Cathi and Dan Johnson marked another bittersweet 9/11 with cake topped in green icing. Saturday would have been daughter Christina's 21st birthday. But Christina, whose favorite color was green, died in 2005 in a car crash near Duluth that also killed the Johnsons' son, Andrew.

Preparing for the anniversary last week, the Johnsons of Rosemount said what no parent ever should have to say -- that they always will grieve the unfathomable loss of two children. But they go on for their daughter, Dani, 23, who recently married.

Little Matthew is helping, too.

"Matthew is not a replacement," said Dan, 50, who works with troubled teens at Harbor Shelter in Hastings on weekends, and is a stay-at-home dad during the week. "He is our fourth child."

Cathi, 47, nods in agreement. The couple's adopted son "doesn't change the pain of the grief. But you get a few really good moments that hadn't been there."

Matthew, 2, is his own survival story. Born in Liberia, Africa, deaf, with a double cleft lip and palate, intestinal abnormalities and an abnormal heart, he was brought to a teaching hospital in Phebe, Liberia, by his mother, who had been told by her husband and village elders to abandon the boy to die. Instead, she traveled for miles to the hospital -- and into the hands of a trauma nurse named Cathi Johnson.

Cathi went to Liberia on a volunteer mission in August 2008, eager to share her medical knowledge but, mostly, desperate to avoid being home for the third anniversary of her children's death on Aug. 28, 2005. That terrible day, Andrew, 21, was driving the car at sundown, with Christina seated behind him. He missed a stop sign.

Cathi signed up for the Liberian program through the Evangelical Lutheran Church in America, and church members helped pay her way.

The west African nation of Liberia, impoverished and wracked by civil wars, was the right choice, Cathi said: "I picked a place that knew grief."

She arrived with insulin, needles, donated books, thermometers, hard drives for computers, everything she could carry. She spent her first two nights on a docked "Mercy Ship" in the capital, Monrovia, before arriving at the Phebe hospital and nursing school, where patients received no food or water, malaria was common and electricity was rare. She did what she could, stitching people up, saving lives.

On Aug. 20, 2008, a young mother arrived with her four-day-old malnourished son. The mother was afraid to touch her "bad-spirit baby," but couldn't bear to abandon him either. Cathi taught her how to express a tiny amount of breast-milk into a container, then feed her son with her finger. But the next day, the mother seemed distant and, soon after, fled. Cathi found the baby in a hospital closet, wrapped in cloth and plastic, with a feeding tube of sugar-water through his nose. He had been left to die.

"I looked around," Cathi recalled. "I said, 'I want the baby. This will be my baby now.'"

Two days later, she was able to get a message to Dan. "It's a little hard to type today," she wrote coyly, "because I'm holding a baby."

She kept the infant boy alive, paying a guard named Matthew to get formula. On Aug. 28, 2008, exactly three years after the deaths of Andrew and Christina, the tiny boy looked up at Cathi "and he calmed. We bonded."

After being assured that the parents had legally abandoned the boy, Cathi adopted him in Liberia on Sept. 1, 2008. She named him Matthew after the guard who helped to save his life. The name means "Gift of God."

Granted humanitarian parole, Cathy and her tiny son flew home in September, a perilous voyage due to Matthew's propensity for aspirating fluids and his high risk for infection. They arrived home on Sept. 11, 2008.

The Johnsons adopted Matthew in the United States on Dec. 24, 2009, "a nice Christmas present," Dan said. They are now working, with pro-bono lawyers from Dorsey & Whitney, as well as U.S. Rep. John Kline, to get Matthew U.S. citizenship before his humanitarian parole expires at the end of this year. Without citizenship and a Social Security card, the Johnsons will not be able to continue his medical insurance and claim him as a dependent.

Since arriving in Minnesota, Matthew has had nine surgeries, three of them for his cleft lip and palate, others on his heart and other internal organs. He's had one cochlear implant and is learning to sign. He's beginning to walk and has already mastered fist-bumps.

His aunt, Karen Johnson, and Matthew's grandparents, Carol and David Solberg, care for him every other weekend. They say he's curious, social and snuggly.

"He is the most easygoing, laid-back boy," said Karen, of Minnetrista. "He doesn't get upset."

His calm demeanor is just one of his many gifts, Dan said. "The biggest gift of Matthew is proving that I could take that risk again, let my heart out. I can't wait to see him first thing in the morning. The love I feel bursting out of my chest for him is the same I felt for my other kids. The difference this time is I don't take it for granted."

But Dan's deepest gratitude is reserved for two special women.

"Cathi had the courage to attack her grief," Dan said. "Matthew's birth mom saved his life. Two tragedies resulted in something beautiful."

Gail Rosenblum • 612-673-7350 • gail.rosenblum@startribune.com