A randomized study on the effects of estrogen/gestagen or high dose oral calcium on trabecular bone remodeling in postmenopausal osteoporosis

Thirty-seven patients with postmenopausal crush fracture osteoporosis were randomized to oral cyclic estrogen/gestagen (n = 20) or oral calcium (2000 mg elemental calcium per day) (n = 17). Fourteen in each group completed 1 year of treatment. Iliac crest bone biopsies were obtained after intravital double labeling with tetracycline before and after treatment in 10 patients on estrogen/gestagen and 11 patients on calcium. In the estrogen/gestagen group the activation frequency in trabecular bone decreased from 0.52 + 0.11 (SEM) year-1 to 0.27 + 0.08 year-1 (p less than 0.01). No significant changes were found in resorption or formation periods. The osteoid surfaces and the mineralizing surfaces decreased (p less than 0.05), whereas the decrease in eroded surfaces was insignificant. Furthermore, no significant changes were observed in final resorption depth, wall thickness or bone balance per remodeling cycle. Serum alkaline phosphatase and renal hydroxyproline excretion decreased during treatment (p less than 0.002), whereas the lumbar bone mineral content (BMC) increased (p less than 0.01). In the calcium group the extent and thickness of osteoid surfaces decreased (p less than 0.05) without significant changes in activation frequency. Serum alkaline phosphatase and renal hydroxyproline excretion decreased during treatment (p less than 0.02). No significant changes were observed in lumbar BMC or the other histomorphometric parameters. The study supports that the positive effect of estrogen/gestagen on BMC can be explained by a reduction in the activation frequency of new remodeling cycles leading to a decreased remodeling space and an increase in mean bone age. There is no evidence of a positive balance per remodeling cycle.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of prostaglandins on regional remodeling changes during tibial healing in beagles: A histomorphometric study

Summary A histomorphometric study was carried out on bone samples in the region of healing defects in the tibias of beagles of various ages. A 5 mm diameter drill hole defect was made in the mid-shaft of the tibia. Eleven of the beagles received either vehicle (n=6) or prostaglandin E₂ orally (n=5) for the 30-day period from surgery to time of necropsy. Ten dogs received local injections of vehicle (n=4) or prostaglandin E₁ directly into the defects for the first 10 days after surgery. Double labels were given with each of two fluochrome markers, calcein prior to surgical treatment, and oxytetracycline hydrochloride prior to 30-day sacrifice. The regional remodeling changes were evaluated in 40–50 μm thick cross-sections taken 2 cm proximal to the defect and matching samples from the contralateral side. In the controls, the changes were variable and reflected primarily increased formation on the surfaces of the cortex. Cortical endosteal bone formation, as indicated by oxytetracycline labeling, was increased in both control groups and there was an increase in labeling in the periosteal and haversian envelopes as well, in the local injection control group. In the dogs given prostaglandin E₂ orally, there was increased periosteal bone formation in addition to increased cortical-endosteal formation. When healing sides were compared to controls, prostaglandin E₂-treated dogs also had increased osteoid formation in all three envelopes and increased resorption surface in the cortical endosteal envelope, indicating accelerated remodeling. The dogs that had received prostaglandin E₁ locally also had more periosteal and cortical endosteal bone formation, with an increased amount of osteoid present. Although osteoid surface was greater in comparison to healing sides in controls, there was no corresponding increase in oxytetracycline-labeled surface. This was also true of the periosteal and haversian envelopes of the dogs treated orally with prostaglandin E₂. The enhanced changes in regional remodeling seen in both prostaglandin-treated groups were associated with less advanced healing in the defect site.     

