The aim of this study was to determine whether reamed or unreamed nailing is more harmful to local bone perfusion and increases fat occlusion of transcortical vessels.Methods: After creating a standard fracture of the sheep tibia, reaming was performed in the first group using an experimental optimised reaming system (RE), in the second group with the conventional AO reamer (RC). Unreamed nailing was performed in the third group (UN). UHN 7 5 mm titanium was. inserted in all three groups. Intramedullary pressure was measured intraoperatively. Quantitative histological analyses of the bone were performed postoperatively.Results: The highest fat occlusion of transcortical vessels occurred in UN (5.7%), the lowest in RE (1.6%). The least harm to intracortical circulation was caused by RE with 28% perfused intracortical vessels compared to 17% (UN) and 18% (RC).Conclusion: The experimental optimised reaming system reduces circulatory disturbance and local fat occlusion compared to the existing nailing procedures. (c) 2009 Elsevier Ltd. All rights reserved.

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.

BACKGROUND:Despite the use of intramedullary fixation devices for the stabilisation of intertrochanteric fractures, the rate of complications is still high. One of the main reasons for burdensome reinterventions in 9-15% of cases is the cutting out of the fixation device through both the spongious bone and the cortical bone at the apex of the femoral head. This phenomenon is strongly connected to the reduction of the fractures achieved, the technical performance of the operation with optimal implant positioning and the resistance of the trabecular bone in the femoral head against deformation by the fixation device. The latter is very low in cases of severe osteoporosis. To prevent the complication of cutting out, it seems sensible to find the limits of load-bearing capacity of individual osteoporosis-associated features (i.e. bone mineral density) at which special additional measures or other techniques for the treatment of these patients are desired.METHODS:In a first step a new biomechanical standard test for implants stabilizing unstable trochanteric fractures was developed, which would provide predictable results depending on bone mineral density. In a second step a cut-off limit was sought for the bone density in the proximal femur that would afford stable fixation as measured by QCT (quantitative computed tomography) and DEXA (dual-energy X-ray absorptiometry).RESULTS:The developed test is realistic; it can be used to study typical cutting out phenomena on cadaver femora. In an unstable fracture model (type A 2.3 of the AO classification), the implants DHS with TSP, PFN and TGN showed a stable long-term load-bearing capacity at a bone mineral density of >0.6 g/cm3. In 5 of 32 specimens a cutting out phenomenon could be demonstrated, in 4 cases if the bone mineral density of the proximal femur was below 0.6 g/cm3 as measured by DEXA, and in one case poor performance of the implant (short screw in the femoral head) was evident.CONCLUSIONS:In cases of bone density of >0.6 g/cm3 in the proximal femur (DEXA), the standard implants for the fixation of unstable trochanteric fractures could guarantee fixation without cutting out. The critical value of sufficient bone density in our few cases seems to be around 0.6 g/cm3 as measured by DEXA. Further investigation is needed to define the limits of bone mineral density for a successful osteosynthesis. An appropriate augmentation of the trabecular bone of the femoral head or a new design of the central loading device could increase the load-bearing capacity and thus help to reduce the cutting out phenomenon. Another alternative could be the primary implantation of an endoprosthesis in the treatment of these patients.

We investigated several factors which affect the stability of cortical screws in osteoporotic bone using 18 femora from cadavers of women aged between 45 and 96 years (mean 76). We performed bone densitometry to measure the bone mineral density of the cortical and cancellous bone of the shaft and head of the femur, respectively. The thickness and overall bone mass of the cortical layer of the shaft of the femur were measured using a microCT scanner. The force required to pull-out a 3.5 mm titanium cortical bone screw was determined after standardised insertion into specimens of the cortex of the femoral shaft. A significant correlation was found between the pull-out strength and the overall bone mass of the cortical layer (r(2) = 0.867, p < 0.01) and also between its thickness (r(2) = 0.826, p < 0.01) and bone mineral density (r(2) = 0.861, p < 0.01). There was no statistically significant correlation between the age of the donor and the pull-out force (p = 0.246), the cortical thickness (p = 0.199), the bone mineral density (p = 0.697) or the level of osteoporosis (p = 0.378). We conclude that the overall bone mass, the thickness and the bone mineral density of the cortical layer, are the main factors which affect the stability of a screw in human female osteoporotic cortical bone.

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.

