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Year of Publication
1.  Improved results of primary total hip replacement 
Acta Orthopaedica  2010;81(6):649-659.
Background and purpose
Over the past 20 years, several changes in treatment policy and treatment options have taken place regarding hip replacement. For this reason, we wanted to investigate the results after hip replacement in terms of revision rate, during a 21-year period among hip replacements reported to the Norwegian Arthroplasty Register.
Methods
110,882 primary total hip replacements were reported to the Norwegian Arthroplasty Register from 1987 through 2007. Risk of revision during the time periods 1993–1997, 1998–2002, and 2003–2007 was compared to that of the reference period 1987–1992. Adjusted Cox regression analyses were performed to compare the risk of revision in different time periods and extended analyses were done to investigate revision within the first postoperative year and after the first year.
Results
There was an overall reduced risk of revision in the time periods 1993–1997, 1998–2002, and 2003–2007 compared to the reference period: RR = 0.81 (95% CI 0.77–0.86), 0.51 (CI 0.47–0.55), and 0.77 (CI 0.68–0.85), respectively. The improved results were due to a marked reduction in aseptic loosening of the femoral and acetabular components in all time periods and in all subgroups of prostheses. A change in the timing of revision took place, with more early revisions and fewer late revisions in the later time periods. Revision due to dislocation and infection increased over time.
Interpretation
The risk of revision decreased during the study period, due to fewer cases of aseptic loosening of prosthetic components. The best results were obtained with the use of cemented prostheses. Prevention of dislocation and infection should be a major goal in the future, as revision due to these causes increased during the study period.
doi:10.3109/17453674.2010.537807
PMCID: PMC3216073  PMID: 21110699
2.  Prevention of deep infection in joint replacement surgery 
Acta Orthopaedica  2010;81(6):660-666.
doi:10.3109/17453674.2010.537805
PMCID: PMC3216074  PMID: 21110700
3.  Incidence of low-grade infection in aseptic loosening of total hip arthroplasty 
Acta Orthopaedica  2010;81(6):667-673.
Purpose
We investigated the hypothesis that many total hip arthroplasty revisions that are classified as aseptic are in fact low-grade infections missed with routine diagnostics.
Methods
In 7 Dutch hospitals, 176 consecutive patients with the preoperative diagnosis of aseptic loosening of their total hip arthroplasty were enrolled. During surgery, between 14 and 20 tissue samples were obtained for culture, pathology, and broad-range 16S rRNA PCR with reverse line blot hybridization. Patients were classified as either not being infected, suspected of having infection, or infected according to strict, predefined criteria. Each patient had a follow-up visit after 1 year.
Results
7 patients were classified as infected, 4 of whom were not identified by routine culture. 15 additional patients were suspected of having infection. 20 of these 22 patients received a cemented prosthesis, fixated with antibiotic-loaded bone cement. All 22 patients received prophylactic systemic antibiotics. 7 of them reported complaints one year after surgery, but only one showed signs of early loosening. However, additional surgery was not performed in any of the patients.
Interpretation
Although the proportions were not as high as previously reported in the literature, between 4% and 13% of patients with the preoperative diagnosis of aseptic loosening were infected. However, as thorough debridement was performed during surgery and prophylactic antibiotics were used, the diagnosis of infection did not have any obvious clinical consequences, as most patients performed well at the 1-year follow-up. Whether this observation has implications for long-term implant survival remains to be seen.
doi:10.3109/17453674.2010.525201
PMCID: PMC3216075  PMID: 20919816
4.  Biofilm development by clinical isolates of Staphylococcus spp. from retrieved orthopedic prostheses 
Acta Orthopaedica  2010;81(6):674-679.
Background
Biofilms are considered the key factor in the development of implant-related infections. However, only a few reports have dealt with the ability of organisms isolated from such infections to develop biofilms in vitro.
Methods
We evaluated different phenotypic techniques (2 microtiter plate assays and confocal laser scanning microscopy (CLSM) and genotypic techniques (detection of the ica operon) related to biofilm development by clinical isolates of Staphylococcus spp.
Results
All 26 strains tested (from 23 specimens) were biofilm producers. Stepanovic test detected biofilm formation in 85% of the strains, microtiter plate assay in 65%, and CLSM in 39%. The ica operon was detected in 73% of all strains (all 13 S. aureus strains and 6 of the 13 coagulase-negative Staphylococcus strains). 7 ica-negative strains were biofilm-positive by phenotypic methods.
