Do You Have to Have Surgery For an ACL Tear?

By Grant Frost · Physiotherapist • Last clinically reviewed: 18 May 2026

If you tear your anterior cruciate ligament (ACL), do you need surgery? For decades, the answer from most surgeons was a resounding "yes." The ACL was thought to have little to no ability to naturally reconnect and heal. The standard message was clear: if you want to return to sport or even live an active life, reconstruction was the only reliable path forward.

A landmark new study published in the British Journal of Sports Medicine (Kooy et al., 2025) has turned this long-held belief on its head. Researchers used the Norwegian Knee Ligament Register to follow 485 patients who chose non-operative treatment for their ACL injury.

The findings are really interesting: two-thirds of patients who started with non-operative management avoided surgery entirely at two years. Even among younger, active patients, the outcomes were surprisingly good. This research is not just an interesting data point - it represents a fundamental shift in how we should think about ACL injuries.

A paradigm shift: rethinking ACL treatment

It is difficult to overstate how significant this research is. For decades, the medical community has largely assumed that ACL reconstruction was the only reliable pathway for active individuals. The ligament was thought to have minimal healing capacity. The message was simple: surgery restores stability; non-operative management leaves you with a "ticking time bomb" of instability, meniscal tears, and early arthritis.

This study challenges that assumption at its core. It is not a small pilot study or a highly selective clinical trial. It is a nationwide, real-world cohort of 485 patients from the Norwegian Knee Ligament Register. These are not carefully selected research subjects - they are everyday people who made the choice to try non-operative management.

The results are stunning: 63% avoided surgery entirely at two years. Even among patients under 25 - the group most aggressively steered toward surgery - half avoided it. This is not a fringe finding. It is a replicable, large-scale observation that demands a fundamental rethink of how we counsel ACL-injured patients.

As the authors note, non-operative treatment with an option of delayed ACLR is a "sensible treatment option for selected ACL-injured patients." That may sound like cautious academic language. But make no mistake: this is a radical departure from the conventional wisdom that has dominated sports medicine for the last 30 years.

Study design: 485 patients, nationwide registry

This was a prospective cohort study using data from the Norwegian Knee Ligament Register (NKLR). Since 2004, the NKLR has recorded nearly 90% of all ACL reconstructions in Norway. In 2017, the registry expanded to include non-operatively treated ACL injuries.

Between June 2017 and December 2023, 485 adults with a primary ACL injury who chose non-operative treatment were enrolled. Non-operative treatment was defined as not undergoing ACL reconstruction within 3 months of injury, with the intention of pursuing non-surgical management.

Patients completed the KOOS (Knee injury and Osteoarthritis Outcome Score) questionnaire at baseline and at follow-up intervals. The registry automatically tracked any subsequent ACL reconstructions via the patient's unique national ID number.

Who were the non-operative patients?

One of the most important findings is that non-operative patients were not just older, sedentary individuals. While the average age was 35 years (older than typical ACLR patients who average 28 years), the group was quite diverse:

• 25% were under 25 years old - young adults who might traditionally be advised to have surgery
• 93% were physically active in sports before their injury - this was not a sedentary population
• 36% participated in pivoting sports (soccer, handball, basketball, alpine skiing) - potentially high-risk activities for ACL injury

Additionally, 40% of patients had isolated ACL injuries (no other damage), while 60% had additional injuries including meniscal tears (40%), MCL injuries (25%), and cartilage injuries (5%).

2-year outcomes: two-thirds avoid surgery

The primary finding is encouraging: at 2-year follow-up, 63% of patients remained non-operatively treated (95% CI 58% to 67%). In other words, nearly two out of three patients who chose non-operative management avoided surgery altogether.

Of the 485 included patients, 178 eventually underwent delayed ACL reconstruction. The average time from injury to surgery was 225 days (about 7.5 months). The remaining 307 patients stayed non-operative throughout the follow-up period (mean follow-up 3.3 years).

This 63% success rate is comparable to previous randomised controlled trials, which reported 40-50% crossover to surgery. The slightly lower crossover rate in this real-world registry may reflect that patients who are strongly averse to surgery are more likely to choose non-operative treatment.

Who is more likely to need surgery later?

The study identified three factors that significantly increased the risk of eventually undergoing ACL reconstruction:

1. Younger age: Patients under 25 years old had nearly double the risk of needing surgery compared to those over 45 (HR 1.95, 95% CI 1.2 to 3.2). This makes clinical sense - younger patients are typically more active and have higher demands on their knees.

2. Pivoting sports pre-injury: Patients active in Level 1 pivoting sports (like soccer, handball, alpine skiing) had a 54% higher risk of eventual surgery compared to those in non-pivoting sports. Notably, 52% of Level 1 athletes eventually underwent ACLR, compared to only 30-36% of those in lower-level activities.

3. Meniscal injury at baseline: Patients with any meniscal injury visible on MRI had a 63% higher risk of needing surgery.

Sex was not a significant predictor - men and women had similar rates of delayed surgery.

What about meniscal injuries?

