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1.  Increasing risk of prosthetic joint infection after total hip arthroplasty 
Acta Orthopaedica  2012;83(5):449-458.
Background and purpose
The risk of revision due to infection after primary total hip arthroplasty (THA) has been reported to be increasing in Norway. We investigated whether this increase is a common feature in the Nordic countries (Denmark, Finland, Norway, and Sweden).
Materials and methods
The study was based on the Nordic Arthroplasty Register Association (NARA) dataset. 432,168 primary THAs from 1995 to 2009 were included (Denmark: 83,853, Finland 78,106, Norway 88,455, and Sweden 181,754). Adjusted survival analyses were performed using Cox regression models with revision due to infection as the endpoint. The effect of risk factors such as the year of surgery, age, sex, diagnosis, type of prosthesis, and fixation were assessed.
Results
2,778 (0.6%) of the primary THAs were revised due to infection. Compared to the period 1995–1999, the relative risk (with 95% CI) of revision due to infection was 1.1 (1.0–1.2) in 2000–2004 and 1.6 (1.4–1.7) in 2005–2009. Adjusted cumulative 5–year revision rates due to infection were 0.46% (0.42–0.50) in 1995–1999, 0.54% (0.50–0.58) in 2000–2004, and 0.71% (0.66–0.76) in 2005–2009. The entire increase in risk of revision due to infection was within 1 year of primary surgery, and most notably in the first 3 months. The risk of revision due to infection increased in all 4 countries. Risk factors for revision due to infection were male sex, hybrid fixation, cement without antibiotics, and THA performed due to inflammatory disease, hip fracture, or femoral head necrosis. None of these risk factors increased in incidence during the study period.
Interpretation
We found increased relative risk of revision and increased cumulative 5–year revision rates due to infection after primary THA during the period 1995–2009. No change in risk factors in the NARA dataset could explain this increase. We believe that there has been an actual increase in the incidence of prosthetic joint infections after THA.
doi:10.3109/17453674.2012.733918
PMCID: PMC3488170  PMID: 23083433
2.  Uncemented and cemented primary total hip arthroplasty in the Swedish Hip Arthroplasty Register 
Acta Orthopaedica  2010;81(1):34-41.
Background and purpose
Since the introduction of total hip arthroplasty (THA) in Sweden, both components have most commonly been cemented. A decade ago the frequency of uncemented fixation started to increase, and this change in practice has continued. We therefore analyzed implant survival of cemented and uncemented THA, and whether the modes of failure differ between the two methods of fixation.
Patients and methods
All patients registered in the Swedish Hip Arthroplasty Register between 1992 and 2007 who received either totally cemented or totally uncemented THA were identified (n = 170,413). Kaplan-Meier survival analysis with revision of any component, and for any reason, as the endpoints was performed. Cox regression models were used to calculate risk ratios (RRs) for revision for various reasons, adjusted for sex, age, and primary diagnosis.
Results
Revision-free 10-year survival of uncemented THA was lower than that of cemented THA (85% vs. 94%, p < 0.001). No age or diagnosis groups benefited from the use of uncemented fixation. Cox regression analysis confirmed that uncemented THA had a higher risk of revision for any reason (RR = 1.5, 95% CI: 1.4–1.6) and for aseptic loosening (RR = 1.5, CI: 1.3–1.6). Uncemented cup components had a higher risk of cup revision due to aseptic loosening (RR = 1.8, CI: 1.6–2.0), whereas uncemented stem components had a lower risk of stem revision due to aseptic loosening (RR = 0.4, CI: 0.3–0.5) when compared to cemented components. Uncemented stems were more frequently revised due to periprosthetic fracture during the first 2 postoperative years than cemented stems (RR = 8, CI: 5–14). The 5 most common uncemented cups had no increased risk of revision for any reason when compared with the 5 most commonly used cemented cups (RR = 0.9, CI: 0.6–1.1). There was no significant difference in the risk of revision due to infection between cemented and uncemented THA.
Interpretation
Survival of uncemented THA is inferior to that of cemented THA, and this appears to be mainly related to poorer performance of uncemented cups. Uncemented stems perform better than cemented stems; however, unrecognized intraoperative femoral fractures may be an important reason for early failure of uncemented stems. The risk of revision of the most common uncemented cup designs is similar to that of cemented cups, indicating that some of the problems with uncemented cup fixation may have been solved.
doi:10.3109/17453671003685400
PMCID: PMC2856202  PMID: 20180715
3.  Surgical procedures in the treatment of 784 infected THAs reported to the Norwegian Arthroplasty Register 
Acta Orthopaedica  2011;82(5):530-537.
Background and purpose
Controversies still exist regarding the best surgical procedure in the treatment of periprosthetic infection after total hip arthroplasty (THA). Based on data in the Norwegian Arthroplasty Register (NAR), we have compared the risk of re-revision after 4 different surgical procedures: 2-stage with exchange of the whole prosthesis, 1-stage with exchange of the whole prosthesis, major partial 1-stage with exchange of stem or cup, and minor partial 1-stage with exchange of femoral head and/or acetabular liner.
Methods
Between 1987 and 2009, 124,759 primary THAs were reported to the NAR, of which 906 (0.7%) were revised due to infection. Included in this study were the 784 revisions that had been performed by 1 of the 4 different surgical procedures. Cox-estimated survival and relative revision risks are presented with adjustment for differences among groups regarding gender, type of fixation, type of prosthesis, and age at revision.
Results
2-stage procedures were used in 283 revisions (36%), 1-stage in 192 revisions (25%), major partial in 129 revisions (17%), and minor partial in 180 revisions (23%). 2-year Kaplan-Meier survival for all revisions was 83%; it was 92% for those re-revised by 2-stage exchange procedure, 88% for those re-revised by 1-stage exchange procedure, 66% for those re-revised by major partial exchange procedure, and it was 76% for those re-revised by minor partial exchange. Compared to the 2-stage procedure and with any reason for revision as endpoint (180 re-revisions), the risk of re-revision increased 1.4 times for 1-stage (p = 0.2), 4.1 times for major partial exchange (p < 0.001), and 1.5 times for minor partial exchange (p = 0.1). With infection as the endpoint (108 re-revisions), the risk of re-revision increased 2.0 times for 1-stage exchange (p = 0.04), 6.0 times for major partial exchange (p < 0.001), and 2.3 times for minor partial exchange (p = 0.02). Similar results were found when the analyses were restricted to the period 2002–2009.