Bisphosphonate treatment delays stress fracture remodeling in the rat ulna

Because bisphosphonates (BPs) are potent inhibitors of bone resorption, we hypothesized that they would retard direct remodeling of stress fractures. The aim of this study was to determine the effect of risedronate on direct remodeling and woven bone callus formation following stress fracture formation in the rat ulna. In 135 adult female Wistar rats, cyclic loading of the ulna created stress fractures. Rats were treated daily with oral saline, or risedronate at 0.1 or 1.0 mg/kg. From each bone, histomorphometry was performed on sections stained with toluidine blue at a standard level along the fracture. The high dose of risedronate caused a significant decrease in the percentage of repaired stress fracture and bone resorption along the stress fracture line at 6 and 10 weeks after loading (p < 0.05). At this dose, intracortical resorption was significantly reduced at 10 weeks after loading and intracortical new bone area was significantly reduced at 6 and 10 weeks. Woven bone formation and consolidation phases of stress fracture repair were not affected by low or high doses of risedronate. In conclusion, high dose bisphosphonate treatment impaired healing of a large stress fracture line by reducing the volume of bone resorbed and replaced during remodeling. We also confirmed that periosteal callus formation was not adversely affected by risedronate treatment. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29:1827–1833, 2011     

Cancellous bone remodeling occurs in specialized compartments lined by cells expressing osteoblastic markers.

We describe a sinus, referred to as a bone remodeling compartment (BRC), which is intimately associated with cancellous bone remodeling. The compartment is lined on its marrow side by flattened cells and on its osseous side by the remodeling bone surface, resembling a roof of flattened cells covering the bone surface. The flat marrow lining cells are in continuity with the bone lining cells at the margins of the BRC. We examined a large number of diagnostic bone biopsy specimens received during recent years in the department. Furthermore, 10 patients (8 women and 2 men, median age 56 [40-69] years) with the high turnover disease of primary hyperparathyroidism who were treated with parathyroidectomy and followed for 3 years were included in the histomorphometric study. Bone samples for the immuno-enzyme staining were obtained from an amputated extremity of child. The total cancellous bone surface covered by BRC decreases by 50% (p < 0.05) following normalization of turnover and is paralleled by a similar 50% decrease in remodeling surface (p < 0.05). The entire eroded surface and two-thirds of the osteoid surface are covered by a BRC. BRC-covered uncompleted walls are 30% (p < 0.05) thinner than those without a BRC. This indicates that the BRC is invariably associated with the early phases of bone remodeling, that is, bone resorption, whereas it closes during the late part of bone formation. Immuno-enzyme staining shows that the flat marrow lining cells are positive for alkaline phosphatase, osteocalcin, and osteonectin, suggesting that they are bone cells. The first step in cancellous bone remodeling is thought to be the lining cells digesting the unmineralized matrix membrane followed by their disappearance and the arrival of the bone multicellular unit (BMU). We suggest that the lining cell barrier persists during bone remodeling; that the old lining cells become the marrow lining cells, allowing bone resorption and bone formation to proceed under a common roof of lining cells; that, at the end of bone formation, new bone lining cells derived from the flattened osteoblasts replace the marrow lining cells thereby closing the BRC; and that the two layers of lining cells eventually becomes a single layer. The integrity of the osteocyte-lining cell system is reestablished by the new generation of lining cells. The BRC most likely serves multiple purposes, including efficient exchange of matrix constituents and minerals, routing, monitoring, or modulating bone cell recruitment, and possibly the anatomical basis for the coupling of bone remodeling.     

High-turnover periprosthetic bone remodeling and immature bone formation around loose cemented total hip joints.

Aseptic loosening and periprosthetic osteolysis are the major problems awaiting solution in total hip surgery. The clinical investigation focused on the analysis of periprosthetic bone remodeling to clarify one important key event in the cascade of periprosthetic connective tissue weakening and osteolysis around loose artificial hip joints. Twelve acetabular bone samples adjacent to granulomatous synovial-like membrane of loose hip prosthesis were retrieved at revision surgery and processed for Villanueva bone staining for morphological observation and bone histomorphometric analysis. Eight well-fixed bony samples were used as control. Although osteoclastic surface and eroded surface by osteoclasts were evident in the periprosthetic bone from loose hip joints (p = 0.003 and p = 0.027), increased osteoid/low-mineralized bone matrix (p < 0.001) and osteoid width (p < 0.001) also were significant findings in structural analysis. In addition, not only elevated mineral apposition rate (MAR; p = 0.044) but also increased mineralizing surface (p = 0.044) and bone formation rate (BFR; p = 0.002) in loose periprosthetic bones were shown in dynamic data analysis. These results were confirmed by precise morphological observation by confocal laser scanning microscopy. Active coupling of bone formation and resorption and increased osteocytes with abundant bone canalicular projections were found in combined with the presence of immature bone matrices (osteoid and low-mineralized bone areas) in periprosthetic bones from loose hip joints. These results indicated that active osteoclastic bone resorption and/or defective bone formation are coupled with monocyte/macrophage-mediated foreign body-type granuloma in the synovial-like interface membrane of loose hip joints. Thus, this unique high-turnover periprosthetic bone remodeling with bad bone quality probably is caused by the result of cellular host response combined with inappropriate cyclic mechanical loading. The fragile periprosthetic bone may contribute to hip prosthesis loosening.     

