Objective To analyze the correlation between the sagittal orientation of lumbar pedicle screws and screw loosening based on the craniocaudal cyclic load and artificial vertebra,and to provide a reference for the improvement of screw orientation during surgery,consequently reducing the incidence of screw loosening postoperatively.Methods Pedicle screws were inserted into artificial vertebrae in the cranial,parallel,and caudal orientations.After the artificial vertebra was installed in the material testing machine,the model was subjected to a 100 N preload and 166 N cyclic load for 10 000 cycles.During loading,displacements were recorded and cycle-displacement curves were drawn.After the test was completed and the screws were removed,the screw hole volume was measured and the screw hole volume ratio(the ratio of screw hole volume to the volume of the screw inserted into the vertebra)was calculated.Results The cyclic displacement curve showed that the cranial group had the largest displacement,followed by the parallel and caudal groups.The screw-hole volume ratio results showed that the cranial group had the highest ratio,followed by the parallel and caudal groups.Correlation analysis showed a negative relationship between screw sagittal orientation and terminal displacement(displacement corresponding to the 10 000th cycle)(ρ=-0.897,P=0.02)and screw hole volume ratio(ρ=-0.902,P=0.01).Conclusions There is a negative correlation between the sagittal orientation of the lumbar pedicle screw and screw loosening.Namely,when the screw sagittal orientation is adjusted from a cranial tilt to a parallel and even caudal tilt at a certain angle range,the incidence of screw loosening is reduced.