Abstract:  Objective    To explore the changes of the abdominal aorta and vena cava in different lumbar intervertebral space levels in supine, prone, and lateral positions, and the thickness and displacement of the psoas muscle were noted as well to define the safe working zone for lateral lumbar interbody fusion. Methods    Fifteen volunteers underwent lumbar magnetic resonance imaging (MRI) examinations in different positions (supine, prone and lateral positions). The position of the abdominal aorta and inferior vena cava, the thickness, and displacement of the psoas major muscle at each intervertebral space level (L1/2~L4/5) on MRI were recorded and compared as well.    Results    In the same segment, the distribution of the inferior vena cava in different positions was similar. However, compared with the supine position, the abdominal aorta moved anteriorly to the anterior edge of the vertebral body in the lateral and prone positions at L1/2~L3/4 levels. There were differences in the thickness of the psoas muscle between different body positions in the same segment (L2/3 A zone, L3/4 A zone, IV zone and P zone, L4/5 II zone and IV zone) (P<0.05). In addition, there were differences in the anterior displacement of the psoas muscle between different segments. At the L1/2 level, the forward movement distances of the prone (-7.53±3.30 mm) and lateral positions (-7.25±3.96 mm) were significantly greater than that of the supine position（-10.90±3.31 mm) (P=0.012). At the L2/3 level, the forward displacement of the lateral position （-0.12±5.59 mm）was significantly greater than that of supine (-5.03±2.49 mm) and prone (-3.38±3.99 mm) positions (P=0.009). There was no significant difference in the L3/4 and L4/5 levels.    Conclusions    For right lateral position, it is safe and feasible to select zone I and II for puncture in the L1/2 and L2/3 levels. And zone II is suitable to puncture in L3/4 and L4/5 levels.

Key words: Blood vessels; ,  ,  Psoas muscle; ,  , Body positions; ,  , Lumbar lateral approach