Common Causes of Knee Pain, Pt II

Dr. Edmund Bruce-Gardner

In the last blog, we considered some common causes of pain in the front (anterior) and back (posterior) knee.

In this instalment, we will discuss some of the reasons for pain on the side of the knee.  Because there are different structures on either side, it is important to distinguish which one we are talking about. 

The medial side of the knee (or, indeed, any body structure) is the one that is closest to the mid-line of the body.  Thus, in your left leg, the right side of the knee is medial, and vice versa.

​The lateral of the knee is the one further from the outside (e.g. right side of right knee).

For reference, towards the head is superior, or proximal, towards the feet inferior or distal, towards the front is anterior, and the back is posterior.

Pain in the knee may, as you have already guessed if you have been following our blogs, be referred from distant areas, most notably the low back; or (rarely) be related to another underlying disease process.  For brevity's sake, we will be focusing on local structural issues, but for a full understanding of your issue, an analysis of your foot, ankle, hip and low back structure and function will likely be required.

Medial Knee Pain

Pain on the inside of the knee may be related to a number of issues, some more common in one stage of life (e.g. childhood/adolescence), and some in others.

Medial meniscal issues

You have both a medial and lateral meniscus, that is to say, one of either side of the knee. Meniscal injuries are among the most common in the human body (What did I say? Badly designed...!). However, due to its shape, and its relative immobility (it is firmly attached to the medial collateral ligament), the medial meniscus is about five times more likely to tear.

Meniscal anatomy and types of tears (image from Physioworks)

In younger patients, this is more likely to be a traumatic onset, normally involving a twisting motion on a bent, weight-bearing knee (very common in football - sorry! 'Soccer', as you tend to say here!). Incidence of these injuries tend to peak at around 20-29 years of age.

In older patients, it is more likely to be due to age-related degeneration.

We see the difference between these in the type of injury:  the traumatic injuries often involve vertical or oblique tears from the shearing force involved; while degenerative tears are often horizontal, the result of layers of connective tissue separating, or delaminating  (Lamina means 'sheet' or 'plate' in Latin).

In either case there may be clicking and/or locking, as swelling, pain or a torn meniscal fragment prevent the knee from fully straightening (or bending too far).

Depending on where the tear is, it may heal on its own (the 'red zone' in the image above, which receives a blood supply. so is much more likely to be able to heal) or require surgery (the 'white zone').

It is worth noting that meniscus injury hugely predisposes you towards osteoarthritis of the knee.  This also applies to inappropriate surgical treatment (they actually use meniscal surgery to give lab animals knee arthritis quickly so they can study it).  Luckily, our knowledge of and attitude towards meniscal injury and surgery has improved massively over the last thirty years or so. 
Guess when I had my torn menisci and operations - the early nineties :-(

Osteoarthritis (OA) of the medial compartment of the knee

Please note that this is a slightly exaggerated representation of knee arthritis! From the American Academy of Orthopaedic Surgeons (which may be why it looks so scary!)

​Osteoarthritis is the most common form of arthritis, and what most of us would probably refer to as "wear 'n tear" or "getting old".  It involves the erosion of the articular cartilage that protects the surfaces of the bones inside your joints from all the force that goes through them (That is a bit of a simplified explanation, but it will do for the present).  

Note: Changes in the way that the joint moves means that force is shifted from areas of cartilage that are adapted for loading to those that are less well-suited to it, changing the way we walk. This accelerates the process of degeneration.  This means that gait modification, that is, learning how to walk differently (and more efficiently), has the potential to reduce pain and slow the progress of OA (Vincent et al, 2012).

If osteoarthritis is the most common form of arthritis (it is - it is most common cause of disability in the United States, for example), then you can imagine how common the most frequently-affected area must be. That's right! It's the medial compartment of the knee!

Also note that there is (unfortunately) nothing stopping you from having both medial and lateral compartment OA of the knee, but medial is much more common.

And as always, things are necessarily that simple.  As anyone familiar with these blogs is likely to have picked up, damage and pain are not necessarily directly related.  Just because you have a knee xray that shows some loss of cartilage - or even apparent bone-on-bone - is not necessarily cause for alarm.
​Like our knowledge of and approach to meniscal issues, our methods of dealing with knee arthritis have become much more nuanced.

While surgery may eventually be necessary, it is by no means a certainty. Ask your osteopath what you can do to help manage your knee arthritis.

Medial Collateral Ligament (MCL) injury

The medial collateral ligament is the most important stabilising support of the inside of the knee.

Sprains or tears to this ligament may cause pain, swelling, stiffness, bruising, and locking.

It is easily injured when force is applied to the outside of the knee, such as in contact sports, or a sudden twisting motion.
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The medial collateral ligament is (yup, you guessed it!) injured more frequently than the lateral.

This is an ancient (well, relatively) picture from Gray's Anatomy, so the Tibial Collateral Ligament (on the right side of the image) has not yet been renamed the Medial Collateral Ligament!

Pes Anserine Burisitis

The arrow points to the pes anserine ('duck's foot') bursa

The pes anserine (or 'duck's foot') bursa is there to help reduce friction and pressure from three tendons that all come together in the same area:
Semitendinosus is a hamstring (bends the knee)
Gracilis is an adductor (so brings the thigh medially)
Sartorius is a complicated bugger.  It lifts the thigh forwards and out, rotates it outwards, and also bends the knee.  If you turn your foot up to look at the sole, or sit cross-legged, you are demonstrating all the actions of sartorius.

As you can imagine, having all these different directions of pull on an area can be stressful. That is why you have a fluid-filled shock absorber that helps the tendons glide.  However, as pointed out in the section on bursitis, even the shock-absorber gets pissed off eventually!

Pain from pes anserine bursitis can typically be felt a few centimetres below and back from the knee-cap, on the inside (the medical lingo would be inferomedial to the patella).  There may be local swelling (oedema) and redness, and it will be tender to the touch.

Medial (or Tibial) Collateral Ligament Bursitis

This is irritation of a bursa that lies deep to the MCL, between the ligament and the meniscus, and between ligament and tibia.

​(Medial) Plica Sydrome

Plica are small folds in the lining of the knee joint. Only around 50% of people have them; they are thought to be remnants of embryonic connective tissue from when you were a foetus, that  Overuse, such as from repeatedly flexing (bending) the knee joint, can cause these folds to become irritated. Although there are up to four of these plicae, the only one that seems to cause problems is... [drumroll] ...the medial plica!

You may be able to see, in the image above, how the plica might rub or 'snap' over the bony medial condyle of the femur with repeated flexion (bending).
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Other factors that may lead to Plica Syndrome include other altered knee motion (such as consequent to ankle or hip problems); blunt trauma, such as an impact to the inside of the knee; or irritation of the fat pad to which the plica attaches.

Often, plica syndrome occurs alongside other knee issues, such as meniscal tears, patellar tendonitis or Osgood-Schlatter's disease.

So those are the most common causes of medial knee pain.
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Phew!
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That ended up being a little longer than anticipated.  Rather than overloading you with too many diagrams and anatomical minutiae, we will save the causes of lateral knee pain for next time.   See you then!