Interpretation
In the Norwegian Arthroplasty Register, the survival after revision of infected primary THA with 2-stage implant exchange was slightly superior to that for 1-stage exchange of the whole prosthesis. This result is noteworthy, since 2-stage procedures are often used with the most severe infections. However, debridement with exchange of head and/or liner but with retention of the fixed implant (minor revision) meant that there was a 76% chance of not being re-revised within 2 years.
doi:10.3109/17453674.2011.623572
PMCID: PMC3242948  PMID: 21992085
4.  Total hip arthroplasty in young adults, with focus on Perthes' disease and slipped capital femoral epiphysis 
Acta Orthopaedica  2012;83(2):159-164.
Background and purpose
Pediatric hip diseases account for 9% of all primary hip arthroplasties in the Norwegian Arthroplasty Register. We wanted to validate the diagnosis as reported to the register and to assess the quality of life of these patients after hip replacement.
Patients and methods
540 patients accepted to participate in this follow-up study (634 hips). All were less than 40 years of age and had been reported to the Norwegian Arthroplasty Register as having undergone a primary total hip arthroplasty (THA) between 1987 and 2007. The underlying diagnosis, age at diagnosis, and type of treatment given prior to the hip replacement were recorded from the original hospital notes.
Results
The diagnoses reported to the Norwegian Arthroplasty Register were confirmed to be correct in 91% of all cases (538/592). For the 94 hips that had been treated due to Perthes' disease or slipped capital femoral epiphysis (SCFE), the diagnosis was verified in 95% of cases (89/94). The corresponding proportion for inflammatory hip disease was 98% (137/140) and it was only 61% for primary osteoarthritis (19/31). The self reported quality of life (EQ-5D) was poorer for these young patients with THA than for persons in age-matched cohorts from Great Britain and Sweden, except for those with an underlying SCFE.
Interpretation
The diagnoses reported to the Norwegian Arthroplasty Register as the underlying cause of THA were correct in 91% of cases. Individuals who undergo THA before the age of 40 have a reduced quality of life, except for those requiring a hip replacement because of SCFE.
doi:10.3109/17453674.2011.641105
PMCID: PMC3339530  PMID: 22112152
5.  Infection after primary hip arthroplasty 
Acta Orthopaedica  2011;82(6):646-654.
Background and purpose
The aim of the present study was to assess incidence of and risk factors for infection after hip arthroplasty in data from 3 national health registries. We investigated differences in risk patterns between surgical site infection (SSI) and revision due to infection after primary total hip arthroplasty (THA) and hemiarthroplasty (HA).
Materials and methods
This observational study was based on prospective data from 2005–2009 on primary THAs and HAs from the Norwegian Arthroplasty Register (NAR), the Norwegian Hip Fracture Register (NHFR), and the Norwegian Surveillance System for Healthcare–Associated Infections (NOIS). The Norwegian Patient Register (NPR) was used for evaluation of case reporting. Cox regression analyses were performed with revision due to infection as endpoint for data from the NAR and the NHFR, and with SSI as the endpoint for data from the NOIS.
Results
The 1–year incidence of SSI in the NOIS was 3.0% after THA (167/5,540) and 7.3% after HA (103/1,416). The 1–year incidence of revision due to infection was 0.7% for THAs in the NAR (182/24,512) and 1.5% for HAs in the NHFR (128/8,262). Risk factors for SSI after THA were advanced age, ASA class higher than 2, and short duration of surgery. For THA, the risk factors for revision due to infection were male sex, advanced age, ASA class higher than 1, emergency surgery, uncemented fixation, and a National Nosocomial Infection Surveillance (NNIS) risk index of 2 or more. For HAs inserted after fracture, age less than 60 and short duration of surgery were risk factors of revision due to infection.
Interpretation
The incidences of SSI and revision due to infection after primary hip replacements in Norway are similar to those in other countries. There may be differences in risk pattern between SSI and revision due to infection after arthroplasty. The risk patterns for revision due to infection appear to be different for HA and THA.
doi:10.3109/17453674.2011.636671
PMCID: PMC3247879  PMID: 22066562
6.  Head Material Influences Survival of a Cemented Total Hip Prosthesis in the Norwegian Arthroplasty Register 
Background
High prosthesis survival is reported for total hip prostheses with metal and alumina heads, but direct comparisons of a single prosthesis design with one of two different head materials has seldom been studied. Prostheses with zirconia heads are less commonly used than metal and alumina heads, and the few reports suggest variable results with zirconia heads.
Questions/Purposes
We therefore asked: (1) Would metal heads provide better survival of a cemented total hip arthroplasty (THA) than alumina heads? (2) Would metal heads provide better survival of a cemented THA than zirconia heads?
Methods
We searched in the Norwegian Arthroplasty Register for cemented primary THA cup/stem combinations that simultaneously had been used with different head materials. The only THA that fulfilled these inclusion criteria was the cemented Reflection All-Poly/Spectron EF (cup/stem) that had during 2001 to 2006 been used both with alumina (n = 448) and cobalt-chromium (n = 5229) heads; that implant had also been used with zirconia (n = 275) and cobalt-chromium heads (n = 3195) during 1997 to 2003, and we included patients with this THA from these two time intervals in the study. All cups were conventional polyethylene. We estimated prosthesis survival and relative revision risks adjusting for age, sex, and diagnosis. The followup in the two study materials was until December 2010.
Results
The survival at 8 years of the Spectron EF/Reflection THAs, inserted with alumina and cobalt-chromium heads during 2001 to 2006, was 92.3% and 94.0%, respectively. The Reflection/Spectron EF THA had inferior survival with zirconia heads compared with cobalt-chromium heads (relative risk, 1.7). At 12 years, the survival rate was 88.1% with cobalt-chromium heads and 74.8% with zirconia heads.
Conclusions
Alumina femoral heads provided no advantage over cobalt-chromium heads on midterm prosthesis survival. THAs with zirconia heads had inferior survival.
Level of Evidence
Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-012-2396-2
PMCID: PMC3462857  PMID: 22644422
7.  Effects of hydroxyapatite coating of cups used in hip revision arthroplasty 
Acta Orthopaedica  2012;83(5):427-435.
Background and purpose
Coating of acetabular revision implants with hydroxyapatite (HA) has been proposed to improve ingrowth and stability. We investigated whether HA coating of revision cups can reduce the risk of any subsequent re-revision.
Methods
We studied uncemented cups either with or without HA coating that were used at a primary acetabular revision and registered in the Swedish Hip Arthroplasty Register (SHAR). 2 such cup designs were identified: Harris-Galante and Trilogy, both available either with or without HA coating. These cups had been used as revision components in 1,780 revisions of total hip arthroplasties (THA) between 1986 and 2009. A Cox proportional hazards model including the type of coating, age at index revision, sex, cause of cup revision, cup design, the use of bone graft at the revision procedure, and the type of cup fixation at primary THA were used to calculate adjusted risk ratios (RRs with 95% CI) for re-revision for any reason or due to aseptic loosening.
