What's causing my knee to ache?

Hi Guys. I’ll try to keep this as brief as possible.

Nearly two years ago I partially dislocated my patella (see this thread:). As a result, a chunk of bone was taken off the back of my knee cap, as well as causing some cartilage damage and a torn ligament.

A week after the injury I had an arthroscopy to remove a loose body that was picked up on an x-ray. Unfortunately, after months of physiotherapy I was still experiencing pain. I had a dynamic MRI scan which showed another loose body. However the MRI also showed that my trochlea groove was shallow and that my knee cap tracked incorrectly. I had another arthroscopy to remove the second loose body.

After more months of physiotherapy, I was still experiencing problems. After another MRI, I was told that there was a lot of fluid in the knee which could possibly be cause by another loose body, however the consultant wasn’t able to tell me if there was definitely a loose body or not. I was also told that I had grade 2 cartilage damage. So I’m now waiting for a third arthroscopy and the possibility of having realignment surgery.

Current symptoms include sharp pain when bending, patella sublaxations now and then (although that hasn’t happened for a while) and the knee also very clicky/crackly.

The main symptoms that are affecting me at the moment is the stiffness and achyness. It occurs when I having been walking, standing or sitting for long periods. The pain I get when sitting is puzzling me the most, and it seems to be getting worse as it doesn’t take as long now for it to bother me. I’m intrigued as to how or why I’m getting pain when I’m not even using it. What could be causing this?

Thanks for taking the time to read.