The Myths of ACL Injuries

A 13-minute read

It’s been over 18 months since I last wrote a blog for several reasons that I won’t go into, but, I want to get back into some writing so I thought I would start by taking a look at Anterior Cruciate Ligament or ACL Injuries commonly seen in sports like soccer. Over the years there has been some interesting research published on ACL injuries and there are still some long-held myths and misunderstandings about them that I would like to explore.

ACL injuries can’t heal on their own

Spontaneous healing of human ACL ruptures has been known since at least 1996 (Ihara et al. 1996). In this little-known study of 50 ACL injuries, 37 of them, or 74% showed spontaneous healing within 3 months without the need for surgery! It’s amazing to me that we have known that ACL ruptures can heal for nearly 30 years yet it’s still considered by most to be an irreversible injury that always needs surgery.

However, other studies have shown that ACL ruptures may heal much less often with Blanke et al 2022 seeing only 14% or 54 of 381 ACL ruptures healing on their own, but this was only when observed for the first 6-9 weeks after injury. The results of this study also suggest that ACL tears at the femoral attachment (proximal end) are more likely to heal, followed by tears in the middle (mid-substance), but, there is a poorer prognosis for those ACLs torn at the tibia attachment (distal end).

Recently Filbay et al. (2022) carried out a secondary analysis of the Frobell et al. (2013) KANON trial which confirmed on MRI that 30% of 54 completely ruptured ACLs had healed within two years, and when they excluded those who opted into reconstruction surgery before the two-year mark 53% of 30 ACL ruptures had healed on their own.

In a more recent study, Filbay et al. (2023) then looked at a novel “Cross Bracing Protocol” where the knee is immobilized at 90° of flexion for 4 weeks and gradually increased until 12 weeks when the brace is removed. This bracing places the torn ACL ends closer together, making it more likely to reconnect. In the 80 patients who participated in this bracing protocol 72 or 90% had ‘healed’ ACL ruptures, and of the 8 that did not heal, in 6 of them the ACL had attached to the lateral wall or the PCL which can also provide knee stability.

Participants in this protocol were prescribed anticoagulants to mitigate the risks of DVT that may arise as a result of long periods of knee immobilization, and a major limitation was that there was no comparison arm/control group to compare these results to.

However, no control group is also an incredibly common issue with all the ACL surgical research which is still considered the gold standard. Kay et al 2017 revealed that only 1 of 412 so-called randomised controlled trials compared ACL surgery to any form of non-surgical treatment, with essentially all studies comparing various different ACL surgeries and graft types to one another.

There is now abundant evidence that a lot of ACL tears, even ones with complete discontinuity, have the potential to heal. However, ACL reconstruction surgery is a big business, generating around $7 billion annually, meaning there is little to no incentive for orthopaedic surgeons to consider nonoperative care, and those that do are often met with criticism, ridicule and disdain.

Healed on a scan does NOT equal healed in real life

A common, and valid criticism of non-surgical ACL research is that just becuase it looks ‘healed’ on a scan, this doesn’t mean the ACL has healed enough to stabilise the knee. In the recent Filbay 2023 cross-bracing study they categorised the ‘healed’ ACLs using a 0-3 scale to highlight the variations. These are; 0=normal ligament with regular thickness and continuity; 1=thickened ligament with normal course and continuity but with high intraligamentous signal, 2=thinned or elongated ligament but with continuity; 3=an absent ligament or complete discontinuity.

In the Filbay 2023 study, they saw that none of the ACL ruptures had healed back to a grade 0, which isn’t surprising. But 50% had healed to grade 1 and the other 40% to grade 2. They also found that none of the grade 1 ACLs had any issues with knee stability, whereas 60% of those with grade 2 ACLs did have issues with knee stability.

However, this still means that 40% of those with only grade 2 ACL healing did have a stable knee. Why there are differences in knee stability is due to many factors such as age, levels of activity, muscle mass, neuromuscular and psychological adaptations and of course good old simple anatomy and biomechanics.

One of the reasons may be due to other ligaments and structures in the knee that may or may not been affected with the ACL injury. One key structure is the Medial Collateral Ligament (MCL) of the knee which plays a key role in stabilising the knee by limiting internal rotation and resisting valgus forces that load the ACL. This ligament may play a role in resisting anterior translation of the tibia in the absence of an ACL, and so if it is not injured or affected and with enough training stimulus it may adapt and help compensate for ACL deficiency to a degree.

Of course, having sufficient knee muscle strength and control will also help improve knee stability to a certain extent. Having strong, reactive knee muscles is important to absorb and manage the forces acting on a knee joint.

Now if you’re concerned that an ACL rupture may heal but forever be thin, weak, and elongated, dont be. There’s evidence that ACLs continue to adapt positively with regular exposure to physical loads. Myrick et al. (2019) measured the changes in the volume of 17 Division 1 female soccer players’ ACLs throughout a season and found significant increases in all of their ACLs with a more notable difference in the athletes’ dominant leg demonstrating ACLs adapt to the demands they are exposed to.

