Mr Christie said he was struck with a baton by one of the officers as he was trying to leave, snapping his C7 vertebra away from his spinal cord.
"I still remember the look on his face - he had his cap on that was kind of covering his forehead a bit, but he just had this real intense look of anger in his eyes and his teeth were gritted and he just looked real, real aggressive," Mr Christie said.
In a letter to Mr Christie about the internal investigation's findings, Wellington district commander Mike Rusbatch said expert medical opinions found there could be "other mechanisms" as to how the injury was caused "as opposed to a blow", but acknowledged force was used.
"The force used was in the nature of pushing people out of the house and some of these pushes occurred while holding a baton in one hand accompanied by forceful verbal commands."
Officers concluded the method was the most appropriate to clear the occupants from the house "given the threat of assault they considered at the time", Mr Rusbatch said.
He also said bottles had been thrown at officers and their vehicles. Affidavits from some partygoers said no bottles were thrown and one, who did not want to be named, said there was no fighting when police arrived.
"In fact, the people I saw were scared and were co-operating. I was sober and have a very clear recollection of the incident."
A teacher who lived across the road but was not at the party said there was no smashed glass around the following morning.
But acting Wellington district commander Inspector Peter Cowan said police had statements from witnesses who had to clean up broken bottles and broken glass the next day.
An Independent Police Conduct Authority investigation into the incident has yet to be released.
Accusations
Some complaints made about police behaviour at the party in September 2009:
• Assault with either batons or hands.
• Screaming at people.
• Pushing.
• Humiliating one person by pulling pants down to his ankles.
• Threatening to arrest people.
• Manhandling and traumatising females.