Changes of bone-perfusion in osteosynthesis of the femur with a marrow-nail (author's transl)

The perfusion of the bone in the hind leg after osteosynthesis (nailing of the bone-marrow) was studied. In 11 shepherd dogs (bastards) an osteotomy of the femur was done; it was treated with a marrow-nail without boring the marrow-cavity. With the "tracer-microsphere"-method the perfusion of femur, tibia and talus of both hind legs was measured. Measurements were performed before and after surgery, in 10 dogs 2 weeks and in 8 dogs 6 weeks after surgery. Immediately after the operation the perfusion was reduced considerably in all the examined bones of the operated leg. Two weeks later the perfusion was increased in all bones of both hind limbs. In the cancellous bone of the femur the perfusion reached the original preoperative values after 6 weeks; in cortical bone a further increase of the perfusion was noted. This increase was most marked in the cortical bone of the operated femur; it was less in the cortical bone of the other bones.     

Effects of immobilization, three forms of remobilization, and subsequent deconditioning on bone mineral content and density in rat femora

Disuse is associated with bone loss, which may not be recoverable. It is not known whether intensified remobilization is beneficial in restoring disuse-related bone loss nor if any such benefit would depend upon continuing mobilization for its maintenance. After an immobilization period of 3 weeks, the effects of free remobilization (11 weeks), and low-and high-intensity treadmill running (11 weeks) with and without subsequent deconditioning (18 weeks) on the bone mineral content (BMC) and density (BMD) of the hindlimb femora of Sprague-Dawley rats (n = 98) were studied using a dual-energy X-ray absorptiometric (DXA) scanner. Our hypothesis was that intensified remobilization is beneficial in restoring the BMC and BMD from disuse to normal while subsequent deconditioning is deleterious to these parameters. Immobilization for 3 weeks produced a significant BMC and BMD loss in the immobilized left femur (range -4.4 to -12.8%; p < 0.05-0.001). In the groups with free remobilization (free cage activity), the body weight-adjusted BMCs and BMDs always remained below those in the controls (range -2.3 to -12.1%; p values ranging from NS to < 0.01). Both low- and high-intensity running restored BMC and BMD in the immobilized limb, the effect being better in the latter group. In both of these groups, the values of the immobilized left limbs and those of the free right limbs exclusively exceeded the corresponding values of the age-matched control rats (left limb values 3.0-21.1% higher with p values ranging from NS to < 0.01; right limb values 7.9-21.4% higher with p < 0.05-0.01). However, after the deconditioning period of 18 weeks, the above described beneficial effects of low- and high-intensity running were lost, the left and right limb BMC and BMD values being lower than those in the age-matched controls (range -3.8 to -8.7%; p values ranging from NS to < 0.05). In conclusion, this study clearly indicates the need for greater than normal activity to restore the BMC and BMD after disuse to normal levels. However, the benefits of intensified remobilization are lost if the activity is terminated, and therefore, after immobilization and disuse, bone loading activities should be continued, perhaps indefinitely.     

Review of autologous and allogeneic blood transfusion practices in patients undergoing radical hysterectomy

We investigated the short-term recuperation of bone mass during skeletal reloading after a period of unloading in young rats. One hind limb of 4-week-old rats was either unloaded irreversibly by sciatic neurectomy, or unloaded reversibly by external fixation. Other animals were sham-operated. After 9 days, the fixation-unloaded limbs were reloaded for 1-3 weeks and were compared with the hind limbs of age-matched unloaded (neurectomized) and sham-operated controls. Cortical and cancellous bone mass was measured using ashing and histomorphometry. Cortical bone mass (expressed as femoral dry and ash weight and tibial cortical bone area) was reduced in both unloaded groups and was accompanied by production of hypomineralized bone, as shown by a reduction in the percent ash of the dry weight. Cancellous bone mass (expressed as bone area and surface at the tibial metaphysis) was also reduced in both unloaded groups. Cortical bone mass deficit was greater in the fixation group than in the neurectomy group. Thereafter it increased in the neurectomy group despite a normal longitudinal growth rate, but returned to age-matched values in the reloaded group by 3 weeks. The changes in tibial cancellous bone mass were more pronounced but followed a similar pattern and normalized by 2 weeks. These data demonstrate that total unloading produced by external fixation causes a greater degree of bone mass deficit than partial unloading (produced by neurectomy); the rate of bone loss during unloading in the rat hind limb is more rapid than its recovery during reloading; and cancellous bone recuperates during the reloading phase faster than does cortical bone.     

