A spinal alignment system can include a rod and a plurality of uniplanar screw assemblies that include a screw, a cap, and a housing. The screw and cap can be configured such that the relative angular displacement between the screw and the cap is limited to a first limit angle in a first plane and to a second limit angle in a second plane that is perpendicular to the first plane, the second limit angle being larger than the first limit angle. The housing can be coupled to the cap and configured to maintain the cap in proximity with the head of the screw. The housing can have two elongated elements forming a U-shaped saddle. The alignment system can also include a plurality of locking cap assemblies that capture the rod within the U-shaped saddle and are tightened to fixedly couple the rod to the respective uniplanar screw assemblies.