According to Katherine Terrell of NOLA.com and The Times Picayune, Lewis "had to go through concussion protocol testing on the sideline" following a play where he hit his head on the ground after successfully defending against Philadelphia Eagles wide receiver Jason Avant.
While the Saints did not officially announce a concussion immediately following the game, the fact that their star defender did not return after the injury all but makes the diagnosis—as does the Picayune's Larry Holder's observation that Lewis could not speak with the media following the game per league rules.
Keenan Lewis wasn't allowed to speak to the media because of concussion protocol. So he is obviously concussed.— Larry Holder (@LarryHolder) January 5, 2014
Following a concussion, NFL players must work through the league's return-to-play protocol. The process provides a semi-standardized set of rules to guide team physicians in safely determining when a player can return from injury.
Recently, multiple writers—such as Football Guys' Dr. Jene Bramel and ESPN.com's Josh Weinfuss—have detailed the precise nature of the protocol. In some ways—but not all—it resembles typical concussion recovery procedures set forth by the medical literature.
First, players must physically and cognitively rest until they return to an asymptomatic neurological state. Symptoms including—but not limited to—headache, nausea and confusion must abate, and the player must also demonstrate a return to normal cognitive and motor function.
Once at baseline, the athlete begins a set of exercises of progressively increasing intensity.
Typical checkpoints include light cardio activity, heavier cardio activity, agility drills or non-contact practice and full practice. He must complete each step in order—and without symptoms recurring—before returning to live games.
Once a player can complete a full workload without setbacks, a team physician can clear him to take the field if he or she feels it is appropriate. A blessing from an independently affiliated neurological consultant constitutes the final hurdle.
If symptoms return at any time, the player must rest until they resolve before resuming the process.
Yet, is there method to this madness?
When a concussion occurs, the brain undergoes biochemical changes—ones that remain at least somewhat unclear even to this day.
For instance, following a concussive blow, a brain enters a period of altered neurotransmission and energy utilization. These abnormalities lead to functional changes at the cellular level, producing concussion symptoms.
Eventually, with rest, most brains recover with time.
The million-dollar question: how much?
Every athlete and concussion is unique, and the graduated return-to-play process allows doctors, athletic trainers and other medical personnel to monitor an individual's progress.
As a player systematically pushes his body through a series of more and more strenuous exercises, it siphons off a larger and larger amount of blood and energy from the brain.
A healthy brain can handle it.
A still-concussed brain cannot.
Unfortunately, the unpredictable and ungeneralizable nature of concussions makes it very difficult to project how well and how soon an individual player will recover from a specific injury.
Even previously cleared players can suffer setbacks.
In December, Washington Redskins tight end Jordan Reed developed a pregame headache stemming from a concussion he suffered two weeks prior. He missed the game as a result after widespread reports stated he would play.
That said, it bears repeating that no player, concussion or concussion history is exactly alike.
As Lewis continues down his road to recovery, his practice status during the week will speak volumes.
Limited or full participation in practice on a given day implies he is at the later phases of the NFL concussion protocol.
How valuable is Keenan Lewis to the Saints defense?
On the other hand, a "did not participate" tag suggests the cornerback has at least a few steps to go.
In other words, if Lewis is taking full practice reps by Wednesday or Thursday, his status for the Saints' matchup against the Seattle Seahawks becomes promising.
Conversely, no practice reps until later in the week—or none at all before Saturday—is an extremely bad omen.
Furthermore, as Reed's case shows, nothing is a guarantee until Lewis takes the field.
After all, the excellent Saints medical staff certainly knows that his health reigns above all else, as demonstrated by the appropriate decision to remove Lewis from Saturday's game following his injury—even during the playoffs.
Dr. Dave Siebert is a resident physician at the University of Washington who has evaluated dozens of concussions in the outpatient, emergency room, training room or sideline settings.