Common Causes Of Knee Pain Pt I

Dr. Edmund Bruce-Gardner

So, we have discussed how the poor 'design' of the knee joint means it is prone to various injuries and dysfunctions, but what does that mean in your everyday life?

Here we will consider the anatomy of the knee a bit further, and discuss some of the ways our knees can give us grief.

It is important to remember that, like most of the other joints in the body, the knee requires its neighbours to be doing a relatively good job in order to perform its own.

The knee joint proper, shown on the left; and with the patella (kneecap) on the right

Primary knee problems are ones in which structures in or surrounding the knee joint are the problem.  You may also have knee pain secondary to a problem with your ankle, hip or low back region.   We will largely be considering primary knee pain in this blog.

You may also have referred pain, where there is little to no issue in the knee at all, but rather, the body is confused as to where the problem is, so just kind of takes a best guess as to the source of the pain or dysfunction.

So the knee joint consists of the tibiofemoral articulation, between the shin bone and thigh bone, and the patellofemoral joint, between the kneecap and thigh bone.

​Anterior (front) knee pain

​The patella, or kneecap, looks as though it is floating in mid-air in the diagram above. It is actually embedded in the common tendon for the quadriceps group of muscles (or 'quads') on the front of the thigh, as seen on the right. It helps them to get better leverage when straightening out the knee.

Because the quadriceps is a big, strong, muscle group, there is a lot of force focusing on the attachments to the patella, as well as the articulation between the patella and rest of the knee joint, and the patellar tendon that runs from the kneecap to the shin bone.

A 'sunrise' view of a laterally tracking (right) patella. The patient is lying down, with their hip and knee bent, and the x-ray is taken as if it were the patient looking down at their knee.

If the balance of these muscles is uneven, the patella will be pulled off to one side (normally towards the outside of the thigh), creating uneven pressure and wear on part of the underside of the kneecap.  This is known as patellar maltracking, and is commonly an issue in juveniles/adolescents and seniors as well as runners, particularly long-distance.

This can also increase the strain on the patellar tendon, leading to patellar tendinopathy​, or "jumper's knee".

Both of these will tend to cause pain around or behind the kneecap, at the front of the knee.
So what about pain on the sides, or back, of the knee?

Posterior knee pain (behind the knee) is actually probably the least common area, compared to the front or sides.  However, given how poorly-designed the knee is, it is still a pretty common patient complaint.

Soft-tissue injury is probably the most common cause, with the hamstrings being a common source, especially with any sport or hobby involving sprinting.  A muscle called popliteus is also a good candidate, and will likely be the topic of a future blog post. LaPrade et al (2010) called the popliteus tendon the "fifth major ligament of the knee", or, as I like to call it, the fifth elastic band.

A Baker's Cyst is a fluid-filled swelling in the back of the knee.  It is often due to an underlying problem with the knee, or inflammatory reaction (such as in rheumatoid arthritis, a meniscal tear, or due to a 'loose body' such as from osteoarthritis). It may cause no symptoms at all, but if it is putting pressure on another structure, such as the popliteal vein, it can cause pain or discomfort.

Other sources of posterior knee pain include the nerves in the area, whether from local insult or irritation in the lumbar (low) spine; the posterior cruciate ligament, or PCL, or the blood vessels in the area (e.g. DVT or deep vein thrombosis, or aneurysms).  Interestingly, the patella may also refer pain to the posterior knee.

Note: Another source of pain (in all aspects of the knee) could also be bursitis.

In the next blog, we will consider pain on the sides of the knee - in medical-speak, the medial (inside) and lateral (outside) aspects.

REFERENCES

LAPRADE R. ​et al, (2010) Analysis of the static function of the popliteus tendon in evaluation of an anatomic reconstruction: “the fifth ligament of the knee”, Am J Sports Med., 38:543