Is 160mm crank too short for me?
160mm crank is abnormally short. This doesn't mean that you shouldn't but as Axemasta mentions, you should have a bike fit before deciding what crank arm length you should have. Plus you've not given any details about your bike or it's size. 

There are so many variables involved in knee pain, it would be foolish for anyone to suggest your first course of action to be crank arm length. 

Bikes related variables for knee pain:


Overall wrong size frame
Bad saddle position (tilt and position on rail)
Stem too long 
Handle tilt 
Crank length 
Pedal choice / fit


Body related variables for knee pain:


Incorrect cycling technique
Muscle imbalance
Muscle tightness
Non-optimal nutrition


These are just examples of a much larger list. 

So, in my opinion, without finding the root cause of your issue, buying extremely short cranks should only be done if you are 100% that is what you need. And I don't think (with the information you have given) that will be what you need.