Torn ACL: What are the pros and cons of surgery?

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A torn ACL (anterior cruciate ligament) can be treated conservatively or with surgery. The advantage of conservative treatment is a faster recovery. One drawback is that the knee may not be stable enough afterwards. Because of this, about half of all people who first have conservative treatment decide to have surgery in the end after all.

The surgery involves replacing the torn ACL with a graft (tissue from your own body). A piece of tendon tissue is taken from the inner side of your thigh, the patellar tendon, or the quadriceps tendon. The tendon graft tissue is then anchored to the knee in the same position as the original ACL, using screws, buttons, or pins. Several months of rehabilitation treatment are recommended after the surgery.

In conservative treatment, the ACL is not treated with surgery. Instead, rehabilitation is started as soon as possible. The goal of rehabilitation is to strengthen the muscles that stabilize the knee so they can take over the job of the missing ACL. Sometimes parts of the torn ACL grow together with the posterior cruciate ligament, which makes the knee more stable.

Swedish researchers did a study to examine and compare the advantages and disadvantages of the two treatment approaches.

Who took part in the study?

The study included 121 athletes with torn ACL injuries. They were aged between 18 and 35 years. More than half of them had also injured one meniscus or both.

People were not included in the study if other ligaments in their knee (the medial or lateral collateral ligament or posterior cruciate ligament) were torn too – or if their knee was very unstable due to injury of the medial or lateral collateral ligament. They were also not included if they had certain types of torn meniscus injuries that had been sewn. This is because people with a stitched meniscus often have to rest their leg for quite a long time and need different rehabilitation treatments.

What treatments did the participants have?

All of the study participants were randomly assigned to one of two groups. This approach allows for a fair comparison.

  • 62 of the participants had surgery where the ACL was replaced with a piece of tendon tissue from their own body. After surgery, the participants had 24 weeks of rehabilitation.
  • 59 participants had conservative treatment. They had 24 weeks of rehabilitation too. But they also had the option of deciding to have surgery later.

In both groups, the goal of rehabilitation was to restore the normal range of motion of the knee, strengthen muscles, and improve the knee function. The rehabilitation included strengthening and range-of-motion exercises, as well as various exercises to improve coordination and balance.

What did the researchers look at?

The researchers examined and compared different treatment outcomes that are important for people with a torn ACL injury:

  • Improvement in symptoms
  • Ability to do sports
  • Side effects and late complications (for example, the likelihood of later developing osteoarthritis of the knee)

To record the participants' knee problems and symptoms, they answered questions about four main types:

  • Pain during various activities like running, kneeling and jumping
  • Symptoms like swelling and reduced range of motion
  • Knee function during sports and leisure activities
  • Subjective problems like lack of confidence in the knee or the need to modify activities due to knee problems

What did the study find?

The study results show that both treatment approaches are successful over the long term. In the study, the treatments relieved pain and other symptoms so well that there were hardly any differences compared to people with healthy knees. The knee function during sports was only slightly worse than in people with healthy knees. Subjective knee problems were a little more common, though.

The results of the study are shown in the illustration below. Knee symptoms and knee function were rated on a scale of 0 to 100, where

  • 0 = extreme symptoms and
  • 100 = no symptoms at all.
Illustration: Change in knee symptoms over time after treatment of a torn ACL

The study also found that:

  • 50% of the participants who first had conservative treatment later decided to have surgery after all.
  • About 25% of the participants developed signs of osteoarthritis that could be seen in an x-ray within five years – regardless of whether they had conservative or surgical treatment. This result is not very reliable, though, because there were so few participants in the study and osteoarthritis can develop over many decades.

What do these results mean for people with a torn ACL?

No long-term differences between the treatment groups were found. Instead, the advantages and disadvantages of the two treatment approaches result from the type of treatment:

Table: Pros and cons of the two treatment approaches
  Only rehabilitation Surgery followed by rehabilitation
Pros
  • About 50% of people can avoid surgery – including the related risks.
  • If conservative treatment is effective, you recover faster than after surgery (faster progress especially within the first six months).
  • People who have surgery right away avoid the risk of needing surgery later.
Cons
  • The knee is always a little less stable without surgery, so the risk of other injuries (like meniscus injuries) is somewhat higher.
  • About 50% of people later decide to have surgery after all because the knee doesn’t feel stable enough.
  • They may then have to do rehabilitation exercises for longer overall.
  • The recovery process takes longer. Progress is especially slower in the first six months.
  • There are surgery-related risks and potential complications, such as infections and thrombosis.