Bone remodeling at the endocortical surface of the human femoral neck: a mechanism for regional cortical thinning in cases of hip fracture.

Endocortical remodeling and wall thickness (W.Th.) were measured in femoral neck bone from 12 female fracture cases (81.3 +/- 1.5 years) and 12 sex-matched controls (81.9 +/- 1.9 years). Regionally, osteoid and eroded surface were increased, whereas W.Th. was reduced. These processes likely contribute to cortical bone loss seen in hip fracture. INTRODUCTION: Because periosteal expression of alkaline phosphatase was similar between cases and controls, we hypothesized that the mechanism causing the marked femoral neck cortical thinning associated with hip fracture may be net endocortical bone loss. METHODS: Twelve female cases of femoral neck fracture (mean age = 81.3 +/- 1.5 years) and 12 age- and sex-matched postmortem controls (mean age = 81.9 +/- 1.9 years) were included in the study. Samples of their femoral neck bone were embedded in methyl methacrylate, sectioned at 10 microm, and stained with Solochrome cyanine R and Goldner's trichrome for the detection of osteoid (%OS/BS) and resorption surfaces (%ES/BS) respectively. In addition, wall thickness (W.Th.) and lamellar thickness (Lm.Th.) data were also collected from identifiable endocortical bone packets as a measure of formative potential. RESULTS AND CONCLUSIONS: %OS/BS was significantly elevated in the anterior (control = 3.4 +/- 0.7: fracture = 11.0 +/- 2.3; p = 0.0001), inferior (3.4 +/- 1.0: 9.9 +/- 3.0; p = 0.0009), and posterior quadrants (3.2 +/- 0.8: 9.1 +/- 2.3; p = 0.0021). Only for anterior region was increased %ES/BS demonstrated in the fracture group (2.8 +/- 0.6: 5.3 +/- 0.7; p = 0.055). W.Th. (mm) was reduced only in the inferior region of the fracture cases (control = 33.7 +/- 1.2: fracture = 30.6 +/- 0.9; p = 0.013), whereas Lm.Th. was also reduced inferiorly (control = 2.7 +/- 0.08: fracture = 2.5 +/- 0.08; p = 0.042). These data suggest that an endocortical remodeling imbalance involving reduced bone formation within inferior region coupled with elevated anterior resorption may make an important contribution to the cortical thinning observed in cases of femoral neck fracture.     

Low-intensity pulsed ultrasound increases bone volume, osteoid thickness and mineral apposition rate in the area of fracture healing in patients with a delayed union of the osteotomized fibula

INTRODUCTION: Low-intensity pulsed ultrasound (LIPUS) accelerates impaired fracture healing, but the exact mechanism is unknown. The aim of this study was to investigate how LIPUS affects bone healing at the tissue level in patients with a delayed union of the osteotomized fibula, by using histology and histomorphometric analysis to determine bone formation and bone resorption parameters. MATERIALS AND METHODS: Biopsies were obtained from 13 patients (9 female, 4 male; age 42-63) with a delayed union of the osteotomized fibula after a high tibial osteotomy, treated for 2-4 months with or without LIPUS in a randomized prospective double-blind placebo-controlled trial. In the histological sections of the delayed union biopsies, 3 areas of interest were distinguished, i.e. 1) area of new bone formation at the fracture ends, 2) area of cancellous bone, and 3) area of cortical bone. Histomorphometrical analysis was performed to determine bone formation and bone resorption parameters (as well as angiogenesis). RESULTS: In LIPUS-treated delayed unions, endosteal callus formation by direct bone formation without a cartilage intermediate as well as indirect bone formation was observed, while in untreated controls only indirect bone formation was observed. In the area of new bone formation, LIPUS significantly increased osteoid thickness by 47%, mineral apposition rate by 27%, and bone volume by 33%. No increase in the number of blood vessels was seen in the newly formed bony callus. In the area of cancellous bone, bone volume was significantly increased by 17% whereas no effect on osteoid thickness and mineral apposition rate was seen. LIPUS did not affect osteoid volume, osteoid maturation time, number of osteocytes, osteocyte lacunae, or osteoclast-like cells in any of the areas of interest. CONCLUSIONS: Our results suggest that LIPUS accelerates clinical fracture healing of delayed unions of the fibula by increasing osteoid thickness, mineral apposition rate, and bone volume, indicating increased osteoblast activity, at the front of new bony callus formation. Improved stability and/or increased blood flow, but probably not increased angiogenesis, might explain the differences in ossification modes between LIPUS-treated delayed unions and untreated controls.     