A common concern with non-operative ACL treatment is the risk of worsening meniscal tears over time. This study provides reassuring data:

• Despite 40% of patients having MRI-verified meniscal injuries at baseline, two-thirds still avoided surgery.
• When patients did undergo delayed ACLR, the meniscal procedure rate (56% repair, 18% partial resection) matched the overall Norwegian registry rate of 60%. This suggests delayed surgery did not lead to more severe or irreparable meniscal injuries compared to early surgery.
• Knee instability, not meniscal injury, was the primary reason for surgery - cited by 85% of those who eventually had ACLR. Only 11% cited meniscal injury as the main reason.

The authors note that while meniscal preservation is important, there was no evidence that non-operative treatment led to a concerning increase in severe meniscal injuries at 2 years.

Patient-reported outcomes: similar results

The study compared KOOS scores (Knee injury and Osteoarthritis Outcome Score) between patients who stayed non-operative and those who eventually had delayed ACLR. The results were remarkably similar:

• Sport/Recreation subscale: Non-operative 69.8 vs delayed ACLR 61.0 (not statistically significant)
• Quality of Life subscale: Non-operative 68.6 vs delayed ACLR 63.4 (not statistically significant)

Both groups improved substantially from baseline (where scores were in the 30-40 range) but still fell short of normal values (which are typically 90-100). Regardless of treatment choice, patients' reported knee function remained below pre-injury levels.

The authors note that KOOS may not fully capture knee instability - the main reason patients chose surgery - so outcomes may be more nuanced than these scores suggest.

From my clinical experience: what this means for patients

In my 20 years of practice as a physiotherapist, the ACL surgery debate has been one of the most challenging conversations I have with patients. Many come in believing that surgery is inevitable - especially if they are young or play sports. This study is a powerful tool to help patients make truly informed decisions.

Here is an up-to-date way of approaching this new information:

Non-operative treatment is a real option, even for active people. Two-thirds of patients who started with non-operative management avoided surgery entirely at 2 years. That is not a small number. Even among young patients under 25, half avoided surgery.

You can always have surgery later if needed. Delaying surgery did not lead to worse outcomes in this study. The main reason people eventually had surgery was persistent instability, not the passage of time itself. You are not "missing your window" by trying rehab first. Clinically, the stronger, more flexible, less painful and swollen your knee is before surgery, the better it tends to be after the surgery - whenever that may be.

Your activity level and goals matter enormously. If you are a competitive pivoting-sport athlete, your risk of eventually needing surgery is higher. But many recreational athletes do well without surgery. The decision should be based on your specific goals, not a one-size-fits-all rule.

Rehabilitation is critical regardless of your choice. The non-operative group in this study received structured rehabilitation. You cannot simply "do nothing" and expect good outcomes. Whether you have surgery or not, you need a good rehab program - which may include long-term bracing.

No option is perfect. Even with successful non-operative treatment, most patients had persistent knee symptoms affecting sport and quality of life. Surgery also has risks, costs, and a long recovery. There is no magic bullet.

This study does not say that surgery is never needed. It says that for many patients - even active ones - non-operative treatment with the option of delayed surgery is a sensible first choice. Committing to at least 3-6 months of structured rehabilitation before deciding on surgery, unless there are clear indications for early surgery (like a locked knee from a bucket-handle meniscal tear), might just be the ideal way forward for the majority of people.

Strengths and limitations

Strengths:

• Largest prospective cohort of non-operatively treated ACL injuries to date (485 patients)
• Nationwide registry with near-complete capture of subsequent surgeries
• Real-world data, not a controlled trial (better generalisability)
• Prospective design with predefined variables
• Long follow-up (mean 3.3 years)
• Included patient-reported outcomes, not just surgical data

Limitations:

• Voluntary registration for non-operative cases - may not capture all eligible patients (unlike mandatory ACLR registration)
• Selection bias - patients who are doing well with non-operative management may be less likely to seek specialist follow-up and thus be under-registered
• Technical glitch affecting KOOS distribution (2017-2020) reduced response rates for some patients
• No details on non-operative treatment content - the study did not capture what rehabilitation protocols were used or adherence to them
• Limited generalisability to elite athletes - the cohort had fewer high-risk patients than the general ACLR population
• Reasons for choosing non-operative treatment not captured - we do not know if decisions reflected patient preference, surgeon recommendation, or guideline influence

Conclusions: a viable option for selected patients

This landmark study provides the clearest evidence yet that non-operative treatment is a viable option for many ACL-injured patients. In a real-world setting, two-thirds of patients who started with non-operative management avoided surgery at two years. Younger patients, those in pivoting sports, and those with meniscal injuries were more likely to eventually need surgery, but even among these groups, many succeeded without surgery.

Patient-reported outcomes were similar between those who stayed non-operative and those who had delayed ACLR. The main reason people chose surgery was persistent instability, not meniscal concerns. And there was no evidence that delayed surgery led to worse meniscal outcomes compared to early surgery.

The authors conclude: "Non-operative treatment with an option of delayed ACLR is a sensible treatment option for selected ACL-injured patients."

For clinicians and patients, this means that a trial of structured rehabilitation should be strongly considered before committing to surgery. You can always have surgery later. You cannot undo surgery once it is done.

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