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Denmark↗
Biomedical subjects
Thomas Kiaer
Publications and source records attributed to Thomas Kiaer.
Pelvic orientation and assessment of hip dysplasia in adults.
BACKGROUND: The study was performed to qualify the source material of 4151 pelvic radiographs for the research into the relationship between unrecognised childhood hip disorders and the development of hip osteoarthrosis, and to investigate the effect of varying degrees of pelvic tilt and rotation on the measurements of radiographic indices of hip dysplasia. MATERIAL AND METHODS: We investigated the effect of varying pelvic orientation on radiographic measurements of acetabular dysplasia using a cadaver model. Results from the cadaver study were used to validate the radiographic assessments of acetabular dysplasia in the longitudinal survey cohort of the Copenhagen City Heart Study (CCHS; Osteoarthrosis Sub-study). 1) Cadaver pelvises and proximal femurs from a male and a female donor were mounted anatomically in holding devices allowing independent inclination/reclination and rotation. An AP pelvic radiograph was recorded at each 3 degrees increment. The most widely used radiographic parameters of hip dysplasia were assessed. 2) Critical limits of acceptable rotation and inclination/reclination of pelvises were determined on 4151 standing, standardised pelvic radiographs of the CCHS cohort. RESULTS: Wiberg's CE angle, Sharp's angle, the x-coordinate of Goodman's Cartesian coordinate system, and the acetabular depth ratio were significantly affected by varying rotation and inclination/reclination of the cadaver pelvises. Femoral head extrusion index was not significantly affected within the applied rotation and inclination/reclination of the cadaver study. Application of the corresponding critical limits of Tönnis' foramen obturator index of 0.7-1.8 meant that 188 of 4151 (4.5%) of the CCHS-III pelvic radiographs had to be omitted from further studies. INTERPRETATION: To ensure a neutral starting point and reproducible readings, especially in epidemiological and clinical studies, and when performing preoperative planning and follow-up of patients undergoing redirectional pelvic osteotomies, it is important that all aspects of the radiographic examination are controlled and reproducible. Furthermore, we found that studies of acetabular dysplasia based on supine urograms or colon radiographs without information about pelvic orientation, centering of the X-ray beam and tube to film distance, run a serious risk of erroneous measurements.
Acetabulum↗
Nonlinear finite-element analysis and biomechanical evaluation of the lumbar spine.
A finite-element analysis (FEA) model of an intact lumbar disc-body unit was generated. The vertebral body of the FEA model consisted of a solid tetrahedral core of trabecular bone surrounded by a cortical shell. The disc consisted of an incompressible nucleus surrounded by nonlinear annulus fibers embedded in a solid ground substance. The purpose was to create a FEA model suitable for clinical purposes as fracture assessment, instrumentation with pedicle screws, and bone remodeling. Testing of the FEA model was performed nonlinear for a number of loading conditions, and the results were compared with experimental data from the literature. The results showed good agreement. The formulation of the FEA model can be justified for the tested loading conditions.
Compressive Strength↗
No difference in clinical outcome after posterolateral lumbar fusion between patients with isthmic spondylolisthesis and those with degenerative disc disease using pedicle screw instrumentation: a comparative study of 112 patients with 4 years of follow-up.
We compared the clinical outcome after spinal fusion between patients with isthmic spondylolisthesis and those with degenerative disc disease of the lumbar spine, using multiple logistic regression analysis. A questionnaire describing medication, pain, vocational status and patient satisfaction was mailed to all the patients at a median interval of 4 years after their operation. Fusion was evaluated on plain radiographs at a minimum of 12 months after surgery, and patients were classified as fused or not fused. The overall satisfaction rate was 70%. The results of the present study showed no difference in the outcome after spinal fusion between the two groups of patients. The factors that significantly increased the likelihood of an optimal result - defined as patient satisfaction, return to work, and reduced medication - were male gender, being in work prior to surgery, and being a non-smoker. Since spinal fusion is an expensive treatment with potentially serious risks, and leaves one-third of the patients with an unsatisfactory result, we believe that more studies focusing on the indications for surgery should be performed.
Adolescent↗