Oh! my goodness - I never heard of such a thing. Maybe that’s what happened with our friend. I thought he should change doctors/surgeons and in the process probably hospitals but that is astounding to learn! How would a person know to ask?
With my husband it was on his sheet over pre op surgery explanations/options/procedure and we selected non-cadaver knee caps.
Have your friend find out via surgeon what knee cap/s they received cadaver or non.