PITTSBURGH — Sean Spence had to look. He didn’t really have a choice if he wanted to move forward with the kind of healing that can’t be addressed with a brace or a wad of tape.

Handed a photograph of the moment that changed his career and his life, the Pittsburgh Steelers linebacker tried not to get nauseous. He nearly failed.

“It was bad,” Spence said. “I couldn’t even believe my body made that movement.”

That’s because it’s not supposed to.

The third-round pick out of Miami (Fla.) was wrapping up a spectacular training camp in August 2012 when he found himself chasing down Carolina Panthers backup quarterback Jimmy Clausen in the third quarter of the preseason finale. Spence was in the midst of reaching out for Clausen when the linebacker’s left knee bent grotesquely underneath him.

In an instant, Spence’s knee exploded. Ligaments shredded. His kneecap dislocated and turned 90 degrees. And that wasn’t the worst of it. Spence severely damaged his peroneal nerve, the kind of injury from which athletes rarely recover.

Laying on the Heinz Field turf, tears in his eyes and agony coursing through his body, Spence wondered if he’d ever play again. He wasn’t the only one.

“It was one of the few times I got emotional about seeing a player go down, a promising young player in camp,” safety Ryan Clark said. “To see him hurt and the way he was, and to see him dealing with that injury on the field, it made me emotional.”

And made the moment Spence donned a helmet and shoulder pads for the first time in 14 months all the more thrilling. After spending more than a year in a grueling rehab program that left Spence feeling “alienated,” he worked with the scout team on Wednesday in what he called a major milestone toward his eventual return.

The Steelers activated Spence off the physically unable to perform list on Tuesday and have three weeks to decide whether to put him on the 53-man roster or injured reserve.

There’s little doubt which avenue Spence prefers, even if he knows he won’t be available this weekend when the Steelers (1-4) host rival Baltimore (3-3).

“I’m definitely hoping (to play this season) but I’m not going to guarantee anything,” Spence said. “I’m going to keep working at it and see how it goes.”

The fact Spence is even at this point is no small miracle. In an era where knee surgery is commonplace, nerve issues are something else entirely. The peroneal nerve is located in the lower half of the leg and can affect everything from leg strength to the ability to move your foot up and down.