Objective      To analyze the incidence

risk factors and prevention measures of proximal junctional kyphosis (PJK) after surgical treatment for ankylosing spondylitis (AS) with thoracolumbar kyphotic deformity.       Methods      A total of 54 patients with thoracolumbar kyphosis caused by AS underwent posterior osteotomy in Chinese PLA General Hospital during January 2007 and December 2009. Radiographic data before surgery

in 2 weeks and 6 months after surgery

and at the last follow-up were collected. The changes of proximal junctional angle (PJA) and correlative sagittal factors were recorded.       Results      All patients were followed up with average time of 2 years. There were 7.4% of patients (4/54) developed into PJK

and almost every patient suffered PJA increasing. At the last follow-up

the PJA in the PJK group and the non-PJK group were 23.7°±4.3° and 10.4°±5.1°

respectively. There were significant differences in the pre-operative thoracic kyphosis (TK)

PJA

and osteotomy angle between the 2 groups (P0.05).       Conclusion      The incidence of PJK is 7.4% in the patients undergoing surgical treatment for AS with thoracolumbar kyphotic deformity. Risk factors of the PJK include the pre-operative TK

PJA10 °

and osteotomy angle.