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Background Aseptic loosening remains a challenging problem after total hip arthroplasty. Accurate cup placement and supplementation of antioxidants in acetabular liners might reduce material failure rates. The aim of this study is to assess the effect of the cup position on the wear behaviour of UHMWPE-XE and UHMWPE-X liners in vivo using virtual radiographs. Methods We conducted a prospective, randomized, controlled, multicenter trial. Clinical data of 372 probands were analyzed. Anteroposterior pelvic X-rays of 324 patients immediately postoperatively and after 1 and 5 years were evaluated by the RayMatch® analysis software regarding cup position and wear behaviour. Results Mean cup anteversion was 20.3° (± 7.4) and inclination was 41.9° (± 7.0) postoperatively. 62.3% of all patients had an anteversion and inclination within the Lewinnek safe zone. Anterior and anterolateral approaches led to significantly higher cup anteversion compared to lateral approaches (27.3° ± 5.5; 20.9° ± 7.2; 17.5° ± 6.6; p p = 0.001, respectively). Mean anteversion increased to 24.6° (± 8.0) after 1 year (p p = 0.012) and this was amplified when inclination angles were ≥ 50° (23.6 µm/year ± 12.8 vs. 38.0 µm/year ± 22.7, p = 0.062). Conclusion Anterior approaches lead to the highest inaccuracy of cup placement, but cup positioning outside the Lewinnek safe zone does not necessarily cause higher dislocation rates. Moreover, mean anteversion increased by approximately four degrees within the first year after operation, which is expected to be functional due to a regularization of pelvic tilt after intervention. Mid-term wear rates of UHMWPE-X and UHMWPE-XE liners are comparable, but steep cup positions lead to significantly increased polyethylene wear. In summary, a re-evaluation of target zones for intraoperative cup positioning might be considered. In the long-term reduced oxidative embrittlement could lead to superior wear behaviour of vitamin E-blended liners.

In 1992 Von Korff and his co-workers developed a simple, brief questionnaire to assess the severity of chronic pain problems, the Chronic Pain Grade (CPG). The present study was conducted to analyse the psychometric properties of the translated German version of the CPG within a population of primary care back pain patients (n=130). Factor analysis yielded two factors which accounted for 72% of the variance of the questionnaire. The first factor 'Disability Score' (53.56% of the variance) revealed a good internal consistency (alpha=.88), the internal consistency of the second factor 'Characteristic Pain Intensity' was moderate (alpha=.68). The reliability of the whole instrument was good (alpha=.82). The CPG and its subscales show moderate to high relations with other instruments assessing the patient's disability (FFbH-R, Pain Disability Index PDI). Additionally weak to moderate but significant correlations were found between the CPG and other measures of grading and staging chronic pain (MPSS, RGS). Further, positive correlations between the CPG and both, the frequency of doctor visits and the frequent use of pain medication have been seen. The reported findings suggest, that the German version of the CPG is a reliable, valid and useful instrument if a brief, simple method of grading the severity of chronic pain is needed. The German version leads to a better comparability between German and English language studies and facilitates an international collaboration in this field of research. Von Korff et al. entwickelten 1992 einen einfachen, kurzen Fragebogen zur Erfassung des Schweregrades von chronischen Schmerzerkrankungen, den "Chronic Pain Grade" (CPG). Die hier vorgestellte Studie wurde durchgeführt, um die psychometrischen Eigenschaften der deutschen Übersetzung des CPG an einer Stichprobe chronischer Rückenschmerzpatienten aus der primärärztlichen Versorgung (n=130) zu überprüfen. Eine Faktorenanalyse führte zu zwei Faktoren, die insgesamt 72% der Varianz aufklären. Der erste Faktor "Disability Score" (53.56% Varianzaufklärung) weist eine gute innere Konsistenz auf (Cronbach's alpha = .88), die Reliabilität des zweiten Faktors "Characteristic Pain Intensity" ist zufriedenstellend (Cronbach's alpha = .68). Die innere Konsistenz für das gesamte Verfahren ist gut (Cronbach's alpha = .82). Der CPG und seine Subskalen weisen mittlere bis hohe Korrelationen mit weiteren Instrumenten zur Erfassung von körperlicher bzw. psychosozialer Beeinträchtigung auf (Funktionsfragebogen Hannover-Rücken FFbH-R, PDI). Des Weiteren konnten schwache bis mäßige, aber statistisch signifikante Korrelationen mit anderen Staging- bzw. Grading-Instrumenten (MPSS, RGS) gefunden werden. Schließlich zeigten sich mit zunehmendem Schweregrad im CPG eine Zunahme der Anzahl von Arztbesuchen sowie eine vermehrte Einnahme von Schmerzmedikamenten. Die deutsche Version des CPG erwies sich damit als ein reliables und valides Instrument zur Erhebung des Schweregrades chronischer Schmerzen, welches einfach in der Handhabung ist und die Vergleichbarkeit zwischen englisch- und deutschsprachigen Forschungsarbeiten erleichtert.