Bone Blood Flow Research Articles

Reperfusion capacity of the femur head after ischemia--an experimental study

The aim of this study was to evaluate bone blood flow of the proximal femur during experimentally induced ischemia and to document the ability of epiphyseal and metaphyseal reperfusion. 11 pigs (danish landrace) were used to investigate the effect of tamponade by increased joint pressure (Dextran 70) on the perfusion of the femoral head. Additional 8 pigs were used as control. The blood flow in the hip joint was studied by means of the microsphere technique. The flow was determined before, during and after intraarticular pressure increase. With the "radioactive tracer microsphere"-method the blood flow of the epiphysis, metaphysis and proximal femoral corticalis could be measured. In the epiphyseal femoral head the initial blood flow rate, 11.7 ml/min/100 g, was not significant different from that of the control side (11.1 ml/min/100 g). The blood flow decreased in the ischemic phase to 1.8 ml/min/100 g followed by reperfusion to 13.5 ml/min/100 g (p < 0.01). The bone blood flow of reperfusion was not significant different from that of the initial blood flow rate but in 2 cases a "blow out" of the epiphyseal bone blood flow was seen. The proximal femoral metaphysis showed the highest of the measured intraosseous flow rates (17.9 resp. 23.3 ml/min/100 g). During ischemia and reperfusion of the epiphysis bone blood flow of the metaphysis remained the same. The proximal femoral corticalis showed the lowest of the measured intraosseous flow rates. The operated (10.1 ml/min/100 g) and contralateral hip side (11.7 ml/min/100 g) showed no significant differences in the initial blood flow rate. During ischemia and reperfusion the blood flow of the proximal corticalis showed no significant difference to the initial blood flow corresponding to the metaphysis. Our study demonstrates disturbances of the circulation of different regions of the femoral head during intraarticular pressure increase and following pressure decrease of the growing pig. 2 "blow outs" document a vulnerable proximal epiphysis already after a 6-hour ischemia. Additional minor "bone quality" in cases of certain diseases (kidney transplantation, leukemia) and special administration of drugs (corticosteroids) seem to create an additional vulnerability of the proximal femoral head. The experiment proves to be a reliable model for decreasing the blood flow of the growing epiphysis temporarily and to document the beginning of normal reperfusion. With this model it is possible to examine the vulnerability of the epiphyseal perfusion after different diseases and under the influence of different medication.

Current knowledge and future directions on bisphosphonate-related osteonecrosis of the jaw in cancer patients

Background: Bisphosphonate-related osteonecrosis of the jaw (BRONJ) is a severe adverse event of long-term use of bisphosphonates that heavily affects the quality of life of cancer patients. Objective: To review epidemiologic data, pathobiology, risk factors, diagnosis and management of BRONJ. Methods: Articles were identified by searching the PubMed and MEDLINE databases and recent meetings abstracts. Results/conclusion: BRONJ pathobiology is thought to be related to bisphosphonate-induced suppression of normal bone remodeling and impairment of bone blood flow. Dental extractions, daily masticatory traumas, oral infections, chemotherapy and antiangiogenic drugs can also play an active role. Collaboration between oncologists and dentists is essential to prevent BRONJ. A conservative approach based on pain control, oral rinses, antibiotics and limited debridement represents the current management. Optimization of therapy based on reduction of bisphosphonate doses or exposure time, newer bisphosphonates and biomolecular agents could favorably impact on BRONJ incidence.

Homocysteine decreases bone blood flow in rats

Elevated levels of homocysteine (Hcy) known as hyperhomocysteinemia (HHcy) are associated with osteoporosis. A decrease in bone blood flow is a potential cause of compromised bone mechanical properties. We hypothesize that HHcy decreases bone blood flow. To test this hypothesis sexually mature male Sprague Dawley rats were treated with Hcy (0.067 mg/ml) in drinking water for 16 weeks. Age matched rats served as controls. At the end of the treatment period the rats were anesthetized. The systolic blood pressure was measured from the right carotid artery. A small incision was made to expose the antero‐medial surface of the tibia. A laser Doppler flow probe was placed against the bone to provide an index of flow. The results suggest that though there was no significant differences in the blood pressure in controls and Hcy treated rats, the flow index of the tibia of control rats was 0.78±0.09 (flow unit) compared to 0.51±0.09 in Hcy‐treated rats. The tibia mass was 1.1±0.1grams in controls and 0.9±0.1 was in Hcy‐treated rats. These results suggest that Hcy causes reduction in bone blood flow and may decrease bone density.Support was provided by NIH #HL‐71010.

