The projection shape of the vertebral pedicle in different segments of the lumbar spine. The outer edge of the cranial articular process was located on the lateral side of the outer edge of the pedicle projection and did not overlap with the pedicle projection. M1: the distances from different insertion points to the articular process joint, M2: the distances from different insertion points to the outer edge of the cranial articular process, M: the distances from different insertion points to the center of the pedicle projection