The incident happened on Friday night, as Cr Hudson was buying food at Port Chalmers New World for a farewell event for Citibus staff.
He was yesterday afternoon waiting to go into surgery, fellow councillor Bill Acklin said.
Cr Acklin said he had visited Cr Hudson in Dunedin Hospital on Sunday night, and he was "definitely in a bad way".
"He put body and soul into saving the runaway trolley," Cr Acklin said, but fell on the kerb, not only fracturing, but also dislocating his shoulder.
The surgery was expected to reconstruct his shoulder and arm. Cr Hudson was still in good spirits despite his injury.
Mayor Dave Cull yesterday said Cr Hudson was "an energetic councillor", and because of that, it might be necessary to rearrange his responsibilities while he was away.
Citibus was owned by the council through Dunedin City Holdings Ltd (DCHL), but was recently sold. Cr Hudson is director of DCHL.
