After injuries to Jose Aldo and Rampage Jackson, the UFC 153 fight card has had plenty of changes. Anderson Silva has stepped up and has become the new main event against Stephan Bonnar. Check out all the other news surrounding UFC 153 below.
Source

Anderson Silva vs. Stephan Bonnar Is New UFC 153 Main Event; Glover Teixeira Gets New Foe
One day after UFC 153's top two fights fell out, two more took their place.

UFC middleweight champion Anderson Silva will step up to 205 pounds and meet veteran Stephan Bonnar in the main event of the Oct. 13 card at HSBC Arena in Rio de Janeiro.

The bout replaces the planned featherweight title bout between champion Jose Aldo Jr. and Frankie Edgar. Aldo had to pull out of the fight on Tuesday due to complications from injuries suffered in a recent motorcycle accident.

The new co-main event features a battle of Brazilian light heavyweights as Glover Teixeira (18-2) faces Fabio Maldonado (18-5). Maldonado replaces Quinton "Rampage" Jackson, who also had to pull out due to injury.

MMAFighting.com confirmed the bouts after an initial USA Today report.

Silva (32-4), who will celebrate his record sixth anniversary as middleweight champion the day after UFC 153, has twice stepped up and fought at 205 during his record streak of 15 consecutive UFC wins. Both were first-round knockouts, as he stopped James Irvin in July 2008, and took out former champ Forrest Griffin at UFC 101.

The world's top pound-for-pound fighter had previously stated that he was done competing at light heavyweight, but the opportunity to step up, save a show, and fight in front of his Brazilian fans was apparently too much to resist.

Bonnar (14-7), meanwhile, is most famous for his bout against Griffin in "The Ultimate Fighter 1" finale. While he's had his career ups and downs, Bonnar has won his past three fights.

Teixeira made an impressive company debut at UFC 146, when he stopped Kyle Kingsbury. While there were strong rumors on Wednesday that Thiago Silva would take Jackson's spot against Teixeira, the spot instead went to Maldonado, who was slated to meet Cyrille Diabate at UFC 154. Maldonado is 1-2 in UFC action, most recently coming out on the wrong end of a highly debatable decision against Igor Pokrajac on May 15.

Source

After all it was good luck in the bad luck that the injuries happend a month before the event and not a week.

So this is what it's like for a champ to step up to plate to save an event.