Functional and radiological outcomes after bridging therapy versus direct thrombectomy in stroke patients with unknown onset: Bridging therapy versus direct thrombectomy in unknown onset stroke patients with 10-point ASPECTS.

BACKGROUND AND PURPOSE: The aim was to assess functional and radiological outcomes after bridging therapy (intravenous thrombolysis plus mechanical thrombectomy) versus direct mechanical thrombectomy (MT) in unknown onset stroke patients. METHODS: A cohort study was conducted on prospectively collected data from unknown onset stroke patients who received endovascular procedures at ≤6 h from symptom recognition or awakening time. RESULTS: Of the 349 patients with a 10-point Alberta Stroke Program Early Computed Tomography Score (ASPECTS), 248 received bridging and 101 received direct MT. Of the 134 patients with 6-9-point ASPECTS, 123 received bridging and 111 received direct MT. Each patient treated with bridging was propensity score matched with a patient treated with direct MT for age, sex, study period, pre-stroke disability, stroke severity, type of stroke onset, symptom recognition to groin time (or awakening to groin time), ASPECTS and procedure time. In the two matched groups with 10-point ASPECTS (n = 73 vs. n = 73), bridging was associated with higher rates of excellent outcome (46.6% vs. 28.8%; odds ratio 2.302, 95% confidence interval 1.010-5.244) and successful recanalization (83.6% vs. 63%; odds ratio 3.028, 95% confidence interval 1.369-6.693) compared with direct MT; no significant association was found between bridging and direct MT with regard to rate of symptomatic intracerebral hemorrhage (0% vs. 1.4%). In the two matched groups with 6-9-point ASPECTS (n = 45 vs. n = 45), no significant associations were found between bridging and direct MT with regard to rates of excellent functional outcome (44.4% vs. 31.1%), successful recanalization (73.3% vs. 76.5%) and symptomatic intracerebral hemorrhage (0% vs. 0%). CONCLUSIONS: Bridging at ≤ 6 h of symptom recognition or awakening time was associated with better functional and radiological outcomes in unknown onset stroke patients with 10-point ASPECTS.

Intra- and inter-observer variability in intracranial aneurysm segmentation: comparison between CT angiography (semi-automated segmentation software stroke VCAR) and digital subtraction angiography (3D rotational angiography).

PURPOSE: To compare size and morphologic features of three-dimensional aneurysm models, obtained with a semi-automated segmentation software (Stroke VCAR, GE, USA) from cerebral CT angiography (CTA) data, to three-dimensional aneurysm models obtained with digital subtraction angiography (DSA, with 3D rotational angiography acquisition-3DRA), considered as the reference standard. METHODS: In this retrospective study, we reviewed 132 patients, with a total number of 137 intracranial aneurysm, who underwent CTA and subsequent DSA examination, supplemented with 3DRA. We compared neck length, short axis and long axis measured on 3DRA model to the same variables measured on 3D-CTA model by two blinded readers and to the automatic software dimensions. Therefore, statistics analysis assessed intra-observer and inter-observer variability and differences between patients with or without subarachnoid hemorrhage (SAH). RESULTS: There were no significant differences in short-axis and long-axis measurements between 3D angiographic and 3D-CTA models, while comparison of neck lengths revealed a statistically significant difference, which tended to be greater for smaller neck lengths (partial volume effect and "kissing vessels" artifact). There were significant differences between manual and automatic data measured for the same three variables, and the presence of SAH did not affect aneurysm 3D reconstruction. Inter-observer agreement resulted moderate for neck length and substantial for short axis and long axis. CONCLUSION: The examined 3D-CTA segmentation system is a reproducible procedure for aneurysm morphologic characterization and, in particular, for assessment of aneurysm sac dimensions, but considerable carefulness is required in neck length interpretation.

Effect of intermittent mechanical force on bone tissue in vitro: preliminary results.

