Super-osteons (remodeling clusters) in the cortex of the femoral shaft: influence of age and gender.

Previous studies of cortical remodeling in the fractured femoral neck indicated that the merging of spatially clustered remodeling osteons could result in the formation of deleteriously large cavities associated with femoral neck fracture. This study aimed to identify whether remodeling osteons in the femoral shaft were also clustered and to assess the influence of age and gender. Microradiographic images of femoral mid-shaft cross-sections from 66 subjects over 21 years of age were analyzed to determine the number, size and location of all Haversian canals. Those most recently remodeled were identified using an edge-detection algorithm highlighting the most marked differential gradients in grey levels. Cluster analysis (JMP software) of these osteons identified the proportion of recently remodeled osteons that were within 0.75 mm clusters. As in the femoral neck, remodeling osteons were significantly more clustered than could occur by chance (real, 59.4%; random, 39.4%; P < 0.0001). The density of these clusters (number/mm(2)) was not significantly associated with subject age or gender but was greatest near the periosteum and decreased toward the marrow cavity (periosteal 0.043 +/- 0.004; mid-cortex 0.028 +/- 0.003; endosteal 0.017 +/- 0.002). Cortical porosity increased with age. The presence of giant canals (diameter >385 microm) was inversely related to the presence of clusters (R(2) = 0.237, P < 0.0001). This data suggest that remodeling osteons tend to be spatially colocalized in the shaft as they are in the neck of the femur and their presence is independent of age or gender. We propose that these remodeling clusters be termed super-osteons. The negative relationship between super-osteons and giant canals raises the intriguing possibility that loss of the control of remodeling depth results in the merging of osteonal systems to form deleteriously large cortical cavities with a marked reduction in bone strength.

Determination of age at death using combined morphology and histology of the femur.

Bone is characterised by age-related morphological and histological changes. We have previously established an automated method of recording bone morphometry and histology from entire transverse sections of cortical bone. Our aim was to determine whether data acquired using this automated system were useful in the prediction of age. Ninety-six specimens of human femoral middiaphysis were studied from subjects aged 21-92 y. Equations predicting specimen age were constructed using macroscopic data (total subperiosteal area (TSPA), periosteal perimeter (PP), endosteal perimeter (EP), cortical bone area (CA) and moments of area) and microscopic data (the number, size and diversity of pores and intracortical porosity) together with sex, height and weight. Both TSPA and PP were independent predictors of age but the number of pores was not a significant predictor of age in any equation. The age predicted by these equations was inaccurate by more than 8 y in over half the subjects. We conclude that we could not predict age at a clinically acceptable level using data from our automated system. This most likely reflects an insensitivity to regional age-related changes in bone histology because we recorded data from each entire cortex. Automated bone measurement according to cortical region might be more useful in the prediction of age. The inclusion of TSPA together with PP as independent predictors of age raises the possibility that a future measure of periosteal shape at the femoral diaphysis could also be helpful in the prediction of age. The accuracy reached with the relatively simple methods described here is sufficient to encourage the development of image-analysis systems for the automatic detection of more complex features.

Regional variations in cortical modeling in the femoral mid-shaft: sex and age differences.

Modern lifestyle changes may result in site-specific alterations in the skeleton. Our aim was to determine sex and age differences in regional geometry at the mid-femur. Complete cross sections from 113 individuals aged 20-97 years from a modern Australian population were obtained. A further subsample of 24, in whom the precise orientation of specimens was known, was subsequently collected. Microradiographs were made of 100-microm sections and the bone was analyzed using image processing software (Optimas, Media Cybernetics). The periosteal boundary was extracted automatically and the centroid of the periosteal outline was calculated. Fourier shape analysis was used to delineate the endocortical surface. Radial and cortical widths in each quadrant were determined. The posterior was identified by the linea aspera, and the medial and lateral were indistinguishable and therefore grouped together. For analysis, the entire sample was divided into three groups: young (20-40 years), middle (41-60 years), and old (61+ years). Raw and height-normalized values were analyzed with SPSS using t-tests, analysis of variance, and Tukey's honestly significant difference (HSD) tests. The results show that with age the femoral mid-shaft in both sexes becomes larger and more circular, with a slight shift towards the anterior. Apposition is least on the posterior and resorption greatest on the anterior, the latter being particularly evident in postmenopausal females. The greatest sex differences are seen in the middle years, lessening again in the old. We conclude that differential circumferential modeling in response to functional and postural changes occurs in both sexes with age.

