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Biomedical subjects

W Rieger

Publications and source records attributed to W Rieger.

13 recordsLinked to original sources
PubMed2002

[Modification of form, material and modularity of threaded acetabulum cups].

The fixation principle of threaded cups ensures high primary stability. Inadequate results with first-generation threaded cups led to modifications of surface machining. 10 threaded cups of the first generation, and 27 of the second and third generations were systematically analysed and their shapes measured using a no-touch light section technique. In addition, measurements of surface roughness were performed. Implants of the first generation made of polyethylene, ceramic or cobalt-chrome have an average surface roughness (Ra) of 1.5 microns. Approximately one-half of these implants have a conical shape, and one-third a height that is greater than the radius. Threaded cups of the second generation are made either of CP-titanium or titanium alloy. The average corundum-blasted surface roughness is 4.5 microns. Hydroxyapatite-coated (HA) implants have a surface roughness of 5.0 microns. Approximately 45% of the implants have a conical, biconical or flattened-conical shape, while one-third are of hemispherical shape. Approximately 90% of the cups have a height that is up to 23% smaller than the radius. A few cups have a height that approximates the radius. Implants of the third generation with identical surface structure can be supplied with crosslinked-polyethylene inlays or, optionally, with metal/metal or ceramic/ceramic contact surfaces. Primary stability, biocompatible materials and a structured surface are essential for ensuring osseointegration over the long-term. Corundum-blasted pure titanium or titanium alloys with corundum-blasted or HA-coated implants can be considered standard for these cups.

Acetabulum↗
PubMed2001

Stress analysis of threaded cups.

Using finite element analysis we have studied the pelvic bony socket and compared it with radiological imaging using threaded acetabular cups of three different shapes (parabolic, conical, hemispherical). The two-dimensional model depicted a planar section through a left pelvic hemisphere. In all three cups the stress in the bony socket increased from lateral towards medial. Compressive stress was found on the superior and inferior parts of the cup, but mainly on the superior aspect, seen radiologically as new trabecular bone formation. The maximum compressive stresses were seen in the cranial curvature of the conical cup, with less in the parabolic form and least in the hemispheric form. The tensile stress at the bottom of the socket increased from the hemispheric to the conical shape. Radiological rarefaction gave an indication of lower stress. There was lower compressive stress between the teeth of the threads. This FE model uses computer simulation to predict bony changes with different designs of implant. The ability to simulate biological conditions is a valuable addition to the testing of mechanical strength.

Hip Joint↗
PubMed1984

Brain function in psychiatric disorders. II. Regional cerebral blood flow in medicated unipolar depressives.

Regional cerebral blood flow was measured during resting baseline and the performance of a verbal and a spatial task in 14 medicated depressives and 25 matched controls. Overall resting flows did not differ, nor were there hemispheric or anteroposterior differences between patients and controls for resting flows. Differences between patients and controls were evident during cognitive activity, and the effects were different for male and female patients. Depressed female patients had higher than normal flows in all conditions, whereas depressed male patients had lower than normal resting flows, which increased to normal during cognitive activity. Their anterior flows increased for the verbal task but not for the spatial task.

Adult↗
PubMed1983

Brain function in psychiatric disorders. I. Regional cerebral blood flow in medicated schizophrenics.

We measured regional cerebral blood flow during resting baseline and the performance of verbal and spatial tasks in 15 medicated schizophrenics and 25 matched controls. Patients did not differ from controls in resting flows but showed different blood-flow changes during task performance. Controls replicated earlier findings in normal subjects: flow increased during task performance, and the hemispheric increase was greater in the left for the verbal and in the right for the spatial task. In contrast, patients showed no flow asymmetry for the verbal task and greater left hemispheric increase for the spatial task. The latter finding is consistent with the hypothesis that schizophrenia is associated with left hemispheric overactivation for spatial tasks. In addition, schizophrenic women had unusual flow changes in that their highest flow increase was for the verbal task.

Adult↗
PubMed1983

Response to dexamethasone in psychotic depression.

The utility of the dexamethasone suppression test (DST) in the diagnosis of psychotic depression was examined by comparing the responses of 11 psychotic and 18 nonpsychotic depressed inpatients. Nine of 11 psychotic patients (81.8%) and 10 of 18 nonpsychotic patients (55.6%) showed nonsuppression (nonsignificant). Using the 0800h cortisol level alone, we found that significantly more psychotic patients (7 of 11; 63.6%) than nonpsychotic patients (3 of 18; 16.7%) showed nonsuppression. Nonsuppression at 0800h postdexamethasone may be a useful biologic marker for patients with psychotic depression. Implications of these data for the nosologic status of psychotic depression are discussed.

Adult↗