MSB 2022 - The road to commercialisation, page-676

The role of a control group is to isolate the effect of the treatment in question.

You want to ensure any effect isn't due to placebo, you are correct. Which is why the patient is ideally blinded.

You want to make sure the effect isn't due to the introduction of a painful stimuli to the area, isn't due to introducing a needle, isn't due to injecting a substance, etc.

Hence the control involved injecting a substance.

Next you want to ensure it is your drug/substance that is causing the desired effect.

So you want the control to generally contain everything that the experimental arm does, aside from your drug/substance. Otherwise, how do we know it's not HA causing the effect?

This is what they didn't do. Not only that, there's evidence HA may actually cause decreased pain on intraarticular injections, this absolutely could be a confounding factor.

This is as simply as I can explain it, if you still don't understand that's on you. And just because you see it one way doesn't mean you are right, because you aren't. Sorry.