Woods' pain was apparent from Thursday's start through Monday's playoff finish. Fans winced along with golf's master as he drove the ball down many a fairway at the U.S. Open, clearly experiencing pain in his left knee, which underwent arthroscopic surgery two days after he finished second in the Masters in April.
On Monday afternoon, after 91 grueling holes, all that pain seemed to have turned into gain for Woods, as he clinched his 14th major championship.
But was it worth it?
Wednesday's news suggests that playing the five-day marathon U.S. Open may have put his near-term future in doubt.
"I know much was made of my knee throughout the last week, and it was important to me that I disclose my condition publicly at an appropriate time," Woods said in a statement on his Web site. "I wanted to be very respectful of the USGA and their incredibly hard work, and make sure the focus was on the U.S. Open. Now, it is clear that the right thing to do is to listen to my doctors, follow through with this surgery, and focus my attention on rehabilitating my knee."
The report on Woods' Web site said his doctors have assured him that his long-term prognosis is good with rehabilitation and training.
How Long Will He Be Out?
"I'm glad I'm done," Woods told reporters shortly after his victory when asked how he felt about playing five days in a row, just two months after surgery. "I really don't feel like playing anymore. It's a bit sore."
"I'm going to shut it down for a little bit here and see what happens," he said.
Woods' return to the game is uncertain, and he will face months of rehabilitation after this second surgery. It will likely involve a reconstruction of the ACL, in which a graft is used to replace the torn ligament.
Many doctors put the timeline of his competitive return well into next season.
"We usually allow patients to do certain movements at six months -- straight-ahead movements like walking or exercise on a stationary bike," says Dr. Michael Bronson, associate professor of orthopedic surgery at Mount Sinai School of Medicine in New York. "But in terms of a return to a sport where they're actually pivoting on the reconstructed knee, we don't allow that for 9 to 12 months."
Like anyone else who undergoes this surgery, Woods will need a considerable amount of time to heal.
"He's such a fine-tuned piece of machinery, but he bleeds like we do," says Dr. Robert Klapper, chief of orthopedic surgery at Cedars Sinai Medical Center in Los Angeles and author of the book "Heal Your Knees: How to Prevent Knee Surgery and What to Do If You Need It."
Doctors say that only Woods and his orthopedic surgeon know the exact nature of the damage to his left knee, and whether pushing through the U.S. Open would have caused additional injury.
"We can only guess," says Dr. C. Thomas Vangsness Jr., professor of orthopedic surgery at the Keck School of Medicine of the University of Southern California.
Along with this recent procedure, Woods underwent surgery on the same knee in 2002 and prior to that in 1994 to have a benign tumor removed.
Woods originally injured his ACL when he was running at his home in Orlando in July 2007. He chose not to have surgery at that time and continued to play.
Dr. Misty Suri, a sports medicine orthopedic surgeon in the Ochsner Health System in New Orleans, says that sitting out the U.S. Open would not have saved Woods' knee from surgery. "Resting it doesn't cure that," Suri says of the ACL tear.
Woods is not the first professional athlete to push through a championship with this injury. Most recently, quarterback Philip Rivers of the San Diego Chargers played in the 2008 Superbowl with a torn ACL, and he had surgery three days later to repair it.
"Every sport has this as an injury," says Klapper.
Though golf may not aggravate the condition as much as football or basketball, Bronson still called Woods' decision to play in the U.S. Open "very bad." He says that Woods' ACL probably wasn't strong enough to support his knee.
Tears to the ACL usually occur after a traumatic event, such as running in Woods' case, but the repetitive motion of Woods' powerful swing could have aggravated this knee injury, Suri says.
On top of that, Woods may be experiencing pain from arthritis in his knee, Vangsness says. If that's the case, the hard cartilage that cushions the end of the bones is breaking down, causing pain and swelling as the bones begin to rub together.
Surgeons likely removed some of the fragments of cartilage from Woods' knee joint during the surgery in April, says Dr. James Gladstone, co-chief of sports medicine at Mount Sinai Medical Center in New York.
But arthritis progresses slowly, so "in terms of further damage to the knee, it's unlikely," Gladstone says about Woods's choice to play through the pain.
"Many elite athletes have a pretty good sense of their bodies ? if there is a malfunction in the system, they are generally good at knowing that something isn't right," Suri says.
When Woods himself was asked if he might have re-injured his knee, he replied, "Maybe."
Though Suri tells most weekend athletes to refrain from playing through an injury, he recognizes that professional athletes have an additional set of concerns.
"The general public isn't getting paid millions of dollars for their athletic prowess," he says. "The decision for an elite athlete has entirely different implications than for the layperson."
Recovering From a Painful Victory
It's too late for Woods to reverse his decision to play, but he can take a few steps now to nurse his knee before his return to the game.
"The best thing for Tiger to do is begin a water exercise program," says Klapper.
Klapper, who treated basketball great Wilt Chamberlain with the same regimen, recommends walking forward and backward in waist-high water for 20 minutes, three days a week. The water provides weightlessness to unload pressure on the joint and resistance to strengthen leg muscles surrounding the knee.
"It's a perfect double punch," he says.
Klapper performs about 500 surgeries a year, including hip and knee replacements. Many of his patients are in their late 30s and early 40s, suffering from damaged joints due to overexercising.
"We are exercising too aggressively for the machinery we've been given," he says. Running, for example, is great for the heart, but it destroys the discs in the back. Water exercises work the heart and other muscles, sparing the joints.
"In our society we're taught, No pain, no gain," he says. "Bad advice. When you have pain, you need to stop."
For Tiger to delete the joint abuse from his life, Klapper says he should commit to spending several months exercising in the water during his recovery from surgery.
Down the road, when Woods is in his 40s or 50s, he may be forced to undergo another surgery for the arthritis -- a knee replacement. The procedure would remove damaged cartilage and bone caused by years of friction on the joint, either from running on the treadmill, walking 18 holes or driving the ball down the fairway.
"Sooner or later this 32-year-old superstar who abuses his knee ? will have to have some metal and plastic in his knee," Vangsness says of the knee replacement surgery. "When that time comes about, he'll be able to play a lot better."