en Orthopedic Surgery Orthopedic Surgery Original Research Original Research <p> <strong> Abstract </strong></p><p> <strong> Background: </strong>To evaluate proximal junctional segment changes in Adolescent Idiopathic </p><p>  Scoliosis(AIS) the posterior spinal fusion and also instrumentation also and </p><p>  finding of probable risk factors, were all considered in this study. </p><p> <strong> Methods: </strong>We retrospectively reviewed radiographs of 121 consecutive patients </p><p>  who underwent posterior spinal fusion for AIS from T3 or below, with a mean follow- </p><p>  up of 32.8 months(range,24-83). All coronal and sagittal measurements including </p><p>  the proximal junctional kyphosis (PJK)angle recorded on standing anteroposterior </p><p>  and lateral radiographs preoperative, early postoperative and on follow-up radiographs. </p><p>  The data were analyzed using the Spss 10.0 software. Dependent(paired) </p><p>  samples student t-test was used for analysis between the groups </p><p> <strong> Results: </strong>There was PJK angle above normal for the same junctional segment preoperatively in 13 patients (10.7%) and the incidence of the PJK postoperatively was </p><p>  7.4% (9 patients, 7 female and 2 male), all detected until 2 years postoperation.The </p><p>  mean increase in the PJK angle from pre-operation until 6 weeks postoperation was </p><p>  5.9° (range,0-13°)(P=0.02) and until 2 years post operation was 14.3° (range, 2- </p><p>  16°)(p=0.000). The mean proximal junctional angle increased 1.6° until 2 years postoperation in non-PJK group(n=112). </p><p> <strong> Conclusion: </strong>The prevalence of Proximal Junctional Kyphosis was low and a </p><p>  silent radiographic problem. In some cases is preventable with perfect pre-operative </p><p>  planning. There is no specific demographic or radiographic variables or instrumentation </p><p>  types associated with developing PJK . </p> adolescent idiopathic scoliosis, posterior spinal fusion, proximal junctional kyphosis. 139 147 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-1-75&slc_lang=en&sid=1 Hamid Behtash 20031947532846001838 20031947532846001838 No Iran university of Medical Sciences. Ebrahim Ameri 20031947532846001839 20031947532846001839 No Iran university of Medical Sciences. Bahram Mobini 20031947532846001840 20031947532846001840 No Iran university of Medical Sciences. Hossein Vahid Tari 20031947532846001841 20031947532846001841 No Iran university of Medical Sciences. Hassan Ghandhari 20031947532846001842 20031947532846001842 No Iran university of Medical Sciences. Mohammad Khaki Nahad khakinahad_m@yahoo.com 20031947532846001843 20031947532846001843 Yes Shafa Yahyaiian Hospital, Iran university of Medical Sciences, Tehran, Iran.