Low back pain in the United States: incidence and risk factors for presentation in the emergency setting.
                             
                            
                            
                                
                            
                            
                                
                            
                            
                            
                                
                                    
                                            
    Waterman BR, Belmont PJ, Schoenfeld AJ. Low back pain in the United States: incidence and risk factors for presentation in the emergency setting. Spine J. 2012 Jan; 12(1):63-70.