Former Wall Street analyst became an ER doctor after sister's horrific subway accident

Full story on "20/20: The Good Doctors: Brilliance and Bravery" airs Sept. 13.

— -- Debbie Yi was working as an investment analyst on Wall Street when she experienced two horrific events that would alter the course of her life forever.

In 2001, Debbie had recently graduated from Brown University with a degree in economics and moved to New York City to start her job as a Goldman Sachs analyst.

On the morning of Sept. 11, 2001, she said her managing director called his team into his office where they could see the burning World Trade Center.

“We all started running,” Debbie said. “I remember I went outside… it was just raining smoke and soot, and it was so sad because I could see children’s photographs that were burned.”

After a panic-filled few hours, Debbie reunited with her middle sister, Christine Yi, with whom she was sharing an apartment in the city.

“After 9/11. I was a very different person,” Debbie said.

Debbie said she left Goldman and started a job at a consulting firm working on projects to rebuild downtown Manhattan. But 18 months later, Debbie said she was vacationing in Mexico when she got a call from her eldest sister Joy in the middle of the night, telling her to come home.

“She said that my sister Christine was in a terrible accident,” Debbie said. “She was hit by a train—a subway train in New York ... [it was] the longest flights of my life.”

It wasn’t until after Debbie arrived at Bellevue Hospital in New York that she learned the specifics of what had happened: her sister had tripped on the subway platform and landed in between two subway cars.

“The train began to drive away and she was still on the track,” Debbie said.

Christine lay on the tracks for hours while rescuers used a crane to lift the train and pull her out. Her right leg was completely shattered. By the time she got to the hospital, she was in a dire situation.

“Her heart stopped,” Debbie said. “She stopped breathing and a surgical intern… provided breaths to her and brought her back to life.”

Dr. Toni McLaurin, now an orthopaedic surgeon at NYU Langone Health, was the orthopedic surgeon on call at Bellevue when Christine arrived. The type of injury Christine was suffering from was known as a “mangled extremity,” she said.

“It really tells you not only is the bone broken but also damage to the skin as well as to the muscles,” McLaurin said.

Fortunately, Christine said she doesn’t remember much from the day of the accident.

“I remember leaving my office that day,” she said. “The next thing I remember is being in the dark, in a lot of pain and someone calling out to me, telling me that help was on the way.”

She said the five weeks after the accident were a blur of surgeries – 15 in total, many aimed at saving her knee.

“You try at all costs to preserve someone’s knee,” McLaurin said. “The difference between having an amputation below the knee, versus an amputation above the knee is very significant.”

Christine said it was a huge deal for her to keep her knee because prosthetic legs for an above-knee amputee don’t always work. But in the end, her knee was saved.

Debbie decided to change her entire career after her sister's experience, deciding to pursue medicine.

“After 9/11, I had thought about my career, and then after my sister’s accident… I realized… I have a greater purpose in life,” Debbie said.

As Debbie began applying for medical schools, she said she had multiple advisers tell her not to include the story of her sister in her essays because it would make it seem like her choosing to go to med school was a rash decision. But Debbie refused to heed their warnings.

“I knew I had to write about my sister’s accident,” she said. “It was a life-defining moment… I would be forever changed by this accident.”

In 2005, Debbie began studying at Albert Einstein College of Medicine in the Bronx and ended up choosing emergency medicine as her specialty. She did her residency at New York-Presbyterian Hospital.

“I remember the first time an ambulance came… to the emergency room,” she said. “I felt like I was reliving what it was like to be in the emergency room when my sister arrived.”

A few years later, Debbie, who was featured on ABC's medical documentary series, "NY Med," was nearing the end of her shift when a patient came in with horrific injuries that she was all too familiar with. The patient had been struck by a subway train.

“It was very personal,” she said. “When I saw that patient, I knew that I had to take my best care with the patient and the patient had to live.”

Yet for Christine, she’s determined to put her accident in the past. Refusing to let her prosthetic slow her down, she is now a star Flywheel spin class student.