An automated analysis of intracortical porosity in human femoral bone across age.

The matrix of human cortical bone is arranged around a network of vascular spaces (hereafter referred to as "pores"). Our aim was to investigate age-related differences in human cortical porosity (total pore area divided by cortical bone area), pore size and number, and surface to volume ratios, while adjusting for sex, height, and weight. Ninety-six specimens of entire transverse sections of human femoral diaphysis, from subjects aged 21-92 years, were examined. We used our established automated image acquisition and analysis system which measures pores from entire sections of multiple specimens of bone. Over 400,000 pores were recorded. Results showed a greater porosity in older bone (p < 0.01) but marked variation in porosity for any given age. The cohort median, of the specimen medians, of pore cross-sectional area was 2050 microns 2. Older specimens did not have more pores than younger specimens but had a greater proportion of larger pores (p < 0.05) and greater intraspecimen variation in pore size (p < 0.001). The pore surface to bone matrix volume ratio was a median 2.3 mm2/mm3. This varied more than 4-fold between individuals but did not relate to age. No simple relationships were found between any of the measured parameters and either sex, height, or weight, even after adjustment for age. We conclude that the greater porosity in older specimens is due to greater pore size rather than a larger number of pores. Age, however, explains little of the inter-individual variation in the parameters studied.

Bone size and mechanics at the femoral diaphysis across age and sex.

The reasons for the increase in fracture rates with age are not fully understood. It is known that there is a decrease in bone mass with a presumed loss of strength. This decrease may possibly be compensated for by changes in cross-sectional geometry. Previous studies, which have been limited by lack of information on subjects' heights and weights, were not able to resolve this issue. In this study, measurements of cross-sectional geometry (area and second moments of area) from 107 specimens of human femoral diaphysis from subjects aged 21-92 years were analysed. Mathematical models of the variation in bone geometry with age were developed. These models included the effects of sex, height and weight. Values of parameters from these models were then used in a biomechanical analysis of the static stresses at the mid-shaft of the femur. Results indicate that although there was a reduction in cortical area in old age, bone tissue was redistributed so that neither bending stresses in the coronal plane nor torsional stresses were higher in old age than in young adulthood. An additional finding was that at any age women had smaller bones, less cortical bone area and higher bone stresses than men. This finding may have some bearing on the higher fracture incidence seen in older women.

Age-related changes in cortical porosity of the midshaft of the human femur.

Complete cross-sections from the femoral midshaft of 180 individuals of known height and weight, aged 21-97 y, from a modern Australian population were examined using automatic video image analysis to quantify total subperiosteal porosity (TSPP). More specifically, the aim was to investigate whether age changes were similar in both sexes in (1) total subperiosteal area (TSPA), cortical area (CA) and medullary area (MA), (2) intracortical porosity (ICP), and (3) the respective contributions to TSPP made by MA and intracortical void area (ICVA). Our findings indicated that both sexes showed a significantly greater height normalised TSPA in the 70s as compared with the 20s. Males had consistently larger bones with a greater height normalised CA. In both sexes CA showed a tendency to increase till the 7th decade and then to decline, more so in females. MA approximately trebled in females and doubled in males over the age range studied. Although ICP also increased, from 4-6% in young adults to over 9% in the elderly, it showed a significant difference between the sexes only in the 3rd decade, being greater in males at this stage. By contrast, TSPP became significantly greater in females (from that recorded in the 3rd decade) by the time they reached the 50s, while in males this did not occur till the 80s. It increased from approximately 25% in young adults of both sexes to approximately 50% in females and approximately 37% in males in their 80s. However, in the elderly there was great variability in both sexes in the appearance of bones from individuals of similar chronological age. Some bones differed little from those in younger subjects, others showed greatly increased ICP, still others displayed reduced cortical widths with low ICP. The femoral midshaft resembles other skeletal sites in that age changes in TSPP are more marked in females than males.

Age trends in remodeling of the femoral midshaft differ between the sexes.

