1. University of California San Francisco, School of Medicine, San Francisco, California, USA
2. Institute for Global Orthopaedics and Traumatology, Department of Orthopaedics, University of California, San Francisco, California, USA
3. University of California San Francisco, Department of Orthopaedic Surgery, San Francisco, California, USA
4. University of California San Francisco, Department of Epidemiology and Biostatistics, San Francisco, California, USA