The structure of metatarsal bones from 18-day-old rats subjected to intermittent mechanical force in organ culture are reported. The application of mechanical force enhances the osteoid thickness and osteoblast number in the periosteum and increases the number of viable osteocytes. These results indicate that (1) the mature bone tissue survives in organ cultures; (2) the mechanical forces better preserve the structure of the osteocytes and stimulate the osteoblasts, and (3) stimulate the osteogenesis.

Distribution of resorption processes in the compacta and spongiosa of bones from lactating rats fed a low-calcium diet.

An attempt has been made to determine if the structural renewal of bone tissue takes place to a greater extent in the spongiosa than in the compacta and how this is related to the more extensive free surface area in the former. To this purpose, on transverse sections of the femur and 2 degrees lumbar vertebral body of the female lactating rats fed a normal (L group) or a calcium free diet (H group) the area of compact and spongy bone, and the perimeter of the trabeculae were measured. Then TBV, MTPT, MTPD, MTPS, Sv and S/V, according to the Parfitt et al. (1983) method were calculated. In the femurs of rats maintained on a normal calcium diet bone loss takes place to a higher degree in the spongiosa than in the compacta. In the distal metaphysis, moreover, the bone loss is more elevated than in other femoral regions. In the second lumbar vertebral body the bone rarefaction appears to have a similar extent in the compacta and spongiosa and in the three levels inspected. In rats maintained on a restricted calcium intake the osteoporosis is enhanced but the bone is removed predominantly from the compacta in all the femoral regions except in the distal metaphysis and, to a similar degree, from the compacta and the spongiosa of the vertebral body. In the centrodiaphyseal compacta the bone is reabsorbed exclusively at the endosteal level, while in the spongiosa the frameworks subjected to a more extensive resorption occupy a topographic position specific for each single region, and are often formed of thin trabeculae. The dynamic of the trabecular resorption seems to be different in the various spongy frameworks: in each of these it would take place by the removal of the entire trabecula or the thinning of the single trabeculae or by both mechanisms. Lastly, significative correlation was found between trabecular bone loss and trabecular thickness, none with trabecular surfaces. This study shows that bone removal is not regulated by the extent of the trabecular free surface. The mechanisms involved in the control of the distribution of bone removal are strictly connected with those controlling the trabecular thickness. They are probably of a mechanical nature.

Morphological and immunocytochemical analyses on the effects of diet-induced hypocalcemia on enamel maturation in the rat incisor.

During the maturation stage of amelogenesis, the loss of matrix proteins combined with an accentuated but regulated influx of calcium and phosphate ions into the enamel layer results in the "hardest" tissue of the body. The aim of the present investigation was to examine the effects of chronic hypocalcemia on the maturation of enamel. Twenty-one-day old male Wistar rats were given a calcium-free diet and deionized water for 28 days, while control animals received a normal chow. The rats were perfused with aldehyde and the mandibular incisors were processed for histochemical and ultrastructural analyses and for postembedding colloidal gold immunolabeling with antibodies to amelogenin, ameloblastin, and albumin. The maturation stage enamel organ in hypocalcemic rats exhibited areas with an apparent increase in cell number and the presence of cyst-like structures. In both cases the cells expressed signals for ameloblastin and amelogenin. The content of the cysts was periodic acid-Schiff- and periodic acid-silver nitrate-methanamine-positive and immunolabeled for amelogenin, ameloblastin, and albumin. Masses of a similar material were also found at the enamel surface in depressions of the ameloblast layer. In addition, there were accumulations of glycoproteinaceous matrix at the interface between ameloblasts and enamel. In decalcified specimens, the superficial portion of the enamel matrix sometimes exhibited the presence of tubular crystal "ghosts." The basal lamina, normally separating ameloblasts and enamel during the maturation stage, was missing in some areas. Enamel crystals extended within membrane invaginations at the apical surface of ameloblasts in these areas. Immunolabeling for amelogenin, ameloblastin, and albumin over enamel was variable and showed a heterogeneous distribution. In contrast, enamel in control rats exhibited a homogeneous labeling for amelogenin, a concentration of ameloblastin at the surface, and weak reactivity for albumin. These results suggest that diet-induced chronic hypocalcemia interferes with both cellular and extracellular events during enamel maturation.