Cross-sectional area properties of the femoral midshaft from 203 individuals of known height and weight. 1-97 years of age, from a modern Australian population were quantified using automatic video image analysis. The aim of this study, taking height and weight into account, was to determine whether (a) age trends in remodeling differ between the sexes, (b) men are better able to compensate for bone loss with age, and (c) this protective mechanism is carried through into old age. Our findings indicated that during adulthood there are distinct gender differences in femoral remodeling. From around the third to the seventh decade, men showed a fairly uniform increase in subperiosteal area, polar moment of inertia, and medullary area. Women displayed two distinct phases during this period: relative stability until around the menopause and then a marked increase in all of the above variables. In old age, gender differences diminished, both sexes showing reduced periosteal apposition and increased endosteal resorption. The resultant decline in cortical area of approximately 4% in men and 15% in women from the third to the eighth decade was significant only in women. For a given height, men had larger, stiffer femoral shafts with a greater cortical width and area and maintained this advantage into old age. Diaphyseal bone was not immune from age-related changes affecting other skeletal sites: however, due to compensatory remodeling, which was particularly evident in men, this was not reflected in increased fracture rates.

Early periosteal changes in translation-induced bone modelling.

This primarily ultrastructural study examines the effects of strain induced in the periosteum using an in vivo translation model with minimal internal bone strain. Caudal vertebrae (CV 7, 8, 9) from 4 d rats were threaded onto the arms of prestressed helical torsion springs and transplanted subcutaneously into 50 g hosts of the same inbred strain. After 7 d the appliances were activated in the experimental rats causing the bones to translate, i.e. to move through the soft tissues. Tissues for histology were obtained at this time (0) and at 1, 3, 5, 7, 10 and 14 d; for electron microscopy, experimental tissues were obtained at 0 time, 30 min, 1, 2, 6, 12, 18 and 24 h and at 0 time and 12 h for the controls. As the arms of the appliance move apart, traction on the enveloping soft tissues produces compression of the periosteum on the leading side and tension on the trailing side with resultant eccentric remodelling of the bones, generally opposite to the direction of movement. A rapid and differential structural response occurs, characterised by accelerated formation on the trailing side with the reverse on the leading, where changes are not as marked initially. Long thin trabeculae oriented in the line of tension form on the trailing side whereas the shaft on the leading side becomes thinner and flatter. Ultrastructural examination of the early stages shows that the fibrous periosteum is first affected, with alterations in collagen packing preceding cellular changes. The midzone shows the greatest change and events here presage those which finally occur at the bone surface and are reflected in altered osteoblastic activity. This study shows that translation-induced stress produces rapid morphological changes in the periosteum which, by acting as an integrated unit, has the capacity to modulate the adaptive bone modelling response.

Sealing ability of three materials used to repair lateral root perforations.

Thirty-five extracted single-rooted human teeth were decoronalized, root filled with AH-26 and gutta-percha, and perforated at the apical one third level. Repairs of the lateral perforations were carried out with three materials: amalgam plus cavity varnish, EBA cement, and silver glass-ionomer cement. Negative controls were not perforated and positive controls had unrepaired perforations. The roots were then implanted subcutaneously in rats for 5 days to place the materials in a surgical environment. Following retrieval, the roots were placed in a solution containing 20 microCi/ml of calcium-45 for 7 days to measure microleakage. They were rinsed, sectioned, and autoradiographs of the repaired perforations were made. The autoradiographs were projected onto a screen and the extent of penetration of the radioisotope measured. Statistical analysis showed that the EBA cement group exhibited significantly less leakage than the silver glass-ionomer cement group (p < 0.05). No differences were found between the other groups. It was concluded that EBA cement provides a superior seal in lateral root perforations to silver glass-ionomer cement while amalgam was intermediate between the two.

The biocompatibility testing of some dental amalgams in vivo.

The biological responses to some dental amalgams were determined in vivo and compared with those of dental porcelain. The technique of implantation employed in the study addressed some of the vagaries of the Recommended Standard Practices for Biological Evaluation of Dental Materials (RSP) and considered both cellular responses (inflammation, infiltration and fibrogenic cell activity) and the organizational status of the resultant encapsulation. The implantation sites for both the experimental and control were biogeometrically similar, unlike those currently recommended in RSP. At the end of the test period, all the dental amalgams tested caused minor responses reflected by the formation of thin capsules with an acceptable matrix organization. The Australian manufactured dental amalgams--Permite C, Lojic, F400, New Ultrafine and GS80 all produced even capsules with quiescent cells. By one hundred days, the capsule around Dispersalloy, although generally well formed, showed some areas of cellular activity and matrix variability. The biological responses to all the dental amalgams examined were mild and considered to be acceptable for clinical usage. The matrix organization of enveloping capsules must be considered in the determination of the biocompatibility of a dental restorative material.