The study results can help you to weigh the advantages and disadvantages of the two treatment approaches. When making the right decision for yourself, other factors play a role too – for example, your sport-specific goals, how unstable your knee is after the ACL tear, and whether other parts of the knee are injured too. It is best to talk about the pros and cons of the different options with your doctor.

Good to know

Based on current knowledge, there are no negative effects on knee function if you have conservative treatment first and then later decide to have surgery.

What complications can surgery lead to?

The possible complications of ACL surgery include knee joint infections, deep vein thrombosis, and pulmonary (lung) embolism. The new ACL might tear, too. Then further surgery is usually needed.

The Swedish study was too small to reliably say how common these complications are. But other studies have provided estimates. The following table gives an overview:

Table: After surgery: The frequency of possible complications
Possible complications Frequency
Tear of the newly grafted ACL (over a period of up to 14 years) About 60 out of 1,000
Infection in the knee joint About 5 out of 1,000
Deep vein thrombosis (DVT) About 20 out of 1,000
Pulmonary embolism About 1 out of 1,000

Other complications, like nerve damage or problems attaching the graft tissue, are very rare.

What are the limitations of this study – and are there any other studies?

The Swedish study is the only conclusive study that has compared conservative treatment with surgery in people who have an acute torn ACL. Similar studies are now being done in the Netherlands and the USA. Their results are expected in the next few years.

The limited research leaves several questions unanswered, including:

  • Do the pros and cons differ in different groups of people – for example, in children and teenagers, older people, or less athletic people?
  • Are there long-term differences between the treatments – for instance, in the risk of getting osteoarthritis later?

These questions can’t be reliably answered yet. As a result, medical professionals sometimes have very different opinions about these things.

Frobell RB, Roos EM, Roos HP et al. A randomized trial of treatment for acute anterior cruciate ligament tears. N Engl J Med 2010; 363(4): 331-342.

Frobell RB, Roos HP, Roos EM et al. Treatment for acute anterior cruciate ligament tear: five year outcome of randomised trial. BMJ 2013; 346: f232.

Janssen RP, Reijman M, Janssen DM et al. Arterial complications, venous thromboembolism and deep venous thrombosis prophylaxis after anterior cruciate ligament reconstruction: A systematic review. World J Orthop 2016; 7(9): 604-617.

Makhni EC, Steinhaus ME, Mehran N et al. Functional Outcome and Graft Retention in Patients With Septic Arthritis After Anterior Cruciate Ligament Reconstruction: A Systematic Review. Arthroscopy 2015; 31(7): 1392-1401.

Monk AP, Davies LJ, Hopewell S et al. Surgical versus conservative interventions for treating anterior cruciate ligament injuries. Cochrane Database Syst Rev 2016; (4): CD011166.

Wright RW, Magnussen RA, Dunn WR et al. Ipsilateral graft and contralateral ACL rupture at five years or more following ACL reconstruction: a systematic review. J Bone Joint Surg Am 2011; 93(12): 1159-1165.

IQWiG health information is written with the aim of helping people understand the advantages and disadvantages of the main treatment options and health care services.

Because IQWiG is a German institute, some of the information provided here is specific to the German health care system. The suitability of any of the described options in an individual case can be determined by talking to a doctor. informedhealth.org can provide support for talks with doctors and other medical professionals, but cannot replace them. We do not offer individual consultations.

Our information is based on the results of good-quality studies. It is written by a team of health care professionals, scientists and editors, and reviewed by external experts. You can find a detailed description of how our health information is produced and updated in our methods.

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Created on February 21, 2023

Next planned update: 2026

Publisher:

Institute for Quality and Efficiency in Health Care (IQWiG, Germany)

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