This is inflammation and swelling of the bursa (fluid filled sac) in front of the kneecap. It occurs when the bursa is irritated or damaged. This can be due to repeated kneeling, but also from a direct blow to the front of the knee, or a fall on the knee.
You will feel pain and swelling at the front of the kneecap, worst when you kneel. Initially the swelling may only come on after activity, but as the condition progresses swelling will become present all the time. Rarely the swelling can become very large.
If you think you have this condition it is well worth getting it checked out by Mr Willis-Owen. In the mean time you should avoid any aggravating activities with may prolong the problem. It generally won't get better on its own. The first thing to do is to avoid all kneeling. Rest, ice, compression and elevation are helpful if there has been an acute injury.
Treatment involves first confirming the diagnosis then establishing the cause. Options may include activity modification and anti-inflammatories. Rarely drawing fluid off, injections or surgery can be required.