Interpretation
The detection of ica genes could not be related to the phenotypic ability of the strains to develop a biofilm in vitro, so both studies (genetic and phenotypic) are required for a better evaluation of the biofilm-producing ability of clinical strains of Staphylococcus isolated from orthopedic infections.
doi:10.3109/17453674.2010.537810
PMCID: PMC3216076  PMID: 21110701
5.  Hip resurfacing arthroplasty 
Acta Orthopaedica  2010;81(6):680-683.
Background and purpose
Hip resurfacing arthroplasty is claimed to allow higher activity levels and to give better quality of life than total hip arthroplasty. In this literature review, we assessed the therapeutic value of hip resurfacing arthroplasty as measured by functional outcome.
Methods
An extensive literature search was performed using the PubMed, Embase, and Cochrane databases.
Results
9 patient series, 1 case-control study, and 1 randomized controlled trial (RCT) were included. Clinically and statistically significant improvement in sporting activity and hip scores were found in 10 studies.
Interpretation
Studies with low levels of evidence have shown improvement in various different hip scores and one RCT showed better outcomes with hip resurfacing arthroplasty. There is no high-level evidence to prove that there is improved clinical outcome using hip resurfacing arthroplasty. More randomized research needs to be done.
doi:10.3109/17453674.2010.501742
PMCID: PMC3216077  PMID: 20860440
6.  The clinical and radiological outcomes of hip resurfacing versus total hip arthroplasty: a meta-analysis and systematic review 
Acta Orthopaedica  2010;81(6):684-695.
Background and purpose
Hip resurfacing (HRS) procedures have gained increasing popularity for younger, higher-demand patients with degenerative hip pathologies. However, with concerns regarding revision rates and possible adverse metal hypersensitivity reactions with metal-on-metal articulations, some authors have questioned the hypothesized superiority of hip resurfacing over total hip arthroplasty (THA). In this meta-analysis, we compared the clinical and radiological outcomes and complication rates of these 2 procedures.
Methods
A systematic review was undertaken of all published (Medline, CINAHL, AMED, EMBASE) and unpublished or gray literature research databases up to January 2010. Clinical and radiological outcomes as well as complications of HRS were compared to those of THA using risk ratio, mean difference, and standardized mean difference statistics. Studies were critically appraised using the CASP appraisal tool.
Results
46 studies were identified from 1,124 citations. These included 3,799 HRSs and 3,282 THAs. On meta-analysis, functional outcomes for subjects following HRS were better than or the same as for subjects with a THA, but there were statistically significantly greater incidences of heterotopic ossification, aseptic loosening, and revision surgery with HRS compared to THA. The evidence base showed a number of methodological inadequacies such as the limited use of power calculations and poor or absent blinding of both patients and assessors, possibly giving rise to assessor bias.
Interpretation
On the basis of the current evidence base, HRS may have better functional outcomes than THA, but the increased risks of heterotopic ossification, aseptic loosening, and revision surgery following HRS indicate that THA is superior in terms of implant survival.
doi:10.3109/17453674.2010.533933
PMCID: PMC3216078  PMID: 21067432
7.  Soft tissue damage after minimally invasive THA 
Acta Orthopaedica  2010;81(6):696-702.
Background and purpose
Minimally invasive surgery (MIS) for hip replacement is thought to minimize soft tissue damage. We determined the damage caused by 4 different MIS approaches as compared to a conventional lateral transgluteal approach.
Methods
5 surgeons each performed a total hip arthroplasty on 5 fresh frozen cadaver hips, using either a MIS anterior, MIS anterolateral, MIS 2-incision, MIS posterior, or lateral transgluteal approach. Postoperatively, the hips were dissected and muscle damage color-stained. We measured proportional muscle damage relative to the midsubstance cross-sectional surface area (MCSA) using computerized color detection. The integrity of external rotator muscles, nerves, and ligaments was assessed by direct observation.
Results
None of the other MIS approaches resulted in less gluteus medius muscle damage than the lateral transgluteal approach. However, the MIS anterior approach completely preserved the gluteus medius muscle in 4 cases while partial damage occurred in 1 case. Furthermore, the superior gluteal nerve was transected in 4 cases after a MIS anterolateral approach and in 1 after the lateral transgluteal approach. The lateral femoral cutaneous nerve was transected once after both the MIS anterior approach and the MIS 2-incision approach.