SummaryThe histomorphometrical cancellous bone parameters of osteoporotic ewes were examined to establish a large animal model for the investigation of fracture treatment and healing in osteoporotic bone. Eighteen animals were divided into 2 groups. Group 1 (n = 8, age 3 to 5 years) served as an untreated control. In Group 2 (n = 10, age 7 to 9 years) osteoporosis was induced by means of ovariectomy, methylprednisolone application (average dose 160 mg/week) and Ca./Vit.D restricted diet during 7 months. Biopsies from iliac crest, femoral head and lumbar spine were harvested. Structural parameters from the biopsies were determined using μCT. In order to investigate static and dynamic parameters of bone remodelling, undecalcified sections were digitized and evaluated by means of image analysing software. Morphologically, bone area and trabecular thickness were reduced in osteoporotic sheep. Bone perimeter (−20%), trabecular number (−16%) and separation (+39%) showed a significant change in the iliac crest. The structure model index indicated a shift from the plate-to the rodmodel. At different skeletal sites of osteoporotic sheep bone resorption was significantly increased (250-675%), and bone formation significantly decreased (77-89%). Osteoid thickness (O.Th) was reduced (28-62%). In osteoporotic sheep the mean length of single labels was significantly shortened (64-73%) and the mineralising surface showed a significant decrease (80-92%). The mineralisation of the osteoid was comparable to the control group. The histomorphometrical changes in this sheep model of osteoporosis are comparable to the human situation of a combined post-menopausal and steroid-induced osteoporosis.

Current methods for fracture treatment in osteoporosis are not always sufficient. To develop new fixation strategies (both mechanical and biological) requires pre-clinical testing utilizing appropriate models. The aim of this study was to apply a recently developed sheep model of osteoporosis to the study of healing in a non-critical long bone defect. A standardized transverse mid-shaft tibial osteotomy (with a fracture gap of 3 mm) was performed in seven osteoporotic and seven normal sheep and stabilized with a special external fixator for 8 weeks. The fixator was used for weekly in vivo bending stiffness measurements. Ex vivo bending stiffness and torsional stiffness of the callus zone were also determined. Callus area, callus density, and osteoporosis status were determined at 0, 4, and 8 weeks using peripheral quantitative computed tomography. The increase of in vivo bending stiffness of the callus was delayed approximately 2 weeks in osteoporotic animals. A significant difference (33%) in torsional stiffness was found between the osteotomized and contralateral intact tibia in osteoporotic animals, but no significant difference occurred in normal sheep (2%). In osteoporotic animals, ex vivo bending stiffness was reduced 21% (p=0.05). Bending stiffness was correlated with callus density (r=0.76, r=0.53); torsional stiffness was correlated with callus area (r=0.60) and to a lesser extent with callus density (r=0.53). This study demonstrated a delay of fracture healing in osteoporotic sheep tibiae with respect to callus formation, mineralization, and mechanical properties.

In a pilot experiment comparing four different modalities for inducing osteoporosis in the sheep, a combination of ovariectomy, calcium/vitamin D-restricted diet and steroid administration was found to generate the highest decrease in bone mineral density (BMD). The aim of the present study was to quantify the outcome of this triple treatment in an animal model of osteoporosis in terms of alteration in bone mass, bone structure and bone mechanics. A total of 32 sheep were divided into two equal groups. Group 1 (age 3–5 years) was used as a normal control. Group 2 (age 7–9 years) was ovariectomized, fed a calcium/vitamin D-restricted diet and injected with methylprednisolone (MP) over 7 months (22 weeks MP solution, 6 weeks MP suspension). The BMD at the distal radius and tibia was determined preoperatively and at repeated intervals bilaterally using quantitative computed tomography. Steroid blood levels were determined 4 and 24 h after selected injections. BMD was measured at L3 and L4 after 7 months. Biopsies were taken from iliac crests, vertebral bodies and femoral heads, and bone structure parameters investigated by three-dimensional micro-CT. Compressive mechanical properties of cancellous bone were determined from biopsies of vertebral bodies and femoral heads. After 7 months of osteoporosis induction the BMD of cancellous bone decreased 36 ± 3% in the radius and 39 ± 4% in the tibia. Steroid blood levels 24 h after injection of MP suspension were significantly higher than after injection of MP solution. Changes in structural parameters of cancellous bone from the iliac crest, lumbar spine and femoral head in group 2 indicated osteoporosis-associated changes. In group 2 there was a significant reduction in BMD of the lumbar spine and a significant reduction in stiffness and failure load in compression testing of biopsies of lumbar vertebrae. In sheep, changes in the structural parameters of bone such as trabecular number and separation during osteoporosis induction are comparable to the human situation. The sheep model presented seems to meet the criteria for an osteoporosis model for fracture treatment with respect to mechanical and morphometric bone properties.