic long-term pain. 4 The use of a Wiltse approach, also called para spinal sacro-spinalis splitting approach, 5 for pedicle fixation of thoracolumbar fractures has been shown to be associated with a lower incidence of multifidus atrophy and denervation and less fatty infiltra- tion when compared with the conventional posterior open approach. 6 The mini-open or minimal invasive surgery (MIS) approach was developed to avoid these adverse events and is now accepted practice for traumatic, neoplastic or degenerative lesions in adults. 7 The use of MIS in patients with spinal deformity remains limited although it may improve significantly peri-operative morbid- ity. Spinal deformity is generally considered to be less rigid and to fuse more readily in adolescents than in adults. MIS techniques may therefore be more suitable for adoles- cents. 8