Interpretation
The MIS anterior approach may preserve the gluteus medius muscle during total hip arthroplasty, but with a risk of damaging the lateral femoral cutaneous nerve.
doi:10.3109/17453674.2010.537804
PMCID: PMC3216079  PMID: 21110702
8.  The Harris hip score: Do ceiling effects limit its usefulness in orthopedics? 
Acta Orthopaedica  2010;81(6):703-707.
Background and purpose
The Harris hip score (HHS), a disease-specific health status scale that is frequently used to measure the outcome of total hip arthroplasty, has never been validated properly. A questionnaire is suitable only when all 5 psychometric properties are of sufficient quality. We questioned the usefulness of the HHS by investigating its content validity.
Methods
We performed a systematic review based on a literature search in PubMed, Embase, and the Cochrane Library for descriptive studies published in 2007. 54 studies (59 patient groups) met our criteria and were included in the data analysis. To determine the content validity, we calculated the ceiling effect (percentage) for each separate study and we pooled data to measure the weighted mean. A subanalysis of indications for THA was performed to differentiate the populations for which the HHS would be suitable and for which it would not. A ceiling effect of 15% or less was considered to be acceptable.
Results
Over half the studies (31/59) revealed unacceptable ceiling effects. Pooled data across the studies included (n = 6,667 patients) suggested ceiling effects of 20% (95%CI: 18–22). Ceiling effects were greater (32%, 95%CI:12–52) in those patients undergoing hip resurfacing arthroplasty.
Interpretation
Although the Harris hip score is widely used in arthroplasty research on outcomes, ceiling effects are common and these severely limit its validity in this field of research.
doi:10.3109/17453674.2010.537808
PMCID: PMC3216080  PMID: 21110703
9.  The natural history of Perthes' disease 
Acta Orthopaedica  2010;81(6):708-714.
Background
The prognosis in Perthes' disease varies considerably according to certain risk factors, but there is no concensus regarding the relative importance of these factors. We assessed the natural history of the disease and defined prognostic factors of value in deciding the proper treatment.
Patients and methods
During the 5-year period 1996–2000, a nationwide study on Perthes' disease was performed in Norway. 425 patients were registered. The present study involved the 212 children (mean age 5.1 years, 77% boys) who were affected unilaterally and who had been treated with physiotherapy only (which is considered not to change the natural history). They were followed by taking radiographs at the time of diagnosis and after 1, 3, and 5 years. At the 5-year follow-up, the outcome was evaluated according to a modification of the Stulberg classification: good (spherical femoral head), fair (ovoid femoral head), and poor (flat femoral head).
Results
The 5-year radiographic results were strongly dependent on 4 risk factors: age 6 years or more at diagnosis, total femoral head necrosis, height of the lateral pillar of the epiphysis less than 50% of normal height, and femoral head cover less than 80%. As the number of risk factors increased from 0 to 4, the proportion of patients with good radiographic 5-year outcome decreased from 79% to 0% and the proportion with poor outcome increased from 3% to 91%.
Interpretation
Most children under 6 years of age do not need any special treatment. In older children, no special treatment is indicated if the whole femoral head is not necrotic and the femoral head cover is > 80%. In the most severe forms of the disease (i.e. more than 2 risk factors), surgical containment treatment seems advisable.
doi:10.3109/17453674.2010.533935
PMCID: PMC3216081  PMID: 21067434
10.  Treatment injuries are rare in children's femoral fractures 
Acta Orthopaedica  2010;81(6):715-718.
Background and purpose
The current treatment for femoral fractures in children is mostly operative, which contrasts with treatment of other long bone fractures in children. We analyzed treatment injuries in such patients in Finland in order to identify avoidable injuries. Our other aims were to calculate the incidence of these fractures and to describe the treatment method used.
Methods
The Patient Insurance Centre (PIC) provides financial compensation of patients who have sustained an injury in connection with medical care. We retrospectively analyzed incidence, treatment methods, and all compensation claims concerning treatment of femoral fractures in children who were 0–16 years of age during the 8-year period 1997–2004.
