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The 37-year-old was competing in his first race of the season, after missing the start of the World Cup campaign following an operation on his back.
But his arm clipped a flag near the end of the super G course in Colorado and his right leg was severely lacerated.
"Feeling lucky since things could have been way worse," Miller later tweeted.
Some 15 skiers did not finish the race at the Beaver Creek resort in Colorado, won by Austrian Hannes Reichelt.
World Cup super-G points leader Kjetil Jansrud was another casualty but was able to finish fourth despite injuring his shoulder in the process.
Miller had the fastest time over the first half among the early starters, before his left arm slammed into a gate at about 100 km/h.
He spiralled down the icy track and appeared to fall on one of his skis, which caused the wound.
At 37 years and 115 days old, Miller was hoping to become the oldest gold medallist in an individual event at the world championships.
He has won six Olympic medals, five world championship medals and was overall World Cup champion in 2005 and 2008.
Former Olympic and world champion Bode Miller will miss the remainder of the Alpine World Ski Championships after having surgery on a torn hamstring.