User blog comment:Xilinoc/Ch. 553 - Frozen Cross/@comment-6342763-20131016153208/@comment-4458023-20131016153734

Well, if i may say, remember Isshin's bankai wears him out and puts a strain on his body and back, so to have an injury on his back would cancel out using his bankai as the strain would possibly kill him, but daiguren hyorinmaru doesn't cost hitsugaya anything to use it