Periosteal response in translation-induced bone remodelling.

Translation of transplanted bones induces strain in the periosteum and subsequent bone remodelling. This study examines the periosteal response on the leading and trailing sides of translated bones using an in vivo model where internal bone strain is virtually eliminated. Caudal vertebrae from 4 days old rats were threaded onto the arms of pre-stressed helical torsion springs and transplanted subcutaneously. In the experimental rats, the appliances were activated seven days later causing the bones to translate. Tissues were examined both optically and by transmission electron microscopy. A connective tissue sheath or capsule forms around the bones and, as the arms of the appliance move apart, traction on the enveloping soft tissues produces compression of the periosteum on the leading side and tension on the trailing side with remodelling occurring in a direction opposite to translation. The control periosteum has an ordered structure with well-delineated osteogenic, mid- and fibrous zones. During translation the periosteum on the leading side is consistently narrower than on the trailing side and shows a gradual reduction in formative activity followed by resorption in select areas. Cells and fibres are aligned predominantly parallel to the bone surface. Accelerated formation characterises the trailing side during the translation phase with increased activity and widening of all three periosteal layers. The fibrous layer merges with the connective tissue sheath which frequently is oriented approximately perpendicular to the bone surface. The direction of remodelling is reversed when translation ceases with corresponding changes visible in the periosteum, the osteoblastic layer being the last to show changes. A normal periosteal structure and remodelling pattern is regained when equilibrium of the bones within the soft tissues is attained. This study shows that the enveloping soft tissues profoundly influence the nature and rate of bone remodelling. The changes are reflected in the periosteum which functions as an integrated unit modulating the signal transmitted to the osteoblasts which play a key role in events occurring at the bone surface. Changes are not attributable to internal bone strain.

Periosteal changes in mechanically stressed rat caudal vertebrae.

When a caudal vertebra is stressed by looping the tail, remodelling results with increased formation of bone on the inner (concave) side of the loop and decreased formation on the corresponding outer (convex) side. The initial morphological changes in periosteum under stress are examined by histology, autoradiography and transmission electron microscopy. Vessel damage appears minimal and thus seems unlikely to be a trigger for the remodelling process. On stress application the connective tissue relationships in the fibrous component of the periosteum are altered immediately but changes in the osteogenic layer are delayed. On the inner side, the midzone between the cellular periosteum and the fibrous periosteum becomes drawn out and enlarged, with reorientation of the cells perpendicular to the bone. This reflects the tension exerted on the bone surface through the elastic recoil of the fibrous periosteum. On the outer side, the midzone becomes narrowed as the taut fibrous periosteum exerts a compressive force on it. The midzone, which shows a delayed response and the greatest structural change with altered stress, may buffer the osteogenic layer and so play an important role in bone remodelling. The results have considerable bearing on the establishment of bone form during normal growth and development.

Periosteal structure and development in a rat caudal vertebra.

Female Sprague-Dawley rats from birth to 300 days were used to study the bone/soft tissue interrelationships of the 14th caudal vertebra with particular emphasis on the periosteum throughout growth, development and maturation. The growth of the rats follows a sigmoid curve with three phases, a developmental, a rapid growth and a maturation phase. The width/length ratio of the bone and the thickness of the periosteum are closely concurrent, with a rapid decrease during the developmental phase and a levelling off during the rapid growth phase. SEM studies established that the caudal vertebra has symmetrical lateral sides and a pronounced concavity on the ventral surface where the main vascular plexus is located. Morphological changes in the periosteum cna be described as occurring in three layers and reflect the stages seen in general somatic growth. The inner cambial layer initially contains elongated but functional osteoblasts; these become cuboidal during the rapid growth phase and ultimately are flattened and quiescent. The mid-zone with its vessels, undifferentiated and mononuclear phagocytic cells also attains its maximum development in the rapid growth period and then gradually involutes. The fibrous periosteum consists of a syncytial arrangement of fibroblasts in a collagenous matrix which becomes increasingly dense although reduced in width. Sharpey fibre bundles connect the bone with the fibrous periosteum and these become thicker with age. The mid-zone of the periosteum has not been described previously. Besides having a nutritive role and providing progenitor cells it is thought to act as a buffer modulating the interaction between bone and the covering soft tissues. With age and the deletion of the mid-zone a less sensitive periosteal response to stress can be expected.

