膝下截肢的英文：
BKA, below-knee amputation

slide off the knee
从膝盖上滑落下来

He has a pain in the knee.
他膝盖酸痛。

The knee is in pristine condition.
膝盖已经恢复到正常的状态。

The vet says amputate or he'll have to be put to sleep.
兽医说要么截肢，要么只有安乐死。

If a man had a gangrenous foot would you have patience with anyone who hesitated to amputate it?
如果一个人的脚得了坏疽而有人对于动截肢手术犹犹豫豫，你难道会对他有耐心吗？

fingers so badly frozen they had to be amputated; badly injured; a severely impaired heart; is gravely ill; was seriously ill.
冻伤太严重了的手指不得不切除；严重受伤；严重受损的心脏；病得很严重；病得很严重。