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1.  Method of Fixation Does Not Influence the Overall Risk of Rerevision in First-time Cup Revisions 
Background
During the last two decades, uncemented fixation has been increasingly preferred worldwide during cup revision surgery. In Sweden, the number of uncemented cup revisions has been increasing during the last decade. However, it is unclear whether the risk of rerevision differs between cemented and uncemented cups.
Question/purposes
We determined (1) the risk of rerevision after cemented and uncemented fixation; (2) the influence of concomitant stem revision on the risk of rerevision of the cup; (3) the difference in risk of rerevision of an uncemented cup revision compared with liner revision only; and (4) whether the surgical incision influenced the risk of rerevision.
Methods
Between 1979 and 2010, 19,342 first-time cup revisions were reported to the Swedish Hip Arthroplasty Register. From these, 749 were excluded (hip resurfacing, cases with tumor diagnoses, and missing data) leaving 18,593 (73% cemented) for further analysis. We used a Cox regression model adjusted for age, sex, primary diagnosis, method of fixation, concomitant stem revision, and cemented/uncemented fixation to assess risk of rerevision.
Results
The relative risk for rerevision for any reason did not differ between cemented and uncemented fixation (relative risk [RR], 0.94). If the stem was not revised at index revision, the risk of further cup revision increased twofold (RR, 1.91). Liner revisions were associated with a 70% increased risk for rerevision of the cup as a result of any reason and especially because of dislocation (RR, 2.94). The surgical incision did not influence the overall risk for rerevision (direct lateral/posterolateral: RR, 1.02) or the risk of rerevision resulting from dislocation (RR, 0.91).
Conclusions
We found no difference in the overall risk of rerevision between cemented and uncemented fixation. Liner exchange had a higher risk for rerevision when compared with cases being rerevised with a new uncemented cup.
Level of Evidence
Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.
doi:10.1007/s11999-013-2872-3
PMCID: PMC3825907  PMID: 23440618
2.  Validation of reoperations due to infection in the Swedish Hip Arthroplasty Register 
Background
Complete or almost complete recording of reoperations is essential to enable a correct interpretation of data in arthroplasty registers. The completeness of recordings due to infection is unknown in the Swedish Hip Arthroplasty Register (SHAR). We therefore used a combination of data from the Swedish Prescribed Drug Register (SPDR) and studies of medical records to validate the data of reoperations due to infection in the SHAR.
Methods
All patients registered for a primary Total Hip Replacement (THR) in the SHAR between July 1, 2005 and December 31, 2008 were selected for the study (45,531 patients with 49,219 THRs) and were matched with the SPDR. All patients with a minimum of 4 weeks of continuous outpatient antibiotic treatment within 2 years after their primary THR (1,989 patients, with 2,219 THRs) were selected for a medical records review to find the THRs reoperated due to infection.
Results
599 (1.3%) of the THRs had been reoperated within 2 years after the index operation and in 47.4% of these the prosthesis had been revised or extracted. 400 of the THRs were registered for a reoperation in the SHAR resulting in a completeness of 67%.
Conclusions
The completeness of registration due to early infection after THR questions whether the SHAR reoperation data can be used in order to evaluate changes in postoperative infection rates.
doi:10.1186/1471-2474-15-384
PMCID: PMC4247680  PMID: 25410189
Arthroplasty Register; Validity; Completeness; Hip replacement; Reoperation; Infection
3.  Person-centred care compared with standardized care for patients undergoing total hip arthroplasty—a quasi-experimental study 
Background
A common approach to decrease length of stay has been to standardize patient care, for example, by implementing clinical care pathways or creating fast-track organizations. In a recent national report, it was found that Sweden’s healthcare system often fails to anticipate and respond to patients as individuals with particular needs, values and preferences. We compared a standardized care approach to one of person-centred care for patients undergoing total hip replacement surgery.
