Why Do I Have Knee Pain? Complete Guide to Patellofemoral Pain Syndrome: Part 1 – Prevalence, Presentation and Anatomy

By djpope

March 18, 2018

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Knee pain is a very common issue people face that affects their training and daily living.  I didn’t expect this, but the most popular article I’ve ever written on my website (10 years of regular blogging) has to do with knee pain.  It’s also one of the most common issues I treat on a regular basis as a physical therapist.  Because of this I wanted to create a fully comprehensive article series on knee pain going over:

  • What is the most common form of knee pain?
  • What is the prevalence and clinical presentation of these injuries?
  • What is the relevant anatomy to understand knee pain?
  • What are the biomechanics of the knee joint and how is that related to knee pain?
  • What are the causes (Mechanism of injury) for knee pain?
  • What are the risk factors for developing knee pain?
  • How do we treat the problem and get out of pain?

So what is the most common form of knee pain?

The most common form of knee pain is known as patellofemoral pain syndrome or PFPS for short.  PFPS is also commonly known as anterior knee pain, chondromalacia patella or runners knee.  It’s the most common knee condition treated in a physical therapy (or physiotherapy) outpatient clinic.  Since I see so many runners, crossfit athletes and weightlifters who engage in running and squatting regularly, it’s even more common in my practice. If you’ve ever dealt with a bout of PFPS (and I’m guessing you have since you’re reading this article now) you’ll know that exercises like deep squats, lunges, running and daily activities like stairs are going to be either pretty painful right now or you’re currently just avoiding them because of pain.  What’s important to understand is that this is a very common issue that usually improves with the right plan of action.  I’ve dealt with this issue hundreds of times with my athletes and I’ve also occasionally dealt with this variety of knee pain myself.

So what is the prevalence of patellofemoral pain syndrome?

  • PFPS consists of 25% of all knee disorders in an orthopedic setting (1)
  • Common in runners, tennis, military (1,5)
  • 3.8% of males and 6.5% of females get it annually (1)
  • Prevalent amongst weight lifters and crossfit athletes (My own personal experience)
  • Seen more commonly in young adults and also occurs during periods of rapid growth (1)

What is the clinical presentation of PFPS?

  • Occurs mainly in young adults especially during periods of rapid growth (1)
  • Usually presents as a gradual onset of anterior (front) knee pain (1)
  • Pain is usually present around or underneath the knee cap (1)
  • Recalcitrant condition that can persist for many years without intervention (13).  In other words this condition tends not to get better with rest and can stay painful for long periods of time.
  • Generally hurts with movements that increase stress in the PF joint (squatting, stair climbing, hiking, running, prolonged sitting) (1)
  • 75% of patients with PFPS present with tenderness along the patella (knee cap) (1)

What is the definition of PFPS? (13):

  • Pain around or behind the patella, which is aggravated by at least one activity that loads the patellofemoral joint during weight bearing on a flexed (bent) knee (squatting, stairs, jogging, running, hopping and jumping) (13)
  • Additional criteria: Crepitus or grinding sensation emanating (coming) from the patellofemoral joint during knee flexion movements.  Tenderness on patellar facet palpation, small effusion (joint swelling).  Pain on sitting, rising on sitting, or straightening the knee following sitting. (13)

Now that was definitely a mouthful and probably a lot of words that don’t make much sense right now.  Don’t worry about that, we’ll go over it all.  Next we’ll define some of the anatomy and help you understand what’s happening in this condition.

Understanding the anatomy of PFPS:

Now, to understand PFPS it’s first important to have an idea of the relevant anatomy of the patellofemoral joint (PFJ).  The PFJ consists of the patella (also commonly known as the knee cap) and the femur. (4)

The PFJ is the connection between the patella and femur (patello-femoral).  The patella sits on the front of the femur and slides along this bone on something called the “trochlear groove”   The patella sliding along the groove is often explained as a train (the patella) sliding along the train tracks (trochlear groove). (4)

SourceAttribution: Jmarchn / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0) Edited by fitness pain free LLC

As we descend down into a squat (or descend stairs, lunge etc.) the knee cap engages into the trochlear groove (track) and is guided down the femur.  As we straighten the knee (coming up from a squat) the patella tracks back up the groove.  We call this patellar tracking.  When doctors speak about patellar tracking (or mal-tracking) they’re discussing this phenomenon. (4)

The inside of the PFJ is covered in articular cartilage, which is a tough connective tissue (15) designed to buffer the stress that occurs in the joint created by the quadriceps (more on this later).

One of guiding principles of PFPS is that if we do not have proper alignment of the patella in the trochlear groove we can end up with increased stress within the PFJ (mainly on the outside or lateral part of the joint) and pain.  This is known as “mal-tracking” (4).

Side Note: I’m getting ahead of myself here but I want to make sure you understand that having tracking issues in the knee is only 1 piece of the equation of PFPS.  Read on for the rest of the story.