Early induction of alterations in cancellous and cortical bone histology after orchiectomy in mature rats

Androgen deficiency is associated with low bone mass in humans and animals, but the remodeling alterations that lead to bone loss are unclear. Our objective was to define early responses in both cancellous and cortical bone to orchiectomy (ORX) using histomorphometry in sexually mature (4-month-old) rats. A total of 62 male rats, 4 months of age, were divided into six groups, sham operated (SH) or orchiectomized (ORX), and sacrificed 1, 2, or 4 weeks after ORX. Calcein was given 5 and 2 days before sacrifice to label mineralizing surfaces. Bone mineral density (BMD) was measured in excised femurs by dual energy X-ray absorptiometry (DEXA). Static and dynamic histomorphometry was evaluated in the cancellous bone of the proximal tibial metaphysis and lumbar vertebral bodies, and in the cortical bone of the tibial diaphysis. Osteopenia began to develop by 2 weeks after ORX, though weight gain and femur length did not change. Femoral BMD was significantly reduced and BMC decreased (NS) by 4 weeks after ORX (p < 0.05). Tibial and vertebral cancellous bone volume decreased 19% and 13%, respectively, while osteoblast and osteoclast surfaces, and numbers of osteoclasts, increased after ORX. At 2 weeks post-ORX, an increase in cancellous bone formation rate was attributable primarily to an increase in mineralizing surfaces and a smaller rise in mineral apposition rate. In contrast, cortical bone periosteal, but not endosteal, bone formation rate and mineralizing surfaces decreased. We conclude that ORX stimulates cancellous and diminishes periosteal bone turnover rapidly after ORX, with subsequent decreases in bone volume and mineral density. The clear divergence in cortical and cancellous bone responses to hypogonadism raises important questions regarding the control of bone formation and its role in defining the skeletal phenotype.     

Load-bearing capacity of corticocancellous bone grafts in the spine

We investigated the relationship between the densities and areas of commonly used autogenous tricortical bone grafts from the iliac crest and the fibula and their mechanical load-bearing abilities. Intact corticocancellous grafts, seven millimeters thick, were obtained during elective spinal arthrodeses from fifty-six patients: from the anterior part of the pelvis in twenty-four patients, the posterior part of the pelvis in twenty-nine patients, and the fibula in three patients. The apparent densities and cross-sectional areas of the cortical and cancellous bone were measured with use of a specific computed-tomographic technique before the specimens were mechanically tested to failure in uniaxial compression. Specimens from the anterior superior iliac spine were able to bear significantly higher axial loads (average, 3230 newtons; range, 430 to 8112 newtons) than were those from the posterior superior iliac spine (average, 1458 newtons; range, 350 to 4639 newtons) (p < 0.001). The cancellous density was the most significant single factor in the prediction of the load to failure of the grafts from the iliac crest (adjusted r2 = 0.58; p < 0.0001). When all of the physical variables (the cancellous and cortical densities and areas) were entered into a multiple-regression model, the combination of the cortical and cancellous densities and the cortical area was a good predictor (adjusted r2 = 0.68; p < 0.001) of the load to failure. The fibular grafts were stronger than those from the other two sites, but they had the least over-all cross-sectional area and cancellous bone.(ABSTRACT TRUNCATED AT 250 WORDS)     

Epidermal growth factor receptor ectodomain in the urine of patients with squamous cell carcinoma

