How can I narrate combat without it getting repetitive?

Although I mostly run D&D games I like to try and distract players from numbers as much as possible and keep the game narrative flowing at a smooth pace. For the most part, this is fine: lots of varied situations in the game call for dice rolls so I assess the situation, the level of success/failure and make something up on the spot.

When it comes to combat, however, I always find that there’s a limited stock of phrases that dry up very quickly because so many combat actions are the same. Even when there are spells involved the end result is very often injury to a participant. For the most part, it’s just a variation on "you swing your [weapon] and it [damages anatomy], causing your opponent [graphic injury]". There’s only so much you can do with this.

Even if you restrict this to criticals/fumbles/death blows there’s still easily enough of it to get very tiresome very fast.

Are there any ways I can try and vary combat narrative? Is it just my imagination that’s letting me down here?