The rate of concussions suffered by National Hockey League players did not go down after the league introduced a rule against hits to the head, researchers have found.

Neurosurgeon and concussion researcher Dr. Michael Cusimano of St. Michael's Hospital in Toronto and his colleagues compared concussion rates before and after the NHL introduced rules against hits to the head.

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Pittsburgh Penguins' Sidney Crosby, centre, sits between his doctors as they talks about his recovery from a concussion he suffered in January 2011. An NHL rule change in 2011-12 made bodychecking another player with the head as the main point of contact illegal. (Gene J. Puskar/Associated Press)

"The rate of concussion did not decrease," Cusimano said in an interview. "It in fact increased the first year and in the second year in the NHL it stayed stable. So we didn't see a decline like I think everyone had hoped, including the NHL, who said brought in primarily for player safety."

The NHL changed its rules to make bodychecking another player with the head as the main point of contact illegal in the 2010-11 season. The following year, the rule was modified to include all hits to the head with referees using their discretion on whether the contacted player put himself in a vulnerable position.

The researchers also looked at the Ontario Hockey League, which introduced a similar rule back in 2006, as a control group.

Writing in Wednesday's issue of the medical journal PLoS One, the researchers said 64 per cent of NHL concussions were caused by bodychecking.

About 28 per cent of concussions, and 28 per cent of suspected concussions, were caused by illegal incidents where the aggressor was given a penalty, fine or suspension.

"We conclude that rules regulating bodychecking to the head did not reduce the number of players suffering concussions during the NHL regular season and that further changes or stricter enforcement of existing rules may be required to minimize the risk of players suffering these injuries," the study's authors concluded.

In the study, the cause of concussions were classified as blindsiding — checking from the player’s blind side with main contact to the head  — other checking to the head, checks to the body, fighting, non-contact or collision with a teammate, hit by at stick or hit by a puck.

Cusimano fears that inaction is harming the "great sport."

He suggested changes such as:

  • A ban on fighting.
  • Harsher penalties for those teams and players who inflict concussions.
  • Altering equipment.
  • Changes to ice size and rink environment.

The major limitation of the study was that team injury reports and publicly available data were used to look at concussions, instead of medical records. Previous research suggested the approach was accurate for studying injuries among professional basketball players.

The study was funded by the Ontario Neurotrauma Foundation and the Canadian Institutes of Health Research.

With files from CBC's Melanie Glanz