[The impact of thoracic and thoracolumbar angular kyphosis on pelvic shape and sagittal alignment].

OBJECTIVE: To analyze the impact of thoracic and thoracolumbar angular kyphosis on pelvic shape and sagittal alignment.

METHODS: From May 2002 to June 2010, the sagittal spino-pelvic parameters were analyzed in lateral standing radiographs of 32 patients (mean age 29.6 years) with thoracolumbar angular kyphosis. The parameters included Cobb angle of kyphosis, lumbar lordosis (LL), pelvic incidence (PI), sacrum slope (SS), pelvic tilt (PT) and sagittal vertical axis (SVA). All pelvic parameters in the patients were compared with those reported in historical normal subjects. All patients were treated by using kyphotic correction and fusion. The preoperative and postoperative parameters were compared. The pelvic parameters were also compared between the patients with kyphotic apex located at T(1-8) and those located at T(9-12) and thoracolumbar junction. The linear regression analysis was used to investigate the independent factors of PI.

RESULTS: The mean kyphosis was 90.1° (31° - 138°). The mean age of kyphosis occurrence was 6.1 years. The mean PI, SS and PT were 34.8°, 35.8° and -0.7° respectively. The PI and PT were significantly smaller (P < 0.001) in the patients than those in normal subjects while the SS was similar. The kyphosis was improved to 27.9° post-operatively. There was no difference in PI values between pre-operation and postoperation (P > 0.05). The PI and SS in patients whose kyphosis located at thoracic spine (T(1-8)) were significantly higher than those at T(9)-L(2). Instead of patients' age and LL, the preoperative Cobb angle of kyphosis and the levels where kyphosis located were two independent impact factors of PI.

CONCLUSIONS: The kyphosis occurred at childhood may influence pelvic shape and alignment significantly. The lower kyphotic apex located and the bigger kyphosis, the greater impact on the pelvic morphology. The surgery can improve the kyphosis, but can not change the sagittal pelvic morphology. Early treatment of thoracolumbar angular kyphosis is beneficial not only to reconstruction of spine alignment but also to the formation of sagittal pelvic morphology.