The medical term for this situation is "patellofemoral instability", where the patella (kneecap) has a tendency to sublux (or even dislocate) as it glides over the femur (thigh bone). I like to explain this to patients as if a train (your kneecap) is coming off of its tracks due to poor alignment.
|Your patella derailing off your femur|
Why does this happen?
Despite what conventional wisdom would tell you that it's weak muscles around the knee that cause the instability, it's actually a bit more involved. The usual suspects in conventional thinking to "blame" are a "weak" vastus medialis obliquus (VMO) and a "tight" iliotibial band (ITB).
In reality, the cause is more functional in that you can think of the knee joint as the middle man in-between the hip/pelvis above and the foot/ankle below. And like all middle men, they react to what's going on with the opposite ends of the chain.
When the patella subluxes, or "goes out of place", it's usually lateral of the femur. In not so severe cases, because the soft tissue structures involved are still contained, the patella usually glides back into place with a straightening and bending motion of the knee (i.e. it falls back into its track)
When the pelvis is in a less than ideal position, it will affect the function of the hip joint which will affect the function of the knee joint below. Likewise with the positioning of the foot and ankle can affect the knee joint above.
You can think of the pelvis/hips as the steering wheel, the knee and the foot/ankle as the wheels. What happens when your steering wheel is out of alignment? More wear & tear of the wheels.
Here's a typical clinical presentation:
The pelvis on the same side of the involved knee is either rotated too far forward or backward, with either way, there's a compensation at the knee where the femur (thigh bone) either wants to roll inward excessively or can't roll inward enough. Either way, the vastus lateralis (VL) quadricep muscle can be overly worked to maintain a stable amount of internal rotation of the femur. Because the ITB covers the VL, it commonly is mistaken as the "culprit". And because the VMO wants to do the opposing motion of external rotation of the femur, it is often "out-classed" by the VL.
Can you see now why doctors prescribe "quadriceps strengthening" and "ITB stretching" for patellofemoral situations?
So the next time you're in the Greenwich Village and/or Union Square neighborhood, consider coming by Michael Jocson Physiotherapy for a check up. You'll be glad you did.....