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1.  Early proximal migration of cups is associated with late revision in THA 
Acta Orthopaedica  2012;83(6):583-591.
Background and purpose
The association between excessive early migration of acetabular cups and late aseptic revision has been scantily reported. We therefore performed 2 parallel systematic reviews and meta-analyses to determine the association between early migration of acetabular cups and late aseptic revision.
Methods
One review covered early migration data from radiostereometric analysis (RSA) studies, while the other focused on revision rates for aseptic loosening from long-term survival studies. Thresholds for acceptable and unacceptable migration were classified according the Swedish Hip Arthroplasty Register and the Australian National Joint Replacement Registry: < 5% revision at 10 years.
Results
Following an elaborate literature search, 26 studies (involving 700 cups) were included in the RSA review and 49 studies (involving 38,013 cups) were included in the survival review. For every mm increase in 2-year proximal migration, there was a 10% increase in revision rate, which remained after correction for age, sex, diagnosis, hospital type, continent, and study quality. Consequently, proximal migration of up to 0.2 mm was considered acceptable and proximal migration of 1.0 mm or more was considered unacceptable. Cups with proximal migration of between 0.2 and 1.0 mm were considered to be at risk of having revision rates higher than 5% at 10 years.
Interpretation
There was a clinically relevant association between early migration of acetabular cups and late revision due to loosening. The proposed migration thresholds can be implemented in a phased evidence-based introduction, since they allow early detection of high-risk cups while exposing a small number of patients.
doi:10.3109/17453674.2012.745353
PMCID: PMC3555453  PMID: 23126575
2.  Early migration of tibial components is associated with late revision 
Acta Orthopaedica  2012;83(6):614-624.
Purpose
We performed two parallel systematic reviews and meta-analyses to determine the association between early migration of tibial components and late aseptic revision.
Methods
One review comprised early migration data from radiostereometric analysis (RSA) studies, while the other focused on revision rates for aseptic loosening from long-term survival studies. Thresholds for acceptable and unacceptable migration were determined according to that of several national joint registries: < 5% revision at 10 years.
Results
Following an elaborate literature search, 50 studies (involving 847 total knee prostheses (TKPs)) were included in the RSA review and 56 studies (20,599 TKPs) were included in the survival review. The results showed that for every mm increase in migration there was an 8% increase in revision rate, which remained after correction for age, sex, diagnosis, hospital type, continent, and study quality. Consequently, migration up to 0.5 mm was considered acceptable during the first postoperative year, while migration of 1.6 mm or more was unacceptable. TKPs with migration of between 0.5 and 1.6 mm were considered to be at risk of having revision rates higher than 5% at 10 years.
Interpretation
There was a clinically relevant association between early migration of TKPs and late revision for loosening. The proposed migration thresholds can be implemented in a phased, evidence-based introduction of new types of knee prostheses, since they allow early detection of high-risk TKPs while exposing only a small number of patients.
doi:10.3109/17453674.2012.747052
PMCID: PMC3555454  PMID: 23140091
3.  5-year clinical and radiostereometric analysis (RSA) follow-up of 39 CUT femoral neck total hip prostheses in young osteoarthritis patients 
Acta Orthopaedica  2012;83(4):334-341.
Background
As the number of young patients receiving total hip arthroplasty increases, bone-saving implantations facilitating possible future revision, such as the CUT femoral neck prosthesis, are gaining importance. There have been few medium-term results reported for this prosthesis, however, and its migration pattern has not been analyzed.
Patients and methods
39 consecutive CUT femoral neck prostheses were implanted in 32 patients, mean age 37 (17–58) years, with symptomatic osteoarthritis and either less than 55 years of age or with an anatomic anomaly preventing implantation of a diaphyseal stem (n = 1). Patients were followed prospectively using routine clinical examination and radiostereometric analysis (RSA) at 6, 12, 26, and 52 weeks postoperatively and annually thereafter. This study evaluated the 5-year follow-up results.
Results
The mean Harris hip score increased from 26 (3–51) points preoperatively to 84 (66–98), 86 (55–98), and 87 (47–98) points at 3, 12, and 60 months. 3 stems were revised: 1 after luxation following excessive subsidence due to an undersized component and 2 due to persistent strong thigh pain. 5-year survival was 95% (95% CI: 87–100). Initial migration varied widely in magnitude; median total tip migration was 0.42 mm (0.09–9.4) at 6 weeks, 0.92 mm (0.18–5.9) at 1 year, and 1.10 mm (0.13–6.4) at 5 years. Even after high initial migration, stabilization was achieved in 31 of the 35 RSA-evaluable implants. 3 prostheses showed progressive continuous migration throughout the entire follow-up period, and were considered to be loose, suggesting reduced long-term survival.
Interpretation
Currently, we cannot recommend the CUT femoral neck prosthesis as a routine treatment option in (young) patients requiring THA. The CUT prosthesis may not reach the 90% survival benchmark at 10 years, and the prosthesis is difficult to implant. If initial stabilization is achieved, however, aseptic loosening is unlikely. A good clinical outcome was seen in the surviving prostheses. We will continue to follow this patient group.
doi:10.3109/17453674.2012.702392
PMCID: PMC3427622  PMID: 22880707
4.  The Exeter femoral stem continues to migrate during its first decade after implantation 
Acta Orthopaedica  2012;83(2):129-134.