So although some ACLs may heal less than others, they can continue to heal, adapt, and thicken with the right exposure to loads and forces, and even if they dont heal the knee can still be stable and functional due to other reasons.

You are at greater risk of meniscal tear if you don’t get surgery

A common argument for ACL surgery after rupture is that it will prevent further damage to other structures in the knee. One of these structures are the pads of cartilage within the knee joint called the meniscus. These are thought to be at greater risk of tearing or wearing out without an intact ACL. However, Ekas et al (2020) concluded, “There is insufficient evidence that choosing early ACL reconstruction over non-operative treatment with optional delayed ACL reconstruction helps patients avoid new meniscal tears”.

And they are not alone, three other literature reviews also found no significant differences in rates of subsequent meniscal tears between surgical and non-surgical interventions (Delincé & Ghafil, 2012; Smith et al., 2014; Monk et al., 2016). The biggest issue with studies that do claim surgery is best to prevent meniscal issues later on, is that they compare a group receiving surgery and excellent post-surgical rehabilitation to a group receiving no treatment whatsoever, then jump to the conclusion that the risk of a meniscus tear is higher in nonoperative patients.

The greatest risk of having further damage to the knee after ACL rupture is if you DONT rehab and strengthen the knee sufficiently after its injury, not if you do or do not get surgery.

You are at greater risk of knee osteoarthritis if you don’t get surgery

In 2018, van Yperen et al. retrospectively evaluated 50 patients who had ACL ruptures, 25 who had unstable knees after 3 months of rehab and were treated with surgery, and 25 who had stable knees after 3 months of rehab were treated without surgery. In a 20-year follow-up, osteoarthritis was found in 80% of the surgery group and 68% in the non-operative group, a difference deemed statistically insignificant. This study is severely limited by the small number of patients and by it being a retrospective analysis.

However, in an umbrella review by Webster et al (2022) evaluating 13 systematic reviews and meta-analyses they found surgical reconstruction does NOT reduce the risk for the development of knee osteoarthritis in the long-term with an estimated 1/3rd who have had ACL surgery will experience knee OA. Three other reviews also found no significant differences in pain, knee function, symptoms, return to sport, future meniscal tears, and OA, with a slightly HIGHER incidence of OA in operative groups (Delincé & Ghafil, 2012; Smith et al., 2014; Monk et al., 2016). However, do keep in mind that these studies are looking at radiographic signs of knee OA, and not all knee OA seen on scans is symptomatic.

The risk of knee OA is by far greater in those with quadriceps weakness (Øiestad et al., 2015) and in those who have had surgery that removes some or all of the meniscus (Migliorini et al., 2023). In fact, partial meniscectomies on degenerative menisci have been shown to do nothing more for knee function than placebo at 5 years (Sihvonen et al., 2020) and osteoarthritis has been reported in up to 89% of all meniscectomy patients (Rangger et al., 1997).

The major takeaway here is that it’s the ACL injury itself that increases the risk of knee OA, not your surgical decision. While there’s not a statistically significant difference in rates of OA with surgery vs. nonoperative care, it’s my suspicion that reconstruction leads to greater rates of radiographic OA, and rates tend to be slightly higher in the research for ACLR patients.

You can’t return to sport without an ACL if you don’t get surgery

One of the most common things people (mostly orthopaedic surgeons) like to say is “You can run in straight lines without an ACL, but you need surgery if you ever want to go back to other sports.” And this is absolutely false both in the literature and the real world. There are many world-class professional athletes performing at top levels without ACLs.

DeJuan Blair, an NBA centre who tore both ACLs in high school and had failed repairs, had a physical that revealed that both his ACLs had deteriorated and were no longer connected shortly before being drafted. He continued to play from 2009-2016 without any further reported injury.

Mitch Short was a professional rugby player who tore his ACL in 2018 and went on to play in his next match two weeks later winning a Man of the Match award. Jets quarterback Joe Namath tore an ACL in college in the 1960s (before surgical options were a choice) and braced for a few weeks before going on to have a Hall of Fame career. Notable Steelers wide receiver Hines Ward played his entire football career missing an ACL.

A good colleague of mine Sports Doctor Richard Weiler was one of the first to publish a case study here of a professional soccer player Alou Diarra’s ACL tear in 2013 when he was at West Ham, in which he returned to play in just 8 weeks. Diarra had no prior strength training experience and refused to perform squats as he did not like the feeling of a barbell on his back, but his medical team found other quad exercises he would comply with and eventually implemented low-level plyometrics before he made his return to the field.

Grindem et al. (2012) conducted a comparison of return to pivoting sports a year after ACL injury with a surgery group and a nonoperative treatment group. The return to sport rate was identical between groups in the cohort of 138 people (68.1%) and the nonoperative group actually performed better on hop tests and had higher scores on knee function scales.