Stress induced periosteal changes.

The tails of Sprague-Dawley rats of approximately 50 g body mass were either left straight or bent to form a loop containing three or five vertebrae (CV). Subsequent treatment was as follows: (a) in situ: segments were removed at 0, 8, 16, 24 h, 3, 5 and 7 days and examined histologically: (b) transplants: skinned segments were transplanted autologously and examined at the same time intervals; (c) normal saline: skinned segments were placed in a 0.9% solution maintained at (i) 4 degrees C and (ii) 37 degrees C and examined 8, 16 and 24 h later. The results show that on bending a bone in situ the remodelling which occurs reflects the displacement of the soft tissues, and more specifically the periosteum, towards or away from the bone surface. Functionally the developing periosteum consists of three zones and when stressed its fibroelastic component moves away from or towards the osteogenic layer either applying tension to it stimulating bone formation, or pressure eventually inducing bone resorption. These changes are mediated via the mid-zone. The effects on the fibroelastic component alone are best seen in transplants or in normal saline at 37 degrees C where the osteogenic layer dies. The periosteum in growing bones is ideally structured to respond rapidly and sensitively to altered strain by initiating adaptive surface remodelling of bone.

Remodeling of bone and bones: effects of altered mechanical stress on the regeneration of transplanted bones.

We divided 116 rats weighing 50 gm into four groups with tails either left in situ or transplanted as follows: straight in situ: untreated controls; bent in situ: five caudal vertebrae (CV) in the loop; straight transplants: three CV skinned and transplanted autologously; and bent transplants: five CV skinned, bent to form a loop, and transplanted autologously. Tails were radiographed weekly up to 6 weeks and at 12 weeks, and microradiographic and histological studies were undertaken on selected specimens. At 12 weeks the bones in the apex of the loop of tails left in situ appeared bent with a straight-to-convex shaft on the outer side and a thicker, more concave one on the inner side. In the transplanted bent segments the bone shaft died and initially the reverse occurred: the outer shaft thickened and the inner resorbed completely. A new concave inner diaphysis then formed so that the bones in both instances were essentially similar in final shape. In the bent transplants the surviving osteogenic tissues regenerated and, adapting to the altered forces, formed a new bone shaft. This involved a change in the direction, amount, and nature of endochondral, periosteal, and regenerative growth and subsequent remodeling of bone. The results support previous observations that, within limits, the strain in the osteogenic envelope is an important factor in adaptation of bones to changing stress and that, where the envelope is deficient, the surviving tissues have the capacity to regenerate and repair defects in the bone so that it best resists the changing stresses applied to it.

Remodelling of bone and bones: effects of altered mechanical stress on caudal vertebrae.

Sprague-Dawley rats weighing 50 g were divided into two groups: (i) control, (ii) rats with tails bent in situ incorporating 7, 5 and 3 caudal vertebrae in the loop. Tails were radiographed weekly up to six weeks and a microradiographic and histological study undertaken on selected specimens. Results showed that the bones in the apex of the loop of the bent tail moved through their investing soft tissues towards the outer side of the bend, the joints became V-shaped and in tails bent acutely the epiphyses and metaphyses tilted. By six weeks the bones appeared bent with a thinner straight to convex shaft on the outer side and a thicker, more concave one on the inner side. The changes observed can be explained by taking into account (i) strain within the bone, (ii) altered growth and (iii) the translation of bones through their investing soft tissues. The results are consistent with the supposition that, on application of a continuous moderate stress, tension induces formation and pressure resorption of bone.

Remodelling of bone and bones: effects of translation and strain on transplants.