Results
71% of the cups were coated with HA and 29% were uncoated. At a mean follow-up time of 6.9 (0–24) years, 159 (9%) of all 1,780 cups had been re-revised, mostly due to aseptic loosening (5%), dislocation (2%), or deep infection (1%). HA coating had no significant influence on the risk of re-revision of the cup for any reason (RR = 1.4, CI: 0.9–2.0) or due to aseptic loosening (RR = 1.1, 0.6–1.9). In contrast, HA coating was found to be a risk factor for isolated liner re-revision for any reason (RR = 1.8, CI: 1.01–3.3). Age below 60 years at the index cup revision, dislocation as the cause of the index cup revision, uncemented cup fixation at primary THA, and use of the Harris-Galante cup also increased the risk of re-revision of the cup. In separate analyses in which isolated liner revisions were excluded, bone grafting was found to be a risk factor for re-revision of the metal shell due to aseptic loosening (RR = 2.1, CI: 1.05–4.2).
Interpretation
We found no evidence to support the notion that HA coating improves the performance of the 2 studied cup designs in revision arthroplasty. In contrast, patient-related factors such as younger age and dislocation as the reason for cup revision, and technical factors such as the choice of revision cup were found to influence the risk of subsequent re-revision of the cup. The reason for inferior results after revision of uncemented cups is not known, but it is possible that these hips more often had pronounced bone loss at the index cup revision.
doi:10.3109/17453674.2012.720117
PMCID: PMC3488167  PMID: 22937978
8.  Increased risk of revision of acetabular cups coated with hydroxyapatite 
Acta Orthopaedica  2010;81(1):53-59.
Background
Hydroxyapatite (HA) is the main inorganic component of bone, and HA coating is widely used on acetabular cups in hip arthroplasty. It has been suggested that this surface finish improves cup survival.
Methods
All patients registered in the Swedish Hip Arthroplasty Register between 1992 and 2007 with an uncemented acetabular implant that was available either with or without HA coating were identified. 8,043 total hip arthroplasties (THAs) with the most common cup types (Harris-Galante, Romanus, and Trilogy) were investigated. A Cox regression model including type of coating, age, sex, primary diagnosis, cup type, and type of stem fixation was used to calculate adjusted risk ratios (RRs) for the risk of revision.
Results
HA coating was a risk factor for cup revision due to aseptic loosening (adjusted RR 1.7; 95% CI: 1.3–2). Age at primary arthroplasty of < 50 years, a diagnosis of pediatric hip disease, the use of a cemented stem, and the Romanus and Harris-Galante cup types were also associated with statistically significantly increased risk of cup revision due to aseptic loosening.
Interpretation
Our findings question the routine use of HA-coated cups in primary total hip arthroplasty. With some designs, this practice may even increase the risk of loosening—resulting in revision surgery.
doi:10.3109/17453670903413178
PMCID: PMC2856204  PMID: 19968603
9.  Risk factors for revision due to infection after primary total hip arthroplasty 
Acta Orthopaedica  2010;81(5):542-547.
Background and purpose
There has been a limited amount of research on risk factors for revision due to infection following total hip arthroplasty (THA), probably due to low absolute numbers of revisions. We therefore studied patient- and surgery-related risk factors for revision due to infection after primary THA in a population-based setting.
Materials and methods
Using the Danish Hip Arthroplasty Registry, we identified 80,756 primary THAs performed in Denmark between Jan 1, 1995 and Dec 31, 2008. We used Cox regression analysis to compute crude and adjusted relative risk (RR) of revision due to infection. Revision was defined as extraction or exchange of any component due to infection. The median follow-up time was 5 (0–14) years.
Results
597 primary THAs (0.7%) were revised due to infection. Males, patients with any co-morbidity, patients operated due to non-traumatic avascular femoral head necrosis, and patients with long duration of surgery had an increased RR of revision due to infection within the total follow-up time. A tendency of increased RR of revision was found for patients who had received cemented THA without antibiotic and hybrid THA relative to patients with cementless implants. Hip diagnosis and fixation technique were not associated with risk of revision due to infection within 1 year of surgery (short-term risk).
Interpretation
We identified several categories of THA patients who had a higher risk of revision due to infection. Further research is required to explain the mechanism underlying this increased risk. More attention should be paid by clinicians to infection prevention strategies in patients with THA, particularly those with increased risk.
doi:10.3109/17453674.2010.519908
PMCID: PMC3214741  PMID: 20860453
10.  Survival of primary total hip arthroplasty in rheumatoid arthritis patients 
Acta Orthopaedica  2010;81(1):60-65.
Background and purpose
There has been a limited amount of research on survival of total hip arthroplasties (THAs) in rheumatoid arthritis (RA). We therefore performed a population-based, nationwide study to compare the survival of primary THAs in RA patients and in osteoarthritis (OA) patients. We also wanted to identify predictors of THA failure in RA patients.
Methods
Using the Danish Hip Arthroplasty Registry, we identified 1,661 primary THAs in RA patients and 64,858 in OA patients, all of which were inserted between 1995 and 2008. The follow-up period was up to 14 years for both groups.
Results
Regarding overall THA survival, the adjusted RR for RA patients compared to OA patients was 0.81 (95% CI: 0.65–1.01). We found no difference in survival of cups between primary THAs in RA and OA patients. In contrast, there was better overall survival of stems in RA patients than in OA patients, both regarding revision due to aseptic loosening (adjusted RR = 0.58; 95% CI: 0.34–0.99) and for any reason (adjusted RR = 0.63; 95% CI: 0.45–0.88). In RA patients, males had a higher risk of revision than females concerning aseptic loosening of the stem, any revision of the stem, and any revision of both components.
Interpretation
The overall survival of primary THAs in RA patients is similar to THA survival in OA patients. Stem survival appeared to be better in RA patients, while survival of the total THA concept did not show any statistically significant differences between the two groups. In RA patients, males appear to have a greater risk of revision than females.
doi:10.3109/17453671003685418
PMCID: PMC2856205  PMID: 20180721
11.  Dual-mobility cups for revision due to instability are associated with a low rate of re-revisions due to dislocation 
Acta Orthopaedica  2012;83(6):566-571.
Background and purpose
Revision total hip arthroplasty (THA) due to recurrent dislocations is associated with a high risk of persistent instability. We hypothesized that the use of dual-mobility cups would reduce the risk of re-revision due to dislocation after revision THA.