Female Sprague-Dawley rats were ovariectomized (OVX) or sham-operated at 3 months of age and maintained untreated for 1 year after surgery. Baseline control and OVX rats were killed at the beginning of treatment when the rats were 15 months of age and 1 year postovariectomy. The remaining rats were treated with hPTH 1-34 (80 micrograms/kg BW, 5 days/week) or vehicle for 10 weeks. Quantitative bone histomorphometry was performed on undecalcified longitudinal sections of the proximal femur from each rat. Baseline OVX rats exhibited cancellous and cortical osteopenia at the femoral neck as their mean cancellous bone volume and cortical width were significantly decreased compared to the means for baseline control rats. In addition, baseline OVX rats had increased osteoblast and osteoclast surfaces and a greater cancellous bone formation rate than baseline control rats. OVX rats remained osteopenic with no further bone loss from the femoral neck after 10 weeks of vehicle treatment. In contrast, cancellous bone volume and cortical width in OVX rats treated with PTH were increased to the level of vehicle-treated control rats. The hormone restored lost bone in the femoral neck of OVX rats by markedly stimulating both cancellous and cortical bone formation. These histomorphometric findings in concert with recent biomechanical studies of bone strength indicate that the femoral neck of aged OVX rats is a promising sample site for studies of the prevention and treatment of bone loss induced by estrogen depletion.     

Overexpression, purification and characterization of Dictyostelium calcineurin A

We examined the mechanical properties of bone in ovariectomized rats treated with tiludronate. 186 Sprague-Dawley (SD) rats, 6 months of age, were assigned to 13 groups and were maintained for 3-9 months after surgery. Ovariectomy (ovx) groups were given tiludronate orally at the respective doses of 0 (vehicle), 12.5 (low), 25 (medium), and 50 (high) mg/kg body weight daily for 3 months beginning 3 months after surgery. Rats were killed at 0 (start), 3, 6, and 9 months. Whereas bone mineral density (BMD) values of the midfemur did not increase after ovx, the values in the sham-operated groups increased age-dependently. Bending moment to failure of the femur in the sham group was larger than that of the ovx control group at 9 months. In the ovx control groups, the ultimate compressive load values of the third lumbar body were reduced compared with those in the sham groups at 3 months and thereafter. Although serum osteocalcin levels were decreased in the medium- and high-dose tiludronate groups, both serum PTH and 1,25(OH)2D levels were increased only in the high-dose group. Femoral BMD, mechanical properties, and the cortical bone area were increased by the high dose at 9 months. Lumbar ultimate compressive load and the circumscribing cortical shell area in the high-dose group were increased at 6 months and thereafter. The trabecular number values were maintained at 6 and 9 months by the high dose. These data demonstrate that tiludronate administration increased the mechanical properties of bone by preserving the age-dependent increases in the cortical bone mass and three-dimensional structure of trabecular bone. These effects seemed to be due to reduced bone turnover by the agent.     

Changes in the aortic endothelium and plasma von Willebrand factor levels during the onset and progression of insulin-dependent diabetes in BB rats

The superior volume maintenance of membranous over endochondral bone has been shown in several studies and provides the basis for its preferred clinical use as an onlay grafting material in the craniofacial skeleton. The scientific rationale for this seeming embryologic advantage, however, has never been proven. Our hypothesis is that the pattern of onlay bone graft resorption is primarily determined by a graft's micro-architecture (relative cortical and cancellous composition) rather than its embryologic origin (membranous versus endochondral). Twenty-five adult New Zealand, White rabbits were used for this study. Eight animals were killed at 3 weeks, eight animals at 8 weeks, and nine animals at 16 weeks. Three graft types were placed onto each rabbit cranium: cortical bone graft of membranous origin and cortical and cancellous bone graft of endochondral origin. Fluorochrome markers were injected into all living rabbits at 1, 6, and 14 weeks. Microcomputed tomography scanning was performed on all of the bone grafts to determine postsacrifice volumes and to obtain detailed information regarding the bone graft's trabecular architecture. In addition, specimens were examined histologically. Volume analysis showed a statistically greater resorption rate in the cancellous endochondral bone graft than in either the endochondral or membranous cortical bone grafts (p < 0.05) for all time points. In addition there was no significant difference in the resorption rates between the endochondral and membranous cortical bone grafts. A post-test power analysis (alpha = 5 percent) of the volume data comparing the two types of cortical bone grafts showed that a difference in resorption of 8.9 percent would be detected with a 90-percent probability. Previous studies, which have shown a seeming superiority of membranous over endochondral bone grafts, used composite grafts composed of both cortical and cancellous portions. By separating these components, we have shown that cortical bone grafts maintain their volumes significantly better than cancellous bone grafts. In addition, we found no statistical difference in the resorption rates between the two cortical onlay bone grafts of different embryologic origins, a finding that has never been previously published. From our results, we believe cortical bone to be a superior onlay grafting material, independent of its embryologic origin. We believe these results challenge the currently accepted theories of bone graft dynamics and may lead to a change in the way clinicians approach bone graft selections for craniofacial surgery.     

