Rav Amram threatened the inheritors [of the wife with the small Ketuva] of Bar Tsartsur to placate the inheritors of the wife with the large Ketuva, and if not he would 'lash them with thorns which don't draw blood' which, according to Rashi, means to put them in Nidduy.
However he sent them - "Shadrinhu" - to Rav Nahman - is that equivalent of Nidduy?Or lashing? What happened here? Why did the case go before Rav Nahman, and what about the Nidduy? Didn't Rav Amram have the right to decide the case? And after all - Rav Nahman's ruling and the prior ruling of rav Amram were the same - the only difference was the injunction of Rav Amram to placate the loosers? Perhaps Rav Amram is to be understood that he did NOT rule, he just told BOTH sides to agree, which they didn't, so they had to go to court - to Rav Nahman!?
Yeshayahu HaKohen Hollander
When Rav Amram said "go and placate them," it means that he was ruling completely in favor of the heirs of the large Kesuvah, saying that they may receive their mother's Kesuvah. The heirs of the small Kesuvah did not accept his ruling, and therefore they (and not Rav Amram) sent their question to Rav Nachman, and he ruled in their favor (according to Rashi's explanation) that they do not have to give the heirs of the large Kesuvah their mother's Kesuvah.
M. Kornfeld