Effects of a low calcium maternal and weaning diet on the thickness and microhardness of rat incisor enamel and dentine.

The deposition and mineralization of incisor hard tissues have been studied in rat pups nursed by mothers on a low calcium diet or weaned with the maternal diet. Animals were killed at 30 days (control and low calcium diets; maternally fed) or 60 days (after 30 days weaning on maternal diet). The degree of mineralization of enamel and dentine was evaluated by a microhardness method on thick transverse sections. The enamel and dentine thickness, and the diameters of the incisor sections and pulp cavity were measured on microradiographs from the sections. Microhardness values of enamel were similar in groups killed after 30 days maternal feeding, but the microhardness of root enamel was 73-74% less in the low calcium-diet weaned group. Peripulpar dentine had mean microhardness values lower than controls in the group fed maternally for 30 days, whereas the whole root dentine appeared significantly less hard in the low calcium-diet weaned group than in the controls. A significant reduction of the incisor bucco-lingual diameter was observed only in this last experimental group. Enamel thickness was significantly lower in the roots of both experimental groups and in the necks of the low calcium weaned group. The reduction in dentine thickness was greater (from -30 to -56%); in the root it was more evident on the lingual aspect. Thus calcium deficiency in the mother's diet did not influence either the deposition or the mineralization of the pup's incisor enamel and dentine. However, when the offspring were weaned with the maternal calcium-deficient diet, mineralization of the tooth hard tissue was retarded.

Morphometric analysis of the deposition and mineralization of enamel and dentine from rat incisor during the recovery phase following a low-calcium regimen.

The administration of a low-calcium diet to pups nursed by a mother on the same diet has been shown to induce a slowing of growth. A reduction of the apposition rate of dentine, which was normally mineralized, and a dramatic reduction of the extent of mineralization of enamel, whose organic matrix was otherwise produced in an almost normal amount, was observed in the incisors of these animals. Modifications of the mineral apposition rate of dentine, measured after administration of tetracycline (10 mg/kg), and the thickness and the microhardness of the two tissues, the latter being an expression of the degree of mineralization, were now investigated when hypocalcic pups were restored to a normal-calcium diet for 10 or 60 days. Enamel microhardness was increased by more than 60% after only 10 days of restored diet and had become the same as in the control tissue after 60 days, without any significant increase in thickness. Dentine thickness and mineral apposition rate increased significantly, to become similar to those of the controls after 60 days of restored diet. In dentine there was no significant variation of microhardness between experimental pups and controls, either during the low-calcium diet or the restorative period. These results indicate that the deposition of the organic matrix of enamel is a process independent from that of its mineralization, and that the mineralization of the organic matrix happens by its replacement even a long time after its deposition. In contrast, the deposition and mineralization of dentine are strictly interdependent processes, at least in these experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Intermittent compressive load stimulates osteogenesis and improves osteocyte viability in bones cultured "in vitro".

The effect of mechanical stresses on osteogenesis, the viability of osteocytes and their metabolic activity in organ culture of bones intermittently loaded "in vitro" are reported. Metatarsal bones, isolated from 12-day-old rats, were cultured in BGJb medium (with 10% foetal calf serum, 75 micrograms/ml of ascorbic acid, 100 U/ml of penicillin and 100 micrograms/ml of streptomycin), in humidified air enriched by 5% CO2 and 30% O2, and loaded in our original device for 1/2 an hour at 1 Hz. homotypic isolated and unloaded bones, cultured in the same medium, were taken as controls. The ALP (alkaline phophatase activity) increases in the media of loaded bones in comparison with the control bones. The percentage of viable osteocytes is significantly greater in loaded than in control bones. TEM observations demonstrate that in both loaded and control unloaded bones, osteocytes show well developed organelle machinery and several gap junctions with adjacent cellular processes. In the cells of loaded bones, however, a higher number of cytoplasmic organelles and gap junctions were found. In particular, RER increases twice, gap junctions three times. The induced osteogenesis and the TEM observations demonstrate the suitability of this experimental model and support the recent advanced hypothesis according to which the mechanical loading may exert a trophic function on osteocytes, stimulating both the proteic synthesis in the above-mentioned cells and the cell-to-cell communication. Furthermore, the loading is likely to exert a biological stimulus on osteoblasts via signalling molecules produced by osteocytes.

