8:13 AM PT -- Adrianne shared an update before heading into surgery ... thanking people for their support and saying "I'm really scared. But, I think I'm in good hands."

Adrianne Haslet -- the woman who ran a marathon after losing her leg in the 2013 Boston Marathon Bombing -- says she's "completely broken" after being hit by a car Saturday.

Haslet was hospitalized Saturday evening and has already undergone surgery. In a photo posted on social media, Haslet is seen in a hospital bed wearing a neck brace.

"Struck by a car on Commonwealth Avenue, while on a crosswalk," Haslet said in a statement ... "Thrown into the air and landed, crushing the left side of my body."

She added, "I’m completely broken. More surgery to come.”

Officials say the accident occurred around 7:15 PM -- the driver told police he didn't see Haslet because it was dark and rainy and she was wearing dark clothing.

Cops say the driver was cited for failing to stop of a pedestrian in a crosswalk.

Haslet's story is famous -- after losing her leg in the marathon bombing (while she was a spectator watching the race), she got a prosthetic running leg and trained her ass off to complete the Boston Marathon in 2016.

She had been training for the upcoming 2019 Boston Marathon in the weeks before she was struck by the car.