What is an ACL injury and how long could it take Leah Williamson to recover?

England captain Leah Williamson’s World Cup dream is all but over after she sustained an anterior cruciate ligament (ACL) injury playing for Arsenal against Manchester United on Wednesday.

Williamson, 26, went down after winning the ball in an innocuous challenge with Katie Zelem on the halfway line and immediately indicated that she was in pain.

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The injury could not have come at a worse time for England. The World Cup in Australia and New Zealand begins on July 20 and the reigning European champions are set to announce their squad next month.

In an ongoing series, The Athletic looks at some of the most common football injuries, giving you the lowdown on what a given problem is and what happens after a player suffers one.

Speaking to Andy Williams, a consultant knee surgeon, we analyse the much-feared ACL tear, as made famous by Paul Gascoigne more than 30 years ago, and suffered more recently by Tottenham’s Rodrigo Bentancur and Chelsea’s Armando Broja, as well as the captain of the England Women’s team.

This piece was updated after news of Williamson’s injury broke.

What is it? 

There are two central ligaments in a knee: the posterior cruciate ligament (PCL) and the anterior cruciate ligament (ACL). The ACL is key for athletes who need to change direction as it allows control of rotation. Imagine the ligament is like a piece of rope with multiple fibres in it. When it ruptures, all those fibres break and it’s like a rope that has been split into two pieces. It is possible to have a partial tear but it’s actually really rare; almost all are complete ruptures.

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What terminology will I hear?

You might hear the words “tear” and “rupture”. A tear is a rupture, so they are the same thing. Often, you will hear the phrase “Grade 1, 2 or 3” with a tear. The grading usually reflects the amount of laxity (looseness) and actually is a bit academic for an ACL rupture because, in reality, it’s either gone or it’s not.

Partial tears do occur but, as mentioned above, they are rare. Unfortunately, on MRI scans, it can be hard to tell if the ligament is completely ruptured, so it may be described as a partial tear, which can be quite misleading. Most people who’ve been told they have a partial tear actually have a complete tear, which they need to get checked out.

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How does it happen?

Two-thirds of ACL tears are non-contact injuries, so the player might make a sudden change of direction that goes wrong; usually, their studs catch or foot slips. The ACL stops the tibia (shinbone) from coming forward and twisting inwards, so the knee gets into a position where the rotational load is excessive (see Robert Pires, Arsenal vs Newcastle, March 2002). Very occasionally, it can happen if the knee goes straight backwards (which is called hyperextension — see Zlatan Ibrahimovic, Manchester United vs Anderlecht, April 2017) but that’s much less common.

If someone’s had a twisting injury to their knee, 75 per cent of those people hear or feel a pop in the knee. Most of them will report some swelling within an hour or two of the injury. If I hear that story from a patient, I know it’s one of two things: either a patellar (kneecap) dislocation, which is less common, or an ACL rupture.

How painful is it?

It varies a lot. Sometimes you see people being stretchered off. At other times, they will play on. Over the years, I’ve had a few people who were able to finish the game after doing it. One Premier League player played two more matches without an ACL but unfortunately, in the third game he played, his knee gave in and he did more damage to it. So if it’s gone it’s usually best to get it fixed in a young, active person.

The variation is because there is a spectrum relating to the amount of damage that comes with an ACL tear. The degree of violence translates to the amount of damage you have. A lot of ACLs are ACL, plus meniscus, plus medial ligament — and the bigger the trauma, usually the worse the injury, and so the more pain. The other thing is that when the ligament tears, it bleeds and the knee rapidly swells. Usually, there is some swelling present within one to two hours of the injury.

How long are you out of action?

I’ve just published a series on 232 consecutive professional footballers with ACL ruptures. My average return to play is about eight months for a pure ACL. It is longer if other structures, such as ligaments and/or menisci are involved, or if complications occur. People talk about six months, but actually, it’s usually a bit longer.

