I feel bad for Sakamoto, i thought that he was just too lazy to use katana again but now everything is clear.
Although Takasugi tries to hide it with throwing some unnecessary words and insults but i can see from his expression that he deeply concern and sad about what happened to Sakamoto on that war.
By the way Gintoki and Takasugi are best pal, they right away try to find the person who is responsible for Sakamoto's hand.