Accurate accuracy assessment: review of basic principles.
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Statistics as Topic↗
Biomedical subjects
L Ryd
Publications and source records attributed to L Ryd.
Radiation dose and image information in computed radiography. A phantom study of angle measurements in the weight-bearing knee.
PURPOSE: To establish a correlation between radiation dose and diagnostic accuracy when employing a new digital method for angle determinations. The specific intention was to determine how far the radiation dose can be reduced without losing measuring accuracy and to compare this radiation dose with that employed with our conventional method. MATERIAL AND METHODS: An image succession of an anthropomorphic phantom was generated with a computed radiography (CR) system, by reducing the exposure stepwise. The images were archived and transferred to a workstation for evaluation. The intraobserver variation of two angle determinations was used as an indicator of the evaluation accuracy. Patient radiation doses were measured with thermoluminescent dosimeters. The energy imparted, indicating the relative risk associated with exposure to ionising radiation, and the effective dose, which determines the absolute risk, were calculated. RESULTS AND CONCLUSION: No significant correlation was found between patient dose and measuring accuracy within the evaluated exposure interval. At the lowest exposure of the CR system, the energy imparted to the patient was 30 microJ. Compared with our conventional analogue method this is a reduction by 98%. The effective dose was as low as 1.5 microSv. The CR technique creates possibilities to adapt exposure parameters, and thus the radiation dose to the patient, according to the purpose of the investigation.
Ankle↗
Hydroxyapatite-enhanced tibial prosthetic fixation.
Sixty-two knees (60 patients) were randomized to four noncemented groups. In Groups 1, 3, and 4, the bone cuts were made with a cooled saw blade. In Group 1, 15 patients were operated on with the porous coated Osteonic 7000 tibial component. In Group 2, 15 patients were operated on with the same tibial component as in Group 1 but with the use of a standard saw blade. In Group 3, 16 patients were operated on with the hydroxyapatite-coated Osteonic tibial component, and in Group 4, 16 patients were operated on with the hydroxyapatite Duracon tibial component. All patients were followed up clinically and with roentgenstereometric analysis. There were no differences among the groups regarding clinical outcome. One knee was revised (Group 2) after 1 year because of loosening of the tibial component. The maximum migration at 1 year was 1.7 mm in Group 1, 1.9 mm in Group 2, 1.3 mm in Group 3, and 1 mm in Group 4. At the 2-year followup, the migrations were 1.8 mm, 1.5 mm, 1.4 mm, and 1 mm in Groups 1, 2, 3, and 4, respectively. The inducible displacement that occurred at 1 year was 0.6 mm in Group 1, 0.5 mm in Group 2, 0.4 mm in Group 3, and 0.4 mm in Group 4. The hydroxyapatite coating had a strong positive effect on the tibial component fixation. No prosthesis in the hydroxyapatite groups showed continuous migration.
Aged↗
Failure of partial cementation to achieve implant stability and bone ingrowth: a long-term roentgen stereophotogrammetric study of tibial components.
Thirty patients with gonarthrosis were operated on with the PCA primary total knee prosthesis and had the tibial component fixed to the bone by partial cementation. In the first two groups of patients, cementation was by a peripheral rim of high and low-viscosity cement, respectively. In the third group, the pegs were cemented with the low-viscosity cement. Follow-up was performed with use of clinical parameters and roentgen stereophotogrammetric analysis. Clinically, the series was successful apart from a problem with tibial component wear, necessitating revision in five patients. At 8 years, the mean Hospital for Special Surgery score was 81 points. Venn-diagram scores revealed four failures and three acceptable cases; the remaining cases were satisfactory. Apart from one loose patellar component, there was no mechanical loosening. Roentgen stereophotogrammetric analysis showed that the tibial components moved relative to the bone; this indicated fibrous tissue fixation, which was corroborated histologically in two patients. The objective, to achieve bone ingrowth, was thus not successfully met. Radiolucent lines were consistently seen, and their size correlated with the migration as measured by roentgen stereophotogrammetric analysis. Furthermore, five continuously migrating prostheses showed significantly larger radiolucent zones than the prostheses that migrated only initially, and they were less well bonded to the bone at 1 year. In conclusion, partial cementation does not appear to be a way to achieve bone ingrowth in porous-coated implants under load.
