hi , i know you probably get enough of these coming through day in day out but Ive got a knee problame. i play for a football team as well as ride, but during one game i went up for a header came down on my right leg and bent my knee the other way, suffered lots of pain and couldn't bend it. once it healed i went out riding where unfortunately i fell on my knee ( wearing knee pads) but it still hurt it alot. now everytime i bend it i get a clicking sound and a griding feeling, that doesn't cause the pain, i think its something else, i also get the pain if i sit with my knees bent for a long time. could anyone help me into what the pain could be? i hope its not arthritis as I'm 15 and shouldn't get it that early right?.

The grinding feeling / clicking sound isn't exactly 'normal'. Your Patella (knee joint) is covered in synovial fluid. Synovial fluid is a thick, stringy fluid and it's main purpose is to reduce friction between the articular cartilage and other tissues in joints, basically acting as a lubricant.

There are many possible reasons for the 'cracking' like sound but linking back to the synovial fluid, it's most probably something commonly known as cavitation. Without going into too much detail cavitation is basically when two parts forming a joint are pulled away from each other, the joint capsule (bubble like layer containing synovial fluid) increases in volume but the synovial fluid in the capsule no longer fills it all. The Gases dissolved in the fluid quickly fill the empty space causing a cracking sound.

Like I said, there are many possible reasons for the cracking sound but this is the most probable reason. Hope thats helped a little?!