Methods
A control group (n =138) was consecutively recruited between 20th September 2010 and 1st March 2011 and an intervention group (n =128) between 12th December 2011 and 12th November 2012, both scheduled for total hip replacement. The primary outcome measures were length of stay and physical function at both discharge and 3 months later.
Results
The mean length of stay in the control group was 7 days (SD 5.0) compared to 5.3 days in the intervention group (SD 2.2). Physical functional performance, as assessed using activities of daily living, was similar at baseline for both groups. At discharge, 84% in the control group had regained activities of daily living level A vs. 72% in the intervention group. At 3 months after surgery, 88% in the control group had regained their independence vs. 92.5% in the person-centred care group.
Conclusions
Focusing attention on patients as people and including them as partners in healthcare decision-making can result in shorter length of stay. The present study shows that the patients should be the focus and they should be involved as partners.
doi:10.1186/s13018-014-0095-2
PMCID: PMC4222396  PMID: 25359278
Person-centred care; Person-centered care; General self-efficacy; Tampa scale of Kinesiophobia; ASA classification
4.  Different patient-reported outcomes in immigrants and patients born in Sweden 
Acta Orthopaedica  2014;85(3):221-228.
Background and purpose
Some patients have persistent symptoms after total hip arthroplsty (THA). We investigated whether the proportions of inferior clinical results after total hip arthroplasty—according to the 5 dimensions in the EQ-5D form, and pain and satisfaction according to a visual analog scale (VAS)—are the same in immigrants to Sweden as observed in those born in Sweden.
Methods
Records of total hip arthroplasties performed between 1992 and 2007 were retrieved from the Swedish Hip Arthroplasty Register (SHAR) and cross-matched with data from the National Board of Health and Welfare and also Statistics, Sweden. 18,791 operations (1,451 in immigrants, 7.7%) were eligible for analysis. Logistic and linear regression models including age, sex, diagnosis, type of fixation, comorbidity, surgical approach, marital status, and education level were analyzed. Outcomes were the 5 dimensions in EQ-5D, EQ-VAS, VAS pain, and VAS satisfaction. Preoperative data and data from 1 year postoperatively were studied.
Results
Preoperatively (and after inclusion of covariates in the regression models), all immigrant groups had more negative interference concerning self-care. Immigrants from the Nordic countries outside Sweden and Europe tended to have more problems with their usual activities and patients from Europe and outside Europe more often reported problems with anxiety/depression. Patients born abroad showed an overall tendency to report more pain on the VAS than patients born in Sweden.
After the operation, the immigrant groups reported more problems in all the EQ-5D dimensions. After adjustment for covariates including the preoperative baseline value, most of these differences remained except for pain/discomfort and—concerning immigrants from the Nordic countries—also anxiety/depression. After the operation, pain according to VAS had decreased substantially in all groups. The immigrant groups indicated more pain than those born in Sweden, both before and after adjustment for covariates.
Conclusion
The frequency of patients who reported moderate to severe problems, both before and 1 year after the operation, differed for most of the dimensions in EQ-5D between patients born in Sweden and those born outside Sweden.
doi:10.3109/17453674.2014.919556
PMCID: PMC4062786  PMID: 24803309
5.  Countrywise results of total hip replacement 
Acta Orthopaedica  2014;85(2):107-116.
Background and purpose
An earlier Nordic Arthroplasty Register Association (NARA) report on 280,201 total hip replacements (THRs) based on data from 1995–2006, from Sweden, Norway, and Denmark, was published in 2009. The present study assessed THR survival according to country, based on the NARA database with the Finnish data included.
Material and methods
438,733 THRs performed during the period 1995–2011 in Sweden, Denmark, Norway, and Finland were included. Kaplan-Meier survival analysis was used to calculate survival probabilities with 95% confidence interval (CI). Cox multiple regression, with adjustment for age, sex, and diagnosis, was used to analyze implant survival with revision for any reason as endpoint.