Aging and ovariectomy alter endothelium‐dependent and –independent vasodilation in the femoral principal nutrient artery

Enhanced bone resorption and bone blood flow (BBF) occurs subsequent to ovariectomy (OVX) whereas BBF declines with age. The potential of the osseous resistance vasculature to alter BBF in postmenopausal and age‐related osteoporosis is unclear. PURPOSE: We studied the effects of age, gender, and estrogen status on endothelium‐dependent and ‐independent vasodilation of the femoral principal nutrient artery (PNA). METHODS: INTACT female (6‐, 14‐, and 24‐ mon), OVX female (6‐, 14‐, and 24‐ mon), and male (6‐ and 24‐ mon) Fischer‐344 rats were studied. PNAs were isolated and cannulated. Endothelium‐dependent (ACh: 10−9 – 10−4 M) and ‐independent (DEA NONOate: 10−10 – 10−4 M) vasodilation were assessed. RESULTS: Declines in endothelial function occurred in aged rats but no differences in gender were observed. Endothelium‐dependent vasodilation in young or middle‐aged rats did not change following OVX. In aged OVX rats, vasodilation was enhanced to similar values observed in young INTACT and young OVX rats. Endothelium‐independent vasodilation was not altered with age or gender except in middle aged OVX rats vs. their INTACT controls. DISCUSSION: These data demonstrate that OVX influences both endothelium‐dependent and –independent vasodilator responses of the osseous resistance vasculature. Supported by the NIH Grant #1 R01 HL077224‐01 (JMD) and the NHLBI Postdoctoral Supplement (RDP).

Measurement of bone blood flow using the hydrogen washout technique—part II: Validation by comparison to microsphere entrapment

Accurate and reproducible measurement of bone blood flow has important clinical and experimental applications. Hydrogen washout is simple, safe, and widely used, but its use in bone tissue has not been validated. To this end, we have compared cortical bone blood flow measurements obtained by radioactive-labeled microsphere entrapment with those from hydrogen washout. Blood flow was measured in tibial cortical bone of 12 New Zealand White rabbits by radioactive microsphere entrapment and by hydrogen washout. Besides a control group (n = 6), four animals were treated with systemic epinephrine (0.8 microg/kg/min) (group 2) and two with nitroprusside (100 microg/kg/min) (group 3). Furthermore, nine femora from seven rats were isolated on their vascular pedicles and repeated bone blood flow measurements were made at each location with the hydrogen washout method to confirm reproducibility of blood flow determinations by hydrogen washout. An average flow of 2.3 +/- 2.0 mL/min/100 g was obtained with the microsphere method and 2.0 +/- 0.5 mL/min/100 g with the hydrogen washout method. There was a significant correlation and agreement: R(2) = 0.97 (p < 0.01). No consistent flow variations were found with systemic vasoactive drug administration. Hydrogen washout provided reproducible results and showed high sensitivity to flow changes. Hydrogen washout is both sensitive and reproducible in measuring bone blood flow. Results agree well with flow values obtained by labeled microsphere entrapment.

Measurement of bone blood flow using the hydrogen washout Technique—Part I: Quantitative evaluation of tissue perfusion in the laboratory rat

The measurement of blood flow in bone is of interest in both clinical and experimental settings. Such determinations would ideally provide accurate, quantitative, and reproducible data with relatively simple and safe technology, even in the small bones of experimental animals. Methods that provide absolute or quantitative measurements include positron emission tomography, "isotope fractioning" using radioactive or fluorescent-labeled microspheres, and measurement of the rate of washout of diffusible tracers delivered either by injection or inhalation. In this article, we describe in detail a modification of the original Whiteside hydrogen washout technique, using modern hydrogen sensors, a micromanipulator for probe placement, and custom software that greatly simplifies blood flow determination and is effective in the small bones of experimental animals.

