Anterior cruciate ligament (ACL) surgery

Surgery Overview

Surgery for anterior cruciate ligament (ACL) injuries involves reconstructing or repairing the ACL.

  • ACL reconstruction surgery uses a graft to replace the ligament. The most common grafts are autografts using part of your own body, such as the tendon of the kneecap (patellar tendon) or one of the hamstring tendons. Other good choices include allograft tissue, which is donor material.
  • Repair surgery generally is only used in the case of an avulsion fracture (a separation of the ligament and a piece of the bone from the rest of the bone). In this case, the bone fragment connected to the ACL is reattached to the bone.

ACL surgery is done by making small incisions in the knee and inserting instruments for surgery through these incisions (arthroscopic surgery) or by cutting a large incision in the knee (open surgery).

ACL surgeries are done by orthopedic surgeons.

Arthroscopic surgery

Many orthopedic surgeons use arthroscopic surgery rather than open surgery for ACL injuries because:

  • It is easy to see and work on the knee structures.
  • It uses smaller incisions than open surgery.
  • It can be done at the same time as diagnostic arthroscopy (using arthroscopy to determine the injury or damage to the knee).
  • It may have fewer risks than open surgery.

Arthroscopic surgery is performed under spinal or general anesthesia.

During arthroscopic ACL reconstruction, the surgeon makes several small incisions—usually two or three— around the knee. Sterile saline (salt) solution is pumped into the knee through one incision to expand it and to wash blood from the area. This allows the doctor to see the knee structures more clearly.

The surgeon inserts an arthroscope into one of the other incisions. A camera at the end of the arthroscope transmits pictures from inside the knee to a TV monitor in the operating room.

Surgical drills are inserted through other small incisions. The surgeon drills small holes into the upper and lower leg bones where these bones come close together at the knee joint. The holes form tunnels through which the graft will be anchored.

The surgeon will take the autograft (replacement tissue) at this point. If it comes from the knee, it will include two small pieces of bone called "bone blocks" on the ends of the tissue. One piece of bone is taken from the kneecap and the other piece is taken from a part of the lower leg bone near the knee joint. If the autograft comes from the hamstring, bone blocks are not taken. The graft may also be taken from a deceased donor (allograft).

See a picture of a bone and tissue graft.

The graft is pulled through the two tunnels that were drilled in the upper and lower leg bones. The surgeon secures the graft with screws or staples and will close the incisions with stitches or tape. The knee is bandaged, and you are taken to the recovery room for 2 to 3 hours.

During ACL surgery, the surgeon may repair other injured parts of the knee as well, such as ligaments, cartilage, or broken bones.

What To Expect After Surgery

Arthroscopic surgery is often done on an outpatient basis, which means that you do not spend a night in the hospital. Other surgery may require staying in the hospital for a couple of days.

To care for your incision while it heals, you need to keep it clean and dry and watch for signs of infection.

Physical rehabilitation after ACL surgery may take several months to a year. The length of time until you can return to normal activities or sports is different for every person. It may range from 4 to 6 months.1

Why It Is Done

The goal of ACL surgery is to restore normal or almost normal stability in the knee and the level of function you had before the knee injury, limit loss of function in the knee, and prevent injury or degeneration to other knee structures.

Not all ACL tears require surgery. You and your doctor will decide whether rehabilitation only or surgery plus rehabilitation is right for you.

You may choose to have surgery if you:

  • Have completely torn your ACL or have a partial tear and your knee is very unstable.
  • Have gone through a rehabilitation program and your knee is still unstable.
  • Are very active in sports or have a job that requires knee strength and stability (such as construction work), and you want your knee to be as strong and stable as it was before your injury.
  • Are willing to complete a long and rigorous rehabilitation program.
  • Have chronic ACL deficiency that is affecting your quality of life.
  • Have injured other parts of your knee, such as the cartilage or meniscus, or other knee ligaments or tendons.

You may choose not to have surgery if you:

  • Have a minor tear in your ACL (a tear that can heal with rest and rehabilitation).
  • Are not very active in sports and your work does not require a stable knee.
  • Are willing to stop doing activities that require a stable knee or stop doing them at the same level of intensity. You may choose to substitute other activities that don't require a stable knee, such as cycling or swimming.
  • Can complete a rehabilitation program that stabilizes your knee and strengthens your leg muscles to reduce the chances that you will injure your knee again and are willing to live with a small amount of knee instability.
  • Do not feel motivated to complete the long and rigorous rehabilitation program necessary after surgery.

For more information, see:

Click here to view a Decision Point. Should I have surgery for an ACL injury?