Results
The 15-year survival, with any revision as an endpoint, for all THRs was 86% (CI: 85.7–86.9) in Denmark, 88% (CI: 87.6–88.3) in Sweden, 87% (CI: 86.4–87.4) in Norway, and 84% (CI: 82.9–84.1) in Finland. Revision risk for all THRs was less in Sweden than in the 3 other countries during the first 5 years. However, revision risk for uncemented THR was less in Denmark than in Sweden during the sixth (HR = 0.53, CI: 0.34–0.82), seventh (HR = 0.60, CI: 0.37–0.97), and ninth (HR = 0.59, CI: 0.36–0.98) year of follow-up.
Interpretation
The differences in THR survival rates were considerable, with inferior results in Finland. Brand-level comparison of THRs in Nordic countries will be required.
doi:10.3109/17453674.2014.893498
PMCID: PMC3967250  PMID: 24650019
6.  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
7.  Posterior approach and uncemented stems increases the risk of reoperation after hemiarthroplasties in elderly hip fracture patients 
Acta Orthopaedica  2014;85(1):18-25.
Background
Hemiarthroplasties are performed in great numbers worldwide but are seldom registered on a national basis. Our aim was to identify risk factors for reoperation after fracture-related hemiarthroplasty in Norway and Sweden.
Material and methods
A common dataset was created based on the Norwegian Hip Fracture Register and the Swedish Hip Arthroplasty Register. 33,205 hip fractures in individuals > 60 years of age treated with modular hemiarthroplasties were reported for the period 2005–2010. Cox regression analyses based on reoperations were performed (covariates: age group, sex, type of stem and implant head, surgical approach, and hospital volume).
Results
1,164 patients (3.5%) were reoperated during a mean follow-up of 2.7 (SD 1.7) years. In patients over 85 years, an increased risk of reoperation was found for uncemented stems (HR = 2.2, 95% CI: 1.7–2.8), bipolar heads (HR = 1.4, CI: 1.2–1.8), posterior approach (HR = 1.4, CI: 1.2–1.8) and male sex (HR = 1.3, CI: 1.0–1.6). For patients aged 75–85 years, uncemented stems (HR = 1.6, 95% CI: 1.2–2.0) and men (HR = 1.3, CI: 1.1–1.6) carried an increased risk. Increased risk of reoperation due to infection was found for patients aged < 75 years (HR = 1.5, CI: 1.1–2.0) and for uncemented stems. For open surgery due to dislocation, the strongest risk factor was a posterior approach (HR = 2.2, CI: 1.8–2.6). Uncemented stems in particular (HR = 3.6, CI: 2.4–5.3) and male sex increased the risk of periprosthetic fracture surgery.
Interpretation
Cemented stems and a direct lateral transgluteal approach reduced the risk of reoperation after hip fractures treated with hemiarthroplasty in patients over 75 years. Men and younger patients had a higher risk of reoperation. For the age group 60–74 years, there were no such differences in risk in this material.
doi:10.3109/17453674.2014.885356
PMCID: PMC3940987  PMID: 24460108
8.  Highly Crosslinked Polyethylene Does Not Reduce Aseptic Loosening in Cemented THA 10-year Findings of a Randomized Study 
Background
Polyethylene (PE) wear particles are believed to cause aseptic loosening and thereby impair function in hip arthroplasty. Highly crosslinked polyethylene (XLPE) has low short- and medium-term wear rates. However, the long-term wear characteristics are unknown and it is unclear whether reduced wear particle burden improves function and survival of cemented hip arthroplasty.
Questions/purposes
We asked whether XLPE wear rates remain low up to 10 years and whether this leads to improved implant fixation, periprosthetic bone quality, and clinical function compared to conventional PE.
Methods
We randomized 60 patients (61 hips) to receive either PE or XLPE cemented cups combined with a cemented stem. At 10 years postoperatively, 51 patients (52 hips) were evaluated for polyethylene wear and component migration estimation by radiostereometry, for radiolucent lines, bone densitometry, and Harris hip and pain scores. Revisions were recorded.
