SummaryDuring osteoporosis induction in sheep, side effects of the steroids were observed in previous studies. The aim of this study was to improve the induction regimen consisting of ovariectomy, calcium/vitamin D- restricted diet and methylprednisolone (-MP)- medication with respect to the bone metabolism and to reduce the adverse side effects. Thirty-six ewes (age 6.5 ± 0.6 years) were divided into four MP-administration groups (n=9) with a total dose of 1800 mg MP: group 1: 20 mg/day, group 2: 60 mg/ every third day, group 3: 3x 500 mg and 1x 300 mg at intervals of three weeks, group 4: weekly administration, starting at 70 mg and weekly reduction by 10 mg. After double-labelling with Calcein Green and Xylenol Orange, bone biopsy specimens were taken from the iliac crest (IC) at the beginning and four weeks after the last MP injection, and additionally from the vertebral body (VB) at the end of the experiment. Bone samples were processed into stained and fluorescent sections, static and dynamic measurements were performed. There were no significant differences for static parameters between the groups initially. The bone perimeter and the bone area values were significantly higher in the VB than in the IC (Pm: 26%, p<0.0001, Ar: 11%, p<0.0166). A significant decrease (20%) of the bone area was observed after corticosteroid- induced osteoporosis (p<0.0004). For the dynamic parameters, no significant difference between the groups was found. Presence of Calcein Green and Xylenol Orange labels were noted in 50% of the biopsies in the IC, 100% in the VB. Group 3 showed the lowest prevalence of adverse side effects. The bone metabolism changes were observed in all four groups, and the VB bone metabolism was higher when compared to the IC. In conclusion, when using equal amounts of steroids adverse side effects can be reduced by decreasing the number of administrations without reducing the effect regarding corticosteroid- induced osteoporosis. This information is useful to reduce the discomfort of the animals in this sheep model of corticosteroid-induced osteoporosis.

Fragestellung: Berstungsfrakturen der Brust- und Lendenwirbelsäule, Spondylitiden mit Destruktion und Metastasen erfordern eine Korporektomie des betroffenen Wirbelkörpers mit anschließender Rekonstruktion. Diese Erkrankungen finden sich gehäuft im Senium. Nach Korporektomie sind solitär ventrale sowie kombiniert dorso-ventrale Verfahren beschrieben, sie werden bezüglich der erreichbaren Primärstabilität kontrovers diskutiert. Unklar ist der Einfluss der Knochendichte auf die Primärstabilität.

In this study we test the hypotheses that mechanical bone strength in elderly individuals displays substantial heterogeneity among clinically relevant skeletal sites, that ex situ dual-energy X-ray absorptiometry (DXA) provides better estimates of bone strength than in situ DXA, but that a site-specific approach of bone densitometry is nevertheless superior for optimal prediction of bone failure under in situ conditions. DXA measurements were obtained of the lumbar spine, the left femur, the left radius, and the total body in 110 human cadavers (age, 80.6 +/- 10.5 years; 72 female, 38 male), including the skin and soft tissues. The bones were then excised, spinal and femoral DXA being repeated ex situ. Mechanical failure tests were performed on thoracic vertebra 10 and lumbar vertebra 3 (compressive loading of a functional unit), the left and right femur (side impact and vertical loading configuration), and the left and right distal radius (fall configuration, axial compression, and 3-point-bending). The failure loads displayed only very moderate correlation among sites (r = 0.39 to 0.63). Ex situ DXA displayed slightly higher correlations with failure loads compared with those of in situ DXA, but the differences were not significant and relatively small. Under in situ conditions, DXA predicted 50-60% of the variability in bone failure loads at identical (or closely adjacent) sites, but only around 20-35% at distant sites, advocating a site-specific approach of densitometry. These data suggest that mechanical competence in the elderly is governed by strong regional variation, and that its loss in osteoporosis may not represent a strictly systemic process.

The material properties of our bones are crucial factors in their risk to fracture. With osteoporosis, bone strength is reduced due to a loss of bone mass and a diminution of structural integrity. Bone mass can be assessed easily and precisely. For this reason prediction of bone fracture risk is nowadays merely based on bone mineral density measurements. Bone mineral density alone, however, does not suffice to predict bone fracture risk for individual patients.1-3Improved risk prediction should include bone structure as well.4-8

s from the Sixth Meeting of the International Society for Fracture Repair; September 23-26, 1998; Strasbourg, France

Mit zunehmendem Alter und Osteoporose ist ein Abfall der kortikalen Knochendicke zu beobachten. Viele Fixationsmethoden mit guten Ergebnissen in gesundem Knochen basieren auf einer Verankerung in der Kortikalis mittels Schrauben. Aus der Klinik werden jedoch Probleme wie Schraubenausrisse oder eine unzureichende Primärfestigkeit berichtet, wenn diese Implantate in osteoporotischem Knochen eingesetzt werden. Das Ausdünnen der Kortikalis ist dabei eine der Hauptursachen für das Versagen, aber auch das Design des Implantats bestimmt, wie physiologische Lasten durch die Schnittstelle von Schraube und Knochen übertragen werden. Ziel der Studie war, den Einfluß der kortikalen Dicke sowie der Lastrichtung am Schraubenkopf auf die maximale Haltekraft einer monokortikal verankerten Schraube zu bestimmen. Es wurden Auszugstests von Schrauben aus kortikalen Rinderknochenplättchen unterschiedlicher Dicke (1–3 mm) durchgeführt. Der Schraubenkopf war dabei wie bei einem internen Fixateur winkelstabil verankert. Der Lastwinkel wurde zwischen einer reinen Auszugsrichtung und einer Scherbelastung senkrecht zur Schraubenachse variiert. Mit Abnahme der Kortikalisdicke konnte ein signifikanter, linearer Zusammenhang zwischen der dadurch reduzierten Anzahl verankerter Gewindegänge im Knochen und der Haltekraft der Schraube beobachtet werden. Des weiteren zeigten die Ergebnisse, daß eine Veränderung der Lastrichtung von einer Auszugs- zu einer Scherbelastung der Schraube zu einer signifikanten Erhöhung der Verankerungsfestigkeit führt.