Sunday night (July 19) at Fenway Park, the Foo Fighters called up a special guest to perform with them onstage. No, it wasn't Steven Tyler or Frank Black or some other famous Boston musician (though they did get Godsmack's Sully Erna later in the show) -- in fact, it wasn't a musician by trade at all.

It was Dr. Lew C. Schon, an orthopedic surgeon at Baltimore's MedStar Union Memorial Hospital, among other hospitals in the area. A random choice? Not entirely. He's the doc who took care of frontman Dave Grohl after a nasty leg break in Sweden last month. Schon didn't do the surgery himself, but Grohl found him for a follow-up.

That's actually why Schon came to Massachusetts: to see his patient and make sure he was doing his rehabilitation exercises. Then, Grohl asked him an utterly cosmic question: "Why don't you perform with us onstage?

Schon said yes, of course.

"He knew from one of his relatives that I was a musician, so we talked about that," Schon told MTV News. "My band’s called The Stimulators, and we had another band briefly called The Sole Heelers. I’m known more for maybe my stage personality and maybe through piano-playing spirit. I usually sing backup harmonies and I usually do character songs."

Grohl wanted to show his appreciation for all Schon had done, but he wasn't going to hand over the mic to just anyone at a Foo Fighters gig. He was interested in Schon's musical ability -- including his role in The Stimulators, made up entirely of orthopedic surgeons -- so he invited the doctor to a jam session the day of the gig.

"I go to Fenway, and the place where we’re going to jam is not wheelchair accessible," Schon said. "It’s a training area, so these guys could run up and down stairs. Well, Dave can’t run up and down stairs. So I’m waiting in the training area to do the jam. I didn’t wanna bother them, and I also thought that maybe somebody had said to him, 'Hey Dave you know what? You’re a great guy and you’re so friendly and inclusive, but enough already.'"

Luckily for Schon, no one had convinced Grohl to nix the idea. The rehearsal was delayed for a bit, but when it finally happened, it happened. Schon suggested The White Stripes' "Seven Nation Army," a tune he plays with The Stimulators, and the Foos were game. Later that night during the concert, they made it happen for real.

"I used to do magic and I juggled and I give lots of lectures, so I’m very comfortable performing because I have a band," Schon said. "I wasn’t so intimated by being in front of 40,000 people or whatever the number was, but I definitely wanted to make sure that the people were going to be happy."

Judging by the chants of "Leeewwww" that rang out after the band smashed through the song, they seemed pretty happy. And Grohl seemed satisfied as well. "Holy sh-t, that's actually my doctor," Grohl said from his majestic rock throne onstage. "What a badass."

Schon felt the love and said he knew precisely how much of the spotlight to steal -- in other words, enough to make it memorable but not too much to stay respectful of the general vibe of the show. You can see his natural rapport with his patient in the middle of the last verse, when he name-checked Grohl and Grohl fired it right back without missing a beat.

"It was great. I felt at one with the band and with the people. I just tried to make it as meaningful an experience for them as I would want if I was in the audience," Schon said. "And knowing you’re going to be a surgeon, you’re going to be always putting forth your best effort. There’s no time for incomplete effort or inadequate results. You gotta deliver! It was a lot of fun. I felt very connected with the crowd, and definitely had the time of my life."

Cheers, Dr. Schon. No army, no matter how many nations it contains, can hold you back.