Results
XLPE cups had a lower mean three-dimensional wear rate between 2 and 10 years compared to conventional PE hips: 0.005 mm/year versus 0.056 mm/year. We found no differences in cup migration, bone mineral density, radiolucencies, functional scores, and revision rate. There was a trend toward improved stem fixation in the XLPE group. The overall stem failure rate was comparably high, without influencing wear rate in XLPE hips.
Conclusions
XLPE displayed a low wear rate up to 10 years when used in cemented THA, but we found no clear benefits in any other parameters. Further research is needed to determine whether cemented THA designs with XLPE are less prone to stem loosening.
Level of Evidence
Level I, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.
Electronic supplementary material
The online version of this article (doi:10.1007/s11999-012-2400-x) contains supplementary material, which is available to authorized users.
doi:10.1007/s11999-012-2400-x
PMCID: PMC3462851  PMID: 22669546
9.  Quantitative proteomics reveals regulatory differences in the chondrocyte secretome from human medial and lateral femoral condyles in osteoarthritic patients 
Proteome Science  2013;11:43.
Background
Osteoarthritis (OA) is a destructive joint disease and there are no known biomarkers available for an early diagnosis. To identify potential disease biomarkers and gain further insight into the disease mechanisms of OA we applied quantitative proteomics with SILAC technology on the secretomes from chondrocytes of OA knees, designated as high Mankin (HM) scored secretome. A quantitative comparison was made between the secretomes of the medial and lateral femur condyle chondrocytes in the same knee since the medial femur condyle is usually more affected in OA than the lateral condyle, which was confirmed by Mankin scoring. The medial/lateral comparison was also made on the secretomes from chondrocytes taken from one individual with no clinically apparent joint-disease, designated as low Mankin (LM) scored secretome.
Results
We identified 825 proteins in the HM secretome and 69 of these showed differential expression when comparing the medial and lateral femoral compartment. The LM scored femoral condyle showed early signs of OA in the medial compartment as assessed by Mankin score. We here report the identification and relative quantification of several proteins of interest for the OA disease mechanism e.g. CYTL1, DMD and STAB1 together with putative early disease markers e.g. TIMP1, PPP2CA and B2M.
Conclusions
The present study reveals differences in protein abundance between medial/lateral femur condyles in OA patients. These regulatory differences expand the knowledge regarding OA disease markers and mechanisms.
doi:10.1186/1477-5956-11-43
PMCID: PMC3851248  PMID: 24090399
Secretome; SILAC; Chondrocyte; Osteoarthritis; Proteomics
10.  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
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
13.  The type of surgical approach influences the risk of revision in total hip arthroplasty 
Acta Orthopaedica  2012;83(6):559-565.
Background and purpose
The most common surgical approaches in total hip arthroplasty in Sweden are the posterior and the anterolateral transgluteal approach. Currently, however, there is insufficient evidence to prefer one over the other regarding risk of subsequent surgery.
Patients and methods
We searched the Swedish Hip Arthroplasty Register between the years 1992 and 2009 to compare the posterior and anterolateral transgluteal approach regarding risk of revision in the 3 most common all-cemented hip prosthesis designs in Sweden. 90,662 total hip replacements met the inclusion criteria. We used Cox regression analysis for estimation of prosthesis survival and relative risk of revision due to dislocation, infection, or aseptic loosening.
Results
Our results show that for the Lubinus SPII prosthesis and the Spectron EF Primary prosthesis, the anterolateral transgluteal approach gave an increased risk of revision due to aseptic loosening (relative risk (RR) = 1.3, 95% CI: 1.0–1.6 and RR = 1.6, CI: 1.0–2.5) but a reduced risk of revision due to dislocation (RR = 0.7, CI: 0.5–0.8 and RR = 0.3, CI: 0.1–0.4). For the Exeter Polished prosthesis, the surgical approach did not affect the outcome for dislocation or aseptic loosening. The surgical approach had no influence on the risk of revision due to infection in any of these designs.
