Pedicle screw pull-out strength is determined in part by the major screw diameter which should be 70–80% of pedicle diameter (in adults, larger screws can break through the pedicle wall or can burst the pedicle; in peds, larger screws may be used as the pedicle can expand). The minor diameter determines the strength of the screw and should be ≥ 5.5 mm in the adult lumbar spine.