There have been reports of increased confusion and heart and lung problems after this operation. Having both knees replaced at the same time increases the risk of these problems.

Confusion or increased confusion seems to occur between days two and five after the operation. This can be caused by medications being given to the patient. Studies show confusion is more common in older adults. Patients who have a history of depression are at increased risk for confusion after surgery.

Other risk factors include living in a nursing home at the time of the operation and vision or hearing problems. Other health problems such as diabetes, asthma, or heart disease also increase the patient's risk for confusion.

A family history of Alzheimer's has not been reported as a risk factor. The patient is at risk if he or she has already been diagnosed with Alzheimer's or some other change in mental status.