OP-1 injection increases VEGF expression but not angiogenesis in a rabbit model of distraction osteogenesis

We have previously shown that a single injection of rhBMP-7 (OP-1) applied to the regenerate early during distraction accelerates bone consolidation in a rabbit model of distraction osteogenesis. In the present study, we hypothesised that the injection of OP-1 improves bone consolidation by increasing blood flow to the distracted site. Blood flow into the regenerate of a rabbit model was measured and vascular endothelial growth factor (VEGF) expression was tested using semi-quantitative PCR. Immunohistochemistry was used for assessing the temporal and spatial expression of platelet endothelial cell adhesion molecule (PECAM), VEGF and its receptors following OP-1 injection. We observed a higher expression of VEGF and its receptors in the regenerate with OP-1 treatment. However, there was no difference in the increase in bone blood flow nor PECAM expression between the treated and control groups of animals. Interestingly, the increased expression of VEGF and its receptors was associated with chondrocyte and fibroblast-like cells, but not with endothelial cells. These results suggest that accelerated ossification by OP-1 may depend on a non-vascular mechanism, possibly involving a non-angiogenic function of VEGF signalling.

A novel femur window chamber for in vivo studies of bone microcirculation

Background: Due to technical difficulties of in vivo observation of blood flow and microvessels in bone, no study has been done concerning the role of blood flow in bone remodeling. Objective: To develop a new window chamber for microscopic observation of the microcirculation in living bone, and to examine the utility of the chamber using rat femur in health and diseases. Methods: A stainless chamber (19 mm in diameter and 5 mm in height) with a circular window (7.5 mm in diameter) for microscopic observation was developed. The chamber was put on rat femur which was exposed for direct observation of the microvasculature. Intravital observation was made of bone blood flow and microvessels, using fluorescence videomicroscopy and confocal laser microscopy. The utility of the chamber was examined based on images of microcirculation (normal and abnormal) in the femur bone. Results and conclusions: Images of rat femur microvasculature were enhanced in the quality by use of the femur window chamber. The new chamber provides a powerful tool for in vivo studies of the bone microcirculation in health and diseases.

O2‐consumption, blood flow and PO2 in bone

AbstractOsteocytes are bone cells encapsulated in a mineralized matrix. Since they are connected to nutrient blood vessels via narrow canaliculii which provide narrow, tortuous and often long diffusion pathways, the question arises as to how osteocytes are sufficiently supplied with O2 and metabolites. Furthermore, different oxygen partial pressures (PO2) ‐ resulting from O2 supply and local oxygen consumption ‐ may influence cellular proliferation and differentiation. In this context, O2 consumption rates of bone cells were measured and results were related to published blood flow values. This should allow to estimate mean venous PO2 and PO2 distribution in bone. O2 consumption of bone cells inside spongious calvarial fragments of neonatal rats and adult guinea pigs were measured polarographically in a thermostabilized recording chamber containing Hepes‐buffered saline. PO2 declined linearly as long as the PO2 ranged above 20 mmHg. At 27°C and 37°C, the O2 consumption rate of calvarial fragments from adult animals amounted to 0.06 and 0.1 ml/100 g✶min, respectively. Calvaria from newborn rats showed 5‐fold higher values. At 45 °C, oxygen consumption was irreversibly abolished. The blood flow to bones amounts to 5–6 ml/100 g✶min being equivalent to an oxygen delivery of about 1 ml/100 g✶min. Based on the hemoglobin‐oxygen binding curve and on an O2 consumption of 0.1 ml/100 g ✶ min, venous PO2 calculates to ca. 60 mmHg. This appears to be a luxurious oxygen supply in bone. With respect to the long diffusion pathways, however, high PO2 values appear necessary to ensure sufficiently steep PO2 gradients for the the supply of cells remote from nutrient vessels. The resulting local oxygen gradients may orchestrate proliferation and differentiation of bone cells via oxygen‐dependent gene expression. Based on these considerations a model is proposed which comprises known factors influencing blood flow and oxygen tension in bone.

