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- Englund, Göran, et al.
(författare)
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Long-term variation of link strength in a simple benthic food web
- 2008
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Ingår i: Journal of Animal Ecology. - : British Ecological Society. - 0021-8790 .- 1365-2656. ; 77:5, s. 883-890
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Tidskriftsartikel (refereegranskat)abstract
- 1. The predatory isopod Saduria entomon (L.) and its amphipod prey Monoporeia affinis (Lindström) are key components of the food web in the northern Baltic Sea, together representing 80-90% of the macrobenthic biomass. We use 20 years of stomach content data for Saduria to investigate how diet dynamics affect the stability of the interaction between Saduria and Monoporeia.2. Consumption of the main prey, Monoporeia, fitted a type III functional response. Consumption rates of the most important alternative prey, mysids, were found to be unrelated to mysid densities but negatively related to the density of Monoporeia. The fit of consumption data to a model that assumes passive prey selection was poor. Thus we conclude that some form of active choice is involved.3. The effect of consumption of mysids, the alternative prey, on the stability of this system was investigated using a ‘one predator-two prey' model with stochastic environmental variation. Analysis of the model suggests that feeding on mysids leads to a decreased extinction risk for the predator, Saduria, and reduced density oscillations for both Saduria and its main prey, Monoporeia
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- Englund, Göran, et al.
(författare)
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Scaling up the functional response for spatially heterogeneous systems.
- 2008
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 11:5, s. 440-9
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Tidskriftsartikel (refereegranskat)abstract
- Scale transition theory is a framework for predicting regional population dynamics from local process functions and estimates of spatial heterogeneity. Using this framework, we estimated regional scale functional responses for a benthic predator-prey system in the Baltic Sea. Functional responses were based on laboratory experiments or field observations of stomach contents, and prey densities measured at a local scale (0.1 m(2)) or a regional scale (300 km(2)). Laboratory data overestimated consumption at high prey densities, whereas predictions based on local scale data tallied closely with consumption observed at the regional scale. The predicted regional functional response was different for increasing and decreasing prey densities, reflecting that predator and prey densities, as well as the covariance between them, exhibit oscillatory dynamics. We conclude that it is important to validate laboratory data with small-scale field observations and that scale transition is a powerful tool for scaling-up process functions in heterogeneous systems.
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- Gjertsen, Jan-Erik, et al.
(författare)
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Hemiarthroplasties after hip fractures in Norway and Sweden: a collaboration between the Norwegian and Swedish national registries
- 2014
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Ingår i: HIP International. - : SAGE Publications. - 1724-6067 .- 1120-7000. ; 24:3, s. 223-230
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Tidskriftsartikel (refereegranskat)abstract
- National registration of hemiarthroplasties after hip fractures has been established in both Norway and Sweden. We aimed to investigate differences in demographics, choice of implant selection, surgical approaches, and reoperations between the Norwegian Hip Fracture Register (NHFR) and the Swedish Hip Arthroplasty Register (SHAR). As part of the Nordic Arthroplasty Register Association (NARA) project a common hemiarthroplasty dataset has been established. 36,989 primary hemiarthroplasties (HAs) for acute hip fractures reported to NHFR (n = 12,761) and SHAR (n = 24,228) for the period 2005-2010 were included. Cemented prostheses were used in 78% of the operations in Norway and in 95% of the patients in Sweden. In Norway HAs almost exclusively had bipolar design (98%), whereas in Sweden HAs with unipolar design were used in 42% of the cases. Monoblock (non-modular) prostheses were uncommon, but still more frequently used in Sweden than in Norway (6.9% and 2.1% respectively). The lateral approach was more common in Norway (83%) than in Sweden (52%), where the posterior approach was used in 42% of the cases. The five-year survival of all HAs was 95.5% (95% CI: 94.8-96.2) in Norway and 94.8% (95% CI: 94.4-95.3) in Sweden. We concluded that surprisingly large differences between the two countries in demographics, implant design, and surgical technique had been revealed. This common dataset enables further investigations of the impact of these differences on revision rates and mortality.
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- Leonardsson, Olof, et al.
(författare)
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Changes in implant choice and surgical technique for hemiarthroplasty: 21,346 procedures from the Swedish Hip Arthroplasty Register 2005-2009
- 2012
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Ingår i: Acta Orthopaedica. - : Medical Journals Sweden AB. - 1745-3682 .- 1745-3674. ; 83:1, s. 7-13
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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- Leonardsson, Olof, et al.
(författare)
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Higher risk of reoperation for bipolar and uncemented hemiarthroplasty : 23,509 procedures after femoral neck fractures from the Swedish Hip Arthroplasty Register, 2005-2010
- 2012
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Ingår i: Acta Orthopaedica. - : Medical Journals Sweden AB. - 1745-3682 .- 1745-3674. ; 83:5, s. 459-466
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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- Leonardsson, Olof, et al.
(författare)
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Outcome after primary and secondary replacement for subcapital fracture of the hip in 10 264 patients.
- 2009
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Ingår i: The Journal of bone and joint surgery. British volume. - 0301-620X .- 2044-5377. ; 91:5, s. 595-600
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Tidskriftsartikel (refereegranskat)abstract
- Between 1999 and 2005, 10 264 patients who had undergone total hip replacement (THR) for subcapital fracture of the hip were compared with 76 520 in whom THR had been performed for other reasons. All the cases were identified through the Swedish Hip Arthroplasty Register. The THRs performed as primary treatment for fracture were also compared with those done after failure of internal fixation. After seven years the rate of revision was higher in THR after fracture (4.4% vs 2.9%). Dislocation and periprosthetic fracture were the most common causes of revision. The risk was higher in men than in women. The type of femoral component and the surgical approach influenced the risk. After correction for gender, type of component and the surgical approach the revision rates were similar in the primary and secondary fracture THR groups. Total hip replacement is therefore a safe method for both the primary and secondary management of fracture of the hip.
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