A driver instrument with dual holding features for use with a combination of a medical staple and movable washer with that are used in a surgical procedure for attaching a ligament, or the like, onto a bone surface. The driver includes a straight body that is preferably cylindrical, is formed of a hard metal and includes a hand engaging central portion. A driver top end is flanged outwardly into flat head end that can be struck, as with a hammer to impart a hammer force therethrough, with the driver lower end portion formed with a threaded portion for turning into a threaded hole formed through a web of the medical staple, and with a spring collet formed with, or connected axially to, the driver lower end portion. Installation of the medical staple and washer onto the driver involves passing the spring collect through the staple web hole ahead of the driver threaded portion, and through a smooth walled hole formed through the movable washer, with a spring collet ring end passing through the washer hole and restricting removal therefrom. The driver that mounts the medical staple and movable washer, is held by a surgeon to position the staple legs onto a bone surface, straddling a ligament, and then is used to seat the staple into which bone by applying a hammer force to the driver head end. Whereafter, the driver threaded portion is turned out of the staple web threaded hole, pulling also the driver spring collet section out of the washer hole.