Looks like a healthy
knee. Sunrise/merchant view would be helpful to look at your patellofemoral
joint. Are stairs your problem or prolonged kneeling? If so, then patellofemoral joint arthrosis. If you have locking/catching/clicking and pain on the inside/medial of your knee then likely meniscus tear. If the pain is bad enough, I'd see your PCP who can get an MRI to rule out other things such as meniscus, ACL, OCD lesions, PVNS, etc. Try nsaids, home pt, quad stretching/strengthening.