TORONTO -- A new study finds that the amount of time NHL players missed because of concussions increased from 1997 to 2004.
The report published Monday in the Canadian Medical Association Journal, the largest and most detailed analysis of concussions in hockey, examined physician reports from seven regular seasons. There were a total of 559 concussions during regular-season games, a concussion rate of 5.8 for every 100 players, or an estimated 1.8 concussions per 1,000 player-hours.
"We found some interesting trends -- one being a gradual increase in post-concussion time loss over the seven years of study," said lead author Dr. Brian Benson of the Sport Medicine Centre at the University of Calgary's faculty of kinesiology. "That may be due to the concussions being severe or physicians being more conservative in their return-to-play decisions."
Benson said the NHL was looking at the data closely.
"They've been careful not to make haphazard decisions and they certainly want to study this well," he said. "That takes time. Concussion changes from season to season. So we have longitudinal data over seven years where they can make informed decisions on any measures they want to take to try to reduce this injury."
The highest-profile player to be sidelined by a concussion in recent months is Pittsburgh Penguins captain Sidney Crosby, who has not played since Jan. 5. His injury will be included in the next round of data.
"The concussion-working group right now is working on analyzing the data from 2006 to 2011, and certainly hope to report some of those findings within the year," Benson said.
In March, commissioner Gary Bettman announced new concussion protocols. Players who display symptoms are given a test by a doctor in a quiet location before returning to the ice, rather than trainers doing an exam on the bench during a game.
The league is also working with the NHL Players' Association on equipment modifications.
Of the 529 cases in which lost time was recorded, 31 percent involved players missing more than 10 days of competition. In 11 percent of those cases, players continued to play and then later reported symptoms to medical staff after the game.
The highest concussion rate recorded was 7.7 per 100 players in the 2000-01 regular season, while the lowest was 4.6 in 1997-98. The last year covered by the statistics -- 2003-04 -- saw a rate of 4.9 per 100 players.
Centers had twice the risk of concussion compared with wings or defensemen, Benson said.
Almost 70 percent of cases were first concussions, 22 percent were a second concussion and the rest were a third or more.
Dr. Michael Cusimano, a neurosurgeon at St. Michael's Hospital in Toronto, said the study probably underestimated concussions because it covered a time period before there was widespread awareness about the dangers of the injury.
"There was probably some under-recognition and players were probably returning too early in some instances," he said. "There were a significant number that returned, in fact, to the game immediately. And that wouldn't be allowed by most doctors who know about the nervous system these days, and those players that return too early, not surprisingly, had significant complication rates."