The patient states the pain is “all around the knee”, anterior and posterior medial and lateral but she can’t identify specific location(s). Stiffness prevents her from flexing her knee greater than 60 degrees. She has had this condition for 8 years. It appeared after surgical correction of a partially torn medial meniscus and has never resolved. There is a slight limp. This patient has adult onset diabetes and her condition is under control with diet. She is not on any medication at this time. She is retired and does not smoke. This patient walks and does yoga as best as she could for exercise.

Question: Based on this clinical history, what are some of the differential diagnoses you are considering?