Depth of pedicle screw into the vertebral body and its stability：a biomechanical analysis / 中国组织工程研究

ABSTRACT

BACKGROUND:Effects of pedicle screw placement on fracture reduction or stability of mechanics are influenced by various factors. Pedicle screw fixation failure is mainly due to fracture, loosening and fatigue. The main influential factors for biomechanical stability of pedicle screw are length and diameter. The research on the depth is less. OBJECTIVE:To analyze the relationship between pedicle screw placement depth of vertebral body and the fixed stability based on the biomechanics. METHODS: A model of single vertebral compression fractures was made in 15 pigs aged 5 months on L2 vertebral specimen. According to the length of anteroposterior diameter, vertebral pedicle screws were inserted in different depths (80%, 90% and 100% of anteroposterior diameter). After fixation, specimens were loaded 10 000 times at the frequency of 0.5 Hz (340±125) N on a WDT-10KN type universal material testing machine. Ranges of motion at anteflexion, backward extension, left bending and right bending and the maximum axial pulout force were measured in each group, and the difference of intergroup data was compared. RESULTS AND CONCLUSION:(1) Ranges of motion at anteflexion, backward extension, left bending and right bending in each group were significantly smaler in the 100% and 90% groups than in the 80% group (P 90% group > 80% group.