640 Acta Orthopaedica 2011; 82 (6): 639–645 Norwegian Arthroplasty Register Sept 1987 – Dec 31, 2009 Primary THRs n = 124,759 Reverse hybrid THR n = 6,630 2000–2009 >100 in each group and operated before 2006 n = 3,963 Cemented THR n = 94,737 2000–2009 n = 46,326 10 most used cemented combinations n = 37,666 Age <60 years n = 1,647 Age <60 years n = 3,480 Elite/ Corail Titan/ Corail Kronos/ Corail Reﬂection PE/ Corail Exeter/ABG II Reﬂection PE/Hactiv Exeter/ Corail Charnley/ Corail Reﬂection PE/Taperloc n = 1,762 n = 722 n = 527 n = 295 n = 172 n = 126 n = 142 n = 105 n = 112 Figure 1. Flowchart of the study. to unexpected complications such as increased wear, loos- ening, or dislocation. This concern was raised by the NAR already in their report from 2005 (Norwegian Arthroplasty Register 2005). As the use of reverse hybrids is increasing, we decided to evaluate the short- to medium-term results with this concept and to compare them with those from all-cemented THRs, using data from the NAR. Patients and methods The NAR was established in September 1987 (Havelin et al. 1993). Data on primary and revision THR surgery are collected, and the patients are followed prospectively until revision, death, or emigration. The unique identification number assigned to each resident of Norway makes it pos- sible to link the primary operation to revision surgery and to the National Population Register, which provides informa- tion on death or emigration. Completeness of registration is high for total hip replacement, for both primary and revision surgery (Arthursson et al. 2005, Espehaug et al. 2006, Hul- leberg et al. 2008). From September 1, 1987 through December 31, 2009, 124,759 primary THRs were registered. Of these, 6,630 cases involved reverse hybrid THR. 15 different cups and 13 dif- ferent femoral stems had been used for these reverse hybrids. Since reverse hybrid THR has mainly been used during the last decade, we included only operations performed after December 31, 1999. This gave 6,485 primary operations. We included only the combinations of cup and stem for which there had been more than 100 procedures since 2005. Thus, 3,963 operations in 3,630 patients were included (Figure 1) for survival estimation at 5 and 7 years, involving 9 implant combinations (cup/stem) (Tables 1 and 2). In these implant combinations, all cups were made from conventional ultra- high-molecular-weight polyethylene (UHMWPE). From the register, we extracted information on the brand(s) of the components, the diameter and the material of the femo- ral heads, the diagnosis, the name of the hospital, the surgi- cal approach to the hip, and reasons for revision surgery. We estimated survival at 3, 5, and 7 years for the total material with any revision as the endpoint. Further subgroup analyses included survival at 3, 5, and 7 years in patients less than 60 years of age, with any revision as endpoint. Furthermore, we compared reverse hybrid THR to cemented THR for the total material, with deep infection, dislocation, aseptically loos- Table 1. Breakdown of numbers of different combinations of prosthesis components in the reverse hybrid group during the study period Combination of cup and stem (reverse hybrid) Elite/ Titan/ Kronos/ Year Corail Corail Corail Reflection PEa/Corail Exeter/ Corail Charnley/ Corail Exeter/ ABG II Reflection PEa/Hactiv Reflection PEa/Taperloc 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 Total 38 43 45 61 83 178 269 365 362 318 1762 3 22 46 50 72 79 82 75 113 180 722 3 14 6 9 14 39 66 98 157 121 527 6 13 37 55 63 69 18 26 5 3 295 1 2 3 8 16 10 11 18 28 45 142 6 4 7 2 9 5 14 34 13 11 105 0 0 0 61 50 61 0 0 0 0 172 0 0 0 0 12 37 29 18 16 14 126 0 0 0 0 0 34 49 29 0 0 112 a Full brand name: Reflection Cemented All-Poly. Total 57 98 144 246 319 512 538 663 694 692 3963