Patients and methods
228 THA cup revisions (in 228 patients) performed due to recurrent dislocations and employing a specific dual-mobility cup (Avantage) were identified in the Swedish Hip Arthroplasty Register. Kaplan-Meier survival analysis was performed with re-revision due to dislocation as the primary endpoint and re-revision for any reason as the secondary endpoint. Cox regression models were fitted in order to calculate the influence of various covariates on the risk of re-revision.
Results
58 patients (25%) had been revised at least once prior to the index cup revision. The surgical approach at the index cup revision was lateral in 99 cases (44%) and posterior in 124 cases (56%). Median follow-up was 2 (0–6) years after the index cup revision, and by then 18 patients (8%) had been re-revised for any reason. Of these, 4 patients (2%) had been re-revised due to dislocation. Survival after 2 years with the endpoint revision of any component due to dislocation was 99% (95% CI: 97–100), and it was 93% (CI: 90–97) with the endpoint revision of any component for any reason. Risk factors for subsequent re-revision for any reason were age between 50–59 years at the time of the index cup revision (risk ratio (RR) = 5 when compared with age > 75, CI: 1–23) and previous revision surgery to the relevant joint (RR = 1.7 per previous revision, CI: 1–3).
Interpretation
The risk of re-revision due to dislocation after insertion of dual-mobility cups during revision THA performed for recurrent dislocations appears to be low in the short term. Since most dislocations occur early after revision THA, we believe that this device adequately addresses the problem of recurrent instability. Younger age and prior hip revision surgery are risk factors for further revision surgery. However, problems such as potentially increased liner wear and subsequent aseptic loosening may be associated with the use of such devices in the long term.
doi:10.3109/17453674.2012.742395
PMCID: PMC3555442  PMID: 23116439
12.  Increasing risk of revision due to deep infection after hip arthroplasty 
Acta Orthopaedica  2009;80(6):639-645.
Background and purpose Over the decades, improvements in surgery and perioperative routines have reduced the incidence of deep infections after total hip arthroplasty (THA). There is, however, some evidence to suggest that the incidence of infection is increasing again. We assessed the risk of revision due to deep infection for primary THAs reported to the Norwegian Arthroplasty Register (NAR) over the period 1987–2007.
Method We included all primary cemented and uncemented THAs reported to the NAR from September 15, 1987 to January 1, 2008 and performed adjusted Cox regression analyses with the first revision due to deep infection as endpoint. Changes in revision rate as a function of the year of operation were investigated.
Results Of the 97,344 primary THAs that met the inclusion criteria, 614 THAs had been revised due to deep infection (5-year survival 99.46%). Risk of revision due to deep infection increased throughout the period studied. Compared to the THAs implanted in 1987–1992, the risk of revision due to infection was 1.3 times higher (95%CI: 1.0–1.7) for those implanted in 1993–1997, 1.5 times (95% CI: 1.2–2.0) for those implanted in 1998–2002, and 3.0 times (95% CI: 2.2–4.0) for those implanted in 2003–2007. The most pronounced increase in risk of being revised due to deep infection was for the subgroup of uncemented THAs from 2003–2007, which had an increase of 5 times (95% CI: 2.6–11) compared to uncemented THAs from 1987–1992.
Interpretation The incidence of deep infection after THA increased during the period 1987–2007. Concomitant changes in confounding factors, however, complicate the interpretation of the results.
doi:10.3109/17453670903506658
PMCID: PMC2823304  PMID: 19995313
13.  Medical Comorbidity is Associated with Persistent Index Hip Pain after Primary THA 
Pain medicine (Malden, Mass.)  2013;14(8):10.1111/pme.12153.
Objective
To characterize whether medical comorbidity predicts persistent moderate-severe pain after total hip arthroplasty (THA)
Methods
We analyzed the prospectively collected data from the Mayo Clinic Total Joint Registry for patients who underwent primary or revision THA between 1993–2005. Using multivariable-adjusted logistic regression analyses, we examined whether certain medical comorbidities were associated with persistent moderate-severe hip pain 2- or 5-years after primary or revision THA. Odds ratios (OR), along with 95% confidence intervals (CI) and p-value are presented.
Results
The primary THA cohort consisted of 5,707 THAs and 3,289 THAs at 2- and 5-years, and revision THA, 2,687 and 1,627 THAs, respectively. In multivariable-adjusted logistic regression models, in the primary THA cohort, renal disease was associated with lower odds of moderate-severe hip pain (OR, 0.6; 95% CI, 0.3, 1.0) at 2-years. None of the comorbidities were significantly associated at 5-years. In the revision THA cohort, heart disease was significantly associated with higher risk (OR, 1.7; 95% CI, 1.1, 2.6) at 2-years and connective tissue disease with lower risk (OR, 0.5; 95% CI, 0.3, 0.9) of moderate-severe hip pain at 5-years follow-up.
Conclusion
This study identified new correlates of moderate-severe hip pain after primary or revision THA, a much-feared outcome of hip arthroplasty. Patients with these comorbidities should be informed regarding the increased risk or moderate-severe index hip pain, so that they can have a fully informed consent and realistic expectations.
doi:10.1111/pme.12153
PMCID: PMC3814009  PMID: 23742141
Pain; Function; functional limitation; Total hip replacement; primary; arthroplasty; joint replacement; outcomes; Patient-Reported Outcomes
14.  No influence of immigrant background on the outcome of total hip arthroplasty 
Acta Orthopaedica  2013;84(1):18-24.
Background and purpose
Total Hip Replacement (THA) is one of the most successful and cost-effective operations. Despite its benefits, marked ethnic differences in the utilization of THA are well documented. However, very little has been published on the influence of ethnicity on outcome. We investigate whether the outcome—in terms of reoperation within 2 years or revision up to 14 years after the primary operation—varies depending on ethnic background.
Methods
Records of total hip arthroplasties performed between 1992 and 2007 were retrieved from the Swedish Hip Arthropalsty Registry and integrated with data on ethnicity of patients from 2 demographical databases (i.e. Patient Register and Statistics Sweden). The first operated side in patients with THA recorded in the Swedish Hip Arthroplasty Register (SHAR) between 1992 and 2007 were generally included. We excluded patients with 1 Swedish and 1 non-Swedish parent and patients born abroad with 2 Swedish parents. After these exclusions 151,838 patients were left for analysis. There were 11,539 Swedish patients born outside Sweden. We used a Cox regression model including age, sex, diagnosis, type of fixation, whether or not there was comorbidity according to Elixhauser or not, marital status and educational level.
