5) Osteonecrosis
Osteonecrosis is a medical condition in which the bone tissue dies due to reduced blood supply. Usually secondary to other underlying causes such as trauma or bone disease. Neither rare nor common as its prevalence rate is about 15,000 patients in the United States per year.
in case of knee joint affection, an orthopedic doctor has to assess the severity of the condition before deciding whether the joint need to be replaced surgically or not.