Acta Orthopaedica 2011; 82 (6): 639–645 641 Table 2. Comparison of different combinations of prosthesis components in the reverse hybrid group N Revisions Median follow-up (range) % < 60 year % male No. of hospitals (max % at hospital) 40 21 12 17 6 5 2 2 3 2.6 (0–10) 3.0 (0–9.8) 1.8 (0–9.7) 5.6 (0–9.9) 5.4 (1.4–7.0) 3.6 (0–5.6) 1.9 (0–9.9) 2.8 (0.4–9.9) 3.8 (2.5–4.7) Mean age (min–max) 60 (21–92) 63 (27–91) 63 (20–92) 58 (18–90) 73 (50–88) 64 (19–91) 64 (19–87) 58 (21–86) 61 (40–82) Table 3. Cup/stem combinations in the cemented group. These have been thoroughly described by Espehaug et al. (2009) Statistics Charnley/Charnley Exeter/Exeter Reflection PE/Spectron Titan/Titan Spectron/ITH Link IP/Lubinus SP(I,II) Contemporary/Exeter Kronos/Titan Elite/Titan Reflection/ITH Manufacturer Depuy Stryker, Osteonics, Howmedica Smith & Nephew Landos, Depuy Smith & Nephew Waldemar Link Stryker, Osteonics, Howmedica Landos, Depuy Depuy/Landos Depuy Smith & Nephew Number of prostheses 12,192 6,419 8,618 2,736 162 2,203 2,707 1,073 1,139 417 ened stem, and aseptically loosened cup as endpoint in the same period. We compared the results to the 10 most commonly used cemented cup/stem combinations in the study period. These cemented implants and the cups in the reverse hybrid group have been described by Espehaug et al. (2009) (Table 3). Details of the stems in the present study are given in Table 4. We excluded patients operated with CMW cement, due to the poor results described by others after use of this cement (Hav- elin et al.1995, Espehaug et al. 2002). Brand name cup/stem Elite/Corail Titan/Corail Kronos/Corail RPE a/Corail Exeter/ ABG II RPE a/Hactiv Exeter/Corail Charnley/Corail RPE a/Taperloc Manufacturer cup/stem Landos Depuy/Depuy Landos Depuy/Depuy Landos Depuy/Depuy Smith & Nephew/Depuy Stryker b/Stryker Smith & Nephew/Scanos c Stryker b/Depuy Depuy/Depuy Smith & Nephew/Biomet a Full brand name: Reflection Cemented All-Poly. b Full brand name: Stryker, Osteonics, Howmedica c Full brand name: Scanos Evolutis 1762 722 527 295 172 126 142 105 112 Table 4. Details of the characteristics of the uncemented femoral stems used in the reverse hybrid group. 97% had HA coating Stem Corail ABG II Hactiv Taperloc Material Ti6A14V Ti alloy Ti6A14V Ti6A14V Shape Straight, tapered Anatomic Straight, tapered Straight, tapered Surface Thickness of HA Company Fully HA-coated HA-coated proximal, polished distally Fully HA-coated Without HA in this study, proximal plasma spray coating 155 µm 50 µm 155 µm DePuy Stryker Evolutis Biomet 48 36 33 58 2 38 35 61 36 40 36 32 37 37 37 18 21 33 15 (34%) 11 (34%) 4 (83%) 11 (35%) 2 (82%) 2 (97%) 5 (67%) 14 (46%) 1 (100%) Risk Ratio (RR) with 95% confidence interval (CI) was esti- mated using Cox regression analyses, with adjustments for age (< 50, 50–59, 60–69, 70–79 and > 80), sex, and diagnosis (osteoarthritis (OA), inflammatory arthritis, and others). We used plots with scaled Schoenfeld residuals for each covariate to test that the Cox proportional hazard model was fulfilled. The Kaplan-Meier method was used for estimation of survival probabilities for the prostheses, with 95% confidence interval (CI). Ranstam and Robertsson (2010) have discussed statis- tical analysis regarding arthroplasty register data and found a negligible effect on survival estimates including bilateral hips. We therefore included bilateral hips. When less than 20 hips remained at risk, survival probabilities were not cal- culated. Median follow-up was calculated using the reverse Kaplan-Meier method. We used chi-squared test to test for binary outcomes between study groups, and the non-para- metric Mann-Whitney test was used to determine whether the distribution of medians was different between study groups. All p-values less than 0.05 were considered to be statisti- cally significant. We used the statistical software packages SPSS (SPSS 17.0 for Windows) and R (version 2.8.1; http:// www.R-project.org).