Hansen was taken from the field during the first quarter of their Round 20 win over Essendon after a clash with Nathan Lovett-Murray, but came back on to boot three goals in the 24-point victory.
The Roos had already lost Leigh Adams and Daniel Wells in the first term to game-ending injuries, and there was some suggestion at the time that Hansen - under league concussion regulations - should not have been called upon.
The AFL investigated the incident and although they ruled there was insufficient evidence to say the Kangaroos had breached the rules regarding concussed players, they did impose a hefty fine after adjudging the club did not offer their full assistance to the inquiry.
"It is extremely concerning that North Melbourne failed to fully co-operate at all times with this investigation into a serious matter involving the welfare of one of its players," AFL general manager of operations Adrian Anderson said.
"Whilst there was no finding that there was any attempt to deliberately mislead investigators, North Melbourne now accepts that its conduct at times was not at a standard acceptable to an AFL investigation.
"It has provided the AFL with an unqualified apology for the delays in the investigation.
"It is pleasing that North Melbourne has now changed its internal processes to improve its response to any future AFL investigations with more direct CEO involvement and the oversight of the club's board."
Anderson said the Hansen incident had resulted in proposals on how the AFL and club doctors could better diagnose and treat concussed players.
"The experts tell us that concussion is often a difficult condition to diagnose and manage due to the complexity of brain dysfunction, the subtle clinical signs and the pressure of game circumstances," he said.
"The AFL has been at the forefront of efforts in Australian sport to better understand the issue of concussion and to implement measures to minimise the risks for AFL players.
"We will consider any opportunity to enhance our procedures and guidelines as well as raise awareness across the AFL community about best practice in concussion management, in the interests of players and the game itself."
Proposed changes are expected to include a requirement for club doctors to make greater use of video footage of incidents in their assessment of player fitness, and a need for medical supervision of any self-assessment tests conducted by players in the days after a head injury.
North Melbourne interim CEO Cam Vale said the club welcomed the AFL's findings, but was keen to reiterate their support for the team's medical staff.
"The club accepts the fine and in doing so, acknowledges it should have handled its part in the investigation better," Vale said.
"First and foremost, we fully support the actions of our doctor and his management of Lachlan Hansen. The concussion issue for the League and all clubs is a great concern, but no one takes the welfare and safety of our players more seriously than us.
"We believe we have the best medical, fitness and conditioning team in the competition."We have apologised to Adrian Anderson and his team and will ensure maximum co-operation for any future investigation. We now consider the matter closed."