Results
The incidence of childhood femoral fractures in Finland was 0.27 per 1,000 children aged < 17 years, and two-thirds of the patients were treated operatively during the study period. 30 compensation claims were submitted to PIC during the 8-year study period. The compensation claims mainly concerned pain, insufficient diagnosis or treatment, extra expenses, permanent disability, or inappropriate behavior of medical personnel. Of the claims, 16 of 30 were granted compensation. Compensation was granted for delay in treatment, unnecessary surgery, and for inappropriate surgical technique. The mean amount of compensation was 2,300 euros. Of the injuries that led to compensation, 11 of 16 were regarded as being avoidable in retrospect.
Interpretation
The calculated risk of a treatment injury in childhood femoral fracture treatment in Finland is approximately 2%, and most of these injuries can be avoided with proper treatment.
doi:10.3109/17453674.2010.533927
PMCID: PMC3216082  PMID: 21067428
11.  Prosthetic overhang is the most effective way to prevent scapular conflict in a reverse total shoulder prosthesis 
Acta Orthopaedica  2010;81(6):719-726.
Background and purpose
Despite good clinical results with the reverse total shoulder arthroplasty, inferior scapular notching remains a concern. We evaluated 6 different solutions to overcome the problem of scapular notching.
Methods
An average and a “worst case scenario” shape in A-P view in a 2-D computer model of a scapula was created, using data from 200 “normal” scapulae, so that the position of the glenoid and humeral component could be changed as well as design features such as depth of the polyethylene insert, the size of glenosphere, the position of the center of rotation, and downward glenoid inclination. The model calculated the maximum adduction (notch angle) in the scapular plane when the cup of the humeral component was in conflict with the scapula.
Results
A change in humeral neck shaft inclination from 155° to 145° gave a 10° gain in notch angle. A change in cup depth from 8 mm to 5 mm gave a gain of 12°. With no inferior prosthetic overhang, a lateralization of the center of rotation from 0 mm to 5 mm gained 16°. With an inferior overhang of only 1 mm, no effect of lateralizing the center of rotation was noted. Downward glenoid inclination of 0º to 10º gained 10°. A change in glenosphere radius from 18 mm to 21 mm gained 31° due to the inferior overhang created by the increase in glenosphere. A prosthetic overhang to the bone from 0 mm to 5 mm gained 39°.
Interpretation
Of all 6 solutions tested, the prosthetic overhang created the biggest gain in notch angle and this should be considered when designing the reverse arthroplasty and defining optimal surgical technique.
doi:10.3109/17453674.2010.538354
PMCID: PMC3216083  PMID: 21110704
12.  Time-dependent improvement in functional outcome following LCS rotating platform knee replacement 
Acta Orthopaedica  2010;81(6):727-732.
Background and purpose
Long-term follow-up studies after total knee replacement (TKR) using an LCS rotating platform have shown survival rates of up to 97%. Few studies have evaluated short-term functional outcome and its improvement over time. We determined the time course of functional outcome as evaluated by the knee injury and osteoarthritis outcome score (KOOS) over the first 4 years after TKR using the LCS mobile bearing.
Patients and methods
50 unselected patients (mean age 70 (40–85) years, 33 women) with osteoarthritis in one knee underwent TKR with an LCS mobile bearing. Data were collected by an independent investigator preoperatively and at 6 weeks, 3 months, 6 months, 1 year, 2 years and 4 years postoperatively. KOOS, a self-assessment function score validated for this purpose, and range of motion (ROM) were determined at all follow-ups.
Results
The mean KOOS pain score increased from 43 before surgery to 66 at 6 weeks and 88 at 2 years. It was 84 at 4 years. The mean KOOS activities of daily living score (ADL) increased from 49 before surgery to 73 at 6 weeks, then gradually to 90 at 2 years. It decreased to 79 at 4 years. Mean passive ROM was 112° before surgery, 78° at departure from hospital, and then gradually increased to 116° at 2 years and 113° at 4 years.
Interpretation
Recovery after TKR is time-dependent. Most of the expected improvement in pain and function is achieved at 6 months postoperatively, but some further improvement can be expected up to 2 years postoperatively. ROM will also gradually improve up to 2 years after TKR, and reach the same level as before surgery.
doi:10.3109/17453674.2010.533929
PMCID: PMC3216084  PMID: 21067429
13.  Subsidence of callotasis zone in distraction osteogenesis after external fixator removal, measured by RSA 
Acta Orthopaedica  2010;81(6):733-736.