The nonlinear transition period of broadband ultrasound attenuation as bone density varies

The purpose of this study was to determine whether a transition period occurs between cortical and cancellous bone in the relationship between ultrasound parameters [broadband ultrasound attenuation (BUA) and ultrasonic velocity] and density. Twenty-two cancellous bone discs wee obtained from proximal bovine tibiae. Also included were three samples of human vertebral cancellous bone from an elderly female and four samples of bovine cortical bone. Ultrasonic velocity did not show any transition period as density varied from cancellous to cortical bone. Ultrasonic velocity exhibited a definite linear dependence on density over the entire range examined. However, BUA has shown a transition period as density varied. Although BUA increased linearly with density for a low density cancellous bone tested (below 0.64 g cm-3), the dependence of BUA on density is nonlinear with a downwardly inflected parabola shape when covering a wide density range (0.130-0.913 g cm-3) of cancellous bone. When one includes cortical bone, the parabola tends to level off in a slow exponential decay. This nonlinear dependence may help to understand the characteristics of BUA measurement.     

Alcohol consumption by young actively growing rats: a study of cortical bone histomorphometry and mechanical properties

Alcohol consumption by young actively growing rats has been previously demonstrated to decrease cortical and cancellous bone density, to reduce trabecular bone volume, and to inhibit bone growth at the epiphyseal growth plate. This study addresses the action of alcohol on cortical bone growth using histomorphometric techniques and on mechanical properties by three-point bending. Four-week-old, female Sprague-Dawley rats were divided into three groups. Alcohol-treated animals were fed a modified Lieber-DeCarli diet ad libitum containing 35% ethanol-derived calories, whereas the pair-fed animals (weight-matched to ethanol rats) received an isocaloric liquid diet in which maltose-dextrin-substituted calories were supplied by ethanol. Chow animals were fed a standard rat chow ad libitum. Femora were removed for analysis after 2, 4, 6, or 8 weeks on the diets. Cortical bone area, bone formation rates, and mineral apposition rates were reduced in the alcohol-fed animals. Bone stiffness, strength, and energy absorbed to fracture were significantly lower in the alcohol-fed animals. This distinctive alcohol effect was revealed to be caused by lower quality bone tissue as reflected by lower elastic moduli and yield strengths.     

Deep-frozen allogeneic cancellous bone grafts in 10 dogs: a case series

Deep-frozen, aseptically collected and processed allogeneic cancellous bone was implanted in eight dogs during the surgical repair of diaphyseal long bone fractures and in two dogs during arthrodeses. A combined allogeneic and autogeneic cancellous bone graft was used in two fractures with a segmental bone loss of more than 5 cm. Bone union occurred in five fractures and in both arthrodeses. Failure of fixation occurred in two dogs with nonunion fractures and in a third dog with an open, infected fracture. Biopsies from the fracture sites were obtained from these dogs following failure of their fracture fixation. The cancellous bone graft appeared to be in the process of normal incorporation in each case. Failure of fixation was attributed to technical or case management errors or both, in each of the three fractures that failed to achieve bony union. Frozen allogeneic cancellous bone grafts were effectively incorporated when used in the primary repair of fractures and arthrodeses. Combined autogenous and allogeneic cancellous bone grafts may be particularly useful in the repair of fractures with large segmental diaphyseal bone defects. The use of allogeneic cancellous bone grafts in nonunion fractures requires further investigation before it can be recommended.     