Interpretation
This observational study shows that the surgical approach affected the risk of revision due to aseptic loosening and dislocation for 2 of the most commonly used cemented implants in Sweden. Further studies are needed to determine whether these results are generalizable to other implants and to uncemented fixation.
doi:10.3109/17453674.2012.742394
PMCID: PMC3555460  PMID: 23116440
14.  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
15.  Low revision rate after total hip arthroplasty in patients with pediatric hip diseases 
Acta Orthopaedica  2012;83(5):436-441.
Background
The results of primary total hip arthroplasties (THAs) after pediatric hip diseases such as developmental dysplasia of the hip (DDH), slipped capital femoral epiphysis (SCFE), or Perthes’ disease have been reported to be inferior to the results after primary osteoarthritis of the hip (OA).
Materials and methods
We compared the survival of primary THAs performed during the period 1995–2009 due to previous DDH, SCFE, Perthes’ disease, or primary OA, using merged individual-based data from the Danish, Norwegian, and Swedish arthroplasty registers, called the Nordic Arthroplasty Register Association (NARA). Cox multiple regression, with adjustment for age, sex, and type of fixation of the prosthesis was used to calculate the survival of the prostheses and the relative revision risks.
Results
370,630 primary THAs were reported to these national registers for 1995–2009. Of these, 14,403 THAs (3.9%) were operated due to pediatric hip diseases (3.1% for Denmark, 8.8% for Norway, and 1.9% for Sweden) and 288,435 THAs (77.8%) were operated due to OA. Unadjusted 10-year Kaplan-Meier survival of THAs after pediatric hip diseases (94.7% survival) was inferior to that after OA (96.6% survival). Consequently, an increased risk of revision for hips with a previous pediatric hip disease was seen (risk ratio (RR) 1.4, 95% CI: 1.3–1.5). However, after adjustment for differences in sex and age of the patients, and in fixation of the prostheses, no difference in survival was found (93.6% after pediatric hip diseases and 93.8% after OA) (RR 1.0, CI: 1.0–1.1). Nevertheless, during the first 6 postoperative months more revisions were reported for THAs secondary to pediatric hip diseases (RR 1.2, CI: 1.0–1.5), mainly due to there being more revisions for dislocations (RR 1.8, CI: 1.4–2.3). Comparison between the different diagnosis groups showed that the overall risk of revision after DDH was higher than after OA (RR 1.1, CI: 1.0–1.2), whereas the combined group Perthes’ disease/SCFE did not have a significantly different risk of revision to that of OA (RR 0.9, CI: 0.7–1.0), but had a lower risk than after DDH (RR 0.8, CI: 0.7–1.0).
Interpretation
After adjustment for differences in age, sex, and type of fixation of the prosthesis, no difference in risk of revision was found for primary THAs performed due to pediatric hip diseases and those performed due to primary OA.
doi:10.3109/17453674.2012.736171
PMCID: PMC3488168  PMID: 23043269
16.  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
17.  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
18.  Higher risk of reoperation for bipolar and uncemented hemiarthroplasty 
Acta Orthopaedica  2012;83(5):459-466.
Background and purpose
Hemiarthroplasty as treatment for femoral neck fractures has increased markedly in Sweden during the last decade. In this prospective observational study, we wanted to identify risk factors for reoperation in modular hemiarthroplasties and to evaluate mortality in this patient group.
Patients and methods
We assessed 23,509 procedures from the Swedish Hip Arthroplasty Register using the most common surgical approaches with modular uni- or bipolar hemiarthroplasties related to fractures in the period 2005–2010. Completeness of registration (individual procedures) was 89–96%. The median age was 85 years and the median follow-up time was 18 months.
