Since the surgery was on Storen's non-throwing hand, he will miss two to three days, and then will continue his throwing program. According to the team, the pitcher is expected to be ready for Opening Day.
From The Washington Post:
Nationals manager Matt Williams said Storen broke the bone, located at the bottom of the hand roughly below the ring and pinky fingers, while swinging earlier this week. Hitters often fracture and subsequently have that bone removed, as constant pressure from the knob of the bat commonly causes trouble.
The injury is not common for pitchers. The only concern now, manager Matt Williams told reporters, is letting the stitches heal in his hand before he can catch the ball.
Storen is entering his sixth MLB season, and has spent his entire career with the Nationals. Last season Storen had an ERA of 1.12, striking out 46 and walking just 11 in 56 1/3 innings.