In this blog, I’m going to teach you everything you need to know about knee valgus!
What Is Knee Valgus?
Technically, knee valgus refers to abduction of the tibia relative to the femur.
I know this is confusing already, so let me explain by starting with the hip.
Imagine a skeleton in standing and drawing a line from the center of the pelvis, straight down to the floor. From here, the hip can abduct in one of two ways:
- In a non weight bearing position, the distal aspect of the femur can move away from the midline of the pelvis. You can think of a little alien or UFO abducting the distal end of the femur. This is what we call standing hip abduction and it is performed by muscles like the gluteus medius and gluteus minimus.
- In a weight bearing position, the pelvis can laterally tilt in such a way that the centerline that we created moves further away from the distal aspect of the femur. This would be like standing on one leg and contracting the glutes on that leg in such a way that you start leaning toward that side.
In both hip abduction scenarios, the distal aspect of the femur is moving further away from the midline of the pelvis. If the two move closer together, that’s known as hip adduction. If it’s helpful for you, you can also think about the angle between them getting bigger or smaller. In either case, we are describing the movement of one bone, the femur, relative to another bone, the pelvis.
So let’s go back to the knee. As I initially said, knee valgus refers to abduction of the tibia relative to the femur. However, if it’s easier for you, you can still think about the distal aspect of the tibia moving away from the midline of the body.
Most people have about 5-10 degrees of knee valgus in standing. This is known as genu valgum. For individuals with more than 5-10 degrees, you might hear the term excessive genu valgum, or “knock knees.”
When most people discuss knee valgus, they are describing what they observe during a movement.
We don’t have muscles that abduct the knee in the same way that muscles abduct the hip, so knee valgus is a byproduct of what’s happening elsewhere. This dynamic knee valgus, as it’s typically called, can be seen during a bilateral squat when the hips adduct and internally rotate, the feet pronate, and, as a result, the knees move toward the midline of the body.
Types of Knee Valgus
Not all knee valgus is created equally, though, especially as it relates to injury. Factors that need to be considered are:
- The speed at which it occurs.
- The forces or loads certain knee structures must tolerate.
- The knee flexion range of motion at which it happens.
- Whether the movement is double leg or single leg.
- Whether the movement is planned, predicted, or reactionary.
Discussions about knee valgus usually revolve around squats, sports, and running, and these are the topics I will cover in the rest of this blog. Based on the factors I just mentioned, it is reasonable for you to assume that the most significant injuries associated with knee valgus involve athletes participating in sports like basketball, soccer, and football.
For now, let’s start with the causes of knee valgus while squatting on two legs.
What Causes Knee Valgus While Squatting?
Keep in mind that the reason for knee valgus in an untrained lifter is likely going to differ from that of a competitive powerlifter or weightlifter, and I’ll discuss the practical implications of that difference.
Starting with the feet, pronation is a natural motion that is required during a squat, but an “excessive” or “uncontrolled” amount is commonly cited as a cause of knee valgus. A systematic review and meta-analysis by Lima et al did find that “ankle dorsiflexion is correlated with knee valgus.” Based on these findings, it’s often inferred that a lack of ankle dorsiflexion encourages someone to use more of their pronation range of motion in order to squat to a sufficient depth, which in turn leads to knee valgus.
While it’s certainly more of a possibility in the untrained lifter, I’ll explain why it’s not a cause for concern shortly.
The most popular theory as to why knee valgus occurs during a squat is weakness of the glutes, particularly as it relates to hip abduction and external rotation. I don’t think this is the case, at least for a double leg squat.
A study by Bell et al discovered that individuals who demonstrated knee valgus during an overhead squat actually had greater hip strength. Perhaps more surprisingly, a systematic review investigating the association between hip muscle strength and knee valgus found inconsistent results – some people were stronger, some people weaker, and some people had no differences.
I say “perhaps more surprisingly” because these studies examined single leg squats, single leg step downs, and forward lunges – movements expected to have an association since they are more reliant on the hip abductors than bilateral squats.
A recent study by Loren Chiu compared squats with the “knees out” (hips externally rotated) vs squats with the “knees in” (hips internally rotated). The researcher found that squats with the “knees in” required participants to use more of their hip external rotation strength. For this reason, he suggests that internal rotation of the hips may simply be a strategy to preferentially load the gluteus maximus.
This aligns with another theory, and one that Chiu also proposes, which is that the adductor magnus contributes to knee valgus. Findings from Kubo et al and Vigotsky and Bryanton demonstrate that the adductor magnus is a primary hip extensor, especially at deeper ranges of motion. Therefore, the gluteus maximus and adductor magnus work together at the hip by using whatever strategy allows for the greatest strength output. In some individuals, this presents as knee valgus.
This makes more sense when we consider when knee valgus happens in highly trained lifters. It is rare to see knee valgus during low effort squats. Instead, it occurs when these athletes start approaching their 1 repetition maximum.
