Half a King by Joe Abercrombie

Yarvi is not suited to being a king. Born with a crippled hand and unable to wield sword or axe he is scorned by his father and viewed as a sort of joke by his people. But when an act of treachery takes the life of his father and brother Yavi has no choice but to ascend to the throne.

Though he is crippled in body, Yavi is strong in mind, but even a strong mind may not be enough. Treachery is never far from the seat of kings, and half a king can topple just as easily as a whole one.