Bone fragility: failure of periosteal apposition to compensate for increased endocortical resorption in postmenopausal women.

The increase in bone fragility after menopause results from reduced periosteal bone formation and increased endocortical resorption. Women with highest remodeling had greatest loss of bone mass and estimated bone strength, whereas those with low remodeling lost less bone and maintained estimated bone strength. INTRODUCTION: Bone loss from the inner (endocortical) surface contributes to bone fragility, whereas deposition of bone on the outer (periosteal) surface is believed to be an adaptive response to maintain resistance to bending. MATERIALS AND METHODS: To test this hypothesis, changes in bone mass and estimated indices of bone geometry and strength of the one-third distal radius, bone turnover markers, and fracture incidence were measured annually in 821 women 30-89 years of age for 7.1 +/- 2.5 years. The analyses were made in 151 premenopausal women, 33 perimenopausal women, 279 postmenopausal women, and 72 postmenopausal women receiving hormone replacement therapy (HRT). RESULTS: In premenopausal women, periosteal apposition increased the radius width, partly offsetting endocortical resorption; therefore, the estimated cortical thickness decreased. Outward displacement of the thinner cortex maintained bone mass and cortical area and increased estimated bending strength. Estimated endocortical resorption accelerated during perimenopause, whereas periosteal apposition decreased. Further cortical thinning occurred, but estimated bending strength was maintained by modest outward cortical displacement. Endocortical resorption accelerated further during the postmenopausal years, whereas periosteal apposition declined further; cortices thinned, but because outward displacement was minimal, estimated cortical area and bending strength now decreased. Women with highest remodeling had the greatest loss of bone mass and strength. Women with low remodeling lost less bone and maintained estimated bone strength. In HRT-treated women, loss of bone strength was partly prevented. These structural indices predicted incident fractures; a 1 SD lower section modulus doubled fracture risk. CONCLUSIONS: Periosteal apposition does not increase after menopause to compensate for bone loss; it decreases. Bone fragility of osteoporosis is a consequence of reduced periosteal bone formation and increased endocortical resorption. Understanding the mechanisms of the age-related decline in periosteal apposition will identify new therapeutic targets. On the basis of our results, it may be speculated that the stimulation of periosteal apposition will increase bone width and improve skeletal strength.     

Bone formation by minimodeling is more active than remodeling after parathyroidectomy

Bone formation using the process known as minimodeling forms only lamellar bone in the absence of prior bone resorption even in uremic patients. In patients undergoing parathyroidectomy for secondary hyperparathyroidism, we compared the contribution of minimodeling to remodeling during the change in bone volume. Iliac bone biopsies were used to measure parameters related to minimodeling and remodeling before, at 3 to 4 weeks and 10 to 12 weeks after parathyroidectomy. Osteoblast surface due to minimodeling was greater than the entire bone osteoblast surface before and at 10 to 12 weeks after parathyroidectomy, but not 3 to 4 weeks after surgery. Minimodeling significantly increased osteoid volume 3 to 4 weeks after parathyroidectomy. The rate of change of osteoid volume by minimodeling was greater than that of osteoid volume during the first 3 to 4 weeks after surgery, indicating osteoid formation was more active at the minimodeling surface than at the entire bone surface. Furthermore, higher mineral apposition rates at the minimodeling sites than at remodeling sites yielded increased minimodeling bone volume at 10 to 12 weeks after surgery. Our results show that bone formation by minimodeling is more active than by remodeling and accounts, in part, for the increase of bone volume following parathyroidectomy.     