As the load increases in a squat, the amount of “hip dominance” increases. This is shown in the research, but this is also something that can often be seen visually during high effort attempts. As the knees cave in, the hips shoot back as a way of shifting more of the load to the hips during the sticking point.
For the untrained lifter, knee valgus during squats is frequently more of a motor control or skill issue from a lack of practice and understanding of the movement, whereas with the trained lifter, it’s simply a strategy to move the most amount of weight.
Before discussing common strategies for fixing knee valgus while squatting, I want to answer the question…
Is Knee Valgus While Squatting Harmful?
To best answer this question, traumatic and non-traumatic injuries must be considered.
When most people think about traumatic injuries associated with knee valgus, ACL tears usually come to mind. However, under normal circumstances, the ACL is not at risk of rupturing during squats. As the knee reaches greater angles of knee flexion, such as when knee valgus occurs, the strain on the ACL is minimal or virtually nonexistent.
As I’ll discuss in the sports section, ACL tears occur at shallow knee flexion angles when the strain on the ACL is highest. Plus, compared to sporting tasks like landing, cutting, or pivoting on one leg, squatting involves a much slower rate of loading, the load is distributed between both legs, and it’s performed in a controlled environment. The same recipe for disaster doesn’t exist. This rationale applies to the Medial Collateral Ligament (MCL) as well.
Now if someone completely folds under the barbell and their knees give out, that’s a different story and it’s not really applicable to the discussion at hand.
Can knee valgus contribute to gradual, overuse-type injuries? Maybe.
Squats load a variety of tissues and how you squat can determine how that load is distributed across those tissues.
For example, an upright, heels elevated barbell front squat is going to be more demanding on the knees, whereas a trunk forward, low bar back squat is going to be more demanding on the hips and low back (assuming all else is equal).
Neither is good or bad. What matters is whether or not you’re able to tolerate those specific stressors in the moment and also over time with regard to your ability to appropriately recover and adapt. Additionally, all of this is highly dependent on your programming as it relates to volume, frequency, and intensity.
Even people with “perfect” technique get injured in the gym and elsewhere because technique is just one piece of a much bigger puzzle. And knee valgus is just one technical variable that may partially shift the distribution of load to different aspects of the hips, knees, and feet at a specific timepoint during squats.
If you challenge your muscles appropriately, they get bigger and stronger. If you don’t, they get smaller and weaker. The same is true for your bones and other tissues in your body. Your tissues either adapt or they don’t. Knee valgus doesn’t somehow make it harder for your tissues to adapt or suddenly negate all of the positive adaptations that come with squats.
So, is knee valgus while squatting inherently harmful?
No. It’s a movement pattern that exists that is no more dangerous than a different movement pattern.
However, that doesn’t necessarily make it ideal at all times for all individuals, so let me explain when it may be appropriate to address and how to best go about changing it.
Fixing Knee Valgus While Squatting
For someone who displays knee valgus during their squats, we have to try to determine if that technique is detrimental or beneficial for performance and accomplishing their goals.
If a competitive powerlifter or weightlifter consistently displays knee valgus when attempting to hit new personal records, is that something that needs to be changed?
More context might be needed.
What if this individual has been predictably squatting this way for 10+ years, has had no major injuries associated with their technique, has progressively gotten stronger each year, and has performed well in competitions?
In this example, it’s possible that trying to alter their knee valgus could worsen their performance because it’s a predictable strategy that they use on a regular basis to successfully lift the most amount of weight.
This is vastly different from a new trainee who looks like a baby giraffe trying to walk for the first time. In this scenario, it’s reasonable to ask:
- Is this knee valgus intentional or predictable like the competitive athlete?
- Is it a somewhat controlled motion?
- Is it going to benefit their performance in the long run?
If the answer is “no” to any of these questions, modifying their technique doesn’t have to be overly complicated. It can be as easy as a two-step process:
- Demonstrate the preferred technique, provide some external cues and feedback, and set them up for success. Setting them up for success could mean using the appropriate weight or having them take a slightly wider stance with the feet rotated out as that alone can reduce knee valgus.
- Let them practice and learn the movement as you slowly reduce the amount of cues and feedback you provide over time. Technique is not meant to be perfect on the first repetition, day, week, or even month.
What if a person has reduced ankle dorsiflexion like I mentioned before? Four things come to mind:
- It might not matter as squat patterns vary significantly between individuals based on their anatomy, preference, etc.
- If this person has never squatted before, it’s reasonable to expect their dorsiflexion to improve with repeated exposure to the movement
- Use heel lifts, weightlifting shoes, or wedges as needed
- Incorporate drills to improve the range of motion if desired
What about the most common recommendation – the use of a band around the knees?
You can use a band, but it’s not absolutely necessary, especially if the previous steps are followed. Additionally, a narrative review by Forman et al in 2023 found that light bands have no effect on knee valgus and heavy bands actually increase knee valgus.