Morphometric study of the equine navicular bone: comparisons between fore and rear limbs

Navicular bones collected from the four limbs of 95 sound horses were studied. The anatomic bases have been laid down about morphometry of the navicular bones and their variations according to limbs, after corrections have been made for morphologic type, gender, weight, size and age. All the dimensions of the navicular bone (except for the thickness) were larger in the fore limb. This phenomenon probably reflects an attempt to compensate for the greater forces exerted upon the fore limbs during exercise and at rest. Navicular bones collected from the four limbs of 61 sound horses were studied and the anatomic bases were described for histomorphometry of the fore and rear navicular bones. Fore navicular bones possess less cortical bone at the level of the articular surface, as well as at the level of the flexor surface and proximal border, but larger amounts of cancellous bone. Articular and flexor surface cortical bone show a larger porosity in the fore navicular bones and a larger amount of mineralized cartilage. The mineralized portion for distal impar- and collateral sesamoidean ligaments are also larger for the fore navicular bones. Two distinct zones are observed for the flexor surface cortex that have never been reported in the literature before: an external zone, which is mainly composed of poorly remodelled lamellar bone, arranged in a disto-proximal oblique direction, and an internal zone, which is mainly composed of secondary bone, with a latero-medial direction of Haversian canals. Bone architecture is discussed with regard to the mechanic load, encountered by the bone during locomotion.     

Quantitative digital subtraction radiography for the determination of small changes in bone thickness: an in vitro study

OBJECTIVE: The objective of this study was to determine the ability of quantitative digital subtraction radiography to detect small changes in bone thickness adjacent to tooth roots. STUDY DESIGN: A series of cortical or cancellous bone slices with a 50 microm-stepwise increasing thickness were attached to 4 porcine mandible sections covering buccal and interproximal "defect" regions. Standardized radiographs were quantitatively evaluated for radiographic density changes with the use of digital subtraction radiography. Furthermore, all radiographs were conventionally evaluated by 10 clinicians. The Wilcoxon signed-rank test and the Mann-Whitney U test were used for statistical analysis (alpha = 0.05). RESULTS: A high linear correlation was found between the actual thickness of bone slices and radiographic density changes (cortical bone: r2 = 0.89 to 0.99; cancellous bone r2 = 0.61 to 0.86, p < or = 0.001). A certain increase in bone thickness caused a 3 times higher increase in radiographic density for cortical bone than for cancellous bone (p < or = 0.05). The detection limits of digital subtraction radiography were 200 microm for cortical and 500 microm for cancellous bone, whereas the detection limits of conventional radiography were 600 microm and 2850 microm, respectively. CONCLUSIONS: This in vitro study demonstrated a very high correlation between the objective, quantitative assessment of subtle changes in alveolar bone by digital subtraction radiography and the true changes in bone thickness.     

Randomized controlled study of effects of sudden impact loading on rat femur

Physical loading creating high peak strains on the skeleton at high strain rates is suggested to be the most effective type of activity in terms of bone mineral acquisition. This study assessed the effects of sudden impact loading on mineral and mechanical bone properties in 13-week-old Sprague-Dawley rats. The rats were randomly assigned as sedentary controls (SED, n = 10), control animals receiving low-intensity exercise (EX, n = 15), and experimental animals receiving low-intensity exercise combined with sudden impact-loading (EX + IMP, n = 15). In the EX group, the rats walked in a walking mill at a speed of 10 cm/s for 20 minutes/day, 5 days/week for 9 weeks. In the EX + IMP group, the program was identical to the EX group except for the additional sudden impacts administered to their skeleton during the walking exercise. At the start, there were 50 impacts per session, after which their number was gradually increased to 200 impacts per session by week 6 and then kept constant until the end of the experiment, week 9. These horizontally and vertically directed body impacts were produced by a custom-made walking mill equipped with computer-controlled high-pressure air cylinders. After sacrifice, both femora of each rat were removed and their dimensions, bone mineral content (BMC) by dual-energy X-ray absorptiometry, and mechanical properties by femoral shaft three-point bending and femoral neck compression were determined. The cortical wall thickness increased significantly in the EX and EX + IMP groups as compared with SEDs (+7.6%, p = 0.049 and +10%, p = 0.020, respectively). The EX + IMP group showed +9.0% (p = 0.046) higher cross-sectional moment of inertia values than the EX group. No significant intergroup differences were seen in the BMC values, while the breaking load of the femoral shaft (EX + IMP vs. SED +8.8%,p = 0.047) and femoral neck (EX + IMP vs. SED +14.1%, p = 0.013) was significantly enhanced by the impact loading. In conclusion, this study indicates that mechanical loading can substantially improve the mechanical characteristics of a rat femur without simultaneous gain in its mineral mass. If this is true in humans too, our finding gives an interesting perspective to the numerous longitudinal exercise studies (of women) in which the exercise-induced gains in bone mass and density have remained mild to moderate only.     

