If you injected it into the shoulders of 100,000,000+ people some number would have shoulder pain after, some would be severe.

In fact, it turns out that perhaps 70,000 people a year die from IV saline.

Using a different intravenous fluid instead of the usual saline greatly reduced the risk of death or kidney damage, two large studies found.
The difference could mean 50,000 to 70,000 fewer deaths and 100,000 fewer cases of kidney failure each year in the U.S., researchers estimate.

https://www.cbsnews.com/news/doctors-sound-the-alarm-on-possible-harms-of-saline-in-iv-bags/