Background and purpose
In clinical practice, achieved lengthening of a callotasis zone should be maintained after the external fixator has been removed. The common understanding has been that the regenerated bone may subside. To investigate this, we used high-resolution radiostereometric analysis (RSA) with accurate measurement of the lengthening zone.
Patients and methods
We assessed the longitudinal subsidence of a callotasis zone after removal of the external fixator in distraction osteogenesis in 16 patients who underwent 17 segmental lengthening operations on the tibia (n = 9) or femur (n = 8). Median lengthening was 32 (6–80) mm. RSA was performed at the end of the consolidation period before the external fixation device was removed, and this was later repeated at a median time of 11 (4–32) weeks after frame removal.
Results
A minimal median longitudinal change of 0.01 (–0.28 to 0.60) mm across the lengthening zone occurred in uncomplicated cases.
Interpretation
Our results indicate that no subsidence of clinical interest occurs after external frame removal.
doi:10.3109/17453674.2010.533934
PMCID: PMC3216085  PMID: 21067433
14.  Lower limb amputations in Trondheim, Norway 
Acta Orthopaedica  2010;81(6):737-744.
Background and purpose
In the city of Trondheim, Norway, diabetic lower-limb amputations accounted for one-third of all lower-limb amputations (LLAs). In an attempt to reduce this rate, a diabetic foot team was established in 1996. We present the incidence of LLA in Trondheim as measured 10 years later.
Patients and methods
In 2004–07, we registered all LLAs performed in Trondheim and then compared the data with previously published data from 1994–1997. From 1996 through 2006, we registered the activity of the diabetic foot team and we also registered the number of vascular procedures performed on citizens of Trondheim from 1998 through 2006.
Results
Comparing the two 3-year periods 1994–97 and 2004–07, we observed a decrease in all non-traumatic LLAs. The incidence of diabetic major LLAs per 103 diabetics per year decreased from 4.0 to 2.4, and in patients with peripheral vascular disease we observed a decrease in LLAs from 18 to 12 per 105 inhabitants per year. 5,915 consultations on diabetic subjects were conducted by the diabetic foot team during the period 1996–2006. From 1998 to 2006, the rate of vascular procedures decreased in the non-diabetic population, and was unchanged in diabetic subjects.
Interpretation
In the population of Trondheim city there appears to have been a reduction in the rate of vascular obstructive lower-limb disease between the two 3-year periods 1994–97 and 2004–07. In our judgment, the decline in diabetic LLA also reflects better care of the diabetic foot.
doi:10.3109/17453674.2010.519164
PMCID: PMC3216086  PMID: 20860446
15.  Use of a trabecular metal implant in ankle arthrodesis after failed total ankle replacement 
Acta Orthopaedica  2010;81(6):745-747.
Background and purpose
Arthrodesis after failed total ankle replacement is complicated and delayed union, nonunion, and shortening of the leg often occur—especially with large bone defects. We investigated the use of a trabecular metal implant and a retrograde intramedullary nail to obtain fusion.
Patients and methods
13 patients with a migrated or loose total ankle implant underwent arthrodesis with the use of a retrograde intramedullary nail through a trabecular metal Tibial Cone. The mean follow-up time was 1.4 (0.6–3.4) years.
Results
At the last examination, 7 patients were pain-free, while 5 had some residual pain but were satisfied with the procedure. 1 patient was dissatisfied and experienced pain and swelling when walking. The implant-bone interfaces showed no radiographic zones or gaps in any patient, indicating union.
Interpretation
The method is a new way of simplifying and overcoming some of the problems of performing arthrodesis after failed total ankle replacement.
doi:10.3109/17453674.2010.533936
PMCID: PMC3216087  PMID: 21067435
16.  Accelerated fracture healing in mice lacking the 5-lipoxygenase gene 
Acta Orthopaedica  2010;81(6):748-755.
Background and purpose
Cyclooxygenase-2 (COX-2) promotes inflammation by synthesizing pro-inflammatory prostaglandins from arachidonic acid. Inflammation is an early response to bone fracture, and ablation of COX-2 activity impairs fracture healing. Arachidonic acid is also converted into leukotrienes by 5-lipoxygenase (5-LO). We hypothesized that 5-LO is a negative regulator of fracture healing and that in the absence of COX-2, excess leukotrienes synthesized by 5-LO will impair fracture healing.