PET as a Diagnositic Tool in Unilateral Condylar Hyperactivity

PET as a Diagnositic Tool in Unilateral Condylar Hyperactivity

Aging Reduces Skeletal Blood Flow, Endothelium-Dependent Vasodilation, and NO Bioavailability in Rats

We determined whether aging diminishes bone blood flow and impairs endothelium-dependent vasodilation. Femoral perfusion was lower in old animals, as well as endothelium-dependent vasodilation and NO bioavailability. These effects could contribute to old age-related bone loss and the increased risk of fracture. Aging has been shown to diminish bone blood flow in rats and humans. The purpose of this study was to determine whether blood flow to regions of the femur perfused primarily through the principal nutrient artery (PNA) are diminished with aging and whether this putative reduction in flow is associated with impaired endothelium-dependent vasodilation. Blood flow was measured in conscious young adult (4-6 mo old) and aged (24-26 mo old) male Fischer-344 rats using radiolabeled microspheres. Endothelium-dependent vasodilation of the PNA was assessed in vitro using acetylcholine (ACh), whereas the contribution of the NO synthase (NOS) and cyclooxygenase (COX) signaling pathways to endothelium-dependent vasodilation was determined using the NOS and COX inhibitors L-NAME and indomethacin, respectively. Femoral blood flow in the aged rats was 21% and 28% lower in the proximal and distal metaphyses, respectively, and 45% lower in the diaphyseal marrow. Endothelium-dependent vasodilation was reduced with old age (young: 83 +/- 6% maximal relaxation; aged: 62 +/- 5% maximal relaxation), whereas endothelium-independent vasodilation (sodium nitroprusside) was unaffected by age. The reduction in endothelium-dependent vasodilation was mediated through impairment of the NOS signaling pathway, which resulted in lower NO bioavailability (young: 168 +/- 56 nM; aged: 50 +/- 7 nM). These data show that reductions in metaphyseal bone and diaphyseal marrow perfusion with old age are associated with diminished endothelium-dependent vasodilation through an impairment of the NOS mechanism. Such age-related changes in bone perfusion and vascular NO signaling could impact clinical bone loss, increase risk of fracture, and impair fracture healing in the elderly.

High Age at the Time of Implant Installation is Correlated with Increased Loss of Osseointegrated Implants in the Temporal Bone

The implant failure rate in temporal bone has been reported to be about 5 to 10% over a 10-year period. A number of our elderly patients have shown increased failure rates over a long time period, which is the reason for the present study. The aim of the present study was to find out if age is correlated with implant failure and to measure blood flow in implant sites. The long-time survival of 131 osseointegrated implants installed in the temporal bones of 81 patients was correlated with the age of the patient at the time of installation. The blood flow in 37 fixture installation sites in 22 patients was recorded by means of laser Doppler flowmetry. The mean implant failure rate in the study group was 9.8% after a mean follow-up time of 7.6 years. There was a significant increase of implant failure in patients above 60 years of age. There was further a trend that implants used for the bone-anchored hearing aid were lost to a higher proportion than implants used for bone-anchored episthesis. There was also a trend that female patients lost fewer implants than males. Blood flow in the temporal bone correlated well with the age of the patient in that the highest values were recorded from the youngest patients. Increasing age affects failures of osseointegrated implants in the temporal bone. Blood flow is higher in the child's temporal bone, a factor that can be of importance to understand why age influences implant survival.

Microvascularity, blood flow and tissue structure at the subchondral plate using an X-ray fluorescence technique

The measurement of blood flow and blood in bone and cartilaginous tissues is crucial to understanding of the development of various diseases, but it presents a formidable technical challenge. We have therefore developed a method based on the detection of metallized microspheres using X-ray fluorescence. This approach provides unrivalled sensitivity and spatial resolution and also allows us simultaneously to measure other markers of the metabolic status of the tissue.

Effect of fatigue loading and associated matrix microdamage on bone blood flow and interstitial fluid flow

