SANTA CLARA (CBS SF) -- The Denver Broncos and the Carolina Panthers are heading to Super Bowl 50 in Santa Clara on Sunday, but the fight to get to Sunday's big game has been especially hard for those players on both teams who have suffered concussions this season.
The National Football League has been receiving increased scrutiny over how they handle head injuries, after dozens of former players have been posthumously diagnosed with chronic traumatic encephalopathy (CTE), including former Oakland Raiders player Ken Stabler. CTE is a progressive degenerative brain disease found in athletes and others with a history of repetitive brain trauma.
The NFL says they have implemented game safety improvements and revamped their concussion protocols, but the 2015 NFL season saw a significant spike in concussions since 2014. The NFL's 2015 season, including the preseason and regular season games and practices, saw 271 NFL players suffer concussions, up 31.6 percent from 2014, according to the NFL's 2015 injury data.
The concussion incidents are at a four-year high and neither the Panthers nor the Broncos were able to avoid concussions this season.
Three Broncos players suffered concussions so far this season, while six players on the Panthers have suffered from the head injuries.
Among the most notable concussions this season were, on the Denver Broncos' side, tight end Vernon Davis, 31. Davis suffered a concussion in the team's 17-3 win over the San Diego Chargers on Dec. 6 - his second head injury since 2013. In that same game, Broncos' linebacker Danny Trevathan, 25, also suffered a concussion that forced him to sit out the next game.
In a season opener, Broncos defensive end Malik Jackson was forced out of the game against the Baltimore Ravens after suffering a head injury, but he was cleared in time for a game against the Chiefs, just four days later.
Peyton Manning, the Bronco's highly-acclaimed quarterback has avoided concussions this season but admitted back in 2011 that he underperforms on baseline concussion tests so that he can pass them if he suffers a concussion later in the season, according to the NFL.
Broncos players became especially aware of the dangers associated with CTE when, in October, an autopsy on the brain of former NFL linebacker Adrian Robinson, who committed suicide in May 2015 at age 25, found evidence of CTE, according to researchers at Boston University's CTE Center. Robinson played for the Broncos in 2013.
On the Panthers side is, most notably, starting linebacker Luke Kuechly, 24, who suffered a concussion during a game against the Jacksonville Jaguars in September and then sat out the next three games, according to the NFL. A video of Keuchly's big hit can be viewed here.
In October, Panthers linebacker A.J. Klein, 24, Keuchly's replacement, suffered a concussion and missed one game.
Panthers cornerback Teddy Williams, 27, also suffered a concussion in October.
In November, Panthers safety JJ Jansen, 30, suffered a concussion and then in December, Panthers defensive tackle, Kyle Love, 29, suffered a concussion during a game against the New York Giants. He missed one game. During the preseason, cornerback Josh Norman, 28, also suffered a concussion.
New measures added to the NFL's concussion protocol may be part of the reason for the increased number of reported concussions in the NFL. The NFL has not said whether there were more concussions sustained during this season, or just more concussions identified and diagnosed.
The new safety measures include an unaffiliated neurological trauma consultants on the sideline, as well as spotters in the press box. Medical personnel are also now able to call a timeout if the on-field staff misses a possible head injury.
The NFL is facing a potential $1 billion concussion settlement, spurred by a lawsuit brought by former NFL players to compensate them for brain damage suffered during their careers. Players are in the process of demanding more money in the settlement. There is even a website, ForThePlayers.com, created to help players receive compensation from the settlement and fervently promoted by former NFL player and Pro Football Hall of Famer Warren Moon.
Along with the NFL, the National Collegiate Athletic Association is also being required to toughen their return-to-play rules after a concussion. All NCAA athletes will be required to take baseline neurological tests to help doctors determine the severity of any concussion that might come later in the season.
In January, a federal judge in Chicago gave preliminary approval to a head-injury settlement between thousands of former college athletes and the NCAA that includes a $70 million fund to test for brain trauma.
The 2011 lawsuit, comprised of 10 separate lawsuits against the NCAA, identified several dozen student athletes who have suffered brain trauma.
In court filings, plaintiffs in the case cited NCAA figures that indicated 29,225 student athletes suffered concussions from 2004 to 2009 alone.
Jeff Miller, the NFL's senior vice president of health and safety policy, said that the league is working to understand the factors that led to this year's spike.
In 2013, Miller said that concussion "awareness needs to be raised in every level of football," but he also said that the league is concerned about the dwindling numbers of participants in youth football, mainly because of head injury concerns.
"People who are engaged in our sport are more likely to be fans and more likely to enjoy the game," Miller said. "It's a great sport for kids and them not playing is a problem."
But a problem for whom? The NFL's bottom line perhaps?
By Hannah Albarazi - Follow her on Twitter
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