Affiliation: | 1. Hospital for Special Surgery, New York, New York, U.S.A.;2. Center for Hip Preservation, Hospital for Special Surgery, New York, New York, U.S.A.;3. Department of Orthopaedic Surgery, University of Michigan, Ann Arbor, Michigan, U.S.A.;4. Kaiser Permanente, South San Francisco, California, U.S.A. |