Results
3.8% underwent reoperation (any further hip surgery), most often because of implant dislocation or infection. The risk of reoperation (Cox regression) was higher for uncemented stems (hazard ratio (HR) = 1.5), mainly because of periprosthetic femoral fractures. Bipolar implants had a higher risk of reoperation irrespective of cause (HR = 1.3), because of dislocation (1.4), because of infection (1.3), and because of periprosthetic fracture (1.7). The risk of reoperation due to acetabular erosion was lower (0.30) than for unipolar implants, but reoperation for this complication was rare (1.7 per thousand). Procedures resulting from failed internal fixation had a more than doubled risk; the risk was also higher for males and for younger patients. The surgical approach had no influence on the risk of reoperation generally, but the anterolateral transgluteal approach was associated with a lower risk of reoperation due to dislocation (HR = 0.7). At 1 year, the mortality was 24%. Men had a higher risk of death than women (1.8).
Interpretation
We recommend cemented hemiarthroplasties and the anterolateral transgluteal approach. We also suggest that unipolar implants should be used, at least for the oldest and frailest patients.
doi:10.3109/17453674.2012.727076
PMCID: PMC3488171  PMID: 22998529
19.  Salvage of failed trochanteric and subtrochanteric fractures using a distally fixed, modular, uncemented hip revision stem 
Acta Orthopaedica  2012;83(5):488-492.
Background and purpose
Treatment options for failed internal fixation of hip fractures include prosthetic replacement. We evaluated survival, complications, and radiographic outcome in 30 patients who were operated with a specific modular, uncemented hip reconstruction prosthesis as a salvage procedure after failed treatment of trochanteric and subtrochanteric fractures.
Patients and methods
We used data from the Swedish Hip Arthroplasty Register and journal files to analyze complications and survival. Initially, a high proportion of trochanteric fractures (7/10) were classified as unstable and 12 of 20 subtrochanteric fractures had an extension through the greater trochanter. Modes of failure after primary internal fixation were cutout (n = 12), migration of the femoral neck screw (n = 9), and other (n = 9).
Results
Mean age at the index operation with the modular prosthesis was 77 (52–93) years and the mean follow-up was 4 (1–9) years. Union of the remaining fracture fragments was observed in 26 hips, restoration of proximal bone defects in 16 hips, and bone ingrowth of the stem in 25 hips. Subsidence was evident in 4 cases. 1 patient was revised by component exchange because of recurrent dislocation, and another 6 patients were reoperated: 5 because of deep infections and 1 because of periprosthetic fracture. The cumulative 3-year survival for revision was 96% (95% CI: 89–100) and for any reoperation it was 83% (68–93).
Interpretation
The modular stem allowed fixation distal to the fracture system. Radiographic outcome was good. The rate of complications, however—especially infections—was high. We believe that preoperative laboratory screening for low-grade infection and synovial cultures could contribute to better treatment in some of these patients.
doi:10.3109/17453674.2012.733917
PMCID: PMC3488175  PMID: 23083435
20.  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
21.  Stable fixation of an osseointegated implant system for above-the-knee amputees 
Acta Orthopaedica  2012;83(2):121-128.
Background and purpose
Rehabilitation of patients with transfemoral amputations is particularly difficult due to problems in using standard socket prostheses. We wanted to assess long-term fixation of the osseointegrated implant system (OPRA) using radiostereometric analysis (RSA) and periprosthetic bone remodeling.
Methods
51 patients with transfemoral amputations (55 implants) were enrolled in an RSA study. RSA and plain radiographs were scheduled at 6 months and at 1, 2, 5, 7, and 10 years after surgery. RSA films were analyzed using UmRSA software. Plain radiographs were graded for bone resorption, cancellization, cortical thinning, and trabecular streaming or buttressing in specifically defined zones around the implant.
Results
At 5 years, the median (SE) migration of the implant was –0.02 (0.06) mm distally. The rotational movement was 0.42 (0.32) degrees around the longitudinal axis. There was no statistically significant difference in median rotation or migration at any follow-up time. Cancellization of the cortex (plain radiographic grading) appeared in at least 1 zone in over half of the patients at 2 years. However, the prevalence of cancellization had decreased by the 5-year follow-up.
