User blog comment:Xilinoc/Ch. 549 - The Stormbringer/@comment-1747976-20130917143559/@comment-6342763-20130918214901

Yhwach said Yamamoto was to proud to ask a human to fix his arm. I guess that's it, and that no one in SS could fix it 'cause it was an injury from forbidden technique (probably the reason why it's forbidden).