What is the actual infection risk after ACL reconstruction?

Infection after ACL reconstruction is divided into two quite different problems. A superficial wound infection involves the skin and the tissue just beneath it, usually at an incision or a graft harvest site, and is generally managed with antibiotics and wound care. Septic arthritis is an infection within the knee joint itself. It is much less common and much more serious, because bacteria inside a joint can damage the cartilage surface, and that damage does not reverse.

This is why suspected joint infection is handled urgently. The typical response is to aspirate or wash out the joint arthroscopically, send fluid for culture, and start antibiotics — often before culture results are back. In most reported series the graft can be retained rather than removed if the infection is addressed early, which is one of the main reasons for acting quickly.

A large single-surgeon series of primary all-soft-tissue quadriceps tendon reconstructions has been published on precisely this question, first-authored by Dr. Seilern. Its headline finding concerns the rate of culture-positive septic arthritis in that series.

The specific numbers from that paper are not reproduced here yet. This site’s standard is that sample sizes and effect estimates come from the full text rather than the published abstract, and this paper is not open access. The figures will be added once the full text has been checked. Until then it is enough to say that the reported rate was low and that the series was drawn from one surgeon’s consecutive practice — which matters, because a single-surgeon result reflects that surgeon’s technique, operating room setting and patient mix as much as it reflects the graft.

It is worth being explicit about that last point in general. A very low complication rate from one surgeon’s series is a meaningful observation, but it is not the same as an expected rate for a different surgeon in a different hospital. When you are quoted an infection rate, the useful question is always: whose rate, in which patients?

For most people, infection risk does not decide whether to have an ACL reconstruction, because the absolute risk is low across all the standard techniques. It is more relevant to the specifics: how the graft is prepared and handled, whether antibiotics are used on the graft, and how the team responds if something looks wrong afterwards.

Some factors do raise risk, and they are the ones worth discussing if they apply to you — diabetes and poor glycaemic control, smoking, immunosuppression, previous surgery or infection in the same knee, and revision procedures generally.

The part that most affects outcome, though, is not prevention but response time. An infection recognized and washed out early usually ends with the graft retained and the cartilage intact. One that is dismissed for two weeks does not reliably end that way. This is why surgical teams would rather see you unnecessarily than late.

The practical version of this is knowing what should prompt a phone call. Increasing rather than decreasing pain after the first few days, a knee that becomes hot, swollen and tense again after starting to settle, fevers or chills, or wound drainage that persists or restarts — any of these warrants contacting your surgical team the same day.

Some swelling, warmth and discomfort is normal after this operation, and it is not always obvious from the outside which is which. That judgement is the team’s job, not yours. Being wrong about it costs you a phone call; being late about it can cost cartilage.

If you have a condition that raises your risk — diabetes in particular — it is worth asking directly what the plan is to manage that around surgery, because it is one of the few parts of this that is genuinely modifiable in advance.