Static and fatigue failure properties of thoracic and lumbar vertebral bodies and their relation to regional density

This study investigated (1) whether a characterization of the macroscopic architecture within the vertebral centrum would improve predictions of vertebral strength, (2) if regions in the centrum where least bone loss with age occurs are more predictive of vertebral strength, and (3) whether different patterns of the macroscopic architecture are predictive of static as compared to fatigue strength. To characterize the vertebral macroscopic architecture, a regional bone mineral density (rBMD) technique was used that estimated the cancellous density distribution (in 18 specific regions of the vertebral centrum) for vertebrae T7-L4, from spines of 20 female cadavers. Static and fatigue failure properties of whole vertebrae were obtained, and predictive models of static and fatigue failure properties of whole vertebrae were examined. We found that (1) vertebral failure properties were better predicted by combinations of vertebral regional cancellous density (multiple linear regressions) rather than by any individual region of cancellous density alone (simple linear regressions); (2) models using regions of density that demonstrated minimum decline with age [from the data of Flynn and Cody (Calcif. Tissue Int. 53, S170-S175 (1993))] resulted in better correlations with ex vivo vertebral static failure properties than models using density regions that showed maximum decline with age, and (3) static and fatigue characteristics required different density regions to reach significance. (A comparison of models predictive of static and fatigue failure properties revealed that anterior density regions were most often included in predictive models of the static properties while posterior regions were more predictive of the fatigue properties).(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhaled nitric oxide therapy for pulmonary disease in pediatrics

Prostaglandin E2 (PGE2) is an anabolic agent of bone in vivo but the mechanism of its action still remains unclear. The aim of this study was to determine whether the effect of PGE2 on skeleton is mediated by pituitary hormones. Forty female, Sprague-Dawley rats were divided into four groups: baseline control (basal), age-matched intact control (CON), hypophysectomy (HX), and HX + PGE2 (2 mg/kg/day) with 10 animals in each group. The basal group was sacrificed at 2 months of age, and the remaining groups after 6 weeks of treatment. Cancellous and cortical bone histomorphometry was performed on double fluorescent-labeled 40 micron-thick sections of the proximal tibia and tibial shaft. Our results show that HX resulted in a cessation of bone growth, a decrease in cancellous bone volume, and cortical bone gain compared with the age-matched, intact CON rats. Compared with the HX group, the HX + PGE2 group had a significantly greater tibial bone density (mean +/- SE, HX + PGE2:1.595 +/- 0.007 versus HX:1.545 +/- 0.013), percent cancellous bone volume (21.4 +/- 2.0 versus 8.41 +/- 1.70), percent cortical bone area (87.2 +/- 0.85 versus 81.7 +/- 0.7), and ratio of cortical area to marrow area (7.14 +/- 0.56 versus 4.52 +/- 0.21). Increased bone masses by PGE2 in the HX animals were accompanied by an increase in the trabecular and endosteal-labeled surface and bone formation rate. The trabecular number and width were increased whereas trabecular separation was decreased in the HX + PGE2 group compared with the HX group (P < 0.05). PGE2 treatment also caused a decrease in the tibial endosteal eroded surface and medullar cavity of the HX animals. In conclusion, this study clearly demonstrates that PGE2 (2 mg/kg/day) in the HX rats increases both cortical and cancellous bones and improves trabecular architecture in the tibia after 6 weeks of treatment. These skeletal alterations are due to a stimulation of bone formation and a suppression of bone resorption activity. These findings suggest that the anabolic effect of PGE2 in bone is independent of pituitary hormones.     