Within the PFJ there are a variety of structures that can get irritated with mal-tracking.  These structures are (1):

  • Synovial plicae
  • Infrapatellar fat pad
  • Retinaculae (medial or lateral)
  • Joint capsule
  • Patellofemoral ligaments
  • Subchondral bone (bone underneath of the cartilage)
  • Prolonged stress to the PFJ could lead to increased cartilage degeneration (wear and tear) (1)

There are a variety of structures within the knee that help with alignment and patellar tracking of the PFJ.  Some of these structures are known as “passive structures” and some as “active structures”.  Active structures refer to muscles that can actively contract and and help stabilize the PFJ in that manner.  Passive structures are non-contractile in nature and refer to things like ligaments and boney structure.  They add to the inherent stability of the joint, but they can not contract and we generally can’t alter these structures through rehabilitation (although surgery can help in this regard) (4).

Passive structures that stabilize the PF joint (4):

  • Boney alignment of the patella and trochlear groove (a more shallow groove increases the risk of patellar subluxation) (4).
  • Patellar tendon
  • Joint Capsule
  • Medial meniscopatellar ligament
  • Medial retinaculum
  • Medial patellofemoral ligament
  • Lateral patellofemoral ligament
  • Iliotibial band (IT Band)
  • Lateral retinaculum

Active structures that stabilize the PF joint:

  • Quadriceps (special emphasis on what’s called the “VMO” or the oblique fibers of the quadriceps muscle called the vastus medialis.  These fibers attach directly to the patella and directly help control the medial (inside) of the knee joint.  More on why this is important in the future)
  • Pes anserine muscle group (adductor / hamstrings group: semitendinosus, gracilis, sartorius)
  • Biceps femoris (part of the hamstrings muscle group)

All of these structures play a role with the tracking of the PF joint and will become important as we discuss PFPS rehabilitation in the next few articles.

Anatomy of the hip, ankle and foot as it relates to PFPS:

Next I’d like to discuss the anatomy of some of the local structures.  It may not make sense now, but the surrounding joints are actually really important when understanding PFPS and how to fix it.  One saying I really find true is, “the knee is a slave to the joints above and below it.”  What I mean by this is that what occurs in the knee joint (patellar tracking specifically) is heavily influenced by both the foot (subtalar and mid-foot joints), ankle (talocrural joint) and hips.  I want to briefly touch on some of the anatomy of these structures and their importance will become much more relevant when we go over the biomechanics of PFPS in future articles.

The Hip

The hip is a very large joint with several equally strong muscles that influence the PF joint directly.    The glute muscles of the hip attach directly to the femur (which remember is part of the PF joint).

  • Glute medius
  • Glute maximus
  • The deep hip lateral rotators (Piriformis, gemellus superior, obturator internus, gemellus inferior, quadratus femoris and the obturator externus)

The strength and control of these muscles (more on this later) plays a direct role in the tracking of the PF joint as well as the total amount of stress the joint takes when we move around.  Strengthening these muscles also helps to eliminate pain during PFPS.

The Foot and Ankle

The two joints we’ll be focusing on are the 2 joints of the ankle:

The talocrural joint: The talocrural joint is the joint in our ankles that is responsible for both dorsiflexion and plantar flexion (motions seen below in images).  The reason why total ankle dorsiflexion is important is because the amount of dorsiflexion present in our ankles will partially determine how much knee flexion (bending) occurs when we perform movements like squatting and running.  As we’ll see later, knee flexion has a direct correlation on how much stress the PF joint takes with our movement.  Limited ankle mobility can also play a role in patellar mal-tracking.  The total amount of motion at this joint is influenced by both our gastrocnemius and soleus (calf) muscles, as well as the joint itself.

The subtalar and mid-foot joints:

These joints have a direct influence on how much of an arch we have in our feet.  This is important because the arch in our foot influences the amount of rotation that occurs in our tibia (shin bone).  The tibia attaches directly to the patellar tendon (which attaches to the patella).  Motion at the subtalar joint will affect patellar tracking.  Now, this is a lot to take in but bear with me.  I just want to introduce this topic and the relevant anatomy and we’ll explain this more in the future.  Some of the major structures that help to control the arch of the foot are:

  • Gastrocnemius and soleus (calf) muscles
  • Tibialis posterior
  • Flexor hallucis longus
  • Subtalar and mid-foot joints

So to recap:

  • PFPS is the most common source of knee pain seen in physical therapy outpatient clinics
  • PFPS is defined as: Pain around or behind the patella which is aggravated by at least one activity that loads the patellofemoral joint (squatting, stairs, jogging, running, hopping and jumping) (13)
  • The patella tracks along a groove during knee flexion 
  • The alignment of the patella in it’s groove is important and if this is altered it can lead to irritation of several tissues in and around the PF joint
  • There are both passive and active structures that control stability and alignment of the PF joint.  Control from these structures is vital to health of the joint.
  • The knee joint is heavily influenced by what’s occurring at both the hip as well as the foot. Stress in the PF joint can be increased or decreased by affecting these joints (more on this later).

That’s it for today.  Click HERE for Part 2:

Never been more excited about knee caps,

Dan Pope DPT, OCS, CSCS, CF L1,

Works Cited:

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