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ACL Surgery

ACL surgery is a repair or reconstruction of the anterior cruciate ligament (ACL). The ACL is an important soft-tissue structure in the knee that connects the femur to the tibia. A partially or completely torn ACL is a common injury among athletes.

An athlete on a field with a knee injury.

Complete ACL tears are usually treated by sports medicine physicians and orthopedic surgeons with an ACL reconstruction surgery, in which the torn ligament is replaced with a tissue graft to mimic the natural ACL. However, HSS takes an interdisciplinary approach to treating ACL injuries: Physiatrists, sports medicine physicians and orthopedic surgeons – along with radiology and rehabilitation professionals – collaborate to determine the best treatment option for each patient. Because people who have had an ACL injury are more likely to develop osteoarthritis in the knee earlier in life than those who do not, HSS physicians and scientists also continually investigate ACL surgery techniques to improve the short-term and long-term outcomes for patients.

How do you know if you need ACL surgery?

The need for surgery depends on the severity of the ACL tear and the lifestyle of the patient. A completely torn ACL cannot heal on its own. Studies have shown, however, that in some patients who experience a partial tear of the ACL, the ligament may heal without the need for surgery.

Partial and complete ACL tears

To determine whether a tear is partial or complete, a doctor will perform two manual tests:

  • Lachman test: The physician will try to pull the shin bone away from the thigh bone. If the ACL is torn but still intact, the bones won’t move or will do so only slightly.
  • Pivot shift test: The patient lies on their back while the doctor lifts their leg and places rotational pressure on the knee. If the bones don’t shift, the test is negative.

In patients who have only a partial tear, it may be recommended to delay surgery and first see if the ligament heals without it.

Patient lifestyle

People who have completely torn their ACL and who maintain an active lifestyle – especially competitive athletes – will need surgery return to their prior level of activity and avoid future injury. In some older patients or others whose lifestyles do not include rigorous exercise, nonsurgical treatments may allow them to return to normal routines without an intact ACL.

However, anyone who returns to unrestricted activity with a completely torn ACL will likely experience some knee instability. In they are much more likely to tear their meniscus. The meniscus is a pad of cartilage that cushions the bones that meet at the knee joint. There are two menisci on each knee: the medial meniscus on the inside of the knee and the lateral meniscus on the outside. A torn meniscus will cause knee pain and, sometimes, swelling. More importantly, however, a damaged meniscus increases a patient's risk of developing osteoarthritis of the knee later in life.

How soon should you get ACL surgery?

For a complete tear of the ACL, reconstruction surgery is generally scheduled for between three and six weeks after the injury occurs. This allows inflammation in the area to subside. If surgery is performed too early, patients may develop a profound scarring response called arthrofibrosis.

Orthopedic surgeons gauge the appropriate timing of reconstruction surgery based on:

  • whether there are other injuries present that need to be treated first
  • the physical appearance of the knee
  • the patient’s level of pain
  • the patient's range of motion and quality of muscle control when flexing (bending) or extending (straightening) the leg

Some evidence suggests that delaying ACL reconstruction surgery for six months or longer after injury reduces a person's chances of having a clinically significant outcome and leads to increased rates of the need for future revision surgeries.

How does ACL reconstruction surgery work?

In ACL reconstruction surgery, a new ACL is made from a graft of replacement tissue from one of two sources:

  • a portion of the patient's own hamstring, quadriceps or patellar tendon
  • an allograft (tissue from a human organ donor)

The type of graft used for each patient is determined on a case-by-case basis.

ACL reconstruction surgery is performed using minimally invasive arthroscopic techniques, in which a combination of fiber optics, small incisions and small instruments are used. A somewhat larger incision is needed, however, to obtain the tissue graft. ACL reconstruction is an outpatient (ambulatory) procedure, in which patients can go home on the same day as their surgery.

Animation video: Torn ACL reconstruction surgery

View this animation for a more detailed description of a minimally invasive ACL reconstruction.


What is the recovery time for ACL surgery?

It usually takes six to nine months for a patient to return to participating in sports after an ACL reconstruction, depending on the level of competition and the type of activity.

Patients are able to walk with crutches and a leg brace on the day of surgery. Very soon after surgery, the patient enters a rehabilitation program to restore strength, stability and range of motion to the knee. The rehabilitation process is composed of a progression of exercises:

  • Strengthening and range-of-motion exercises are started early in the recovery period.
  • Running exercises begin at about four months.
  • Pivoting exercises are started at around five months.
  • Return to playing competitive sports can begin as early as six months.

The degree of pain associated with ACL recovery varies and can be addressed successfully with medication. Recovery time also varies from patient to patient. The determination of when a patient has fully recovered is based on the restoration of muscle strength, range of motion and proprioception of the knee joint.

Arthroscopic surgical techniques have made recovery times quicker and easier in comparison to open surgery, which is how ACL reconstruction performed in the past. But to achieve a successful outcome, it is critical that the patient have a rehabilitation period that is carefully supervised by an appropriate physical therapist, as well as to have follow-up appointments with the surgeon.

MRI of Complete ACL Tear
Side-view MRI showing a completely torn ACL

MRI of ACL rear reconstruction
Side-view MRI showing an intact, reconstructed ACL after surgery

Types of ACL surgery

In most cases, it is not possible to repair or reattach a torn ACL. ACL surgery usually involves a complete rebuilding of the ligament. This procedure, called ACL reconstruction, is the current standard of care for surgically treating a torn ACL. Choosing the right surgical option for an ACL tear from the start can have lifelong implications, and it is critical to get ACL surgery right the first time.

