Hi, thanks for writing to HCM.
By your description, it is very much evident that you have degenerative joint disease
affecting the knee joint and propably the underlying cause could be psoriasis
induced arthropathy as well.
If conservative management (medicines and physiotherapy
) failed to give symptom relief, then I feel "arthroscopy" is an alternate option which could be both diagnostic as well as therapeutic.
Also, an xray of the joint is needed to see the involvement of joint surfaces for degeneration.
I advice you to consult an orthopedic surgeon and act according to his suggestion. Hope this helps