Aged↗
Gait affects tibial component fixation.
The prognosis of fixation in patients with total knee arthroplasty was classified as either good or poor based on migration results over 4 to 8 years using roentgen stereophotogrammetry. Gait analysis with the Vicon system was performed in 27 asymptomatic patients (1 bilateral), selected according to gender, implant design, age, and fixation principle to form two equivalent groups with different prognoses. The poor prognosis group walked with a predominantly flexing moment and higher moment peaks in the sagittal plane compared with the good prognosis group, in which moments were abnormally small. We conclude that individual gait patterns and subsequent differences in joint loading affect tibial component fixation.
Aged↗
Major bone transplantation in total knee arthroplasty: a 2- to 9-year radiostereometric analysis of tibial implant stability.
Eight total knee arthroplasties involving major bone grafting to repair noncontained defects of the proximal tibia were studied. In all knees, autologous bone was used. Cement was used for implant fixation. At follow-up evaluation 5 years after surgery, 7 knees had excellent results, and 1 had fair results; the mean Hospital for Special Surgery score was 84. Radiostereometric analysis showed a mean migration of 0.5 mm (range, 0.2-1.5 mm). None of the knees in which major structural autologous bone grafting was used showed increased micromotion of the adjacent tibial implant.
Aged↗
Accurate accuracy assessment: review of basic principles.
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Humans↗
The use of isolated patellar prostheses in Sweden 1977-1986.
During 1977 to 1986, 106 patients had isolated patellar prostheses, with both patellar and femoral components, inserted in 20 different hospitals in Sweden. At follow up, 7 years (range 3 to 14 years) after operation, 9 patients had died so that 97 patients with operations on 113 knees were included in this study. Thirty-three (38 knees) had been operated on before or after a prosthesis had been inserted. At follow-up, 75% were satisfied with the operation; 83% had improved, 59% could walk without an aid and 44% had no, or only occasional, pain in the knee. These results encourage the use of an isolated patellar prosthesis in cases of advanced and disabling localised patellar arthrosis. There is no place for this operation in the treatment of chondromalacia.
Adolescent↗
Longitudinal and cross-sectional variability in markers of joint metabolism in patients with knee pain and articular cartilage abnormalities.
OBJECTIVE: To determine the within- and between-patient variability in the concentrations of synovial fluid, serum and urine markers of joint tissue metabolism in a cohort of patients with knee pain and cartilage changes consistent with early-stage knee osteoarthritis. DESIGN: Samples of synovial fluid, serum, and urine were obtained from 52 patients on eight different occasions during 1 year, as part of a clinical trial in patients with cartilage abnormalities and knee pain. In joint fluid, aggrecan fragments were quantified by dye precipitation and enzyme-linked immunosorbent assay (ELISA), and matrix metalloproteinases-1 and -3, and tissue inhibitor of metalloproteinases-1 by sandwich ELISAs. In serum, keratan sulfate was quantified by ELISA. Type I collagen N-telopeptide cross-links in urine were determined by ELISA. RESULTS: The degree of cross-sectional variability in marker concentrations did not vary between the different sampling occasions, and did not differ between the periods of weeks 0 (baseline), 1-4 (treatment) and 13-26 (follow-up). Both between-patient and within-patient coefficients of variation varied for markers in different body fluid compartments, with the lowest variability for serum keratan sulfate, followed by urine type I collagen N-telopeptide crosslinks, and the highest for synovial fluid markers. For synovial fluid, aggrecan fragments showed the least variability, and matrix metalloproteinases the highest. One patient with septic arthritis showed a fivefold peak increase in joint fluid aggrecan fragment concentrations, while the concentration of matrix metalloproteinase-3 increased 100-fold. CONCLUSIONS: Molecular markers of joint tissue metabolism have been suggested as, for example, outcome measures for clinical trials of disease-modifying drugs in osteoarthritis. This report is the first to present data on between- and within-patient variability for such molecular markers in three different body fluid compartments in stable cohort of patients. The availability of such data enables calculations to determine the number of patients needed in prospective studies using these markers as outcome measures.
Adult↗
Simultaneous measurements of sagittal knee laxity with an external device and radiostereometric analysis.