ACL reconstruction versus ACL repair

ACL reconstruction is the current standard-of-care surgical treatment for ACL tears. This procedure typically uses a graft, or a piece of tissue, placed in the knee in a minimally invasive surgery that uses small incisions. Most ACL surgeries performed at HSS are ACL reconstructions.

ACL repair is an older technique that involved sewing the torn ACL tissue back together with sutures, rather than rebuilding it with a graft. ACL repair was performed in the 1970s at select institutions, including Hospital for Special Surgery, but was abandoned due to unacceptably high failure rates of up to 50%. Today, ACL repair has been modernized and can be performed through a minimally invasive approach. Some surgeons feel that modern ACL repair techniques may be performed safely and may lead to a quicker recovery than ACL reconstruction. However, the data on outcomes is limited, and failure rates for ACL repair appear to be between 5 and 10 times higher than those for ACL reconstruction in people of all ages.

When ACL surgery fails, surgeons must do a revision surgery (a second operation) to fix any problems that were not successfully addressed the first time. If a repaired ACL fails, it can only be revised with an ACL reconstruction. Having to redo any kind of ACL surgery may result in higher rates of failure, lower rates of successful return to sports activity, and increased risk of developing osteoarthritis in the knee. It is important for patients of all ages to have a successful surgery the first time, but it is particularly important for young athletes. For them, a failed surgery can be devastating: In the short term, it can mean that they lose years away from their chosen sport. In the longer term, it can lead to chronic pain and loss of knee function.

ACL reconstruction surgery steps

Reconstruction of the ACL follows a number of basic steps, although they may vary slightly from case to case:

  • The orthopedic surgeon makes small incisions around the knee joint, creating portals of entry for the arthroscope and surgical instruments.
  • The arthroscope is inserted into the knee and delivers saline solution to expand the space around the joint. This makes room for surgical tools, including the arthroscopic camera, which sends video to a monitor so that the surgeon can see inside the knee joint.
  • The surgeon then evaluates structures that surround the torn ACL, including the left and right meniscus and the articular cartilage. If either of these soft tissues have any lesions, the surgeon repairs them.
  • Next the graft will be harvested (unless a donor allograft is used). A section of tendon from another part of the patient's body is cut to create a graft, which is then attached at each end to plugs of bone taken from the patella and tibia. These plugs help to anchor the graft that will become the new ACL.
  • The surgeon inserts the new ACL into the femur and tibia using a flexible guide wire.
  • Screws are used to secure the plugs of bone. Over time, these plugs will grow into the surrounding bone.
  • The surgical instruments are removed to complete the procedure.

What kind of anesthesia is used for ACL surgery?

At HSS, most patients who undergo ACL reconstruction are given an epidural nerve block during their surgery, rather than being placed fully unconscious under general anesthesia. This epidural is the same type of regional anesthesia many women receive during childbirth.

Can a teenager have ACL surgery?

Children and younger teenagers who are still growing cannot have the same type of ACL surgery as an adult or older adolescents, but recent surgical innovations have made it possible for youth athletes to have ACL reconstruction surgery.

The standard method of ACL reconstruction can be performed successfully on older teenagers. But performing ACL reconstruction on a growing child is difficult, because the typical method used for adults can cause damage to open growth plates, which can lead to uneven limb lengths or deformities. Therefore, it used to be that surgeons postponed ACL surgery until children stopped growing, or used surgical techniques that were not anatomically accurate.

But innovations in surgical techniques now provide a variety of options for treating an ACL tear in younger children and adolescents. One option developed at HSS is called the All-Inside, All-Epiphyseal Reconstruction (AE). The technique is similar to adult ACL surgery but uses new technology and intraoperative X-rays to place the new ACL graft anatomically in the knee, without the graft crossing the adjacent growth plates. It is performed arthroscopically and results in a near anatomic ACL reconstruction with a very high rate of return to play. This can be welcome news to child athletes who, without surgery, would simply have to stop playing sports until they had finished growing.

ACL Surgery Success Stories


  • Forsythe B, Lu Y, Agarwalla A, Ezuma CO, Patel BH, Nwachukwu BU, Beletsky A, Chahla J, Kym CR, Yanke AB, Cole BJ, Bush-Joseph CA, Bach BR, Verma NN. Delaying ACL reconstruction beyond 6 months from injury impacts likelihood for clinically significant outcome improvement. Knee. 2021 Oct 30;33:290-297. doi: 10.1016/j.knee.2021.10.010. Epub ahead of print. PMID: 34739960.
  • Hughes JD, Lawton CD, Nawabi DH, Pearle AD, Musahl V. Anterior Cruciate Ligament Repair: The Current Status. J Bone Joint Surg Am. 2020 Nov 4;102(21):1900-1915. doi: 10.2106/JBJS.20.00509. PMID: 32932291.
  • Nwachukwu BU, Patel BH, Lu Y, Allen AA, Williams RJ 3rd. Anterior Cruciate Ligament Repair Outcomes: An Updated Systematic Review of Recent Literature. Arthroscopy. 2019 Jul;35(7):2233-2247. doi: 10.1016/j.arthro.2019.04.005. PMID: 31272646.

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