Results
The mean age was lowest in the group of patient coming from outside Europe including the former Soviet Union (61 years), and highest in the Swedish population (70 years). Before adjustment, for covariates, patients born in Europe outside the Nordic countries showed a lower risk to undergo early reoperation (HR = 0.73, 95% CI: 0.56–0.97), which increased after adjustment to (HR = 0.76, 95% CI: 0.58–1.01). Before adjustment, patients born in the Nordic countries outside Sweden and those born outside Europe (including the former Soviet Union) showed a higher risk to undergo revision than patients born in Sweden (HR = 1.14, 95% CI: 1.02–1.27; HR = 1.49, 95% CI: 1.2–1.9), but this difference disappeared after adjustment for covariates.
Conclusion
We did not find any certain differences in reoperation within 2 years, or revision within 14 years, between patients born in Sweden and immigrants. Further studies are needed to determine whether our observations are biased by the attitude of health providers regarding performance of these procedures, or by a reluctance of certain patient groups to seek medical attention should any complications requiring reoperation or revision occur.
doi:10.3109/17453674.2013.765640
PMCID: PMC3584597  PMID: 23343377
15.  Increased risk of revision in patients with non-traumatic femoral head necrosis 
Acta Orthopaedica  2014;85(1):11-17.
Background and purpose
Previous studies of patients who have undergone total hip arthroplasty (THA) due to femoral head necrosis (FHN) have shown an increased risk of revision compared to cases with primary osteoarthritis (POA), but recent studies have suggested that this procedure is not associated with poor outcome. We compared the risk of revision after operation with THA due to FHN or POA in the Nordic Arthroplasty Register Association (NARA) database including Denmark, Finland, Norway, and Sweden.
Patients and methods
427,806 THAs performed between 1995 and 2011 were included. The relative risk of revision for any reason, for aseptic loosening, dislocation, deep infection, and periprosthetic fracture was studied before and after adjustment for covariates using Cox regression models.
Results
416,217 hips with POA (mean age 69 (SD 10), 59% females) and 11,589 with FHN (mean age 65 (SD 16), 58% females) were registered. The mean follow-up was 6.3 (SD 4.3) years. After 2 years of observation, 1.7% in the POA group and 3.0% in the FHN group had been revised. The corresponding proportions after 16 years of observation were 4.2% and 6.1%, respectively. The 16-year survival in the 2 groups was 86% (95% CI: 86–86) and 77% (CI: 74–80). After adjusting for covariates, the relative risk (RR) of revision for any reason was higher in patients with FHN for both periods studied (up to 2 years: RR = 1.44, 95% CI: 1.34–1.54; p < 0.001; and 2–16 years: RR = 1.25, 1.14–1.38; p < 0.001).
Interpretation
Patients with FHN had an overall increased risk of revision. This increased risk persisted over the entire period of observation and covered more or less all of the 4 most common reasons for revision.
doi:10.3109/17453674.2013.874927
PMCID: PMC3940986  PMID: 24359026
16.  18 years of results with cemented primary hip prostheses in the Norwegian Arthroplasty Register 
Acta Orthopaedica  2009;80(4):402-412.
Background and purpose Few studies have compared the long-term survival of cemented primary total hip arthroplasties (THAs), and several prostheses have been used without adequate knowledge of their endurance. We studied long-term outcome based on data in the Norwegian Arthroplasty Register.
Patients and methods The 10 most used prosthesis brands in 62,305 primary Palacos or Simplex cemented THAs reported to the Register from 1987 through 2007 were included. Survival analyses with revision as endpoint (for any cause or for aseptic loosening) were performed using Kaplan-Meier and multiple Cox regression with time-dependent covariates. Revision rate ratios (RRs) were estimated for the follow-up intervals: 0–5, 6–10, and > 10 years.
Results 5 prosthesis brands (cup/stem combinations) (Charnley, Exeter, Titan, Spectron/ITH, Link IP/Lubinus SP; n = 24,728) were investigated with 0–20 year follow-up (inserted 1987–1997). After 18 years, 11% (95% CI: 10.6–12.1) were revised for any cause and 8.4% (7.7–9.1) for aseptic loosening. Beyond 10 years of follow-up, the Charnley cup had a lower revision rate due to aseptic loosening than Exeter (RR = 1.8) and Spectron (RR = 2.4) cups. For stems, beyond 10 years we did not find statistically significant differences comparing Charnley with Titan, ITH, and SP stems, but the Exeter stem had better results (RR = 0.5). 10 prosthesis brands (9 cups in combination with 6 stems; n = 37,577) were investigated with 0–10 years of follow-up (inserted from 1998 through 2007). The Charnley cup had a lower revision rate due to aseptic loosening than all cups except the IP. Beyond 5 years follow-up, the Reflection All-Poly cup had a 14 times higher revision rate. For stems, beyond 5 years the Spectron-EF (RR = 6.1) and Titan (RR = 5.5) stems had higher revision rates due to aseptic loosening than Charnley. The analyses also showed a marked improvement in Charnley results between the periods 1987–1997 and 1998–2007.
Interpretation We observed clinically important differences between cemented prosthesis brands and identified inferior results for previously largely undocumented prostheses, including the commonly used prosthesis combination Reflection All-Poly/Spectron-EF. The results were, however, satisfactory according to international standards.
doi:10.3109/17453670903161124
PMCID: PMC2823190  PMID: 19857178
17.  Hip prosthesis introduction and early revision risk 
Acta Orthopaedica  2013;84(1):25-31.
Background and purpose
Little is known about the effect of the learning curve for different types of total hip arthroplasties (THAs). We investigated the prostheses survival of THAs just after the implementation of a model new to the hospital, and compared these results with the results of THAs done when more than 100 implantations had been undertaken. In addition, we investigated whether differences exist between different types of femoral stems and acetabular cups at the early implementation phase.
Patients and methods
We used comprehensive registry data from all units (n = 76) that performed THAs for primary osteoarthritis in Finland between 1998 and 2007. Complete data including follow-up data to December 31, 2010 or until death were available for 33,819 patients (39,125 THAs). The stems and cups used were given order numbers in each hospital and classified into 5 groups: operations with order number (a) 1–15, (b) 16–30, (c) 31–50, (d) 51–100, and (e) > 100. We used Cox’s proportional hazards modeling for calculation of the adjusted hazard ratios for the risk of revision during the 3 years following the implementation of a new THA endoprosthesis type in the groups.
Results
Introduction of new endoprosthesis types was common, as more than 1 in 7 patients received a type that had been previously used in 15 or less operations. For the first 15 operations after a stem or cup type was introduced, there was an elevated risk of revision (hazard ratio (HR) = 1.3, 95% CI: 1.1–1.5). There were differences in the risk of early revision between stem and cup types at implementation.