We obtained simultaneous measurements of sagittal knee laxity in 12 consecutive patients after reconstruction of the anterior cruciate ligament (ACL), using the Stryker laxity tester and radiostereometric analysis (RSA). The mean anteroposterior (AP) displacement when a 90 N load was applied in both directions was 5.3 +/- 2.7 mm with RSA and 9.8 +/- 1.6 mm with the external device (p < 0.001). The corresponding measurements at a load of 180 N were 5.7 +/- 2.4 mm and 13.8 +/- 3.7 mm, respectively (p < 0.001). More than 50% of the sagittal knee movement, as measured by the external device at a load of 180 N, was not true femorotibial displacement of the joint but was due to soft-tissue deformation.
Adolescent↗
Fixation of the tibial component of total knee arthroplasty after high tibial osteotomy: a matched radiostereometric study.
To assess migration of the tibial component we used roentgen stereophotogrammetric analysis in 40 patients who had had a total knee arthroplasty after failure of a closing wedge osteotomy and compared them with 40 matched patients after primary total knee arthroplasty. We found no difference in migration over time or in the tendency for continuous migration between the two groups. There were no differences in alignment or position of the knee prosthesis or in the clinical outcome. Our findings show that revision of a failed high tibial osteotomy to a total knee arthroplasty is effective.
Aged↗
Assessment of image post-processing and of measuring assistance tools in computed radiography. Evaluation of the weight-bearing knee.
PURPOSE: A system for the examination and measurement of the weight-bearing knee was adapted to computed radiography (CR) and to a picture archiving and communication system (PACS). The examination and measurement system was developed on examination equipment used for QUESTOR precision radiography (QPR). For an easier and more standardised localisation of bony landmarks on the screen, 4 measuring assistance tools (MATs) were developed. The aim of this study was to evaluate the usefulness of the tools developed and of image post-processing, specifically as magnification (zoom) and filtering (edge enhancement), by determining intra-observer variation in the measurement of angles and distances. MATERIAL AND METHODS: The original QPR measurement program, generating 19 angles and distances corrected for parallax and magnification, was converted and installed on a multi-modality workstation (Imtec Image 1200). A CR system (Fuji AC-2) was used for the generation of the related images and the measurements were made on the workstation. Four unilateral examinations of weight-bearing knees were undertaken. These examinations were measured twice under 5 different measurement conditions by 4 viewers. RESULTS AND CONCLUSIONS: The most important factor in reducing intra-observer variation was the ability to magnify (zoom) the images. The MATs also reduced variation. Filtering (edge enhancement), however, did not affect precision.
Biomechanical Phenomena↗
Restoration of the mechanical axis of the lower limb--a case report of perichondrium grafting of the medial femoral condyle.
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Adult↗
Early inducible displacement of tibial components in total knee prostheses inserted with and without cement: a randomized study with roentgen stereophotogrammetric analysis.
The fixation of tibial components randomized to insertion with or without cement in twenty-six knees was examined for inducible displacement at six weeks and one year postoperatively with use of roentgen stereophotogrammetric analysis. Furthermore, migration was studied during the first two postoperative years. Inducible displacement was found in all knees at both the six-week and the one-year follow-up examination, but no differences were detected with respect to the type of fixation (p > 0.05). All tibial components migrated for as long as one year postoperatively, after which most stabilized. No difference was found between the groups with respect to migration during the first two years postoperatively (p > 0.05), with the exception of subsidence of the component, which was found to be 0.0+/-0.1 millimeter (mean and standard error of the mean) for the components inserted with cement and 0.5+/-0.1 millimeter for the components inserted without cement (p < 0.01). Migration after one year was the same for both groups. We found a relationship between inducible displacement at six weeks and at one year as well as one between inducible displacement and migration at one year. To our knowledge, the present study is the first in which the micromotion of an interference-fit prosthesis was found to be similar to that of a device inserted with cement. The results of the present study emphasize the importance of the initial prosthetic fixation.
Aged↗
Error propagation for relative motion determined from marker positions.