Interpretation
The RSA analysis for the OPRA system indicated stable fixation of the implant. The periprosthetic bone remodeling showed similarities with changes seen around uncemented hip stems. The OPRA system is a new and promising approach for addressing the challenges faced by patients with transfemoral amputations.
doi:10.3109/17453674.2012.678799
PMCID: PMC3339524  PMID: 22489885
22.  Changes in implant choice and surgical technique for hemiarthroplasty 
Acta Orthopaedica  2012;83(1):7-13.
Background and purpose
Treatment of displaced femoral neck fractures in Sweden has shifted towards more arthroplasties, especially hemiarthroplasties. We describe the hemiarthroplasty population in Sweden 2005 through 2009.
Methods
Since 2005, the Swedish Hip Arthroplasty Register has registered hemiarthroplasties on a national basis. We assessed hemiarthroplasty procedures in the Register 2005–2009 regarding patient details, implants, and surgical techniques. Completeness of recordings was calculated compared to the Swedish National Patient Register.
Results
Completeness increased from 89% to 96% during the study period. 21,346 hemiarthroplasty procedures were assessed. The relative number of patients with femoral neck fracture as diagnosis increased from 91% to 94%; the proportion of men increased from 27% to 30%. The median age increased from 83 to 84 years in men and from 84 to 85 years in women. Patients classified as having evident cognitive impairment increased from 19% to 22%. More men than women were ASA 4. The proportion of monoblock-type implants (Austin-Moore and Thompson) decreased from 18% to 0.9%. Modular implants increased generally, but in 2009 bipolar implants decreased in favor of unipolar implants. Lubinus and Exeter stems, and Mega Caput and Vario Cup implant heads were most common. The use of uncemented implants decreased from 10% to 3%. Use of the anterolateral approach increased from 47% to 56%.
Interpretation
Important changes in surgical technique and implant choice occurred during the observation period. We interpret these changes as being reflections of the continuing effort by Swedish orthopedic surgeons to improve the quality of treatment, because the changes are consistent with recent findings in the Swedish Hip Arthroplasty Register and in other scientific studies.
doi:10.3109/17453674.2011.641104
PMCID: PMC3278650  PMID: 22112151
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.  Statistical analysis of arthroplasty data 
Acta Orthopaedica  2011;82(3):253-257.
It is envisaged that guidelines for statistical analysis and presentation of results will improve the quality and value of research. The Nordic Arthroplasty Register Association (NARA) has therefore developed guidelines for the statistical analysis of arthroplasty register data. The guidelines are divided into two parts, this one with an introduction and a discussion of the background to the guidelines, and the second one with a more technical statistical discussion on how specific problems can be handled (Ranstam et al. 2011b, see pages x-y in this issue). This first part contains an overview of implant survival analysis and statistical methods used to evaluate factors with a potential influence on this outcome.
doi:10.3109/17453674.2011.588862
PMCID: PMC3235301  PMID: 21619499
25.  Statistical analysis of arthroplasty data 
Acta Orthopaedica  2011;82(3):258-267.
It is envisaged that guidelines for statistical analysis and presentation of results will improve the quality and value of research. The Nordic Arthroplasty Register Association (NARA) has therefore developed guidelines for the statistical analysis of arthroplasty register data. The guidelines are divided into two parts, one with an introduction and a discussion of the background to the guidelines (Ranstam et al. 2011a, see pages x-y in this issue), and this one with a more technical statistical discussion on how specific problems can be handled. This second part contains (1) recommendations for the interpretation of methods used to calculate survival, (2) recommendations on howto deal with bilateral observations, and (3) a discussion of problems and pitfalls associated with analysis of factors that influence survival or comparisons between outcomes extracted from different hospitals.
doi:10.3109/17453674.2011.588863
PMCID: PMC3235302  PMID: 21619500

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