Once again, you can use a band if that’s what’s been helpful for you or your clients. Please don’t come after me. It’s probably just not the solution for every problem.
Knee Valgus While Playing Sports
With regard to sports, there is no denying that the most common mechanism of injury for an ACL tear is valgus of a slightly bent knee combined with a large force applied quickly in a chaotic and unpredictable environment.
But the important question to ask is… Can we predict who is going to tear their ACL based on movement screens like the single leg squat and drop vertical jump?
In 2005, a prospective study examining 205 female athletes did find that “Female athletes with increased dynamic valgus and high abduction loads are at increased risk of anterior cruciate ligament injury.”
However, studies done on thousands of athletes since then have found no association between dynamic knee valgus and ACL injury risk (example, example, example). Some of the leading researchers in this area made their findings and stance very clear with the title of their paper in 2023 – “Kiss goodbye to the ‘kissing knees’: no association between frontal plane inward knee motion and risk of future non-contact ACL injury in elite female athletes.”
The same group of researchers published a study titled, “I spy with my little eye … a knee about to go ‘pop’? Can coaches and sports medicine professionals predict who is at greater risk of ACL rupture?”
The answer is no. It doesn’t matter if you’re a coach, physical therapist, athletic trainer, or medical doctor, you cannot predict who is going to go on to tear their ACL. In fact, you’d do just as well by flipping a coin.
This has nothing to do with the skill or knowledge of the coach or clinician. It has more to do with the fact that injuries are complex and multifactorial, and a simple movement screen evaluating knee valgus cannot account for or predict all the possible variables that contribute to injury.
Even if we could predict injuries with some certainty (which we can’t), some individuals who display knee valgus will never go on to tear their ACL while other individuals with seemingly perfect technique will eventually tear their ACL.
What’s the solution here?
Well, it’s to provide an injury prevention program to every athlete rather than trying to be selective. These types of programs that include strengthening and plyometric movements work for reducing the incidence of injuries even if the athletes don’t demonstrate a reduction in knee valgus during biomechanical assessments.
Not all knee valgus is dangerous either.
We see it in skateboarders who use it to reduce their impact on landing, surfers use it for better control of their board, golfers use it to wind up their shot, and so on.
Knee Valgus While Running
As for runners, dynamic knee valgus observed during a lateral step-down test is not correlated with dynamic knee valgus during running.
A 2019 systematic review examining the biomechanical risk factors associated with running‑related injuries found that “Limited evidence indicated greater peak hip adduction in female runners developing patellofemoral pain and iliotibial band syndrome…” which can be visualized as an increase in knee valgus.
If someone presents with these running mechanics and reports symptoms, getting a detailed history is key. For example, if the individual mentions doubling their running mileage in the past month in preparation for an upcoming race, having a detailed discussion about load management is likely a better focus of rehab. However, if there have been no changes in their training or other aspects of their life, it may be worth addressing. Fortunately, a systematic review by Neal et al in 2016 found that running retraining and strengthening exercises lead to favorable outcomes, so the plan doesn’t have to be overly complex.
If you want to learn more about patellofemoral pain, IT band pain, or running-related injuries in general, check out our full-length videos about the topics.
Knee Valgus Summary
Let’s end with a brief summary.
Technically, knee valgus refers to abduction of the tibia relative to the femur. However, we don’t have muscles that abduct the knee in the same way that muscles abduct the hip, so knee valgus is a byproduct of what’s happening elsewhere. This dynamic knee valgus, as it’s often called, can be seen during a bilateral squat when the hips adduct and internally rotate, and as a result, the knees move toward the midline of the body.
When knee valgus is observed in highly trained lifters performing heavy squats, it is usually due to the gluteus maximus and adductor magnus working together at the hip to use whatever strategy is optimal to lift the most weight.
When knee valgus is observed in untrained lifters, it’s more of a motor control or skill issue from a lack of practice and understanding of the movement. The solution, as a coach or clinician, is no different than any other exercise – demonstrate the preferred technique and provide external cues and feedback that sets the individual up for success.
Knee valgus during bilateral squats does not increase the risk of ACL injury and is not inherently more dangerous than other movement patterns. However, technique modifications should be considered if it does not support a person’s long-term performance or goals.
With regard to sports, there is no denying that the most common mechanism of injury for an ACL tear is valgus of a slightly bent knee combined with a large force applied quickly in an unpredictable environment. But, despite popular belief, coaches and clinicians cannot predict who is at greater risk of tearing their ACL through the use of screening tests like the single squat and drop vertical jump. Therefore, every athlete, regardless of whether they display knee valgus or not, should follow an injury prevention program that includes strengthening and plyometric exercises, as these have been shown to reliably reduce injury risk.
Lastly, runners with knee symptoms who demonstrate greater peak hip adduction and have not recently changed their training or lifestyle can successfully rehabilitate their knee through running retraining and strengthening exercises.
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Want to learn more? Check out some of our other similar blogs:
Posture, Shoulder Impingement, Flat Feet
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