Tail segments, from 4-day-old Sprague-Dawley rats, consisting of caudal vertebrae (CV) approximately 7-9 were impaled on 0.23-mm diameter Elgiloy wire and transplanted subcutaneously into 50-70 g male hosts to study the effects on transplants of (a) impaling (b) strain and (c) translation. The CV were impaled onto straight lengths of wire to serve as controls (a); onto a wire curved to form a loop and exert a bending force (b) and onto the arms of a spring which moved bones through the surrounding tissues, i.e. translation (c). Tissue changes were studied up to 28 days by radiographic and histological techniques. Control bones grow relatively normally along the straight wire. The CV subjected to strain bend initially and then grow in an arc along the curve of the wire. The outer bone shaft usually becomes straighter while the inner one becomes concave and rarefied. In the translated bones remodelling occurs in a direction generally opposite to the direction of movement but this is modified by the influence of soft tissue tension and pressure. Bone resorbs on the outer leading side under continuous pressure and forms on the inner trailing side under continuous tension. The process is essentially the same as that seen in 'cortical drift'; however, since translation is rapid there is an alteration in the shape of the translated bones as formation on the trailing side is faster than resorption on the leading side.(ABSTRACT TRUNCATED AT 250 WORDS)

Remodelling of bone and bones: growth of normal and transplanted caudal vertebrae.

Changes in the rate of growth, shape and structure of the 8th, 16th and 22nd caudal vertebrae of 4 and 24-27 days old Sprague-Dawley rats were studied in situ and in three different non-functional transplantation sites for 12 weeks. With increasing size, maturity and age the three vertebrae showed progressively decreasing growth, changes in shape and structural abnormalities. The smallest anlages grew faster and matured sooner than normal, so that their length equalled that of controls. Central endochondral necrosis in older bones was associated with decreased longitudinal growth but in some younger ones, despite a perforation of the cartilage and herniation of the nucleus pulposus into the marrow cavity of the shaft, growth proceeded at near normal rates. The free ends of older, larger transplants grew faster than the abutting ends joined by joint connective tissue, indicating that central necrosis of cartilage resulted from impaired nutrient diffusion. The results suggest that the cartilage model may possess an inherent capacity to produce a certain limited amount of bone tissue which may be distributed either in the form of long and thin or short and inwaisted bones, depending on the balance of forces between interstitial cartilage expansion and the restraining ensheathing periosteal-perichondrial tissues. This basic form may be modified further by functional forces.

Remodelling of bone and bones. Effects of altered mechanical stress on anlages.

Tails from 4-day-old Sprague-Dawley rats were bent in situ or skinned bent tail segments were transplanted s.c. into 50 g hosts. Tissue changes were studied for up to 24 weeks by radiographic and histological techniques. The early changes in situ resulted largely from limited translation of bones within their encasing tissues with resorption on the leading (pressure) side inducing thinning, and on the trailing (tension) side thickening of bone. The changes in transplanted anlages occurred in 3 stages: initially, bending of the anlages, with tension between the stretched periosteum and the outer bone surface inducing formation, and compression of cartilage and bone on the inner aspect leading to resorption; then resumption of longitudinal growth and expansion of the bent loop leading to translation of bones within the encasing soft tissues with resorption and thinning of bone on the leading pressure side and formation, with thickening of the inner shaft, on the trailing tension side; and finally with cessation of growth and translation, a reversal to the previous phase. The results support the hypothesis that 2 processes are involved: first, internal stress, and second, translation of bones with, in all instances, pressure inducing resorption and tension inducing formation of bone.

Joint changes in transplanted caudal vertebrae.

Both straight and bent segments of tails from 4-d-old and weaning Sprague-Dawley rats were used to study the changes which occur in symphyseal joints on transplantation to non-functional sites. In the joints from the younger donors ankylosis occurred almost invariably in the proximal end of the tail, while distally it was rarely seen unless the tail was curved, when ankylosis was visible on the inner side of the bend. The joints from the older donors showed a more varied response on transplantation. Some appeared unaltered, in others where growth continued, calcific changes were seen. In bent segments, unlike in younger ones, ankylosis occurred preferentially on the outer side of the bend. Histological examination revealed that ankylosis of the joint occurred through a process of chondroid metaplasia of the intervertebral connective tissue with subsequent replacement by bone. The metaplastic joint changes were primarily the results of pressure producing compression of the annulus fibrosus in tissues with a reduced vitality due to transplantation and lack of function.