How Well It Works

About 60% of people who have ACL surgery return to the full level of activity they had before their injury.2 But between 80% and 90% of people who have ACL surgery have favorable results, with reduced pain, good knee function and stability, and a return to normal levels of activity.3 ACL repair is usually successful for an ACL that has torn away from the upper or lower leg bone (avulsion).

Between 3% and 10% of people who have ACL surgery still have knee pain and instability and may need another surgery (revision ACL reconstruction).4 Revision ACL reconstruction is generally not as successful as the initial ACL reconstruction.


ACL reconstruction surgery is generally safe. Complications that may arise from surgery or during rehabilitation and recovery include:

  • Problems related to the surgery itself. These are uncommon but may include:
    • Numbness in the surgical scar area.
    • Infection in the surgical incisions.
    • Damage to structures, nerves, or blood vessels around and in the knee.
    • Blood clots in the leg.
    • The usual risks of anesthesia.
  • Problems with the graft tendon (loosening, stretching, reinjury, or scar tissue). The screws that attach the graft to the leg bones may cause problems and require removal.
  • Limited range of motion, usually at the extremes. For example, you may not be able to completely straighten or bend your leg as far as the other leg. This is uncommon, and sometimes manipulation under anesthesia can help. Rehabilitation usually attempts to restore a range of motion between 0 degrees (straight) and 130 degrees (bent or flexion). You may lack a few degrees at either end of the range of motion after surgery and rehabilitation.
  • Grating of the kneecap (crepitus) as it moves against the lower end of the thighbone (femur), which may develop in people who did not have it before surgery. This may be painful and may limit your athletic performance. In rare cases, the kneecap may be fractured while the graft is being taken during surgery or from a fall onto the knee soon after surgery.
  • Pain, when kneeling, at the site where the tendon graft was taken from the patellar tendon or at the site on the lower leg bone (tibia) where a hamstring or patellar tendon graft is attached.
  • Repeat injury to the graft (just like the original ligament). Repeat surgery is more complicated and less successful than the first surgery.

What To Think About

In an avulsion fracture, repair surgery is always performed as soon as possible.

In reconstruction of a partial or complete tear of the ACL, the best time for surgery is not known. Surgery immediately after the injury has been associated with increased fibrous tissue leading to loss of motion (arthrofibrosis) after surgery.5 Some experts believe that surgery should be delayed until the swelling goes down, you have full range of motion in your knee again, and you can strongly contract (flex) the muscles in the front of your thigh (quadriceps).5 Many experts recommend starting exercises to increase range of motion and regain strength shortly after the injury.

In adults, age is not a factor in surgery, although your overall health may be. Surgery may not be the best treatment for people with medical conditions that make surgery a greater risk. These people may choose nonsurgical treatment and try to change their activity level to protect their knee from further injury.

Current research on the surgical treatment of ACL injuries includes different techniques and places to attach grafts; different types of screws; different types of grafts, such as tendon, muscle, or fascial grafts from your body (autograft); and grafts from a donor (allograft). When choosing a graft, consider the following:

  • The success of surgery may be more dependent on the surgeon's skill and preference than the type of graft used.
  • A kneecap tendon graft may result in some pain when kneeling.
  • The knee functions the same with either a kneecap graft or a hamstring graft.6
  • A kneecap graft entails more rehabilitation considerations than a hamstring graft, such as increased pain and swelling that may limit exercises for the thigh muscles for a while.

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  1. McMahon PJ, Kaplan LD (2006). Anterior cruciate ligament injuries section of Sports medicine. In HB Skinner, ed., Current Diagnosis and Treatment in Orthopedics, 4th ed., pp. 180–183. New York: McGraw-Hill.
  2. Biau DJ, et al. (2007). ACL reconstruction: A meta-analysis of functional scores. Clinical Orthopaedics and Related Research, 458: 180–187.
  3. Fu FH, et al. (2000). Current trends in anterior cruciate ligament reconstruction. American Journal of Sports Medicine, 28(1): 123–130.
  4. Noyes FJ, Barber-Westin SD (2001). Revision anterior cruciate ligament reconstruction: Report of 11-year experience and results in 114 consecutive patients. AAOS Instructional Course Lectures, 50: 451–461.
  5. D'Amato MJ, Rach BR Jr (2003). Anterior cruciate ligament reconstruction in the adult section of Anterior cruciate ligament injuries. In JC DeLee, D Drez Jr, eds., Orthopaedic Sports Medicine, 2nd ed., vol. 2, pp. 2012–2067. Philadelphia: Saunders.
  6. Pinczewski LA, et al. (2007). A 10-year comparison of anterior cruciate ligament reconstructions with hamstring tendon and patellar tendon autograft: A controlled prospective trial. American Journal of Sports Medicine, 35(4): 564–574.

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