| 1. |
- Ericson, Anne, et al.
(författare)
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Computed tomography analysis of radiostereometric data to determine flexion axes after total joint replacement : Application to the elbow joint
- 2010
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Ingår i: Journal of Biomechanics. - : Elsevier BV. - 0021-9290 .- 1873-2380. ; 43:10, s. 1947-1952
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Tidskriftsartikel (refereegranskat)abstract
- Kinematic analysis for in vivo assessment of elbow endoprostheses requires knowledge of the exact positions of motion axes relative to bony landmarks or the prosthesis. A prosthesis-based reference system is required for comparison between individuals and studies. The primary aim of this study was to further develop an earlier described algorithm for fusion of radiostereometric analysis (RSA) data and data obtained in 3D computed tomography (CT) for application to the elbow after total joint replacement. The secondary aim was to propose a method for marking of prostheses in 3D CT, enabling definition of a prosthesis-based reference system. Six patients with elbow endoprostheses were investigated. The fusion of data made it possible to visualize the motion axes in relation to the prostheses in the 3D CT volume. The differences between two repeated positioning repetitions of the longitudinal prosthesis axis were less than 0.6 degrees in the frontal and sagittal planes. Corresponding values for the transverse axis were less than 0.6 degrees in the frontal and less than 1.4 degrees (in four out of six less than 0.6 degrees) in the horizontal plane. This study shows that by fusion of CT and RSA data it is possible to determine the accurate position of the flexion axes of the elbow joint after total joint replacement in vivo. The proposed method for implant marking and registration of reference axes enables comparison of prosthesis function between patients and studies.
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| 2. |
- Ericson, Anne, et al.
(författare)
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Fusion of radio stereometric analysis data into computed tomography space : Application to the elbow joint
- 2007
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Ingår i: Journal of Biomechanics. - Oxford, UK : Elsevier Science Ltd. - 0021-9290 .- 1873-2380. ; 40:2, s. 296-304
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Tidskriftsartikel (refereegranskat)abstract
- Improvement of joint prostheses is dependent upon information concerning the biomechanical properties of the joint. Radiostereometric analysis (RSA) and electromagnetic techniques have been applied in previous cadaver and in vivo studies on the elbow joint to provide valuable information concerning joint motion axes. However, such information is limited to mathematically calculated positions of the axes according to an orthogonal coordinate system and is difficult to relate to individual skeletal anatomy. The aim of this study was to evaluate the in vivo application of a new fusion method to provide three-dimensional (31)) visualization of flexion axes according to bony landmarks. In vivo RSA data of the elbow joint's flexion axes was combined with data obtained by 3D computed tomography (CT). Results were obtained from five healthy subjects after one was excluded due to an instable RSA marker. The median error between imported and transformed RSA marker coordinates and those obtained in the CT volume was 0.22mm. Median maximal rotation error after transformation of the rigid RSA body to the CT volume was 0.003 degrees. Points of interception with a plane calculated in the RSA orthogonal coordinate system were imported into the CT volume, facilitating the 3D visualization of the flexion axes. This study demonstrates a successful fusion of RSA and CT data, without significant loss of RSA accuracy. The method could be used for relating individual motion axes to a 3D representation of relevant joint anatomy, thus providing important information for clinical applications such as the development of joint prostheses.
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| 3. |
- Jedenmalm, Anneli, et al.
(författare)
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Validation of a 3D CT method for measurement of linear wear of acetabular cups : A hip simulator study
- 2011
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Ingår i: Acta Orthopaedica. - : Medical Journals Sweden AB. - 1745-3674 .- 1745-3682. ; 82:1, s. 35-41
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Tidskriftsartikel (refereegranskat)abstract
- Material and methods Ultra-high molecular weight polyethylene cups with a titanium mesh molded on the outside were subjected to wear using a hip simulator. Before and after wear, they were (1) imaged with a CT scanner using a phantom model device, (2) measured using a coordinate measurement machine (CMM), and (3) weighed. CMM was used as the reference method for measurement of femoral head penetration into the cup and for comparison with CT, and gravimetric measurements were used as a reference for both CT and CMM. Femoral head penetration and wear vector angle were studied. The head diameters were also measured with both CMM and CT. The repeatability of the method proposed was evaluated with two repeated measurements using different positions of the phantom in the CT scanner. Results The accuracy of the 3D CT method for evaluation of linear wear was 0.51 mm and the repeatability was 0.39 mm. Repeatability for wear vector angle was 17 degrees A degrees. Interpretation This study of metal-meshed hip-simulated acetabular cups shows that CT has the capacity for reliable measurement of linear wear of acetabular cups at a clinically relevant level of accuracy.
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| 4. |
- Olivecrona, Henrik, et al.
(författare)
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A new CT method for measuring cup orientation after total hip arthroplasty : A study of 10 patients
- 2004
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Ingår i: Acta Orthopaedica Scandinavica. - : Medical Journals Sweden AB. - 0001-6470. ; 75:3, s. 252-260
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Tidskriftsartikel (refereegranskat)abstract
- Background It is difficult to assess the orientation of the acetabular component on routine radiographs. We present a method for determining the spatial orientation of the acetabular component after total hip arthroplasty (THA) using computed tomography. Patients and methods Two CT-scans, 10 min apart, were obtained from each of 10 patients after THA. Using locally developed software, two independent examiners measured the orientation of the acetabular component in relation to the pelvis. The measurements were repeated after one week. To be independent of the patient position during scanning, the method involved two steps. Firstly, a 3D volumetric image of the pelvis was brought into a standard pelvic orientation, then the orientation of the acetabular component was measured. The orientation of the acetabular component was expressed as operative anteversion and inclination relative to an internal pelvic reference coordinate system. To evaluate precision, we compared measurements across pairs of CT volumes between observers and trials. Results Mean absolute interobserver angle error was 2.3degrees for anteversion (range 0-6.6degrees), and 1.1degrees for inclination (range 0-4.6degrees). For interobserver measurements, the precision, defined as one standard deviation, was 2.9degrees for anteversion, and 1.5degrees for inclination. A Student's West showed that the overall differences between the examiners, trials, and cases were not significant. Data were normally distributed and were not dependent on examiner or trial. Interpretation We conclude that the implant angles of the acetabular component in relation to the pelvis could be detected repeatedly using CT, independently of patient positioning.
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| 5. |
- Olivecrona, Lotta, et al.
(författare)
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Standard orientation of the pelvis : Validation on a model and ten patients
- 2005
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Ingår i: Acta Radiologica. - London, UK : Informa Healthcare. - 0284-1851 .- 1600-0455. ; 46:1, s. 74-82
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To validate an image post-processing method for re-orienting the pelvis in CT volumes to a standardized orientation in a model and in 10 patients. Material and Methods: Twenty-four CT volumes of a pelvic model and 10 pairs of postoperative total hip arthroplasty (THA) patient CT scans were rotated to a defined pelvic standard orientation and the rotation was recorded. For precision, a test-retest procedure was used. For accuracy, three exactly represented coordinate points were used. For clinical application, the standard orientation was used for calculating the direction of acetabular cup migration from a previous model study. Results: Precision of pelvic standard orientation, calculated as maximal directional error, was better than 1degrees in the model study and better than 1.5degrees in the patient study. Accuracy, expressed as angle between ideal and measured coordinate axes, was 0.1degrees for x, y, z axes. No measurable systematic errors were found. When applied to acetabular cup migration in the model, standardization of pelvic orientation had no significant effect on the measurements. Conclusion: Reorienting the pelvis during image post-processing was shown to be accurate. It enables measurements relative to the pelvis and minimizes the dependency of patient positioning.
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