My issue is that pain is one of the most difficult endpoints for...

My issue is that pain is one of the most difficult endpoints for a trial to meet. It is just too subjective and almost invariably the control arm performs better than expected. I have had a few bad experiences over the years running trials with a pain primary endpoint (and a couple of good ones, to be fair).

To some extent, MSB have sought to mitigate this problem by using a composite responder analysis to back up VAS, but even the ODI is subjective in parts (and includes pain). Also, IIRC, the ODI results in the Phase 2 did not reach statistical significance.

For those that remember, a long time ago MSB produced some absolutely stunning results in sheep, showing actual regrowth of the disc. Unfortunately, this was not replicated in the Phase 2 human trial and so the endpoint has evolved from disc height by MRI (secondary to safety as the primary in the Phase 2) to pain/disability measured by VAS/ODI.

To me, the Phase 2 results were not sufficiently compelling on the pain front to advance into Phase 3 with a pain endpoint.

But who knows, I could be wrong, DYOR!!