Bone tissue kinetics in the surgically disarticulated dog incus.

The incus of the right ear from 4 growing mongrel dogs was surgically disarticulated and left in the middle ear space. The external auditory canal was then filled with teflon paste and sutured. After 6 weeks (D-6 group) and 13 weeks (D-13 group) the animals were sacrificed. The right experimental incus and the left control one were embedded in methyl methacrylate and sectioned in single 50-microns-thick sections according to the principal axis of the two processes. On the microradiographs of each section we evaluated the thickness of the body and of both processes and the percentage area of the primary channels of the secondary osteons and that of the appositional bone tissue. The thickness of the body and of the two processes was more pronounced in all the experimental incuses, in which 6% (in D-6) and 8% (in D-13) of the total area were occupied by new appositional woven bone. In the body of the D-13 group, 9% of the pre-existing bone was substituted by secondary osteons. The results indicate that the incus react to the variations of mechanical stimuli.

The barrier systems in the choroidal plexuses of the chick embryo studied by means of horseradish peroxidase.

The development of the blood-cerebrospinal fluid (CSF) and cerebrospinal fluid-blood barriers, and the differentiation of the choroidal vessel wall, have been ultrastructurally investigated in the choroidal plexuses of the lateral ventricles of 10, 15, 18 and 21 day chicken embryos, fixed in normal conditions and also after intracardial and intraventricular injection of horseradish peroxidase. In all the analyzed developmental stages the choroidal epithelial cells seem able to endocytose and degradate, in their lysosomal apparatus, the tracer molecules reaching their ventricular and basolateral sides. The intravascularly injected horseradish peroxidase can enter the ventricular cavity by interepithelial route only at 10th incubation day, when the tight intercellular junctions are not formed everywhere, while a transepithelial transport is always hindered. The marker injected into the ventricular cavity reaches the subepithelial compartment and the blood stream, at 10th incubation day by interepithelial as well as transepithelial route and, successively, by transepithelial vesicular transport alone. The differentiation processes undergone by the choroidal blood vessels consist in a progressive thinning of the endothelial cells, appearance of pores, already numerous at 15th incubation day, and formation of the endothelial basement lamina, the final event in vessel wall maturation.

A topographical analysis of the post-natal bone growth in the cochlea of the dog.

The distribution of post-natal bone deposition was examined in the cochlea of 10-, 25-, 50- and 90-day-old dogs that had been intraperitoneally injected with tetracycline (20 mg/kg) five days before sacrifice. The temporal bones were embedded in methylmethacrylate and sectioned in a single mid-modiolar section 30 microns thick. The post-natal bone deposition occurs both on the periosteal surfaces and on the vascular canals of the endochondral layer until the age of 90 days. Scattered bone deposition is also shown on the endosteal layer of the three turns and on the spiral lamina until the age of 25 and 10 days respectively. The percentage extension of the osteogenetic fronts shows a higher value at the periosteal layer than at the endochondral or endosteal layers.

[Ultrastructure of the myocardial junctions of the chick embryo at an early stage in the organogenesis of the heart]. / L'ultrastruttura delle giunzioni del miocardio dell'embrione di pollo in uno stadio precoce dell'organogenesi del cuore.