Methods
Fracture healing was assessed in mice with a targeted 5-LO mutation (5-LOKO mice) and control mice by radiographic and histological observations, and measured by histomorphometry and torsional mechanical testing. To assess effects on arachidonic acid metabolism, prostaglandin E2, F2α, and leukotriene B4 levels were measured in the fracture calluses of control, 5-LOKO COX-1KO, and COX-2KO mice by enzyme linked immunoassays.
Results
Femur fractures in 5-LOKO mice rapidly developed a cartilaginous callus that was replaced with bone to heal fractures faster than in control mice. Femurs from 5-LOKO mice had substantially better mechanical properties after 1 month of healing than did control mice. Callus leukotriene levels were 4-fold higher in mice homozygous for a targeted mutation in the COX-2 gene (COX-2KO), which indicated that arachidonic acid was shunted into the 5-LO pathway in the absence of COX-2.
Interpretation
These experiments show that 5-LO negatively regulates fracture healing and that shunting of arachidonic acid into the 5-LO pathway may account, at least in part, for the impaired fracture healing response observed in COX-2KO mice.
doi:10.3109/17453674.2010.533931
PMCID: PMC3216088  PMID: 21067431
17.  Cobalt ions induce chemokine secretion in a variety of systemic cell lines 
Acta Orthopaedica  2010;81(6):756-764.
Background and purpose
Metal ion toxicity both locally and systemically following MoM hip replacements remains a concern. Cobalt ions have been shown to induce secretion of proinflammatory chemokines locally; however, little is known about their effect systemically. We investigated the in vitro effect of cobalt ions on a variety of cell lines by measuring production of the proinflammatory chemokines IL-8 and MCP-1.
Method
Renal, gastrointestinal, and respiratory epithelium and also neutrophils and monocytes were exposed to cobalt ions at 4, 12, 24, and 48 hours.
Results
We found that cobalt ions enhanced the secretion of IL-8 and MCP-1 in renal epithelial cells, gastric and colon epithelium, monocytes and neutrophils, and small airway epithelial cells but not in alveolar cells. Secretion of IL-8 and MCP-1 was markedly elevated in renal epithelium, where a 16-fold and 7-fold increase occurred compared to controls. There was a 6-fold and 4-fold increase in IL-8 and MCP-1 secretion in colon epithelium and a 4-fold and 3-fold increase in gastric epithelium. Small airway epithelial cells showed a maximum increase in secretion of 8-fold (IL-8) and of 4-fold (MCP-1). The increase in chemokine secretion observed in alveolar cells was moderate and did not reach statistical significance. Monocytes and neutrophils showed a 2.5-fold and 2-fold increase in IL-8 secretion and a 6-fold and 4-fold increase in MCP-1 secretion at 48 and 24 hours, respectively.
Interpretation
These data demonstrate the potent bioactivity of cobalt ions in a variety of cell types and the potential to induce a proinflammatory response.
doi:10.3109/17453674.2010.537806
PMCID: PMC3216089  PMID: 21110705
19.  Female patients with low systemic BMD 
Acta Orthopaedica  2010;81(6):768-769.
doi:10.3109/17453674.2010.537811
PMCID: PMC3216091  PMID: 21110706
20.  Vertebroplasty and kyphoplasty—evidence-based methods? 
Acta Orthopaedica  2010;81(5):521-523.
doi:10.3109/17453674.2010.519168
PMCID: PMC3214737  PMID: 20860449
21.  Overtreatment of cruciate ligament injuries 
Acta Orthopaedica  2010;81(5):524-525.
doi:10.3109/17453674.2010.525192
PMCID: PMC3214738  PMID: 20929420
22.  Effects of metal-on-metal wear on the host immune system and infection in hip arthroplasty 
Acta Orthopaedica  2010;81(5):526-534.
Background and purpose
Joint replacement with metal-on-metal (MOM) bearings have gained popularity in the last decades in young and active patients. However, the possible effects of MOM wear debris and its corrosion products are still the subject of debate. Alongside the potential disadvantages such as toxicity, the influences of metal particles and metal ions on infection risk are unclear.
Methods
We reviewed the available literature on the influence of degradation products of MOM bearings in total hip arthroplasties on infection risk.
