Ulbrich plays through painHE MUST DECIDE ON SURGERY THAT COULD END HIS YEARBy Dennis Georgatos and Daniel BrownMercury NewsJeff Ulbrich, one of the 49ers' steadiest defenders, suffered a torn left biceps Sunday and must decide whether to undergo season-ending surgery or keep playing and risk the possibility of permanent damage.The linebacker's arm snapped back as he tackled Colts running back Edgerrin James during the second quarter. The force of the collision tore the muscle from the bone, Ulbrich said, though he resumed playing and finished with a team-high 10 tackles in a 28-3 loss.``He's in a lot of pain,'' fellow linebacker Derek Smith said. ``But he's going to play with pain and that's just a testament to what kind of guy he is. He's able to go out there and play with an injury and still be competitive.''Ulbrich said he will meet with team doctors today to discuss his options.He said he has been told that surgery to reattach the muscle would sideline him for the rest of the season. Doctors also told him that the injury could worsen if he tried to keep playing.``If I play with it, they might not be able to fix it,'' Ulbrich said.Ulbrich said he is tempted to keep playing, despite the cautionary words from doctors.``I really think we're going to do something special here,'' he said. ``I don't want to be on the sideline watching it when it happens.''Thornton holds his ownBruce Thornton, signed from the practice squad two weeks ago, was the 49ers' third starting left cornerback in three weeks after injuries to Ahmed Plummer and Derrick Johnson. In his first career start, he went up against one of the best.Thornton was covering Marvin Harrison for most of Sunday's game and won his share of the battles. Harrison was limited to two catches for 17 yards, and Thornton intercepted a pass at the goal line that Harrison had deflected. The swipe prevented Manning and Harrison from breaking the record they share with Steve Young and Jerry Rice for most touchdown passes by a quarterback-receiver tandem (85).``Marvin is fast, and he and Peyton have great timing between them,'' Thornton said. ``But he tipped the ball and I was able to make a play.''Thornton said he took pride in helping to prevent Harrison and Manning from hooking up for a score.``That's exciting, but I know I can do better because we lost the game,'' he said.