title: Comparison of pullout strength of the thoracic pedicle screw between intrapedicular and extrapedicular technique: a meta-analysis and literature review.
abstract: BACKGROUND
  Intrapedicular fixation in thoracic spine is often limited, because of high risk of complication, especially in scoliosis patients. Extrapedicular screws fixation techniques provide an alternate solution for extremely small or abnormal thoracic pedicles deformity. However, the pullout resistance of extrapedicular screws has not been clearly defined. The aim of our study was to systematically review the existing evidence regarding the pullout resistance of thoracic extrapedicular screws compared with intrapedicular screws.
  
  
  METHODS
  A systematic search of all studies published through Nov 2014 was performed using Medline, EMBASE, OVID and other databases. All studies that compared the pullout resistance of thoracic extrapedicular screws with intrapedicular screws were selected. The data from the included studies were extracted and analyzed regarding pullout resistance force. Forest plots were constructed to summarize the data and compare the biomechanical stability achieved.
  
  
  RESULTS
  Five studies were included, with a total of 27 cadaveric specimens and 313 screws. The vertebral levels of the cadavers potted were T1-T8, T2-T12, T7-T9, T6-T11 and T4-T12 respectively. Overall, the results demonstrated that there was no significant difference in ultimate pullout strength between intrapedicular screws and extrapedicular screws (95% CI=-63.73 to 27.74; P=0.44); extrapedicular screws significantly increased the length of placements by a mean of 6.24 mm (95% CI=5.38 to 7.10; P<0.001); while the stiffness in intrapedicular screws was significantly stronger by a mean of 45.82 N/mm compared with extrapedicular screws (95% CI=-70.09 to -21.56; P<0.001).
  
  
  CONCLUSIONS
  Meta-analysis of the existing literature showed that thoracic extrapedicular screws provided comparable but slightly lower pullout strength compared with intrapedicular screws, extrapedicular screws placement is much safer than intrapedicular screws. So thoracic extrapedicular screws offer a good alternative when it is hard to insert by intrapedicular approach, especially in scoliosis patients with severe vertebral deformities.
authors.affiliation: Department of Orthopaedics, First Affiliated Hospital of Sun Yat-sen University 58 Zhongshan Second Road, Guangzhou, P. R. China.
authors.forename: Hua
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Spine Surgery, Fuzhou Second Hospital of Xiamen University No 47 Shangteng Road Cangshan District, Fuzhou 350007, Fujian, P. R. China.
authors.forename: Huafeng
authors.initials: H
authors.lastname: Wang
authors.affiliation: Department of Orthopaedics, First Affiliated Hospital of Sun Yat-sen University 58 Zhongshan Second Road, Guangzhou, P. R. China.
authors.forename: Shilabant Sen
authors.initials: SS
authors.lastname: Sribastav
authors.affiliation: Department of Orthopaedics, First Affiliated Hospital of Sun Yat-sen University 58 Zhongshan Second Road, Guangzhou, P. R. China.
authors.forename: Fubiao
authors.initials: F
authors.lastname: Ye
authors.affiliation: Department of Orthopaedics, First Affiliated Hospital of Sun Yat-sen University 58 Zhongshan Second Road, Guangzhou, P. R. China.
authors.forename: Chunxiang
authors.initials: C
authors.lastname: Liang
authors.affiliation: Department of Orthopaedics, First Affiliated Hospital of Sun Yat-sen University 58 Zhongshan Second Road, Guangzhou, P. R. China.
authors.forename: Zemin
authors.initials: Z
authors.lastname: Li
authors.affiliation: Department of Orthopaedics, First Affiliated Hospital of Sun Yat-sen University 58 Zhongshan Second Road, Guangzhou, P. R. China.
authors.forename: Jianru
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Orthopaedics, First Affiliated Hospital of Sun Yat-sen University 58 Zhongshan Second Road, Guangzhou, P. R. China.
authors.forename: Hui
authors.initials: H
authors.lastname: Liu
authors.affiliation: Department of Bone and Soft Tissue, He-Nan Cancer Hospital, Zhengzhou University Zhengzhou, P. R. China.
authors.forename: Xin
authors.initials: X
authors.lastname: Wang
authors.affiliation: Department of Orthopaedics, First Affiliated Hospital of Sun Yat-sen University 58 Zhongshan Second Road, Guangzhou, P. R. China.
authors.forename: Zhaomin
authors.initials: Z
authors.lastname: Zheng
keywords: Thoracic spine; biomechanics; extrapedicular screw; intrapedicular screw; meta-analysis