A system includes a screw tower, an instrument, and a housing. The instrument includes a driver shaft extendable longitudinally through the screw tower, and a threaded sleeve mounted on a proximal portion of the driver shaft. The housing includes one or more retention members coupleable to the screw tower, and a threaded button threadably coupleable to the threaded sleeve. The threaded sleeve is rotatable about a longitudinal axis to urge the driver shaft longitudinally relative to the screw tower.