Question Details:The surjury was done 12 years ago. I tried to get legal help then but they told me that I did not have a case unless it botherd me; it's bothering me now.
If it is impairing your ability to function and/or your enjoyment of life, impairing your ability to work, and/or will cost you out-of-pocket (i.e. not reimbursed by insurance) medical costs to address the problem, then it may be worthwhile suing--but it's also probably too late.
Leaving a drill bit inside your knee is almost certainly malpractice, or careless or negligent medical practice. If you have significant costs, impairment, etc., you could potentially recover enough to make a lawsuit worthwhile (though bear in mind that malpractice suits are expenses--you need your own medical experts to testify).
Unfortunately, in Texas, the "statute of limitations," or time period during which you can bring a lawsuit, is only 2 years after the malpractice. Sometime this can be "tolled," or extended for some time, if you did not know and reasonably could not have known, of the injury--not of how much it's worth, but of the fact of malpractice--until later. However, at the absolute latest, you would have at most 2 years from when you first learned of the drill bit to sue.