Treating an Infected Knee After ACL Surgery

One of the potential problems that can occur at the time of ACL surgery is an infection of the ACL graft. Surgical treatment of an ACL tear involves the placement of a new ligament, followed by several months of rehabilitation.

Doctor examining female patient's leg
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Infection after ACL reconstruction surgery is a rare complication. Studies estimate the chance of developing a joint infection (called a septic joint) after an ACL reconstruction surgery are less than 1 percent (0.3 percent in the largest study).

The anterior cruciate ligament, or ACL, is one of four major knee ligaments. The ACL is critical to knee stability, and people who injure their ACL often complain of symptoms of their knee giving out from under them. Therefore, many patients who sustain an ACL tear opt to have surgical treatment ​for this injury.

Causes of Infection After ACL Surgery

Infections occur when bacteria are able to grow inside your body. Your immune system can fight infections when they are small, but some infections may be too severe for your immune system to adequately eradicate.

Infections are a concern after ACL surgery for two reasons:

  • Joints are susceptible to infection: Joints are spaces occupied by fluid that has little immune defenses. Therefore, when infections get inside a joint, the body has a limited defense against the infection. Surgery is necessary to clean out the joint for the treatment of the infection.
  • ACL grafts have no blood supply: The graft used for ACL surgery has its normal blood supply disrupted; this is true for both grafts harvested from your own body or grafts donated from a cadaver. The graft has no blood supply, and thus antibiotics have no way to get to the graft tissue.

Blood supply is critical to fighting infections because the bloodstream carries immune defenses and antibiotics. That is a problem with infections in joints or infections of grafts. After ACL surgery, infections have the ability to thrive because you have little immune defenses in a joint and no blood supply to the ACL graft.

Treatment of Infections After ACL Surgery

Joint infections after ACL surgery are treated with surgery and antibiotics. Surgical treatment is necessary to clean the joint of bacteria, and antibiotics are intended to prevent a recurrence of the infection.

When the infection is found early in its onset, a surgical procedure to clean the joint may be sufficient for treatment. However, when the infection has been present longer, the entire ACL graft may need to be removed in order to cleanse the infection.

When this more aggressive step is necessary, the ACL graft is removed, the infection is eradicated, and several months later, a new ACL reconstruction surgery is performed. Deciding when the graft can be retained depends on the appearance of the ACL graft at the time of surgery, and the response to treatment. If multiple surgeries are performed without improvement in the infection, the graft will likely need to be removed.

Can You Avoid ACL Infections?

Yes and no. We know there are steps that can be taken to minimize the risk of infection, but there is no way to make the risk of infection 0 percent. Steps that can be taken include ensuring sterile procedures in the hospital operating room, giving antibiotics at the time of surgery, and appropriate sterilization of the affected knee. Ask your doctor about steps you can take to ensure you have the lowest chance of developing an infection.

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Evans J, Nielson Jl. Anterior Cruciate Ligament (ACL) Knee Injuries. In: StatPearls [Internet]. Updated 8 Mar 2019.

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  5. Kim HJ, Lee HJ, Lee JC, Min SG, Kyung HS. Evaluation of Infection after Anterior Cruciate Ligament Reconstruction during a Short PeriodKnee Surg Relat Res. 2017;29(1):45–51. doi:10.5792/ksrr.16.019

Additional Reading

By Jonathan Cluett, MD
Jonathan Cluett, MD, is board-certified in orthopedic surgery. He served as assistant team physician to Chivas USA (Major League Soccer) and the United States men's and women's national soccer teams.