Hi
I would agree, it is so well known among surgeons that for years the guidelines were clear , less than 50 and you got a mechanical, greater than 50 it was choice. Now (perhaps in responce to patient complaints about ticking and compliance concerns with anticoagulation therapy) they (in some countries) give anyone who pushes for a tissue prosthesis what they want.
My wife used to always say to me "be careful what you ask for, you may just get it"
There is enough evidence however to my reading that at 50 with no other issues (co-morbidities) that you will be better off (statistically) with a mechanical valve. That Mayo Clinic link produces some clear points about that too.
Ask your sugreon this question : in a 30 year follow up of patients who were under 50 at time of surgery, what percentage remained free of reoperation.
If you find a single study I'll be surprised ... nobody studies against the obvious.
I can however point you to studies done on homografts where 29 year followups were done. There were zero free of reoperation who were under 50 at time of initial surgery.
In this journal
http://www.hindawi.com/journals/iji/2011/263870/
I found the following interesting. It provides a clue to support why tissue prosthesis degrade faster in athletic people.
so essentially a tissue prosthesis can not undergo any renewal in response to mechanical loading stresses. Just like any "leather hinge" of old it will begin to fray, and be calcified. The mechanical valves avoid this.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2696738/table/T1/