....................................................................................................................................... 7 Background .................................................................................................................................7 Objective .....................................................................................................................................7 Patients and methods .....................................................................................................................7 Results .......................................................................................................................................7 Conclusion ..................................................................................................................................7 Introduction ................................................................................................................................. 9 Background ................................................................................................................................11 Total hip replacement ....................................................................................................................11 Low back surgery ....................................................................................................................... 12 Hip-spine syndrome ..................................................................................................................... 15 Orthopedic registers ..................................................................................................................... 16 Swedish Hip Arthroplasty Register ................................................................................................. 18 Swespine ................................................................................................................................... 18 Importance of register data quality .................................................................................................. 19 Prospective observational studies ..................................................................................................... 19 PROMs ................................................................................................................................... 19 Other measurements used in these studies .......................................................................................... 22 Aims ........................................................................................................................................... 23 Patients and methods ................................................................................................................ 25 Patients .................................................................................................................................... 25 Ethical considerations .................................................................................................................. 26 Methods ................................................................................................................................... 26 Statistical methods ...................................................................................................................... 31 Summary of papers ................................................................................................................... 33 Paper I ..................................................................................................................................... 33 Paper II ................................................................................................................................... 33 Paper III .................................................................................................................................. 36 Paper IV .................................................................................................................................. 37 Paper V ................................................................................................................................... 38