Interpretation
The first 15 operations with a new stem or cup model had an increased risk of early revision surgery. Stems and cups differed in their early revision risk, particularly at the implementation phase. Thus, the risk of early revision at the implementation phase should be considered when a new type of THA is brought into use.
doi:10.3109/17453674.2013.771299
PMCID: PMC3584598  PMID: 23368748
18.  Total Hip Arthroplasty for the Sequelae of Legg-Calvé-Perthes Disease 
Background
The durability and risks associated with total hip arthroplasty (THA) for patients with a history of Legg-Calvé-Perthes disease (LCPD) are not well known.
Questions/purpose
We sought to (1) determine the survivorship of THAs performed for LCPD; (2) assess hip scores and complications associated with THA in this patient population; and (3) compare results between patients who had undergone surgery in childhood with patients who had conservative treatment.
Methods
We reviewed 99 primary THAs performed in 95 patients with a history of LCPD with minimum 2-year followup (mean ± SD, 8 ± 5 years). Mean age at THA was 48 ± 15 years.
Results
A total of 10 revisions were performed. Using revision for any reason as the end point, the 8-year survival rate was 90% (95% confidence interval [CI], 76%–96%) for cementless implants compared with 86% (95% CI, 57%–96%) for hybrid implants. The mean Harris hip score improved by 31 ± 16 (n = 76). Complications occurred in 16% of hips. The most common major complication was intraoperative fracture (eight femoral, one acetabular). Three patients developed sciatic nerve palsy after a mean lengthening of 2.2 ± 1 cm compared with a mean of 1.4 ± 1 cm in patients with intact sciatic nerve (p = 0.3).
Conclusions
Cementless THAs for the sequelae of LCPD demonstrate 90% survival from any revision at 8 years followup. THAs for the sequelae of LCPD can be complicated and technically difficult. Intraoperative fractures and nerve injuries are common. Care should be taken to avoid excessive limb lengthening.
Level of Evidence
Level IV, retrospective case series. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-013-3006-7
PMCID: PMC3734404  PMID: 23633183
19.  Improved Survival of Uncemented versus Cemented Femoral Stems in Patients Aged < 70 Years in a Community Total Joint Registry 
Background
Aseptic loosening of the femoral stem remains a significant reason for revision in total hip arthroplasty (THA). Although stem fixation methods have changed over time, there is relatively little evidence supporting cemented or uncemented stems as more durable constructs.
Questions/purposes
We examined whether there was a difference in survival to revision between cemented and uncemented THA stems (1) for any reason; (2) for aseptic loosening or loosening related to wear/osteolysis; (3) based on patient age groupings (as a proxy for patient activity level); and (4) based on procedural timeframe groupings between cemented and uncemented stems.
Methods
A total of 6498 primary cemented and uncemented THAs were registered in our community total joint replacement registry between 1991 and 2011. Analysis was performed to compare age, sex, procedural timeframe, and diagnosis for both groups. Our primary outcome was revision of the stem component for aseptic loosening or loosening secondary to wear/osteolysis. Analyses were done using Wilcoxon rank sum tests, Pearson’s chi-square tests, Kaplan Meier methods, and Cox regression.
Results
After adjusting for age, sex, primary diagnosis, and procedural timeframe as confounders, cemented femoral stem components were 1.63 times as likely as uncemented stems to be revised for any reason (p = 0.02) and 3.76 times as likely as uncemented stems to be revised for aseptic loosening or loosening related to wear/osteolysis (p < 0.001). When grouped by age, specifically in regard to revisions for aseptic loosening or loosening related to wear/osteolysis, uncemented stems had lower cumulative revision rates in patients aged < 70 years (p < 0.001) compared with cemented stems. There was a trend away from cemented fixation in our registry, which shifted from over 80% cemented stem use in 1996 to 3% in 2011.
Conclusions
We found that uncemented stems were associated with fewer revisions for aseptic loosening in patients < 70 years old, but when all reasons for revision were considered, neither group demonstrated superior survival. With a mean followup of 6.5 years, longer followup is needed to verify these results over time.
Level of Evidence
Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-013-3182-5
PMCID: PMC3792261  PMID: 23873609
20.  Revision Rates after Primary Hip and Knee Replacement in England between 2003 and 2006 
PLoS Medicine  2008;5(9):e179.
Background
Hip and knee replacement are some of the most frequently performed surgical procedures in the world. Resurfacing of the hip and unicondylar knee replacement are increasingly being used. There is relatively little evidence on their performance. To study performance of joint replacement in England, we investigated revision rates in the first 3 y after hip or knee replacement according to prosthesis type.
Methods and Findings
We linked records of the National Joint Registry for England and Wales and the Hospital Episode Statistics for patients with a primary hip or knee replacement in the National Health Service in England between April 2003 and September 2006. Hospital Episode Statistics records of succeeding admissions were used to identify revisions for any reason. 76,576 patients with a primary hip replacement and 80,697 with a primary knee replacement were included (51% of all primary hip and knee replacements done in the English National Health Service). In hip patients, 3-y revision rates were 0.9% (95% confidence interval [CI] 0.8%–1.1%) with cemented, 2.0% (1.7%–2.3%) with cementless, 1.5% (1.1%–2.0% CI) with “hybrid” prostheses, and 2.6% (2.1%–3.1%) with hip resurfacing (p < 0.0001). Revision rates after hip resurfacing were increased especially in women. In knee patients, 3-y revision rates were 1.4% (1.2%–1.5% CI) with cemented, 1.5% (1.1%–2.1% CI) with cementless, and 2.8% (1.8%–4.5% CI) with unicondylar prostheses (p < 0.0001). Revision rates after knee replacement strongly decreased with age.
Interpretation
Overall, about one in 75 patients needed a revision of their prosthesis within 3 y. On the basis of our data, consideration should be given to using hip resurfacing only in male patients and unicondylar knee replacement only in elderly patients.
Jan van der Meulen and colleagues show that about one in 75 patients with a primary hip or knee replacement needed a revision of their prosthesis within 3 years.
Editors' Summary
Background.
Though records show attempts to replace a hip date back to 1891, it was not till the 1960s before total hip replacements were successfully performed, and the 1970s before total knee replacements were carried out. These procedures are some of the most frequently performed surgical operations, with a total of 160,00 total hip and knee replacement procedures carried out in England and Wales and about half a million in the US in 2006. Hip and knee replacements are most commonly used as a treatment for severe arthritis once other approaches, such as pain relief medications, have failed. A total hip replacement involves replacing the head of the femur (the thigh bone) with an artificial component, typically metal; the socket into which the new femur head will insert is also replaced with artificial components. In an alternative procedure, resurfacing, rather than replacing the entire joint, the diseased surfaces are replaced with metal components. This procedure may be better suited to patients with less severe disease, and is also thought to result in quicker recovery. The techniques for hip and knee replacement can also be divided into those where a cement is used to position the metal implant into the bone (cemented) versus those where cement is not used (cementless).
