They are injuries that have affected dozens of NHL teams – from the contenders to the bottom feeders – and a considerable chunk of the league's 963-member player base.
So it should come as little surprise that concussions have also played a role for the Toronto Maple Leafs and their tumble down the standings.
Not that head injuries have taken out their top players, as has been the case in Pittsburgh and Philadelphia with Sidney Crosby, Kris Letang, Claude Giroux, Chris Pronger and others.
No, what's been remarkable in Toronto is how head injuries have weakened four players who were able to return to their lineup after being deemed healthy.
It's a trend that shows just how unpredictable – and difficult to manage – concussions can be.
The most prominent example has been netminder James Reimer, who was off to a 4-0-1 start when Montreal Canadiens captain Brian Gionta's elbow clipped him in mid-October and took him out of the next 18 games.
Reimer's numbers have been well down since, across the board, with a .912 save percentage before the injury having become an ugly .898 after.
There are less obvious examples on the Leafs, too, with veteran John-Michael Liles – projected as the team's No. 2 man on the blueline in training camp – labouring mightily since missing 16 games with a concussion.
Liles's before-and-after numbers are even more alarming than Reimer's, as the 31-year-old was on pace for a career year with 21 points in 34 games before going down.
Since his return, however, he's been remarkably out of sorts, recording only four points and a minus-18 in 28 games as the Leafs have crashed and burned in the standings.
Add in career worst seasons for teammates Matt Lombardi and Colby Armstrong, both of who are coming off head injuries, and the impact of concussions even on players in the lineup is hard to ignore.
None of that's to say the Leafs' record-setting fall in the standings – which continued with an ugly 7-1 loss to the Flyers on Thursday – is directly attributable to their players suffering blows to the head.
That's too hard an argument to make when other teams, led by the Flyers, Penguins and St. Louis Blues, have all weathered concussion after concussion to put together strong, playoff-calibre seasons even as bodies have come in and out of the lineup.
(Philadelphia, in particular, has had a remarkable year – with their 45th win Thursday – given seven players have missed time with concussions.)
What it does highlight, however, is that how the league measures the damage done by head injuries should extend well beyond simply the man games spent on the sidelines.
Not everyone is a Crosby, who has come back and excelled twice, as many concussed players will admit they simply aren't quite the same when they return to the game – with a loss of timing or split-second reflexes likely at fault.
Nowhere has that been more evident than with Buffalo Sabres netminder Ryan Miller, who has had a stunning resurrection after being bowled over and concussed by Milan Lucic in mid-November.
It really wasn't until two months later that Miller began to start to look like himself again, a shift that has helped the Sabres rack up a 19-5-5 run to put them on the cusp of an unlikely playoff berth.
Recovery, in other words, is possible – and that's what the Leafs will be hoping for when it comes to Reimer, who at this point appears unlikely to play again this season after his symptoms have mysteriously returned.
But concussions have definitely already made their mark on Toronto's season – just as they have for so many other teams around the league.