In this paper, the error propagation for relative motion reconstructed from noisy marker position data was investigated, particularly the influence of the distance between two rigid bodies was explored. Based on a mathematical derivation, an error propagation model for relative motion was proposed and computer simulations were used to validate the proposed model. The results indicated that the error in the translation components for relative motion between two rigid bodies are proportional to the distance between the rigid bodies. The maximum absolute difference between the model and the simulation is 0.58% which strongly validated the accuracy of the error propagation model.
Computer Simulation↗
Wear in retrieved condylar knee arthroplasties. A comparison of wear in different designs of 280 retrieved condylar knee prostheses.
The plastic components of 280 retrieved unicondylar and total knee arthroplasties were studied. Wear was visually scored using a relative ranked data method. Although wear on the components was highly variable, several conclusions could be drawn regarding the nature and causes. Wear was associated more with the medial than the lateral condyle. Delamination was the most severe type of wear and occurred in short (< 5 year)-, medium (5-10 years)-, and long (> 10 years)-term retrievals. In the short term, delamination wear was associated with hot pressing of the tibial plastic or with fracture of the tibial baseplate. For a single design, a significant difference in the amount of delamination on hot-pressed and non-hot-pressed tibial components was observed. In medium- and long-term retrieved specimens of the designs with moderately high conformity, delamination wear was associated with restriction of rotational movement of the femoral component or with abrupt changes in the radius of the tibial component. In flatter, less conforming designs, wear was associated with laxity, such that the polyethylene delaminated toward the edges of the tibial component. Wear attributed to cement abrasion or entrapment occurred on the more conforming designs. Delamination was associated with the presence of fusion defects in the polyethylene but could also occur in the absence of such defects. That delamination was the principal were type and that this is caused by a fatigue mechanism mean that the incidence of failure could accelerate considerably over follow-up periods beyond 10 years. Designs of moderate conformity without abrupt changes in radii may prolong the duration of plastic tibial components before serious delamination occurs.
Cementation↗
Computed radiography for characterisation of the weight-bearing knee.
PURPOSE: A new method for examining and measuring the weight-bearing knee in computed radiography (CR) and picture archiving and communication systems (PACS) has recently been developed on examination equipment used in QUESTOR Precision Radiography (QPR). QPR is a method for the standardised examination of the knee, and generates 9 angles (e.g. hip-knee-ankle (HKA) angle) and 10 distances, corrected for parallax and magnification. The aim of this present study was to evaluate the reproducibility of this newly developed method and to determine intra- and interobserver variation in its measurements. MATERIAL AND METHODS: The images were generated on a CR system, archived, and transferred to a multimodality work-station that had a monitor with a resolution of 1280x1024 (1kx1k). Photostimulable phosphor plates were used to generate images with a matrix of 1760x2140 pixels (pixel size 0.2 mm, corresponding resolution 2.5 1p/mm). Ten volunteers without knee problems were examined twice, bilaterally, by 2 different radiology technologists. RESULTS: The total reproducibility of the method was good, offering an HKA reproducibility of +/-2.64 degrees in slight flexion and +/-1.62 degrees in extension, at 95% confidence. The intra- and inter-observer variations were low with a reduction of the intra-observer variations in all measurements (except one) by a factor of 2.8 on average compared with the original QPR method for conventional film-screen radiography. CONCLUSION: When QPR is modified for CR, it fulfils the requirement of reproducibility in measurements of the weight-bearing knee.
Adult↗
Persistent stability 3 years after reconstruction of the anterior cruciate ligament. A radiostereometric analysis (RSA) of 20 patients.
We measured, by radiostereometric analysis (RSA), the sagittal knee laxity in 20 consecutive patients with chronic anterior cruciate ligament injuries before, 1 year and 3 years after reconstruction with a free bone-patellar tendon-bone graft. The grafts had been perioperatively tensioned, using a 10-15 N load. An increased displacement with increasing load was present before reconstruction, but we found no differences between 100 and 150 N stress load 1 and 3 years after the operation. The total anteroposterior displacement decreased from 12.7 mm before the reconstruction to 5.1 mm 1 year and 5.6 mm 3 years postoperatively, using a stress load of 150 N. Thus, we found both a definite end-point of joint displacement and persistent stability without elongation of the graft with time, when care was taken not to over-constrain the knee by a high initial graft tension.
Adult↗