Results
Wear products were found to influence the risk of infection by hampering the immune system, by inhibiting or accelerating bacterial growth, and by a possible antibiotic resistance and heavy metal co-selection mechanism.
Interpretation
Whether or not the combined effects of MOM wear products make MOM bearings less or more prone to infection requires investigation in the near future.
doi:10.3109/17453674.2010.519169
PMCID: PMC3214739  PMID: 20860450
23.  Inferior outcome after hip resurfacing arthroplasty than after conventional arthroplasty 
Acta Orthopaedica  2010;81(5):535-541.
Background and purpose
The reported outcomes of hip resurfacing arthroplasty (HRA) vary. The frequency of this procedure in Denmark, Norway, and Sweden is low. We therefore determined the outcome of HRA in the NARA database, which is common to all 3 countries, and compared it to the outcome of conventional total hip arthroplasty (THA).
Methods
The risk of non-septic revision within 2 years was analyzed in 1,638 HRAs and compared to that for 172,554 conventional total hip arthroplasties (THAs), using Cox regression models. We calculated relative risk (RR) of revision and 95% confidence interval.
Results
HRA had an almost 3-fold increased revision risk compared to THA (RR = 2.7, 95% CI: 1.9–3.7). The difference was even greater when HRA was compared to the THA subgroup of cemented THAs (RR = 3.8, CI: 2.7–5.3). For men below 50 years of age, this difference was less pronounced (HRA vs. THA: RR = 1.9, CI: 1.0–3.9; HRA vs. cemented THA: RR = 2.4, CI: 1.1–5.3), but it was even more pronounced in women of the same age group (HRA vs. THA: RR = 4.7, CI: 2.6–8.5; HRA vs. cemented THA: RR = 7.4, CI: 3.7–15). Within the HRA group, risk of non-septic revision was reduced in hospitals performing ≥ 70 HRAs annually (RR = 0.3, CI: 0.1–0.7) and with use of Birmingham hip resurfacing (BHR) rather than the other designs as a group (RR = 0.3, CI: 0.1–0.7). Risk of early revision was also reduced in males (RR = 0.5, CI: 0.2–0.9). The femoral head diameter alone had no statistically significant influence on the early revision rate, but it eliminated the significance of male sex in a combined analysis.
Interpretation
In general, our results do not support continued use of hip resurfacing arthroplasty. Men had a lower early revision rate, which was still higher than observed for all-cemented hips. Further follow-up is necessary to determine whether HRA might be useful as an alternative in males.
doi:10.3109/17453674.2010.525193
PMCID: PMC3214740  PMID: 20919812
24.  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
25.  Competing risks survival analysis applied to data from the Australian Orthopaedic Association National Joint Replacement Registry 
Acta Orthopaedica  2010;81(5):548-555.
Background and purpose
The Kaplan-Meier (KM) method is often used in the analysis of arthroplasty registry data to estimate the probability of revision after a primary procedure. In the presence of a competing risk such as death, KM is known to overestimate the probability of revision. We investigated the degree to which the risk of revision is overestimated in registry data.
Patients and methods
We compared KM estimates of risk of revision with the cumulative incidence function (CIF), which takes account of death as a competing risk. We considered revision by (1) prosthesis type in subjects aged 75–84 years with fractured neck of femur (FNOF), (2) cement use in monoblock prostheses for FNOF, and (3) age group in patients undergoing total hip arthroplasty (THA) for osteoarthritis (OA).
Results
In 5,802 subjects aged 75–84 years with a monoblock prosthesis for FNOF, the estimated risk of revision at 5 years was 6.3% by KM and 4.3% by CIF, a relative difference (RD) of 46%. In 9,821 subjects of all ages receiving an Austin Moore (non-cemented) prosthesis for FNOF, the RD at 5 years was 52% and for 3,116 subjects with a Thompson (cemented) prosthesis, the RD was 79%. In 44,365 subjects with a THA for OA who were less than 70 years old, the RD was just 1.4%; for 47,430 subjects > 70 years of age, the RD was 4.6% at 5 years.
Interpretation
The Kaplan-Meier method substantially overestimated the risk of revision compared to estimates using competing risk methods when the risk of death was high. The bias increased with time as the incidence of the competing risk of death increased. Registries should adopt methods of analysis appropriate to the nature of their data.
doi:10.3109/17453674.2010.524594
PMCID: PMC3214742  PMID: 20919809

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