Citation needed? I'm unfamiliar with what metric or data you could be referring to in order to conclude that the US is the worst country in the West for prisoner mistreatment.
Any metric. Pick a country with a well regarded prison system (e.g: Norway) and then compare the U.S. system on every metric to see the disparity. Injury, sickness, malnourishment, violence, education, recidivism, drugs, forced labor, mental health. No country that is typically considered as part of “the west” comes close to any of these metrics when compared to the United States.
A question for you: which country in “the west” can you think of that has worse prisoner treatment than the US?
Apples and oranges. Norway is a tiny country with a very homogenous population. The US is huge and very diverse socioeconomically, racially, and culturally.
A question for you: which country in “the west” can you think of that has worse prisoner treatment than the US?