The operation to remove a portion of the femur is called a trochanteric osteotomy. This is done to help give the surgeon better access to the hip joint. It's a procedure used most often in complex cases requiring revision surgery of a total hip replacement already in place.
The trochanteric bone removed is reattached using a wire or cable system of fixation. Sometimes the device breaks or it isn't tightened enough and the bone migrates (moves).
Trochanteric migration can be a major complication. It causes the hip muscles to lose their mechanical advantage. Walking without pain and/or a limp may become impossible.
The surgeon will use X-rays to measure how much the fragment has moved. Migration less than two centimeters can be watched and monitored carefully. If functional changes are already present, then surgery to stabilize the fixation is usually advised.