Bone resorption and formation on the periosteal envelope of the ilium: a histomorphometric study in healthy women.

Continuation of net periosteal bone gain after cessation of longitudinal growth has been inferred from sequential radiographic morphometry. Accordingly, we performed histomorphometry of the periosteal surfaces of transilial bone biopsies from 57 healthy women aged 24-74 years, 29 premenopausal and 28 postmenopausal. Compared to the endocortical surface, the extents of eroded and osteoid surfaces were very similar, but the extents of osteoclast- and osteoblast-covered surfaces were 80-90% smaller, and both wall thickness and osteoid thickness were about 30% lower. Double tetracycline labels were present in only 11 cases. The second (demethylchlortetracycline) label was almost four times as long as the first (oxytetracycline) label, a much greater difference than on the endocortical surface, so that the extent of mineralizing surface was based only on the second label. Even so, adjusted apposition rates and bone formation rates were only about 20% of the endocortical values, and unlike the endocortical surface, formation rates were not higher in the postmenopausal than in the premenopausal women. Resorption, reversal, and formation periods were each much longer than on the endocortical surface. There was no correlation between periosteal and endocortical values for any variable. At least 54% of total cement line length was scalloped, implying reversal of remodeling direction from resorption to formation, and at least 18% of total cement line length was smooth, implying temporary arrest of bone formation. Convincing evidence of modeling, related to growth or mechanical stimulation, was not observed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Does early PTH treatment compromise bone strength? The balance between remodeling,porosity, bone mineral,and bone size

The treatment of osteoporotic women with recombinant human parathyroid hormone (rhPTH[1-34]) increases bone mineral density and reduces fracture risk. However, there has been concern that the initiation of therapy in women with low bone mass may cause an early and transient increased fracture risk because PTH stimulates bone remodeling, which in its first phase is associated with bone resorption. Animal and human studies suggest, however, that the stimulation of remodeling caused by rhPTH(1–34) does not lead to a deterioration of bone’s mechanical properties or to an increased fracture risk even early in the treatment. There are several reasons for this. Bone biomarkers associated with formation rise earlier than those associated with resorption, suggesting that there is an initial period prior to the stimulation of remodeling during which bone formation occurs on surfaces without prior resorption. This initial period of formation may protect the patient from the later small and transient losses that occur through remodeling. Moreover, the increased remodeling occurs on cancellous surfaces or close to the endosteal surface of bone, where its mechanical effect is minimal. Additionally, these transient losses may be compensated by periosteal apposition that maintains the overall strength of the bone. Thus, the early stimulation of bone formation without prior resorption, and the redistribution of bone from cancellous and endocortical surfaces to the periosteal surface combine to prevent the mechanical deterioration that could otherwise occur with a transient acceleration of bone remodeling in a patient with low bone mass.     

A study of fracture callus material properties: relationship to the torsional strength of bone

This study was designed to quantitate the local material properties of fracture callus during gap healing and to relate these local properties to the torsional strength of bone in a canine model under external fixation. Bilateral tibial transverse osteotomies were performed in 32 dogs and stabilized using unilateral external skeletal fixators with a 2-mm gap. Dogs were divided into four equal groups and euthanized at either 2, 4, 8, or 12 weeks. The torsional properties of one bone of each pair were determined. In both bones of each pair, the indentation stiffness, calcium content, and histomorphometric properties of six sites of periosteal callus, six sites of endosteal callus, four sites of cortical bone, and two sites of gap tissue were determined. Each of the four types of tissue had a specific structural or material property change during the study period. The indentation stiffness of periosteal callus increased up to 8 weeks and then plateaued. Endosteal callus stiffness peaked at 8 weeks and then decreased by 12 weeks. Gap tissue stiffness increased linearly over time. Cortical bone stiffness decreased over time. Indentation stiffness was significantly associated with the calcium content of periosteal callus (R2 = 0.50, p less than 0.0001) and gap tissue (R2 = 0.66, p less than 0.0001). The local stiffnesses of gap tissue and periosteal callus were significantly associated with the maximum torque (gap, R2 = 0.50, p less than 0.0001; periosteal, R2 = 0.34, p less than 0.05) and the torsional stiffness (gap, R2 = 0.44, p less than 0.0001; periosteal, R2 = 0.65, p less than 0.0001) of the bone.(ABSTRACT TRUNCATED AT 250 WORDS)     

