Dear friend, welcome and thanks for entrusting your query here at HCM!
I am Dr. Prasad Akole (Critical Care Expert- http://bit.ly/Dr-Prasad-Akole) and am glad to address to your query here.
Knee repalcement surgery at such an advanced age may be associated with complications.
Brain ischaemia is common so also altered mentation, delirium
Luckily the MRI
supposedly did not show any infarct (as per description). She must be having chronic brain ischaemia as per age and got unmsked after surgical stress
is usually given for Parkinsonian features.
Please be guided by a good neurologist's advice. She may be on/ need aspirin
I hope you are fully satisfied with the guidance I gave.
Hope I have answered all your questions. I would be glad to answer any further queries. Please ask for any clarifications before closing and rating this answer.
Thank you and Good luck!