The elbow joint and its total arthroplasty. Part II. Finite element study

The stresses in various sections of two-dimensional models of the elbow joint, without and with a prosthesis (the humeral component of a total elbow prosthesis), were obtained using the finite element analysis method. Three parameters were varied: type of applied load; method of fixation of the prosthesis to the contiguous bone; and shape of the head of the prosthesis. The results are discussed with particular reference to stress shielding and overload in the cortical and cancellous bones, respectively, and a qualitative comparison between the present values and those given by previous workers who used three-dimensional models. Comments are made regarding the clinical implications of the results.     

Comparative investigations of algorithms for the detection of breaths in newborns with disturbed respiratory signals

There is a widespread clinical need for bone augmentation and replacement. The major solid phases of bone are collagen and calcium phosphate and a bone analogue based on these two constituents should have some useful properties. In this review this theme is developed and the properties of natural and naturally based composites are compared. Composites have been produced by the precipitation of calcium phosphates on to collagen and a summary of the methods and results from mechanical testing and scanning electron microscopy are presented. Composites with mechanical properties intermediate between cancellous and cortical bone have been produced. The review concludes by explaining some of the mechanical properties of the composites, using knowledge of the hierarchical architecture of bone and results from microscopical examination of the fractured composites.     

Ibuprofen controlled-release formulation. A clinical trial in dental impaction pain

The effects of 17 beta-estradiol (E2) and treadmill exercise on tibial bone mass, tibial uptake of 45Ca, and proximal tibia osteoblast and osteoclast cell number were determined in adult ovariectomized rats. Female rats aged 10 months were ovariectomized and divided into five groups: (1) sham-operated; (2) ovariectomized; (3) ovariectomized, given 10 micrograms E2 biweekly; (4) ovariectomized, trained to exercise on a treadmill daily; and (5) ovariectomized, given E2 and exercised. E2 and/or exercise interventions were started 2 months following surgery and continued for 4 months. The calcium content of the tibial metaphysis and diaphysis and the proximal cancellous bone (BV/TV) were lower in the ovariectomized than in the sham-operated controls 6 months after ovariectomy. This lower bone content was associated with a greater bone uptake of 45Ca and a greater number of osteoblasts and osteoclasts in the proximal tibia compared to the control rats. The metaphyseal calcium content was higher and the 45Ca uptake and osteoblast and osteoclast number were lower in the E2-treated rats than in the nontreated rats. In the exercised group, higher diaphyseal calcium content and proximal cancellous bone were associated with lower bone resorption parameters without a significant effect on bone formation. This study demonstrates that E2 primarily influences tibial cancellous bone of the ovariectomized rat and a positive adaptation to exercise occurs in both cancellous and cortical bone. Under estrogen deficiency, E2 replacement suppresses increased bone formation and resorption; exercise suppresses mainly bone resorption. The effects of E2 replacement and exercise training are independent and additive.     

Biomechanical and densitometric bone properties after callus distraction in sheep

Assessment of biomechanical stability of diaphyseal bone lengthened by callus distraction is an unsolved problem. A middiaphyseal corticotomy was performed in the left tibia of 24 sheep. After 7 days, callus distraction was begun at a rate of 0.5 mm every 12 hours for 30 days using a standard unilateral fixator system. Animals were euthanized 4, 8, or 12 weeks after the end of distraction. The lengthened tibia and the contralateral control tibia from each animal were evaluated by radiographic, densitometric (dual energy xray absorptiometry, quantitative computed tomography), and biomechanical (axial compression testing, torsion testing to failure) methods. The bone mineral density and maximum torque for the lengthened tibia were significantly greater in the 8-week group than in the 4-week group. However, the values in the 12-week group were significantly smaller than in the 8-week group. In the lengthened tibias, there was a correlation between the maximum torque and the bone mineral density, and between the maximum torque and the bone density. Bone density measurements are useful prognosticators for the safe removal of external fixators after leg lengthening procedures. By using these methods, clinical fractures after leg lengthening could be avoided in the future.