Background
Due to its collarless, double-tapered polished design, the Exeter femoral stem is known to migrate distally in the first 5 years after implantation. However, its long-term migration pattern has not been investigated.
Patients and methods
39 consecutive patients (41 total hip arthroplasties) received a cemented Exeter stem and had prospective clinical and RSA follow-up. Patients were evaluated postoperatively at 6, 12, 26, and 52 weeks, and annually thereafter. Short-term results have been reported. In this study, the mean length of follow-up was 9.4 years (SD 3.2 years). No patients were lost to follow-up. 15 patients died during follow-up.
Results
No stems were revised. In 4 stems, fractures of the cement mantle were noted within the first 3 postoperative years. In 3 stems, this resulted in a complete circumferential cement mantle discontinuity. For the 37 well-performing stems, continuous but small migration was measured between 2 and 12 years of follow-up. Continued subsidence of 0.08 mm/year (95% CI: 0.05–0.12, p < 0.001) was seen in combination with continued rotation in retroversion of 0.07°/year (95% CI: 0.02–0.12, p = 0.01). At 10 years of follow-up, mean subsidence was 2.1 (SD 1.2) mm and mean retroversion was 1.8° (SD 2.0). Two-thirds of this occurred during the first 2 postoperative years. In the 3 stems with a complete circumferential cement fracture, a sudden and disproportionately high increase in subsidence was measured in the time period of occurrence.
Interpretation
The Exeter femoral stem continues to migrate during the first decade after implantation. Absolute stability is not required for good long-term survival if this is compatible with the design of the implant.
doi:10.3109/17453674.2012.672093
PMCID: PMC3339525  PMID: 22401676
5.  The beneficial effect of hydroxyapatite lasts 
Acta Orthopaedica  2012;83(2):135-141.
Background and purpose
In contrast to early migration, the long-term migration of hydroxyapatite- (HA-) coated tibial components in TKA has been scantily reported. This randomized controlled trial investigated the long-term migration measured by radiostereometric analysis (RSA) of HA-coated, uncoated, and cemented tibial components in TKA.
Patients and methods
68 knees were randomized to HA-coated (n = 24), uncoated (n = 20), and cemented (n = 24) components. All knees were prospectively followed for 11–16 years, or until death or revision. RSA was used to evaluate migration at yearly intervals. Clinical and radiographic evaluation was according to the Knee Society system. A generalized linear mixed model (GLMM, adjusted for age, sex, diagnosis, revisions, and BMI) was used to take into account the repeated-measurement design.
Results
The present study involved 742 RSA analyses. The mean migration at 10 years was 1.66 mm for HA, 2.25 mm for uncoated and 0.79 mm for the cemented group (p < 0.001). The reduction of migration by HA as compared to uncoated components was most pronounced for subsidence and external rotation. 3 tibial components were revised for aseptic loosening (2 uncoated and 1 cemented), 3 for septic loosening (2 uncoated and 1 cemented), and 1 for instability (HA-coated). 2 of these cases were revised for secondary loosening after a period of stability: 1 case of osteolysis and 1 case of late infection. There were no statistically significant differences between the fixation groups regarding clinical or radiographic scores.
Interpretation
HA reduces migration of uncemented tibial components. This beneficial effect lasts for more than 10 years. Cemented components showed the lowest migration. Longitudinal follow-up of TKA with RSA allows early detection of secondary loosening.
doi:10.3109/17453674.2012.665330
PMCID: PMC3339526  PMID: 22329667
6.  RSA prediction of high failure rate for the uncoated Interax TKA confirmed by meta-analysis 
Acta Orthopaedica  2012;83(2):142-147.
Background and purpose
In a previous radiostereometric (RSA) trial the uncoated, uncemented, Interax tibial components showed excessive migration within 2 years compared to HA-coated and cemented tibial components. It was predicted that this type of fixation would have a high failure rate. The purpose of this systematic review and meta-analysis was to investigate whether this RSA prediction was correct.
Materials and methods
We performed a systematic review and meta-analysis to determine the revision rate for aseptic loosening of the uncoated and cemented Interax tibial components.
Results
3 studies were included, involving 349 Interax total knee arthroplasties (TKAs) for the comparison of uncoated and cemented fixation. There were 30 revisions: 27 uncoated and 3 cemented components. There was a 3-times higher revision rate for the uncoated Interax components than that for cemented Interax components (OR = 3; 95% CI: 1.4–7.2).
Interpretation
This meta-analysis confirms the prediction of a previous RSA trial. The uncoated Interax components showed the highest migration and turned out to have the highest revision rate for aseptic loosening. RSA appears to enable efficient detection of an inferior design as early as 2 years postoperatively in a small group of patients.
doi:10.3109/17453674.2012.672092
PMCID: PMC3339527  PMID: 22530953
7.  AQUILA: assessment of quality in lower limb arthroplasty. An expert Delphi consensus for total knee and total hip arthroplasty 
Background
In the light of both the importance and large numbers of case series and cohort studies (observational studies) in orthopaedic literature, it is remarkable that there is currently no validated measurement tool to appraise their quality. A Delphi approach was used to develop a checklist for reporting quality, methodological quality and generalizability of case series and cohorts in total hip and total knee arthroplasty with a focus on aseptic loosening.
