Is a rupture the same thing as a tear of the mcl?

Yes. Sprain, tear and rupture are all basically the same thing thing. Sprains are graded 1 though 3 where grade 1 is a strain, grade 2 is a partial tear, and grade 3 is complete tear or "rupture" of the ligamant. This is true for injuries of the mcl (medial collateral ligament) or any other ligament.