Abstract：Objective To investigate the effect of different bone cement volume injected after vertebroplasty on stress distribution of the upper and lower endplates of the injured vertebra in the flexion and extension positions by finite element analysis.Methods Two patients with osteoporotic compression fractures of L2 vertebral body were chosen.Bone cement volumes of 25％ and 50％ were respectively injected into the fractured vertebral body bilaterally.Pre-and post-operative finite element models of fractured and adjacent vertebral bodies were developed after extracting the CT data.Stress changes at L2 superior-and inferior-vertebral endplates were observed in the vertical,flexion,and extension loading.Results Stress at the upper and lower endplates of the fractured vertebra increased after bone cement injection and more increase was observed in 50％ bone cement group than in 25％ bone cement group.In the neutral position,the stress mainly concentrated at posterior vertebral body,with stress of the upper endplate improving from 0.91 × 106 N · mm to 0.93 × 106 N · mm and stress of the lower endplate from 0.98 × 106 N ·mm to 1.03 × 106 N · mm.In the anterior flexion,the stress mainly concentrated at anterior vertebral body,with stress of the upper endplate improving from 4.44 × 106 N · mm to 5.55 × 106 N · mm.In the posterior extension,the stress mainly concentrated at medial vertebral body,with stress of the upper endplate improving from 21.95 × 106 N · mm to 22.10 × 106 N · mm and stress of the lower endplate from 30.60 ×106 N · mm to 30.88 × 106 N · mm.The finite element model revealed stress at the upper and lower endplates was higher in the anterior flexion and posterior extension than in the neutral position,while in the anterior flexion the stress was comparatively higher.Conclusions A small amount of implanted bone cement act no evident effect on stress distribution of the upper and lower vertebral endplates.However,the stress changes are significant as cement volume reached up to 50％,especially in the flexion position,as may suggest an enhanced risk of adjacent intervertebral disc degeneration and adjacent vertebral body fractures.
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