降钙素对正常成年雄性大鼠骨重建过程的影响

目的 在体研究降钙素对成年雄性大鼠松骨重建过程的影响,并分析其影响机制。方法 １２只大鼠平均分成对照组和降钙素组,后皮内注射鳗鱼降钙素１Ｕ／１００ｇ／日,连续２日。７日后取第４、５腰椎,行不脱钙骨组织切片,骨组织形态计量学分析,方差分析比较两组结果。结果 骨吸收陷窝表面、活性吸收表面、破骨细胞平均细胞核数,降钙素组明显小于对照组。类骨质表面、类骨质相对体积、类骨质厚度,降钙素组明显小于对照组,成     

Subchondral bone thickness, hardness and remodelling are influenced by short-term exercise in a site-specific manner.

It was hypothesised that subchondral bone thickness, hardness and remodelling are influenced by exercise intensity, and by location within a joint. Dorsal carpal osteochondral injury is a major cause of lameness in horses undergoing high intensity training. This project aimed to determine the subchondral bone thickness, formation, resorption and hardness at sites with high and low incidence of pathology in 2 year-old horses undergoing 19 weeks high intensity treadmill training or low intensity exercise, and to compare these factors between exercise groups. Dorsal and palmar test sites were identified on radial, intermediate and third carpal articular surfaces after euthanasia. Adjacent osteochondral samples from each test site underwent histomorphometric analysis (for subchondral bone thickness, osteoid perimeter, osteoid seam width, eroded cavity area and eroded cement line surface length) and microhardness testing. Bone from horses undergoing high intensity training was thicker with a greater osteoid perimeter, and at individual sites had a smaller osteoid seam width and eroded cavity. Exercise-related differences were most marked at dorsal locations. Maximal differences in bone formation indices were observed at dorsal radial and medial third carpal locations. Overall subchondral bone from dorsal sites was thicker with a greater osteoid perimeter. Subchondral bone from dorsal sites was approximately 35% harder than bone from palmar sites. These results show topographical variations in subchondral bone structure, formation, resorption and material properties and a site-specific response to exercise. The maximal response to exercise was at high load sites with a clinical predisposition to injury. These findings indicate that the combined effect of exercise and local load variations within a joint may lead to maximal adaptive responses or overload of these responses at sites predisposed to injury.     

Experimental study on the effect of direct currents on the internal remodeling of a long bone cortex

The effects of direct currents on internal remodeling were examined using femurs of 21 adult mongrel dogs. The left femurs of all dogs, used as a control, were inserted electrodes only, which were not electrically stimulated. In Group 1, no surgery was done on the right femur. In Group 2, 1 microA continuous direct current (D. C.) was applied for 6 weeks; in Group 3, 10 microA for 2 weeks; in Group 4, 10 microA for 4 weeks; in Group 5, 10 microA for 6 weeks; in Group 6, 10 microA for 16 weeks; and in Group 7 100 microA for 6 weeks. Each group was composed of three dogs. The following histomorphometric parameters were measured to evaluate the effects of electrical stimulation: number of resorption cavities (Ar), number of secondary osteons with osteoid seam (osAf), linear rate of mineralization of osteoid seam (Mo), perimeter of osteoid seam (Sf), cross-sectional area of secondary osteon (Ah) and bone formation rate (Vf). The following results were obtained: In Group 1, resorption cavities and secondary osteon with osteoid seam were observed more in the left femur than in the right. Then, mechanical stimulation of periosteal stripping or cortical drilling enhanced internal remodeling of cortical bone. In other groups (electrical stimulation was applied on the right femur), it seems that internal remodeling, especially activation frequency, was enhanced by D. C. No significant change was noted in the linear rate of mineralization of osteoid seam and cross-sectional area of the secondary osteons. Bone formation rate in the right femur showed increment when length of stimulating period had increased from 2 to 6 weeks. In Group 6 and 7, the enhanced area of bone formation has increased in cross-section, although in Group 7, bone necrosis was observed around the electrode in the right femur. Therefore, the optimum current of electrical stimulation may be just or slightly more than 10 microA. Bone formation rate was correlated with volume of callus in the marrow cavity within the period of six weeks.     