Why Was This Study Done?
To date, little evidence has been available to compare patient outcomes following hip or knee replacement with the many different types of techniques and prostheses available. National registries have been established in a number of countries to try to collect data in order to build the evidence base for evaluating different types of prosthesis. Specifically, it is important to find out if there are any important differences in revision rates (how often the hip replacement has to be re-done) following surgery using the different techniques. In England and Wales, the National Joint Registry (NJR) has collected data on patient characteristics, types of prostheses implanted, and the type of surgical procedures used, since its initiation in April 2003.
What Did the Researchers Do and Find?
The researchers linked the records of the NJR and the Hospital Episode Statistics (HES) for patients treated by the NHS in England who had undergone a primary hip and knee replacement between April 2003 and September 2006. The HES database contains records of all admissions to NHS hospitals in England, and allowed the researchers to more accurately identify revisions of procedures that were done on patients in the NJR database.
They identified 327,557 primary hip or knee replacement procedures performed during that time period, but only 167,076 could be linked between the two databases.
76,576 patients in the linked database had undergone a primary hip replacement. The overall revision rate was 1.4% (95% confidence interval [CI] 1.2%–1.5%) at 3 years, with the lowest revision rates experienced by patients who had cemented prostheses. Women were found to have higher revision rates after hip resurfacing, and the revision rate was about twice as high in patients who had had a hip replacement for other indications than osteoarthritis. A patient's age did not appear to affect revision rates after hip surgery.
80,697 patients in the linked database had undergone a primary knee replacement. The overall revision rate was 1.4% (95% CI 1.3%–1.6%) at three years, again with the lowest rates of replacement experienced by patients who had cemented prostheses. Revision rates after knee replacement strongly decreased with age.
What Do These Findings Mean?
Overall, about one in 75 patients required a revision of their joint replacement, which is considered low, and cemented hip or knee prosthesis had the lowest revision rates. Post hip replacement, the highest revision rate was in patients who had undergone hip resurfacing, especially women. Following knee replacement, the highest revision rate was in patients who had undergone unicondylar prosthesis. However, in this study patients were only followed up for three years after the initial knee replacement, and it's possible that different patterns regarding the success of these differing techniques may emerge after longer follow-up. Importantly, this study was entirely observational, and data were collected from patients who had been managed according to routine clinical practice (rather than being randomly assigned to different procedures). Substantial differences in the age and clinical characteristics of patients receiving the different procedures were seen. As a result, it's not possible to directly draw conclusions on the relative benefits or harms of the different procedures, but this study provides important benchmark data with which to evaluate future performance of different procedures and types of implant.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0050179.
The website of the British Orthopaedic Association contains information for patients and surgeons
The website of the National Institute for Health and Clinical Excellence contains guidance on hip prostheses
Information is available from the US National Institutes of Health (Medline) on hip replacement, including interactive tutorials and information about rehabilitation and recovery
Medline also provides similar resources for knee replacement
The NHS provides information for patients on hip and knee replacement, including questions patients might ask, real stories, and useful links
The National Joint Registry provides general information about joint replacement, as well as allowing users to download statistics on the data it has collected on the numbers of procedures carried out in the UK
doi:10.1371/journal.pmed.0050179
PMCID: PMC2528048  PMID: 18767900
21.  Eleven Year Results of Total Hip Arthroplasty in Patients with Secondary Osteoarthritis Due to Slipped Capital Femoral Epiphysis 
Background:
Total hip arthroplasty (THA) in patients with a history of Slipped Capital Femoral Epiphysis (SCFE), is typically indicated to address the consequent deformity of the proximal femur and/or acetabulum. It can be a challenging procedure for the orthopaedic surgeon. Previous studies have focused on prevention of osteoarthritis post-SCFE. However, there is a paucity of data on the outcomes of total hip arthroplasty in patients with osteoarthritis secondary to SCFE. This study was performed to assess the mid-term results of total hip arthroplasty in this patient cohort.
Materials and Methods:
All patients with secondary osteoarthritis due to slipped capital femoral epiphysis, treated with total hip arthroplasty between 1987 and 2005, were included in this retrospective study (n=30). Thirty patients (17 male, 13 female) met the inclusion criteria with one patient lost to follow-up and one unrelated death one year before follow up examination, thereby leaving 28 patients (32 hips) eligible for the study with a mean follow-up time period of 11.2 years. The Harris Hip Score (HHS) and MOS 36 short form health survey (SF36) were determined preoperatively and at most recent follow-up for all patients. Complications were also noted for all cases.
Results:
The mean Harris Hip Score increased significantly from 47 (32-59; SD=8.3) to 92.3 (65-100; SD=8.2) (p<0.0001). The SF-36 health survey showed an improvement of quality-of-life in all sub-scales. Overall, revision surgery was required in six cases (19 %). Aseptic loosening, leading to implant removal, was noted in five cases. A single-stage revision to address infection was performed in one case. The cumulative survival rate at latest follow-up was 81 %. No other complications were encountered during the study.
Conclusions:
Despite a higher failure rate, compared to total hip arthroplasty in the treatment of primary osteoarthritis, total hip arthroplasty can be considered a feasible option for patients with secondary osteoarthritis of the hip due to slipped capital femoral epiphysis. The current study demonstrates good outcomes in patients treated with a cementless column-preserving prosthesis, which is of particular relevance for this young patient cohort. However, further clinical prospective randomized studies are warranted to provide more definitive evidence.
doi:10.2174/1874325001307010158
PMCID: PMC3664464  PMID: 23730379
Total hip arthroplasty; slipped capital femoral epiphysis.
22.  The risk of revision due to dislocation after total hip arthroplasty depends on surgical approach, femoral head size, sex, and primary diagnosis 
Acta Orthopaedica  2012;83(5):442-448.
Background and purpose
The effects of patient-related and technical factors on the risk of revision due to dislocation after primary total hip arthroplasty (THA) are only partly understood. We hypothesized that increasing the femoral head size can reduce this risk, that the lateral surgical approach is associated with a lower risk than the posterior and minimally invasive approaches, and that gender and diagnosis influence the risk of revision due to dislocation.
Patients and methods
Data on 78,098 THAs in 61,743 patients performed between 2005 and 2010 were extracted from the Swedish Hip Arthroplasty Register. Inclusion criteria were a head size of 22, 28, 32, or 36 mm, or the use of a dual-mobility cup. The covariates age, sex, primary diagnosis, type of surgical approach, and head size were entered into Cox proportional hazards models in order to calculate the adjusted relative risk (RR) of revision due to dislocation, with 95% confidence intervals (CI).
