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.
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.
Guess when I had my torn menisci and operations - the early nineties :-(
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).
Like our knowledge of and approach to meniscal issues, our methods of dealing with knee arthritis have become much more nuanced.
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.
The medial collateral ligament is (yup, you guessed it!) injured more frequently than the lateral.
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!
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!
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.
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!