Reaching that first double-digit age of 10 is a milestone for any kid, but for these Guatemalan twins born conjoined at the head, it's cause for joyous celebration _ they've repeatedly defied the odds against survival at all.

The girls, Maria de Jesus and Maria Teresa Quiej-Alvarez, garnered international attention when they were separated in 2002 in a 23-hour surgery that riveted the world as it unfolded at Mattel Children's Hospital at the University of California Los Angeles Medical Center.

On Saturday, the sisters, known as Josie and Teresita, celebrated their 10th birthday at a private home in Malibu with a party complete with bounce house and a steel-drum band. Guests at the Hawaiian-themed bash included many members of the 50-person surgical team, as well as two dozen of the girls' school chums. Hula dancers adorned two birthday cakes.

"It is a miracle," said Jenny Hull, an executive board member of Mending Kids International, the organization that arranged the $1.5 million surgery and has financed much of their care through donations.

Also among the guests was Mel Gibson, a long-time supporter of Mending Kids who has known the sisters for most of their lives. The actor walked with the girls up a hill to the party, laughing with Josie and blowing bubbles with Teresita.

"It's good to be here. It's good to see the twins," Gibson said to reporters before heading inside.

Dr. Henry Kawamoto, who headed the plastic-surgery team, said there was little in medical texts a decade ago about separating craniophagus or head-conjoined twins. He and neurosurgeon Dr. Jorge Lazareff outlined their own procedure.

"It went off like we planned it," said Kawamoto. "That was really such a great feeling."

The operation, however, lasted longer than the 15 hours Kawamoto anticipated. Equalizing the girls' vital signs under anesthesia was tricky, he recalled.

After months of recovery, the sisters, known as Josie and Teresita, returned to Guatemala, but several months later Teresita contracted meningitis.

They returned to the United States to be near sophisticated medical care and now live with two host families in Los Angeles County. Their parents remain in their rural village in Guatemala and visit the girls several times a year. They speak to them every Sunday.

Josie attends a public elementary school where she's entering fourth grade. She's very social and loves singing, drawing and performing with her synchronized swim team. "She's quite a fish," said Hull, who is her host mother.

She has suffered delayed motor skills in her legs, however. With intensive physical therapy, she walks aided by a cane and a walker, and expects to be fully ambulatory eventually, Hull said.

At Saturday's party, Josie went straight for the pool, where she frolicked with her friends.

Teresita's bout with meningitis left her unable to speak, but she expresses herself through humming and laughing. She enjoys art, music and computers at school and loves swimming and horseback riding.

The twins see each other several times a week. "They love being together," Hull said. "They totally have that twin connection. Josie always talks to Teresita and she'll hum back. She'll tell her something funny and Teresita will laugh."

Lazareff called the meningitis "a severe setback. My dream was for them both to lead independent lives _ one may not, but who knows." Still, he noted the sisters have thrived. "It speaks to the wonderful care of the people around them," he said.

Conjoined twins are extremely rare, occurring in about one in 2.5 million births, with craniophagus twins the rarest kind. If they survive birth, many do not live beyond their first birthday. Others do not survive separation surgery.

The survival odds in the twins' case were improved because they each had their own brain.

Josie and Teresita's story has brought renown to Burbank, Calif.-based Mending Kids. Both donations of cash and physician services increased, bringing life-changing medical treatment to more kids from underdeveloped countries, Hull said.

Lazareff said the case also opened doors to establish pediatric neurology programs and teaching partnerships in developing countries.

"They have indirectly helped hundreds of other children," he said.

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Contact the reporter at http://twitter.com/ChristinaHoag.