Results
After a mean follow-up of 2.7 (0–6) years, 399 hips (0.5%) had been revised due to dislocation. The use of 22-mm femoral heads resulted in a higher risk of revision than the use of 28-mm heads (RR = 2.0, CI: 1.2–3.3). Only 1 of 287 dual-mobility cups had been revised due to dislocation. Compared with the direct lateral approach, minimally invasive approaches were associated with a higher risk of revision due to dislocation (RR = 4.2, CI: 2.3–7.7), as were posterior approaches (RR = 1.3, CI: 1.1–1.7). An increased risk of revision due to dislocation was found for the diagnoses femoral neck fracture (RR = 3.9, CI: 3.1–5.0) and osteonecrosis of the femoral head (RR = 3.7, CI: 2.5–5.5), whereas women were at lower risk than men (RR = 0.8, CI: 0.7–1.0). Restriction of the analysis to the first 6 months after the index procedure gave similar risk estimates.
Interpretation
Patients with femoral neck fracture or osteonecrosis of the femoral head are at higher risk of dislocation. Use of the minimally invasive and posterior approaches also increases this risk, and we raise the question of whether patients belonging to risk groups should be operated using lateral approaches. The use of femoral head diameters above 28 mm or of dual-mobility cups reduced this risk in a clinically relevant manner, but this observation was not statistically significant.
doi:10.3109/17453674.2012.733919
PMCID: PMC3488169  PMID: 23039167
23.  Effects of hydroxyapatite coating on survival of an uncemented femoral stem 
Acta Orthopaedica  2011;82(4):399-404.
Background and purpose
Hydroxyapatite (HA) is widely used as a coating for uncemented total hip arthroplasty components. This has been suggested to improve implant ingrowth and long-term stability. However, the evidence behind the use of HA coating on femoral stems is ambiguous. We investigated survival of an uncemented, tapered titanium femoral stem that was available either with or without HA coating (Bi-Metric).
Patients and methods
The stem had been used in 4,772 total hip arthroplasties (THAs) in 4,169 patients registered in the Swedish Hip Arthroplasty Register between 1992 and 2009. 59% of the stems investigated were coated with HA and 41% were uncoated. Kaplan-Meier survival analysis and a Cox regression model with adjustment for age, sex, primary diagnosis, and the type of cup fixation were used to calculate survival rates and adjusted risk ratios (RRs) of the risk of revision for various reasons.
Results
The 10-year survival rates of the HA-coated version and the uncoated version were about equal when we used revision for any reason as the endpoint: 98% (95% CI: 98–99) and 98% (CI: 97–99), respectively. A Cox regression model adjusting for the covariates mentioned above showed that the presence of HA coating did not have any influence on the risk of stem revision for any reason (RR = 1.0, 95% CI: 0.6–1.6) or due to aseptic loosening (RR = 0.5, CI: 0.2–1.5). There was no effect of HA coating on the risk of stem revision due to infection, dislocation, or fracture.
Interpretation
The uncemented Bi-Metric stem showed excellent 10-year survival. Our findings do not support the use of HA coating on this stem to enhance implant survival.
doi:10.3109/17453674.2011.597699
PMCID: PMC3237027  PMID: 21751858
24.  Hip resurfacing arthroplasty: short-term survivorship of 4,401 hips from the Finnish Arthroplasty Register 
Acta Orthopaedica  2012;83(3):207-213.
Background and purpose
Population-based registry data from the Nordic Arthroplasty Register Association (NARA) and from the National Joint Register of England and Wales have revealed that the outcome after hip resurfacing arthroplasty (HRA) is inferior to that of conventional total hip arthroplasty (THA). We analyzed the short-term survival of 4,401 HRAs in the Finnish Arthroplasty Register.
Methods
We compared the revision risk of the 4,401 HRAs from the Register to that of 48,409 THAs performed during the same time period. The median follow-up time was 3.5 (0–9) years for HRAs and 3.9 (0–9) years for THAs.
Results
There was no statistically significant difference in revision risk between HRAs and THAs (RR = 0.93, 95% CI: 0.78–1.10). Female patients had about double the revision risk of male patients (RR = 2.0, CI: 1.4–2.7). Hospitals that had performed 100 or more HRA procedures had a lower revision risk than those with less than 100 HRAs (RR = 0.6, CI: 0.4–0.9). Articular Surface Replacement (ASR, DePuy) had inferior outcome with higher revision risk than the Birmingham Hip Resurfacing implant (BHR, Smith & Nephew), the reference implant (RR = 1.8, CI: 1.2–2.7).
Interpretation
We found that HRA had comparable short-term survivorship to THA at a nationwide level. Implant design had an influence on revision rates. ASR had higher revision risk. Low hospital procedure volume worsened the outcome of HRA. Female patients had twice the revision risk of male patients.
doi:10.3109/17453674.2012.693016
PMCID: PMC3369143  PMID: 22616745
25.  Survival of uncemented acetabular monoblock cups 
Acta Orthopaedica  2012;83(3):214-219.
Background and purpose
Monoblock acetabular cups represent a subtype of uncemented cups with the polyethylene liner molded into a metal shell, thus eliminating—or at least minimizing—potential backside wear. We hypothesized that the use of mono​block cups could reduce the incidence of osteolysis and aseptic loosening, and thus improve survival compared to modular designs.
Patients and methods
We identified all 210 primary total hip arthroplasty (THA) procedures in the Swedish Hip Arthroplasty Register that used uncemented monoblock cups during the period 1999–2010. Kaplan-Meier and Cox regression analyses with adjustment for age, sex, and other variables were used to calculate survival rates and adjusted hazard ratios (HRs) of the revision risk for any reason. 1,130 modular cups, inserted during the same time period, were used as a control group.
Results
There was a nearly equal sex distribution in both groups. Median age at the index operation was 47 years in the monoblock group and 56 years in the control group (p < 0.001). The cumulative 5-year survival with any revision as the endpoint was 95% (95% CI: 91–98) for monoblock cups and 97% (CI: 96–98) for modular cups (p = 0.6). The adjusted HR for revision of monoblock cups compared to modular cups was 2 (CI: 0.8–6; p = 0.1). The use of 28-mm prosthesis heads rather than 22-mm heads reduced the risk of cup revision (HR = 0.2, CI: 0.1–0.5; p = 0.001).
Interpretation
Both cups showed good medium-term survival rates. There was no statistically significant difference in revision risk between the cup designs. Further review of the current patient population is warranted to determine the long-term durability and risk of revision of monoblock cup designs.
doi:10.3109/17453674.2012.688726
PMCID: PMC3369144  PMID: 22574820

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