Comparison of pull-out strength between middle-upper thoracic semi-pedicular screwing versus conventional pedicular screwing

Abstract

Objective To compare the pull-out strength between middle-upper thoracic semi-pedicular screwing versus conventional pedicular screwing. Methods Three specimens of middle-upper thoracic vertebrae with 24 vertebral bodies were used in this experiment. The vertebral bodies were divided into 2 equal groups which were subjected to conventional fixation with transpedicular screws (group A) and fixation with trans-semi-pedicular screws (group B), respectively. Each group were tested with screws of different specifications: C1 screws of 4.0 mm in diameter and 40 mm in length, C2 screws of 5.0 mm in diameter and 45 mm in length, C3 screws of 6.0 mm in diameter and 45 mm in length. The pull-out strengths of different screws were compared between the 2 groups. Results The pull-out strength of C1 in group A (890.0±102.0 N) was significantly larger than in group B (780.0±100.2 N) (P 0.05). The pull-out strength of C3 in group A (899.3±119.2 N) was also similar to that in group B (962.0±119.2 N) (P > 0.05). Conclusions When a small screw is used, middle-upper thoracic semi-pedicular screwing is not as strong as conventional pedicular screwing. When a large screw is used, there is no significant difference between middle-upper thoracic semi-pedicular screwing and conventional pedicular screwing in pull-out strength but the former may be superior in safety due to its more lateral approach. Key words: Thoracic vertebrae; Fracture fixation; Bone, nails; Biomechanics