The ultrastructural features of the myocardiocyte junctional systems have been studied in the heart right myocardium of 6 day chick embryos in order to analyze the relationships between the spatial arrangement of the myocardial fibres and the formation of the myocardiocyte junctions. The myocardiocytes are remarkably branched, joined in small fibres to form a loose network with large intercellular spaces and appear well differentiated, rich in organelles, myofibrils and glycogen. Adherent-type junctions and well differentiated desmosomes are detectable at the level of the termino-terminal contacts between myocardiocytes, where the plasma membranes appear more or less complicately interconnected; nexus-type junctions are seen in the latero-lateral contact regions. The results indicate that already at an early stage of the heart organogenesis the myocardium intercellular junctions are similar, on the whole, to those described in the adult, so that they would not seem to be transitory or modifiable structures. The changes in the spatial orientation of the myocardial fibres, which take place after the 6th incubation day, could be allowed by the network-like arrangement of the primitive myocardium and presumably conditioned by the blood flow in the developing heart.

The structure of the trabeculae of cancellous bone. 1. The calcaneus.

87 either cylindroid or laminar trabeculae, isolated from the perpendicular or inferior bundles of the human calcaneus, were embedded in methylmatecrylate and serially cut along longitudinal and transversal planes with a rotatory-blade saw. The microscopical study of the sections showed that in 83% of the samples secondary osteons run along the longitudinal axis of the trabeculae and their lumina either form a continuous channel network throughout each trabecula (37% of cases) or are restricted to discrete segments (46% of cases). The trabeculae entirely devoid of osteons (17%) are the thinnest, never exceeding 400 microns in thickness. This value is not even exceeded by the segments devoid of osteons in the trabeculae in which the Haversian canals occur only intermittently; conversely, the segments containing Haversian canals can reach and exceed 600 microns in thickness. The maximum distance of the osteocytic lacunae from filtering surfaces--i.e. outer surface of the trabeculae or inner surface of the Haversian canals--was found to be almost the same in the segments of the trabeculae that enclose or not osteons, even though the average trabecular thickness is greater in the former than in the latter regions. On the basis of these findings the formation of endotrabecular osteons may be viewed as a device that indirectly favours the metabolic exchange of deep-seated osteocytes while increasing the free surface area available for bone tissue reconstruction. It remains doubtful whether the Haversian systems may also contribute to improve the mechanical properties of the trabeculae. The arrangement of the collagen fibrils, which differs between cylindroid and laminar trabeculae, is apparently well suited to ensure the resistance of the trabeculae to mechanical loading through the use of the least amount of building material, in accordance with Wolff's law.

The rate of bony tissue deposition in the spongiosa of the extremities of long bones in the dog.

9 mongrel dogs ranging from 5 months to 3 years of age were given 3 single endovenous Alizarin injections at 20-day intervals. In transverse sections of the epiphyses and metaphyses of the proximal and distal ends of the femur, tibia, radius and humerus, we measured the thickness of the bony tissue newly formed during the period between the 1st and 2nd Alizarin administration, and separately of that laid down between the 2nd and the 3rd. The weighted means and histograms set up by us of the values severely gathered in the tubular (peripheral) and lamellar (deeply placed) spongiosa in each metaphyseal and epiphyseal sections, are the expression of the mean linear rate of bony tissue deposition. The mean linear rate of bone deposition (1) declines with age; (2) is higher in the metaphyses than in the epiphyses; (3) in single metaphyses it is higher in the tubular than in the lamellar type of trabeculae. These differences are much marked in the animals undergoing body growth, tending to become appreciably reduced in adult specimens. Significant differences in bone deposition rates between corresponding regions of different bones from the same individual were not seen to occur. The differences in bony tissue deposition rate between the tubular and lamellar spongiosa networks seem to depend upon the action exerted by local factors functionally closely associated with the remodelling of metaphyses during growth in length of the skeletal segments, hence upon predominantly mechanical factors.

