Watch: ANTHRAX Joined By MACHINE HEAD's ROBB FLYNN For 'I Am The Law' At MILWAUKEE METAL FEST

MACHINE HEAD frontman Robb Flynn joined ANTHRAX on stage Saturday night (May 27) at the Milwaukee Metal Fest at The Rave/Eagles Ballroom in Milwaukee, Wisconsin to perform the classic ANTHRAX song "I Am The Law". Video of his appearance can be seen below.

Flynn previously played "I Am The Law" with ANTHRAX on February 18 at the Fox Theater in Oakland, California.

ANTHRAX performed at the Milwaukee Metal Fest without longtime drummer Charlie Benante, who was scheduled to play two shows with PANTERA in Europe this weekend, including a May 27 concert in Bucharest, Romania. Filling in for Benante in Milwaukee was Derek Roddy, who has previously played with HATE ETERNAL, NILE, MALEVOLENT CREATION and TODAY IS THE DAY, among others.

Roddy previously filled in for Benante this past January when Charlie was forced to miss a few shows on ANTHRAX's North American tour with BLACK LABEL SOCIETY and EXODUS in order to undergo an undisclosed operation.

ANTHRAX played its first concert with Roddy on January 20 at the PNE Forum in Vancouver, British Columbia, Canada.

Beginning around 2012, Benante missed certain shows on ANTHRAX's tours due to his long-running battle with carpal tunnel syndrome, a repetitive stress condition that happens when a person does repeated movements with the hand and wrist. He was replaced at the gigs initially by Jason Bittner (OVERKILL, SHADOWS FALL) and then by Jon Dette (SLAYER, TESTAMENT).

A few years ago, Charlie told San Antonio Metal Music Examiner about his inability to make all the dates on ANTHRAX's tours: "Unfortunately, we're like athletes, and like athletes, they suffer from certain things. I suffer from carpal tunnel problems. But I try and do as much as I could when I can. So we still wanna keep the band… We don't wanna disappoint people. So that's why we do it that way."

Two years ago, Benante spoke to the "Drum For The Song" podcast about how he was finally able to overcome his battle with carpal tunnel syndrome. He said: "I was suffering so much from it because I would go out and start playing the show, and then, by the fifth song, my hand would just go numb; I couldn't feel the stick. I tried so many different things, from acupuncture to physical therapy. I even had a can of the spray air that when you turn it upside down, it gets really cold — I would do that to try to get the feeling back. I tried so many things, but I knew at the end of the day I was gonna have to have the surgery. And Paiste cymbals referred me to a doctor that one of their other drummers went to and was such a great doctor. [He] talked me through the whole thing, and my recovery was quick, and, to this day, it's awesome."

Benante urged fellow drummers suffering from carpal tunnel syndrome to find a surgeon with experience and expertise in the condition before undergoing the operation. "Make sure you find a good doctor, because I've seen drummers that have had [huge] scars," he said. "And [on my arm] you can't even see anything, where he went in. So you have to be careful."