When introducing yourself or being introduced to a disabled person whose right hand or arm is deformed or missing, extend your right hand as usual for a handshake. Allow the disabled person to either respond with their left hand or say, “Please forgive me for not shaking hands. It’s a pleasure to meet you.”
There is no need for awkward conversation about how to shake hands. Treat this person as you would any other individual and allow them to guide you through the situation in a way that is comfortable for them.