A quantitative analysis of bone tissue formation in different regions of the spongiosa in the dog skeleton.

An investigation has been carried out on the relationship between the extent of bone tissue formation and the architecture of the "tubular" and "lamellar" components of the spongiosa within shaft bone ends, the anterior and posterior epiphyses and the intermediate portions of vertebral bodies in 3 dogs (aged 6 months, 2 and 3 years) treated for 3 consecutive days with tetracycline. The ratio of the extent of labelled surfaces to the sum of labelled plus unlabelled ones indicates the bone formation rate, referred to as osteogenic activity (OA). In the growing animal, a higher osteogenic activity is displayed by the "tubular" spongiosa, which lies peripherally in the metaphyses of shaft bones and consists of strong trabeculae nearly parallel to one another, and apparently arranged according to the distribution of mechanical stresses. In the adult dogs, the relatively higher osteogenic activity recorded in "lamellar" spongiosa appears to depend on a marked reduction in the osteogenic activity in the "tubular" spongiosa. In the vertebrae, osteogenic activity is higher in the central portion than in extremities solely during the period of growth in length: in the adult, the value of osteogenic activity was found to be practically uniform throughout the vertebral body. The "tubular" spongiosa, therefore, would be more actively involved in the remodelling of the metaphyses while the bone increases in length; the same would occur in the intermediate portion of the vertebral body. The reconstruction of the "lamellar" spongiosa, presumably less involved mechanically than the "tubular" spongiosa, would rather be an expression of bone mineral metabolism. A close relationship between spongiosa structure and osteogenic activity would occur at the ends of long bones and within the vertebral body.

Density of trabecular framework and osteogenic activity in the spongiosa of long bones subjected to drastic changes in mechanical loading in the dog.

In 2 groups of dogs aged from 4 months to 3 years, we estimated the density of the spongiosa and the distribution of osteogenic activity in transverse sections of the metaphyses and epiphyses of the experimentally overloaded or unloaded right radii, together with those of the contralateral control bones. Overloading elicited an increase in the density of the spongiosa framework to a higher degree within the peripheral than the deeper metaphyseal spongiosa or within the epiphyses. Some time after operation, the osteogenic activity appeared reduced through the spongiosa in every district although to a greater extent in the regions in which its more pronounced condensation had occurred, i.e. within the metaphyseal subcortical spongiosa. In the unloaded bones, the density of the spongiosa was markedly reduced compared to the control. The differences in the architectural pattern between subcortical and deeper spongiosa were attenuated. Conversely, osteogenic activity was enhanced in every district, being evenly distributed within the spongiosa framework both in the metaphysis and the epiphysis. From comparison between the results obtained by the 2 sets of experiments it seems reasonable to infer that mechanical stress appreciably stimulates bone mass increase and the ensuing remodelling of the spongiosa architecture; at the same time, the more heavily loaded portions of the framework would be subjected to a lesser degree of structural renewal than that occurring in the spongiosa regions less essential to mechanical resistance. The latter, therefore, would rather perform the function of labile stores of mineral salts.

[The rate of bone tissue deposition in the spongiosa of long bones subjected to mechanical overload]. / La velocità di deposizione del tessuto osseo nella spugnosa di ossa lunghe sottoposte a sovraccarico (1).

In three dogs of various age (8-11 months, 3 years), injected twice with Alizarin red (20 mg/Kg) 27 and 7 days before sacrifice, the linear appositional growth rate of bone tissue have been studied in the distal metaphysis and epiphysis of the right radius submitted to mechanical overload by removing a piece of the ulnar shaft. The normally loaded left radius was used as control. In the overloaded metaphysis the linear appositional growth rate appeared significantly increased in the peripherally located spongiosa; no change in the linear appositional accretion of bone tissue as compared to the control was observed in the deep-seated spongiosa and in the epiphysis. These findings are briefly discussed in connection with the role presumably played by the mechanical stresses on osteogenesis.

