Scrum coaches, props and O'Brien were involved in the UK-based laboratory study to look at the scrum, which he described as "a nightmare" to referee.
"Since crouch, touch, pause, engage, apart from being a mess, we have only had one catastrophic injury.
"Safety [in the scrum] must be paramount if we want our kids to play in the front row. It works - I don't know how, but it works."
More than 120 people attended O'Brien's presentation where he said, overall, he was delighted with Rugby World Cup 2011 - and the standard of the refereeing.
"There were 48 games in the World Cup, and the quality of refereeing was as good as any I've ever seen."
However, there were "some" games O'Brien was not happy with, with issues around decision making.
- Otago Daily Times