Long-Term Risk of Knee Replacement After ACL Reconstruction
Key points
- This study used NHS records from 135,881 people who had an ACL reconstruction in England, followed for up to 26 years.
- It compared each person's reconstructed knee with their own opposite, uninjured knee – a fair “internal” comparison.
- The reconstructed knee was about three times more likely to need a knee replacement than the uninjured knee.
- The absolute risk stayed low: at 20 years, around 2.4% of reconstructed knees had needed a replacement, versus around 0.9% of uninjured knees.
- The raised risk most likely reflects the original injury, not the operation – and most people who have an ACL reconstruction will not need a knee replacement.
What Was This Study About?
An anterior cruciate ligament (ACL) injury is one of the most common serious knee injuries, particularly in younger, active people. It is well established that an ACL injury raises the long-term risk of developing osteoarthritis (wear within the joint). What has been much harder to answer is a more personal question: after an ACL reconstruction, how much higher is your own long-term risk of eventually needing a knee replacement?
In this study, my colleagues and I set out to answer that as fairly as possible. We used the National Hospital Episode Statistics database, which records NHS operations across the whole of England, and identified 135,881 people who underwent ACL reconstruction between 1997 and 2023, following them for up to 26 years.
The novel part of our approach was the comparison we chose. Rather than comparing people who had an ACL reconstruction with the general population – who differ in many ways – we compared each person's reconstructed knee with their own opposite, uninjured knee. Because both knees belong to the same person, this “internal control” naturally accounts for individual factors such as activity level, genetics and body type, giving a far fairer estimate of the risk specifically linked to the ACL injury and its reconstruction.
What Did We Find?
Over the long term, a reconstructed knee was about three times more likely to need a knee replacement than the person's own uninjured knee.
Crucially, the absolute risk remained low. Twenty years after surgery, around 2.4% of reconstructed knees had needed a replacement, compared with around 0.9% of the uninjured knees. In other words, the great majority of people who had an ACL reconstruction had not needed a knee replacement, even two decades later.
The increased risk was strikingly consistent. It was similar for men and women, across all age groups, and regardless of ethnicity or social background. It was slightly higher in people who also needed surgery to the meniscus (the cushioning cartilage) at the same time, which fits with the idea that additional damage inside the knee adds to the long-term risk.
Why Does This Matter for Patients?
The most important point to understand is what this increased risk does, and does not, mean. It does not mean that the operation damages the knee. Much of the harm is done at the moment of the original injury, when the cartilage and meniscus are often injured too, and by any further episodes of the knee giving way. ACL reconstruction is performed to restore stability and help people return to activity. This study could not separate the effect of the injury from the effect of the surgery, because people with very unstable knees understandably choose to have them reconstructed – so there is no fair “untreated” group to compare against.
For patients, the value of this work is honest, realistic information. If you have had, or are considering, an ACL reconstruction, it is reasonable to know that the injured knee carries a higher long-term chance of wear than your other knee – while also being reassured that the absolute risk of needing a knee replacement stays low for most people. It also reinforces how worthwhile it is to rehabilitate the knee thoroughly and protect it from further injury.
Because this is the largest study of its kind, and the first to use the opposite knee as a comparison, it gives me robust, population-level data to draw on when discussing the long-term outlook with patients after an ACL injury.
Frequently asked questions
Does an ACL injury increase the risk of needing a knee replacement?
Yes. In this study the reconstructed knee was about three times more likely to need a knee replacement than the person's own uninjured knee over the long term, although the absolute risk stayed low at around 2.4% at 20 years.
Does ACL reconstruction surgery itself cause arthritis or a knee replacement?
The study found no evidence that the operation damages the knee. Much of the harm is done at the time of the original injury and by episodes of the knee giving way; reconstruction is performed to restore stability. The study could not fully separate the effect of the injury from the effect of the surgery, because people with very unstable knees understandably choose to have them reconstructed.
What is the actual risk of needing a knee replacement after ACL reconstruction?
About 2.4% of reconstructed knees had needed a replacement 20 years after surgery, compared with about 0.9% of uninjured knees. The great majority of people who had an ACL reconstruction had not needed a knee replacement, even two decades later.
Is the risk higher if I also had meniscus surgery?
Slightly. The increased risk was a little higher in people who also had surgery to the meniscus at the same time as their ACL reconstruction, which fits with the idea that additional damage inside the knee adds to the long-term risk.
Does the risk differ by age, sex or background?
The increase in risk was strikingly consistent. It was similar for men and women, across all age groups, and regardless of ethnicity or social background.
Read the Full Paper
This paper is published in the British Journal of Sports Medicine. The version below is the author accepted manuscript, made freely available under a Creative Commons licence (CC BY 4.0) through the University of Bristol research repository. You can also read the final published version on the BMJ website, or via the University of Bristol repository.
Full citation: Hennessy C, Murray J, Price AJ, Abram SGF. Long-term risk of knee replacement after ACL reconstruction using the contralateral knee as an internal control: a National Hospital Episode Statistics database study of 135 881 patients. British Journal of Sports Medicine. 2026;60(12):865–873. doi:10.1136/bjsports-2025-111503
This summary is written for general information and explains the research in patient-friendly terms. It does not replace individual medical advice. If you have questions about an ACL injury or your knee, please get in touch to arrange a consultation.
