There's several ways to 'crack' the ribs. The most common is to separate the brisket from the ribs as in St. Louis style. Another is to cut half way thru the joints and bend them over and under the ribs, the fat from the brisket basting the leaner rib meat. Another is to cut through the ligaments about every other rib down thru the brisket so you can finish the cuts between the ribs after cooking. Yet another meaning is to similarly cut through the breastbone on the large end of the ribs with a cleaver three or four times, so you can pass through it with a knife down thru the cartilages and between the ribs (this was the method I learned from my dad). All methods are meant to ease carving of the ribs thru the cartilages and bone of the brisket.