Not Exactly Par for the Course

A second ligament, the posterior cruciate, crosses the ACL and stabilizes the knee in the opposite way. The ACL is slightly weaker, however, and more often is injured.

The announcement yesterday also revealed that Woods has a "double stress fracture of his left tibia," the large bone of the lower leg. The fractures were discovered last month and "were attributed to Woods' intense rehabilitation and preparation for the U.S. Open," which Woods won this week in a dramatic sudden-death playoff.

Stress fractures generally are injuries of chronic overuse. They are most commonly associated with distance runners who increase their mileage too quickly, causing constant, low-impact stress on a weight-bearing bone.

"Rehab exercises are usually low impact. It would be very rare to get that [injury] in the physical therapy room. I have never seen it," DiNubile said.

What relationship the stress fractures may have to the ACL tear -- and what either may have on the unspecified cartilage damage that surgeons treated in the arthroscopic surgery in April -- is unknown.

The surgery Woods is likely to undergo will require getting a replacement ligament from elsewhere in his body or from a cadaver. If the former strategy is chosen, surgeons could use part of the patellar ligament, which attaches the kneecap to the lower leg. An alternative would be to use part of the tendon of the hamstring muscles at the back of the thigh.

The new tendon is attached to the bones at both ends using screws or staples. Cadaver tendons, unlike other organ transplants, do not require a patient to take immune-suppressing drugs. However, they do take somewhat longer to heal.

The operation usually is done with fiber-optic arthroscopes. A small incision is made below the kneecap, through which the surgeon tunnels into the joint.

"The procedure is light years from what it was when I was training," said DiNubile, who is 55. "This has gone from being a disastrous surgery with a huge incision to something that is usually done with an overnight stay."

Whatever strategy is used, a main issue after the operation is that the patient usually feels ready to fully use the knee well before it is ready to bear the stress of high-level athletic activity. The grafted tendon does not reach full strength for 18 months.

The failure rate for first-time ACL repair is about 5 percent. If a second operation is required, the failure rate rises to about 25 percent.

"Our goal is for the athlete to be back playing their sport at the six-month point," Levine said. He speculated that Woods could be putting three months after the surgery and chipping at four, but not swinging hard until after that.

Staff researcher Madonna Lebling contributed to this report.