[1] Emory Univ, Sch Med, 100 Woodruff Circle, Atlanta, GA 30322 USA
[2] Emory Spine Ctr, Dept Orthopaed Surg, 59 Execut Pk South,Suite 3000, Atlanta, GA 30329 USA
[3] Emory Univ, Rollins Sch Publ Hlth, Dept Biostat & Bioinformat, 1518 Clifton Rd NE, Atlanta, GA 30322 USA