[The rate of linear deposition of bone tissue in the bone spongiosum of lactating rats on a low calcium diet]. / La velocita' di deposizione lineare del tessuto osseo nella spu gnosa di ossa lunghe di ratte allattanti a dieta ipocalcica.

In the epiphysis and metaphysis of lactating rats, submitted to a Ca++ depletion for 10 and 30 days and a Ca++ repletion diet for 10 days, the density of spongiosa framework and the bone tissue linear accretion rate were compared with those of control rats. The distal metaphyses of femora of the rats fed a calcium free diet for 10 and 30 days lose 50% and 90% of the trabecular framework respectively, while the epiphysis of the same bone lose only 45% and 56%. The linear accretion rate in these regions increases by 7.9 and 24.7% in the epiphysis and by 11.3% and 75.6% in the metaphysis of rats fed a calcium-free diet for 10 and 30 days respectively. Our data indicate that the bone tissue linear accretion rate changes not only between the corresponding regions of control and experimental rats but, in the latter, also in different regions of the same bone. Moreover, the higher the bone loss is, the higher bone accretion rate will be. The correlation between the bone tissue linear accretion rate and the bone loss indicates that the same local factor - probably mechanical - controls the activity and distribution of osteoblasts and osteoclasts.

The structure of the trabeculae of cancellous bone. 2. Long bones and mastoid.

The trabeculae of the mastoid, the upper end of the femur, and the tibia were examined to ascertain whether they contain vascular channels according to a pattern similar to that observed in the calcaneus. The trabeculae were serially sectioned in transverse planes. Each section was microradiographed and photographed under ordinary and polarized light. On the photos of the individual sections (1) the number of the vascular channels, (2) the thickness of the trabecular segments with or without osteons, and (3) the maximum distance of the osteocytic lacunae from filtering surfaces (i.e., haversian canal walls or trabecular surfaces), were evaluated. About 80% of the vascular channels are haversian. Their frequency increases through the increase of the trabecular thickness and reaches 100% in those thicker than 428 microns. The distance of the deep-seated osteocytes from filtering surfaces appears almost the same in the thinner trabeculae, devoid of osteons, and in the thicker ones, containing osteons. Evidence is provided that osteons are present in numerous spongy trabeculae. Osteon formation is strictly related to the trabecular thickness so that the distance of the osteocytes from filtering surfaces does not exceed the critical value of 230 microns (in the mastoid). These findings are in agreement with those recorded in the calcaneus spongiosa. As the trabeculae studied in this research and those of the calcaneus are submitted to different mechanical loads, the main function of the endotrabecular osteons is conceivably to improve the deep-seated cell metabolism rather than the mechanical resistance of the trabeculae. On the other hand, the circumstance that most of the osteons are secondary indicates that they participate to the renewal of bone tissue.

[Quantitative evaluation of the degree of bone tissue deposition in sponge-like skeletal segments submitted to a physiological overload]. / Valutazione quantitativa dell'entita' della deposizione di tessuto osseo nella spugnosa di segmenti scheletrici sotto posti a carico soprafisiologico.

In a 14-month old dog, injected twice with Alizarian red 27 and 7 days before sacrifice, both the distribution of the osteogenic areas and the rate of new bone tissue formation have been studied in the distal metaphysis of the right radius submitted to mechanical overloading by removing a piece of the ulnar shaft. The normally loaded left radius was used as a control. Following a four-month overloading, the bone tissue deposition rate appeared markedly reduced in the more peripherally located "tubular" spongiosa which underwent in parallel conspicuous structural changes. No alterations in the reconstruction rate and in the microscopical structure as compared to the control radius were observed instead in the deep-seated "laminar" spongiosa. The present, as well as previous findings, seem to support the view that (1) the two types of trabecular bone, i.e. the "tubular" and the "laminar" spongiosa, are subjected to quantitatively diverse loading, and (2) mechanical factors play a significant role in the control of the topographic distribution of bone tissue reconstruction.