Increased cancellous bone in the femoral neck of patients with coxarthrosis (hip osteoarthritis): a positive remodeling imbalance favoring bone formation

Osteoporosis is caused by an imbalance between bone resorption and formation which results in an absolute reduction in bone mass. In a previous study we highlighted a condition, osteoarthritis of the hip (coxarthrosis, cOA), where an imbalance between resorption and formation provided beneficial effects in the form of an absolute increase in bone mass. We demonstrated that the femoral neck in patients with cOA had increased cancellous bone area, connectivity and trabecular thickness which might contribute to the protection against fracture associated with the condition. The aim of the present study was to analyze forming and resorbing surfaces in coxarthritic cancellous bone to assess whether increased formation or reduced resorption could be responsible for these structural changes. Whole cross-sectional femoral neck biopsies were obtained from 11 patients with cOA and histomorphometric parameters compared with 14 age- and sex-matched cadaveric controls. The ratio of osteoid surface to bone surface was 121% ( p<0.001) higher in the cases but there was no significant difference in resorptive surface. The percentage osteoid volume to bone volume (%OV/BV; +270%, p<0.001) and osteoid width (O.Wi; +127%, p<0.001) were also higher in the cases. This study suggests that the increased cancellous bone mass seen in cases of cOA is due to increased bone formation rather than decreased bone resorption. Investigation of the cellular and biochemical basis for these changes might provide new insights into the pathogenesis of osteoarthritis and highlight novel biological mechanisms regulating bone multicellular unit (BMU) balance that could be relevant to developing new interventions against hip and other osteoporotic fractures.     

The ratio of messenger RNA levels of receptor activator of nuclear factor kappaB ligand to osteoprotegerin correlates with bone remodeling indices in normal human cancellous bone but not in osteoarthritis.

The determinants of cancellous bone turnover and trabecular structure are not understood in normal bone or skeletal disease. Bone remodeling is initiated by osteoclastic resorption followed by osteoblastic formation of new bone. Receptor activator of nuclear factor kappaB ligand (RANKL) is a newly described regulator of osteoclast formation and function, the activity of which appears to be a balance between interaction with its receptor RANK and with an antagonist binding protein osteoprotegerin (OPG). Therefore, we have examined the relationship between the expression of RANKL, RANK, and OPG and indices of bone structure and turnover in human cancellous bone from the proximal femur. Bone samples were obtained from individuals with osteoarthritis (OA) at joint replacement surgery and from autopsy controls. Histomorphometric analysis of these samples showed that eroded surface (ES/BS) and osteoid surface (OS/BS) were positively associated in both control (p < 0.001) and OA (p < 0.02), indicating that the processes of bone resorption and bone formation remain coupled in OA, as they are in controls. RANKL, OPG, and RANK messenger RNA (mRNA) were abundant in human cancellous bone, with significant differences between control and OA individuals. In coplotting the molecular and histomorphometric data, strong associations were found between the ratio of RANKL/OPG mRNA and the indices of bone turnover (RANKL/OPG vs. ES/BS: r = 0.93, p < 0.001; RANKL/OPG vs. OS/BS: r = 0.80, p < 0.001). These relationships were not evident in trabecular bone from severe OA, suggesting that bone turnover may be regulated differently in this disease. We propose that the effective concentration of RANKL is related causally to bone turnover.     