What’s the recovery process?

Over the years, we’ve learnt that in the athletic population, an ACL tear is not something that can be dealt with by physiotherapy alone (for others, non-surgical treatment is appropriate). Some ligament injuries, such as those to the MCL (medial collateral ligament) rarely need surgery but in pretty much all cases of ACL rupture in an athlete, they are best treated with a good operation.

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After the injury first occurs, you have to get the knee “quiet”, which usually means a week or two of letting it settle down because if you operate shortly after a big trauma, you just add to it and increase the risk of stiffness. During this period, physiotherapy (prehab) is vital. When the person has the knee completely straight and can bend it to about 100 degrees and there’s not much swelling, it’s a good time to operate.

I operate with a combination of keyhole and open surgery. Stitching the ends of the ligaments together isn’t reliable in professional sport, so we do a reconstruction, not a repair — which means we place some tissue where the original ACL was.

There are a number of choices for this. I never use synthetic ligaments, which people can get reactions to because of the polyester that’s used. I also wouldn’t use donated tendons (someone who gives their organs for transplant will often give their tendons as well). It’s an attractive option because you don’t take anything out of your patient, you just plug in a new ligament. But since it’s not your tissue, they don’t heal well and the re-rupture rate is up to seven times as high.

So in professional football, I take a quarter to a third of the tendon at the front of the knee, between the kneecap and the tibia, that has a nice bit of bone at each end and I slide it in through a couple of drill-holes that enter the joint at the attachment site, and fix it with a screw at either end.

The first two to three weeks after the operation are all about getting the knee out straight and reducing swelling. I want the patient to be able to drive their knee straight with their quadriceps (thigh muscles). Bending it depends a bit on the damaged structures in the knee as a whole but usually, by two weeks, you’ve got a right angle of 90 degrees. Usually, my patients will be fully weight-bearing (after the operation) but they use crutches for balance for three weeks.

After about three weeks, once they have the knee quiet, they start a strengthening programme. Then, at 12 weeks, the ligament has healed, so there’s a visit to me to check it’s OK. If it feels great, we can relax a bit, but then they need to restore muscle strength and control in the limb. If you play before the muscles are restored, you can re-break it.

I work closely with the sports physicians at the teams concerned but also with the physios. We help each other with advice. Team physios have taught me a lot over the years and, equally, they sometimes need guidance from me for various reasons.

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From about four months, you can do some on-pitch training but we try to get people into more natural function as early as 10 weeks. In the bad old days, we used to stick the knee in plaster for six to 12 weeks. If we still did that, it would take a year to get it going, plus you’d lose an enormous amount of muscle and normal coordination of the muscles and the limb.

Most common setbacks/secondary injuries?

The classic one we see is that because they’re out for so long, they lose conditioning — that match hardness — so you’ll often hear a player who’s done brilliantly with their ACL, they come back, then they tear their groin, calf, hamstring or something else. It’s just that they’ve lost match fitness. The worry about the knee is getting back too soon before you’re ready because, obviously, it can be re-injured. The most common problem, though, is loss of straightening and persistent swelling.

Is that part of your body left vulnerable going forward?

One thing we’ve learnt in professional sport is that if I also tighten up the tissues on the outside of the knee (as well as reconstruct the ACL), it greatly reduces the re-tear rate. In professional football, if you use a patellar tendon and graft and add this operation on the outside of the knee, the re-rupture rate has gone down to two per cent in my practice, which is really low. The best published figures before were about six to eight per cent.

The truth is that the final result is probably as long as two years from surgery — or certainly 18 months.

Often, the player isn’t right for the first season back but their sport is what fine-tunes them, so their final bit of physio is the playing.

Andy Williams is a consultant knee surgeon who has worked in professional sport since 1999, looked after 54 English football clubs as well as top-flight English rugby union clubs and has operated on approximately 4,500 ACLs (around 2,000 of which have belonged to professional sportspeople).

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