Hi, I Developed Knee Pain Last Year After Cycling For

Hi, I developed knee pain last year after cycling for 25 miles. I had a consultation with an orthopaedic surgeon and he recommended an MRI scan. It showed a cyst on the back of my knee. I later had a steroid injection and an intervention to extract the fluid from the cyst. However as the fluid had gone too thick it could not be extracted. Last week I had another scan which showed that my bone ( where the femur joins the knee) had weakened and also inflammation of the bone marrow. There was still a cyst visible behind the knee. The surgeon did not explain what the cause was or recommend any treatment. I feel concerned and I think I should seek second opinion. In your opinion is there cause for concern?