If you’re involved in a sport such as basketball, football, or soccer, you may know someone who has had an anterior cruciate ligament (ACL) surgery. An ACL injury can bring an active life to a halt, whether you are a young athlete who plays a high-impact sport or a middle-aged "weekend warrior" hitting the tennis court without a warmup after sitting at a desk all week.

ACL injuries can happen when you’re playing a sport and collide with another player. They can also occur when you stop or change direction suddenly, land improperly, or slow down while running.

“From the internal damage within the knee joint to the psychological stress of time spent away from sporting activities, the effects of an ACL injury can be devastating,” says Elizabeth Gardner, MD, an orthopaedic surgeon for Yale Medicine. “My goal is to help patients navigate all aspects of this injury, including ACL surgery, to allow them to return safely to their desired activities and regain their quality of life.”

The knee's bone structure consists of three parts: the femur, the tibia, and the patella. The ACL is one of the ligaments that forms a cross, connecting the tibia to the femur and keeping the knee stable during quick direction changes. This stability is important for cutting and pivoting activities in such sports as soccer and basketball.

ACL injuries can range from a sprain of the ligament to a full rupture. Most commonly, people tend to tear, or rupture, the whole ACL, says Dr. Gardner. Sprains and partial tears are more unusual and may go unrecognized. About half of ACL injuries occur in conjunction with other knee injuries, such as injuries to the meniscus, a thickened crescent-shaped cartilage pad between the thigh and shin bones.

Though every ACL injury is unique, patients typically describe a sharp pain initially and most report difficulty walking, at least until the swelling subsides. After that, the knee might not hurt as much, but there may still be instability. The knee may give out, sometimes during a sport, and even while walking. If you ignore the injury and continue to pursue your activities, you can cause further damage to the cartilage that protects the knee.

There are many reasons why women are at higher risk for ACL injuries than men, Dr. Gardner says. Hormonal differences may be part of the explanation because estrogen can affect women’s ligaments.

But the difference is more likely the result of biomechanics and how a woman’s body is put together. Women’s knees and hips move at different angles than men’s, and women's muscles support the joints differently. Women tend to position their bodies in a relatively upright stance, straight at the hips and knees, and when they jump, they have a knock-knee component to the landing. “All of these things put women at higher risk for ACL tears,” Dr. Gardner says.

The doctor will want to know how you injured your knee—most injuries happen during a movement that involves pivoting, twisting, or turning. The doctor will compare your injured knee with your other knee, checking for swelling soon after the injury, as swelling is a sign of bleeding inside the knee. The patient may notice knee instability immediately or even after many months following the injury.

Depending on what the physical examination shows, the doctor may recommend an X-ray to check for bony injuries. The doctor may also ask for a magnetic resonance imaging (MRI) scan, which can provide better pictures of soft tissue injuries, confirm the diagnosis, and show any related problems in the rest of the knee. About 50% of people who injure their ACL will find that they have injured other structures in the knee as well. The goal is to be optimally prepared at the time of surgery to address anything within the knee that needs to be fixed.

There are two treatment options for ACL injury:

• Nonsurgical treatment such as a brace to protect from instability and physical therapy to strengthen the surrounding ligaments to provide greater stability
• Surgical reconstruction of the ACL to restore the internal structures of the knee to enable maximal stability

Your choice of treatment will depend on such factors as your age, your activity level, and the severity of your injury. You should also talk to your doctor about any preferences and concerns. Patients usually choose ACL surgery (or reconstruction) if they want to continue their sport or other activity, or if they are younger and want to prevent or prolong the time until they develop arthritis in the area. An older adult who just wants to walk and work out on a treadmill may choose to avoid surgery.

It’s important to know that recurrent knee instability caused by a dysfunctional ACL may result in additional damage to the menisci (the “shock absorbers” of the knee) and cartilage. Over time, these associated injuries may predispose the knee joint to degenerative changes.

ACL reconstruction is typically an outpatient procedure. The surgeon will remove the damaged ligament, then replace it with a new one—either an autograft (tissue taken from another part of the body, such as the kneecap tendons or hamstring) or an allograft (tissue from a deceased donor).

The procedure is arthroscopic, which means it involves several small incisions and the insertion of a tiny camera and instruments to allow the surgeon to see inside the knee joint and to perform the operation.

The duration of the ACL surgery will vary depending on the extent of the damage in the knee. While recovery from the procedure is fairly straightforward, following instructions for physical therapy and rehabilitation is imperative. So is clear communication between the therapist and the surgeon. A return to sports, depending on the individual’s goals, typically occurs between six and 12 months, and may include some work tailored toward the person’s particular activities.

“The decision of when to return to sports and unrestricted activities requires collaboration between the patient, the surgeon, and the physical therapist,” Dr. Gardner says. “To minimize the chance of re-tearing the ACL, I use a series of functional and strength tests to ensure that the patient is, in fact, optimally rehabilitated from the injury.”

The success rate for ACL surgery done correctly and with proper rehabilitation is very high, Dr. Gardner adds.

There are several important advantages to having a Yale Medicine orthopaedic surgeon perform an ACL surgery. Many of our doctors were high-level athletes and understand the toll an injury can take on an athlete. They have also worked with professional and college sports teams, and have been involved in managing all aspects of surgery and rehabilitation of ACL tears and other sports injuries for those players.

“For me, the greatest advantage of working at an academic medical center like Yale is my access to a team of researchers and physical therapists who aspire to improve patient outcomes and, perhaps even more importantly, work to prevent ACL tears. With the use of the most cutting-edge research, we aim to keep patients active and doing what they love safely,” Dr. Gardner says.