[1] Univ Texas Southwestern Med Ctr Dallas, Dept Orthopaed Surg, Dallas, TX 75390 USA
[2] Univ Southern Calif, Keck Sch Med, Dept Orthopaed Surg, Los Angeles, CA USA
[3] Kaiser Permanente, Dept Biostat, Programming Serv, Pasadena, CA USA
[4] Kaiser Permanente, Dept Biostat, Res Database Serv, Pasadena, CA USA
[5] Kaiser Permanente Southern Calif, Dept Orthopaed Surg, Baldwin Pk, CA USA