It is one of the most popular operations in sports medicine. It comes in various forms, all with the same name: Hip impingement or bone shaving surgery. World-renowned athletes have had the operation — the Yankees’ third baseman Alex Rodriguez  had it  about two years ago and the sprinter Tyson Gay  had it last summer.
But some sports medicine researchers are asking: where is the evidence that shaving bone helps? Might the bumps or irregular shapes they call impingement be just normal variations? Does the shaved bone grow back?
And it is not just professional athletes who are having the operation. Now some surgeons are even operating on teenage athletes with hip pain .
The idea is that bone that has rough edges or an irregular shape in the hip is rubbing against soft tissue in the joint, causing tendons to fray or muscles to tear. The hope is that by shaving and smoothing the bone, surgeons can protect patients from further injury and also protect them from developing arthritis . The amount of bone removed varies but can be significant — sometimes, as much as a third of the thigh bone’s top.