The pain is so crippling that by the time these kids reach adulthood, they can become immobile -- unable to use their knees, shoulders and hands.
Ginamarie Russo doesn't wear the gloves, but she writes about the boxers who do.
"It just fascinates me. I started going down to the gym," she said.
Like a lot of these guys, she knows what it feels like to get hit hard. At just 12, she got a diagnosis that would affect her for the rest of her life.
"It started in one of my wrists -- shooting, shooting pain that wouldn't go away. It just completely took over my hand. I couldn't function anymore," she said.
Diagnosed with juvenile arthritis, Ginamarie's identical twin watched as her sister's right hand became crippled.
"I would hold the toothbrush, everything. The fork, I would help her eat," Annamarie Russo said.
"I thank God for my twin sister. She's my right hand. Still is," Ginamarie Russo said.
Beth Israel's orthopedic hand surgeon Dr.Charles Melone watched Ginamarie's hand deteriorate.
"By the time I saw her, she could barely write," Melone said.
Melone replaced four of the knuckles in Ginamarie's right hand with silicone implants and realigned her tendons.
After five months of therapy, including using a hand out-rigger, she's back in the gym.
"I was so excited for my new hand. No pain, and I'm back to writing again," she said.
Melone said the silicone knuckles used for Ginamarie usually last for at least 15 years.