The knee is basically a hinge joint, allowing backwards and forwards motion. It is also able to rotate slightly in on itself. The bending and straightening is controlled by the hamstring and quadriceps muscles at the back and front of the thigh bone respectively. Their size and position affects the angles the legs move at, and particularly the way that the patella (kneecap) moves. Your anatomy and the patterns of your muscle use determine many of the injuries you will suffer.
“Runner’s knee” used to be known as chondromalcia patellae, but is now more often referred to as patella-femoral pain (PFP). It occurs when the patella fails to move smoothly and centrally through the femoral groove at the lower end of the femor bones. This is sometimes due to muscle imbalance or abnormal anatomy. It can also be the result of improper or dead footwear, improper training techniques ie: too much too soon or not adhering to the 10% rule. The 10% rule: Do not increase your long run by more than 10 % per week. Do not increase weekly mileage by more than 10 %.
You’ll either suffer a persistent ache in or under the kneecap, which worsens with certain exercise, or you will feel a sudden, stabbing pain in the knee while running, which eases off when you rest. Sitting with your knees bent prior to a race can make things worse, as can running on hills or hard surfaces. It is also called movie goers knee due to the pain experienced when straightening your knee after long periods of sitting or knee flexion.
Despite the acute pain, your joint may look normal. Your knee may swell up, but this is more often due to other knee problems. You will probably have wasted inner quadriceps muscles (the vastus medalis), weak gluteals and may overpronate.
What Else It Could Be
While primary PFP is simply that, there may well be other influences. Disruption of the ligaments within and outside of your knee, arthritis in its many forms and ankle, shin, thigh and hip injuries may all affect knee movement and produce secondary PFP.
Ice and rest may provide immediate benefit for pain relief.
Thankfully steroid injections and surgery are not often used to treat PFP. Some physiotherapists successfully tape the patella, drawing it back towards the mid-line, and can teach you how to do this yourself. (Knee supports may effectively shift your patella towards the middle).
Physiotherapy is very useful to provide strengthening and stretching exercises for the hip and leg muscles. Ice, modalities, treadmill gait analysis, shoe analysis may also be beneficial.