Insertion angle (β): Taking the intersection of the median sagittal plane and the median coronal plane of the intervertebral disk as point o, make the tangent line a between point o and the left side of the abdominal aorta (left common iliac artery) and tangent line b between point o and the front side of the left psoas muscle. The angle formed by the tangent line a and the tangent line b is ∠α. As the angle bisector c of ∠α, the angle formed by the c-line and the coronal diameter line of the median of the intervertebral disk is ∠β, which is the angle β when the OLIF surgical channel is placed