Should I get a second opinion?

Alright so I've dislocated my knee cap and broke it at the same time. The doctor said I tore a lot of cartialidge and some ligaments to.  He suggested that I was looking at surgery early next week.  He said he may have to use this putty and pins that absorb into the body to fix my knee and gain stability again.  As of right now I have no use of my left knee.  He said that if he is unable to fix the knee cap that in another year I will need a knee replacement.  I am 27 years old and he said that no doctor in their right mind would attempt such a thing.  I am puzzled by this because if I need one then why not?  I am just scared the damage is too extensive and I won't walk the same again.