It's gonna be a hairline metacarpal fracture.

就是掌骨轻微骨裂。

Broken knuckles, also known as metacarpal fractures, are fairly common, leading to the term “boxer’s fracture” or “brawler’s fracture”.

指关节骨折， 也称为掌骨骨折， 相当常见，导致术语“拳击手骨折”或“斗殴者骨折” 。