Methods
A web-based Delphi was conducted consisting of two internal rounds and three external rounds in order to achieve expert consensus on items considered relevant for reporting quality, methodological quality and generalizability.
Results
The internal rounds were used to construct a master list. The first external round was completed by 44 experts, 35 of them completed the second external round and 33 of them completed the third external round. Consensus was reached on an 8-item reporting quality checklist, a 6-item methodological checklist and a 22-item generalizability checklist.
Conclusions
Checklist for reporting quality, methodological quality and generalizability for case series and cohorts in total hip and total knee arthroplasty were successfully created through this Delphi. These checklists should improve the accuracy, completeness and quality of case series and cohorts regarding total hip and total knee arthroplasty.
doi:10.1186/1471-2474-12-173
PMCID: PMC3155910  PMID: 21781327
Total Knee Arthroplasty; Total Hip Arthroplasty; Reporting Quality; Methodological Quality; Generalizability
8.  Measuring femoral lesions despite CT metal artefacts: a cadaveric study 
Skeletal Radiology  2011;41(5):547-555.
Objective
Computed tomography is the modality of choice for measuring osteolysis but suffers from metal-induced artefacts obscuring periprosthetic tissues. Previous papers on metal artefact reduction (MAR) show qualitative improvements, but their algorithms have not found acceptance for clinical applications. We investigated to what extent metal artefacts interfere with the segmentation of lesions adjacent to a metal femoral implant and whether metal artefact reduction improves the manual segmentation of such lesions.
Materials and methods
We manually created 27 periprosthetic lesions in 10 human cadaver femora. We filled the lesions with a fibrotic interface tissue substitute. Each femur was fitted with a polished tapered cobalt-chrome prosthesis and imaged twice—once with the metal, and once with a substitute resin prosthesis inserted. Metal-affected CTs were processed using standard back-projection as well as projection interpolation (PI) MAR. Two experienced users segmented all lesions and compared segmentation accuracy.
Results
We achieved accurate delineation of periprosthetic lesions in the metal-free images. The presence of a metal implant led us to underestimate lesion volume and introduced geometrical errors in segmentation boundaries. Although PI MAR reduced streak artefacts, it led to greater underestimation of lesion volume and greater geometrical errors than without its application.
Conclusion
CT metal artefacts impair image segmentation. PI MAR can improve subjective image appearance but causes loss of detail and lower image contrast adjacent to prostheses. Our experiments showed that PI MAR is counterproductive for manual segmentation of periprosthetic lesions and should be used with care.
doi:10.1007/s00256-011-1223-2
PMCID: PMC3310131  PMID: 21732221
Computed tomography; Metal artifact reduction; Osteolysis; Segmentation; Beam hardening
9.  Co-contraction in RA patients with a mobile bearing total knee prosthesis during a step-up task 
It was hypothesized that rheumatoid arthritis (RA) patients with a total knee prosthesis that allows axial rotation of the bearing (MB) will show more co-contraction to stabilize the knee joint during a step-up task than RA patients with a fixed bearing total knee prosthesis (FB) where this rotational freedom is absent while having the same articular geometry. Surface EMG, kinematics and kinetics about the knee were recorded during a step-up task of a MB group (n = 5), a FB group (n = 4) and a control group (n = 8). Surface EMG levels of thigh muscles were calibrated to either knee flexion or extension moments by means of isokinetic contractions on a dynamometer. During the step-up task co-contraction indices were determined from an EMG-force model. Controls showed a higher active ROM during the step-up task than the patient group, 96° versus 88° (P = 0.007). In the control group higher average muscle extension, flexion and net moments during single limb support phase were observed than in the patient group. During the 20–60% interval of the single limb support, MB patients showed a significant higher level of flexor activity, resulting in a lower net joint moment, however co-contraction levels were not different. Compared to the control group arthroplasty patients showed a 40% higher level of co-contraction during this interval (P = 0.009). Control subjects used higher extension moments, resulting in a higher net joint moment. Visual analysis revealed a timing difference between the MB and FB group. The FB group seems to co-contract approximately 20% later compared to the MB group. RA patients after total knee arthroplasty show a lower net knee joint moment and a higher co-contraction than controls indicating avoidance of net joint load and an active stabilization of the knee joint. MB and FB patients showed no difference in co-contraction levels, although timing in FB is closer to controls than MB subjects. Since visual analysis revealed a timing difference between the MB and FB group, this may express compensation by coordination. Rehabilitation programs for RA patients should include besides muscle strength training, elements of muscle-coordination training.
doi:10.1007/s00167-008-0537-7
PMCID: PMC2516179  PMID: 18478203
Mobile bearing knee; Knee stability; Co-contraction; Total knee arthroplasty; Rheumatoid arthritis

Results 1-9 (9)