You are zig-zagging down the soccer field, leaving other players in your wake. Just as you move to kick the ball into the net, you twist your foot against the turf, feel the pop in your knee and fall to the ground. You have just torn a ligament, and like any athlete, you wonder: what happened, and will I play again?

In all likelihood, ligament tears don't mean the end of your athletic days, says C. Thomas Vangsness Jr., M.D., USC associate professor of orthopaedic surgery. But outcome depends on some key questions:

Which ligament did you tear?

The knee has four stretchy ligaments that hold the top thigh bone of the leg (the femur) to the long, bottom bone (the tibia). The one athletes often hear about is the anterior cruciate ligament, known as the ACL, located in the center of the knee. It keeps the knee from twisting or rotating too much, as well as keeping the tibia from moving too far forward. When side ligaments are town, the ACL is often torn, too. It's typical for a knee with this type of damage to buckle when weight is put on it.

If the ACL is completely torn, Vangsness said, it cannot heal. If the patient chooses, an orthopedic surgeon can reconstruct the ligament through an operation. Reattaching the torn ends of the ligament doesn't work, so surgeons must reconstruct the ACL using one of several tendons located around the knee or a donor ligament.

How old are you, and are you a pro athlete?

If you are a teenager or in your 20s, Vangsness suggests getting the ACL surgically repaired, especially if you are active in sports. But perhaps if you are in your 30s, and especially in your 40s or above, he suggests trying to go without fixing the ACL. Anyone can still walk the dog, pick up the groceries and go on a hike with a torn ACL. In fact, those with such ligament damage can even ski or play a game of tennis. Surgery for those in their 30s and 40s is usually most appropriate for serious athletes or people who have ongoing instability in their knee (buckling or giving way). Otherwise, the knee can continue functioning in daily activities without the intact ACL-and without pain, he says.

Did you have an accompanying injury?

The doctor usually asks for a patient's medical history and performs X-rays and an magnetic resonance imaging (MRI) scan of the knee to see exactly what's going on. The doctor also examines how the knee and leg move to assess where the knee is injured. Sometimes surgeons use an arthroscope, a tiny lens attached to a camera that is inserted into the knee through a thin tube, to more carefully look at the inside of the joint on a monitor.

In half of all ACL tears, Vangsness says, the meniscus is also damaged. The knee has two menisci, tough, fibrous crescent-shaped pads of tissue between the femur and tibia that act like shock absorbers. When the ACL tears, it may let the knee pivot too much, tearing the meniscus and causing pain and swelling. In one of five tears, patients have potentially painful lesions in their articular cartilage.

What can be done for the meniscus?

Arthritis is likely to develop in the knee once the meniscus is damaged. When the meniscus is torn and very painful, an orthopedic surgeon can do arthroscopic surgery to see the extent of the injury, and remove the torn portion of the meniscus to relieve pain. Today, surgeons such as Vangsness have the technology to arthroscopically repair the meniscus without removing it all, without open surgery. He also performs meniscus transplants, taking a healthy meniscus from a cadaveric donor and implanting it in the knee if the entire meniscus is destroyed.

Recovery depends partly on the extent of the injury and the expectations of the person who suffered it. It is also important to consult a doctor who specializes in these injuries. "Our goal is to get people back to ordinary living, not necessarily extreme sports," Vangsness says. "Extreme twisting and turning motions can be deleterious to the knee. We focus on getting people back to their daily activities without pain. We also return our athletes to their sports. "