Board Thread:Theories and Speculation/@comment-25093611-20160322113057/@comment-734582-20160401080554

Tengen Toppa Ita-Sasuke wrote: Yeah, why didn't Sasuke get a new arm? Two ways to explain:

or
 * he's used to power costing something
 * he feels that it's his punishment, his "mark" of losing against Naruto and being a reminder of his mistakes.

Either way, because of his Rinnegan it doesn't matter, he can use Asura to conjure more arms as needed. But as the Boruto Movie shows he clearly handles just fine with one arm.