Bone histomorphometry in 22 male patients with normocalciuric idiopathic osteoporosis

Osteoporosis is associated with increased bone resorption together with a decrease in bone formation. In women, there is an increase of resorption surfaces and in the number of osteoclasts. These changes, however, are not found in males. This purpose of this study was to examine clinical, laboratory, and histomorphometric data in a series of 22 male patients with primary osteoporosis and normocalciuria undergoing transiliac bone biopsy. All of them gave written informed consent for bone biopsy. Automated biochemical profile, urinary calcium excretion, and bone marker assays were performed. Histomorphometric studies were carried out in transiliac bone biopsies obtained with a Bordier-Lepine needle with previous tetracycline labeling. The histomorphometric values of cancellous bone showed significantly lower values of bone volume and values of osteoid surface (OS/BS) and osteoblast surface (Ob.S/BS), and a modest increase in osteoid thickness (O.Th) without changes in the mineralization lag time or eroded surface in patients compared with controls. In cortical bone, there was a low cortical volume (Ct.V/TV) and cortical width (Ct.Wi) in patients compared with controls, without differences in cortical porosity (Po.V/TV). These results suggest that normocalciuric idiopathic osteoporosis in men is characterized by decreased cancellous osteoblasts and bone turnover.     

Pantoprazole, a Proton Pump Inhibitor, Delays Fracture Healing in Mice

Proton pump inhibitors (PPIs), which are widely used in the treatment of dyspeptic problems, have been shown to reduce osteoclast activity. There is no information, however, on whether PPIs affect fracture healing. We therefore studied the effect of the PPI pantoprazole on callus formation and biomechanics during fracture repair. Bone healing was analyzed in a murine fracture model using radiological, biomechanical, histomorphometric, and protein biochemical analyses at 2 and 5 weeks after fracture. Twenty-one mice received 100 mg/kg body weight pantoprazole i.p. daily. Controls (n = 21) received equivalent amounts of vehicle. In pantoprazole-treated animals biomechanical analysis revealed a significantly reduced bending stiffness at 5 weeks after fracture compared to controls. This was associated with a significantly lower amount of bony tissue within the callus and higher amounts of cartilaginous and fibrous tissue. Western blot analysis showed reduced expression of the bone formation markers bone morphogenetic protein (BMP)-2, BMP-4, and cysteine-rich protein (CYR61). In addition, significantly lower expression of proliferating cell nuclear antigen indicated reduced cell proliferation after pantoprazole treatment. Of interest, the reduced expression of bone formation markers was associated with a significantly diminished expression of RANKL, indicating osteoclast inhibition. Pantoprazole delays fracture healing by affecting both bone formation and bone remodeling.     

Trabecular remodeling processes in the ovariectomized rat: modified node-strut analysis

The purpose of this study was to evaluate the trabecular bone remodeling processes in ovariectomized rats, focusing on diminishing trabecular connectivity. We used modified node-strut analysis defining three areas in the trabecular surfaces for the three-dimensional understanding of trabecular resorption derived from two-dimensional conventional sections, in addition to conventional bone histomorphometry and node-strut analysis. Seven-month-old female Wistar rats were used and treated with bilateral ovariectomy (ovx) and sham operation. Six rats in each group were examined at 4 and 8 weeks. We prepared undecalcified sections from the left tibiae with Villanueva bone and Goldner stains. We divided the trabecular bone surfaces (BS) into three areas: node (Nd), terminus (Tm), and strut (St), and measured the bone resorption and formation parameters, including eroded surface (ES), osteoclast surface (Oc.S), osteoid surface (OS), and double-labeled surface (dLS) in each defined area. In conventional bone histomorphometry, the ovx group showed high turnover osteopenia compared with the sham operation group. In node-strut analysis, the ovx group showed significantly lower values for node-related parameters than did the sham operation group. In the modified node-strut analysis, bone resorption parameters in the ovx group showed significantly higher values, particularly for strut and terminus-eroded surfaces (StES/BS, TmES/BS), and for each area of osteoclast surface (NdOc.S/BS, TmOc.S/BS, and StOc.S/BS) compared with the sham operation group. Bone formation parameters in the ovx group also showed significantly higher values, particularly for strut and terminus osteoid surfaces (TmOS/BS, StOS/BS), and for each area of double-labeled surface (NddLS/BS, TmdLS/BS, and StdLS/BS) compared with the sham operation group at 4 weeks. At 8 weeks, each area of bone formation parameter in the ovx group showed significantly higher values than that in the sham operation group. These results suggest that in the ovx group, the trabecular plates became perforated and the perforative cavities progressively enlarged, and/or the edges of plates were eroded regardless of elevated bone formation, resulting in diminished trabecular connectivity, and the node area might not be influenced relatively by bone remodeling in the early resorption.