The U.S. Food and Drug Administration has classified a voluntary recall by Zimmer Holdings (NYSE: ZMH) last week as a "Class I" recall. On its website, the FDA defines a Class I recall as "a situation in which there is a reasonable probability that the use of or exposure to a violative product will cause serious adverse health consequences or death." 

On Dec. 20, Zimmer had announced its "worldwide recall of all 315 units of the PEEK Ardis Inserter," an instrument used during spinal surgery. Noting that the recall applied to models of the instrument sold during the four-and-a-half-year span between June 2008 and December 2012, the release also listed all relevant part numbers. 

Today's release from the FDA says the tool was at risk of breaking into smaller pieces during surgery and that it was unsafe to operate with.

Zimmer, an $11.4 billion medical devices company, was down 1.8% on the day, and the stock has lost nearly 5% in the past five trading days.