These parameters increased ( L3-L5 ) : mean distance ( transverse plane ) between the starting point and middle of the spinous process , 1.2 ( 0.18 cm ) , 1.3 ( 0.2 cm ) , and 1.6 ( 0.3 cm ) , respectively ; mean screw sagittal angle with respect to the posterior skin , 15.5 ( 5.0 ) , 24.3 ( 6.5 ) , and 43 ( 5.8 ) , respectively ; and mean distance for guide wire entry , 28.8 ( 10.6 cm ) , 20.1 ( 5.4 cm ) , and 11.9 ( 2.1 cm ) , respectively .