Myklebust et al. (2003) found the following in a 6-11 year follow-up of professional handball players with torn ACLs: Among the 57 operatively treated patients who returned for follow-up, 33 (58%) returned to team handball at their preinjury level, compared with 18 of 22 (82%) in the nonoperative group. Hurd et al. (2009) demonstrated that 63/88 (72%) of those who met the coper criteria returned to sports without reinjury over ten year follow up.

One limitation of these papers is that they often exclude people with concomitant injuries such as a tear in another ligament or meniscus (but not always); however, we also know that both lateral and medial meniscal tears have the potential to heal without surgery as well, even the more serious bucket-handle tears that everyone says MUST always be operated on (Rabelo et al. 2013, Han et al. 2015).

You can’t do open-chain exercises with ACL injury or surgery

This myth is one of the biggest misconceptions limiting recovery for many ACLs, and you will encounter many surgeons and physios who tell you it’s ‘dangerous’ to perform open chain knee extensions or that it will loosen your graft and that you should do something more “fUnCtiOnAl” like a squat. First of all, no exercise is dangerous, it’s only opinions and parameters around exercises that are dangerous!

While there is indeed some benefit in choosing different exercises for different people for different issues, the idea that open chain leg extensions are not “functional” because we don’t do that movement in daily life is utter bullshit. Getting your quads stronger on a leg extension machine has the same benefits and overall effects as getting them stronger through a squat, there are just slight differences in where your quad grows at most.

So far, data has found no differences in knee joint laxity between ACLR patients avoiding open-chain knee extension exercises and those who implement them in rehab (Fleming et al., 2005; Perriman et al., 2018). Its also been shown that ACL strain is 2-3 times greater when walking than it is when doing some open chain inner range quad exercise sets. So if you’re saying these exercises are dangerous for ACLs then you also need to say walking is as well (Noehren et al 2020).

Also, something that leg extension machines do far better than squatting is they stop a person from shifting load off their quad muscles. As a squat involves both knee extension and hip extension, it is easy for people to move in ways that make a squat less knee/quad-dominant by bending more at the hip than the knees, and many do not notice themselves doing this.

As much as I love squats and lunges it can be difficult to know if your quads are working as hard as they could be with these multi-joint exercises. However, with a leg extension machine, there is no place for the quads to hide. I also think it is good practice to start with knee extensions unilaterally so that your healthy leg also doesn’t hide the weakness of your injured leg.

Another suggestion from my good mate Erik Meira, who is the man when it comes to ACL rehab, is to also not worry about hitting the end range of motion on leg extension machines at the beginning – not because it is dangerous, but just because you can load significantly more weight by skipping out on the last few degrees of knee extension. Now I can hear the ‘Full ROM’ bois screaming already about how a greater range of motion under load produces a greater hypertrophy response. However, we are after strength first and heavier loads are best for this and a counter-argument is that training at longer muscle lengths can also stimulate a greater hypertrophy response (Wolf et al., 2023).

I think using between 90-60° of knee flexion is a good range for leg extensions for ACL issues to start with as there is no additional strain on the ACL with the force applied to the leg (Beynnon et al., 1995). I do think it is worthwhile to eventually implement the full range of motion on knee exertion exercises as strength is somewhat specific to the joint angles that you train in and you do want to be strong at near-terminal knee extension where ACLs often tear.


So there you go, my first blog in 18 months. If you made it this far well done, because very few people these days read anything anymore over 10 words. I hope this ‘short-ish’ look into some of the common myths of ACL injuries has been useful and given you something to think about, but in summary

  • Many ACL ruptures CAN heal on their own WITHOUT surgery
  • A healed ACL often (but not always) provides a more stable knee
  • Surgery does NOT give you a better chance to return to sports
  • Surgery does NOT reduce your risk of further issues or injuries
  • Not rehabbing after an ACL injury IS the far bigger risk of further injuries

As always thanks for reading,





  1. In 2018, van Yperen et al. retrospectively evaluated 50 patients who had ACL ruptures, 25 who had unstable knees after 3 months of rehab and were treated with surgery, and 25 who had stable knees after 3 months of rehab were treated without surgery. In a 20-year follow-up, osteoarthritis was found in 80% of the surgery group and 68% in the non-operative group, a difference deemed statistically insignificant. This study is severely limited by the small number of patients and by it being a retrospective analysis.

    What is the follow up time here?

    Excellent read –

  2. I tore both of my ACLs simultaneously 3.5 weeks ago while skiing. I had scheduled 2 surgeries, as I thought that was my only option. I was dreading it. I was so depressed. While interviewing a PT, he enlightened me to the fact that the ACL can possibly heal on its own. No one I saw told me that. Even if you ask Google, it says “The ACL cannot heal on its own because there is no blood supply to this ligament.” I’m looking forward to the natural rehab journey. Even if it saves one surgery. And I accept even if I will still have to have surgery some day. Thank you for the information!

  3. I found this article so interesting. I have recently been diagnosed with a Grade 1 partial ACL tear after a year of feeling something was off with my knee. They have said they will not consider surgery and that I just need comprehensive physio. Up until I read this article I have been desperate to have surgery as the internet has made me feel it is my only option. Thank you for the belief it may heal.

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