Why Do I Have Knee Pain? Complete Guide to Patellofemoral Pain Syndrome: Part 3 – Biomechanics of the Hip, Foot and Ankle

By djpope

April 1, 2018

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Patellofemoral pain syndrome (PFPS) is the most common form of knee pain treated in physical therapy clinics.  I made this series to help people better understand this condition, why it occurs and how to fix it.

In case you missed it:

Today we’ll be discussing how the hip, tibia, ankle and foot can affect knee pain.  Remember that in part 1 of this series we spoke a bit about how seemingly unrelated joints can be related to knee pain.  I’m not sure where I first heard this but it really is true for PFPS:

“The knee joint is a slave to the joints above and below it”

What this really means is that the knee joint will move (or not move) depending on what’s going on at the hip and foot/ankle complex.  This can directly affect stress to the PF joint.

First let’s discuss the hip.  As we discussed in the first article the muscles of the hip help to control motion at the femur.  One motion they help to control is internal rotation of the hip and femur.  If we lack control of the hip the femur can fall into internal rotation.

Some studies have shown that individuals with PFPS have increased hip femoral internal rotation (5, 6).  The reason why this is not ideal is because it can alter patellar alignment and cause lateralization of the patella, thus increasing stress to the lateral side of the joint.

Femoral internal rotation also reduces contact area of the PF joint.  Remember how more surface area is generally good and less surface area increases PF stress?  If we’re lacking control of femoral rotation, we’re increasing stress on the PF joint by decreasing surface area and placing more stress on the lateral side of the joint. This can happen during movements like squatting, running, lunging and stair climbing.  Below you’ll see me performing a single leg squat, first with optimal alignment.

When the angle between the hip and pelvis is neutral (90 degrees as seen above), we’re setting ourselves up for optimal alignment of the PF joint.

In this demonstration you can see how the hip comes toward midline (adduction) and the femur internally rotates.  When the hip comes toward midline (adduction) or the opposite hip drops (same motion except now the pelvis is moving and not the femur) we also get some issues downstream at the knee.  Observe below:

As the opposite hip drops it will stretch the TFL and glute musculature, both of which attach to the IT band.  The IT band attaches to the lateral retinaculum and again, pulls the patella laterally.  Increased hip internal rotation and adduction is a risk factor associated with PFPS (4).  Females with PFPS consistently have weaker hip extensor, abduction, external rotation strength (4).  This weakness also correlates with hip adduction and internal femoral rotation with activity (stair descent, running, cutting, jumping) (4).

If we don’t control either femoral adduction or internal rotation, we may be setting ourselves up for knee problems.  Now you can see why the hip is important.

On the other side of the knee we’ve got the good old foot, ankle and tibiofemoral joint.  Before we talk specifics, let’s start by understanding the movements at these joints that can lead to issues.  These movements are a little tough to wrap your head around so Ive made some handy videos and images to help illustrate the major points:

In the video above you’ll find foot pronation and supination

In the video above you’ll see tibial rotation (yes the knee is meant to rotate some)

In this video you have tibial rotation in closed chain.  This is essentially the same movement as the video prior except the foot is now fixed to the ground while the hip rotates.  Closed chain tibial rotation is more important because most of the movements we perform in our lives and training occur in closed chain (stairs, squatting, lunges etc…).

As we explained earlier, the tibia attaches directly to the patella via the patellar tendon.  When we externally rotate our tibia the attachment point of the patellar tendon goes laterally.  Now when we flex the quad the angle of pull will be directed laterally.  Check out the video below to get a better idea of what’s occurring here.

Now the most obvious way to tell if someone is squatting, running or jumping with excessive tibial rotation is to look at where the knee cap is facing in relation to the foot.  Check out the video below and notice how the toes are not facing the patella during the squat:

Now it makes sense that if we’re sitting in external rotation when we perform knee bending tasks we’re lateralizing stress to the PF joint.  Again, this decreases surface area within the PF joint and increases stress to the lateral part of the joint.

The next concept to understand is that what happens at the foot will affect all of the joints above the foot.  Most importantly, foot pronation can cause femoral internal rotation.  Recall that femoral internal rotation alters patellar tracking.  Check out the image below to see what I’m talking about:

As the foot falls into pronation, the entire chain follows.  They’ve even named the combination of foot pronation, tibial external rotation and femoral internal rotation “Miserable Mal-alignment” because of it’s effects on the knee.  Although it is maybe a little harsh describing this condition as “miserable” it does help to illustrate the point.  You can certainly now see how excessive motion at the foot and ankle can cause issues at the knee.

Next we’ll take a closer look at the ankle.  The ankle actually has 2 main joints that allow motion.  The first we already alluded to.  It’s called the subtalar joint and controls pronation in the foot.  If we have too much pronation this leads to femoral internal rotation of the hip.  The other joint is called the talocrural joint.  This is the joint responsible for dorsiflexion and plantarflexion of the foot:

Activities like squatting, lunging and even running require a pre-requisite amount of dorsiflexion.   The trouble is, not everyone has the required amount of ankle dorsiflexion to perform these movements.  However, the body finds a way to perform these tasks if we ask it to.  What ends up happening in this situation is that when we run out of talocrural range of motion, we’ll start compensating with motion from the subtalar joint (pronation) and with tibial external rotation.  I made a video several years ago (with an accompanying article) to help illustrate this point better:

https://www.instagram.com/p/BHuQh_JBmDM/?taken-by=fitnesspainfree

What we end up with is “toe out” or “knee in” as we descend into a squat.  Check out the video below to see this in action:

Now this can also occur during squatting tasks using 2 legs.  Observe the image below:

If you’ve been squatting or observing other squat for long enough I’m sure you may have seen this situation.  Since the PF joint forces are already very high in the bottom of a loaded squat, having poor motion at the foot or hip definitely doesn’t help the situation.

Just keep in mind that in a deep squat pronation, tibial rotation and hip internal rotation can be major players in this pattern.  However, a lack of adductor mobility can also potentially drive this problem too.

Side Note:  I know I just made an enormous case for “poor movement ” at the hip, tibia and ankle as drivers of patellofemoral pain syndrome.  I think it’s important to note that not all people with PFPS move with poor mechanics.  Only 50% of people with PFPS move “poorly” as shown by Chris Powers’s (2) research. The evidence is also mixed as to whether or not poor movement leads to PFPS.  Some studies support it and some others do not.  It does however seem that after people develop PFPS they tend to move differently (10) (and show more of the characteristics described in this article).  We’ll discuss some other potential drivers of pain in future articles.

So to recap:

  • Patellofemoral pain syndrome can be influenced by the joints above and below the knee
  • Femoral adduction and internal rotation can increase stress within the PF joint
  • Lack of ankle dorsiflexion and tibial rotation can increase stress within the PF joint
  • Excessive foot pronation can drive femoral internal rotation of the hip
  • This can occur during single leg tasks like running and stairs but also during squatting patterns

So now we should have a pretty in depth understanding of the stresses on the PF joint and how our movement can increase or decrease this stress.  In the next article in the series we discuss how overuse injuries occur within the joint and what is going on within the knee when we have pain.

Click HERE for Part 4:

Always capped,

Dan Pope DPT, OCS, CSCS CF L1

Works Cited:

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