If you have patellofemoral pain syndrome, you probably already know the feeling well: a dull, aching pressure behind or around the kneecap that flares when you go down stairs, sit for long periods, squat, or run.

If your knee pain sits just below the kneecap, worsens when you fully extend your leg, and has persisted despite rest, anti-inflammatories, and a round or two of physical therapy, you may already know the diagnosis: Hoffa's fat pad syndrome, also called infrapatellar fat pad impingement.

A knee ganglion cyst rarely announces itself as a complex problem. It shows up as a lump — maybe some dull aching when you bend deeply — and then a physician either recommends aspiration or tells you to watch it.

If you have been told you have patellofemoral arthritis, you have probably received the standard advice: lose weight, strengthen your quadriceps, avoid stairs when flared, and take anti-inflammatories as needed.

There is a particular kind of frustration that comes with extensor mechanism disruption. The injury itself — whether a quadriceps tendon tear, patellar tendinopathy, patellar tendon rupture, or chronic patellofemoral instability — is already limiting enough.

If you're reading this, you probably know the specific ache already: a dull, sometimes sharp pain just below or around the kneecap that flares after kneeling, squatting, sitting with a bent knee for too long, or climbing stairs.