Functional adaptation of bone to cyclic fatigue involves a complex physiological response that is targeted to sites of microdamage. The mechanisms that regulate this process are not understood, although lacunocanalicular interstitial fluid flow is likely important. We investigated the effect of a single period of cyclic fatigue on bone blood flow and interstitial fluid flow. The ulnae of 69 rats were subjected to cyclic fatigue unilaterally using an initial peak strain of -6000 muepsilon until 40% loss of stiffness developed. Groups of rats (n=23 per group) were euthanized immediately after loading, at 5 days, and at 14 days. The contralateral ulna served as a treatment control, and a baseline control group (n=23) that was not loaded was also included. After euthanasia, localization of intravascular gold microspheres within the ulna (n=7 rats/group) and tissue distribution of procion red tracer were quantified (n=8 rats/group). Microcracking, modeling, and remodeling (Cr.S.Dn, microm/mm(2), Ne.Wo.B.T.Ar, mm(2), and Rs.N/T.Ar, #/mm(2) respectively) were also quantified histologically (n=8 rats/group). Cyclic fatigue loading induced hyperemia of the loaded ulna, which peaked at 5 days after loading. There was an associated overall decrease in procion tracer uptake in both the loaded and contralateral control ulnae. Tracer uptake was also decreased in the periosteal region, when compared with the endosteal region of the cortex. Pooling of tracer was seen in microdamaged bone typically adjacent to an intracortical stress fracture at all time points after fatigue loading; in adjacent bone tracer uptake was decreased. New bone formation was similar at 5 days and at 14 days, whereas formation of resorption spaces was increased at 14 days. These data suggest that a short period of cyclic fatigue induces bone hyperemia and associated decreased lacunocanalicular interstitial fluid flow, which persists over the time period in which osteoclasts are recruited to sites of microdamage for targeted remodeling. Matrix damage and development of stress fracture also interfere with normal centrifugal fluid flow through the cortex. Changes in interstitial fluid flow in the contralateral ulna suggest that functional adaptation to unilateral fatigue loading may include a more generalized neurovascular response.

Host‐derived angiogenesis maintains bone blood flow after withdrawal of immunosuppression

A novel method of living bone allotransplantation combining microvascular repair of the nutrient circulation, implantation of host-derived arteriovenous (AV) bundles, and short-term immunosuppression is described. We hypothesized that neoangiogenesis from the implanted vessels would maintain graft viability and circulation after withdrawal of FK506 (Tacrolimus) immunosuppression. Vascularized femoral transplantation was performed between DA and PVG rats. In addition to microsurgical pedicle anastomoses, a saphenous AV bundle from the recipient animal was implanted in the medullary space. Ninety-seven rats were randomly allocated to groups differing in immunosuppression and AV bundle patency. Implanted vessels significantly improved capillary density and bone blood flow in nonimmunosuppressed and immmunosuppressed groups, respectively. A lower incidence of spontaneous AV bundle thrombosis was found with Tacrolimus treatment. More viable osteocytes were seen at 4 weeks when the AV bundle was patent. Further investigations may confirm host-derived neoangiogenesis as an alternative to tolerance induction or immunosuppression in bone allotransplantation.

Host-Derived AV Bundles Maintain Bone Blood Flow in Experimental Vascularized Bone Allotransplants after Withdrawal of Short-Term Immunosuppression

At present, long-term immunosuppressive therapy is required to maintain tissue perfusion of allogeneic tissue, with potential serious complications. The authors hypothesized that living bone allografts could maintain perfusion and osteocyte viability when host-derived arteriovenous (AV) bundles are implanted at the time of microsurgical tissue transfer, combined with short-term immunosuppression. Survival would depend on development of a neoangiogenic circulation from host-derived vessels after rejection-mediated thrombosis of the bone nutrient system occurs.

Short‐term immunosuppression and surgical neoangiogenesis with host vessels maintains long‐term viability of vascularized bone allografts

Currently available methods to reconstruct large skeletal defects have limitations. These include nonunion and stress fractures in structural allografts, and inability to match the size, shape, and/or strength of most recipient sites using vascularized fibular autografts. Prosthetic diaphyseal replacements may loosen or produce periprosthetic fractures. Transplantation of living allogenic bone would enable matching donor bone to the recipient site, combined with the desirable healing and remodeling properties of living bone. We propose a novel method by which the transplantation of such tissue might be done without the risks of life-long immunosuppression, using surgical neoangiogenesis to develop a new host-derived osseous blood supply. We performed vascularized femoral allografts from 86 female Dark Agouti donor rats to male Piebald Virol Glaxo recipients across a major histocompatibility (MHC) barrier. In addition to microvascular reconstruction of the nutrient vessel, we surgically implanted a host arteriovenous (AV) bundle into the medullary canal to promote host vessel neoangiogenesis. Independent variables included patency of the implanted AV bundle, and use of 2 weeks' FK-506 immunosuppression. After 18 weeks, bone blood flow was measured, and neoangiogenic capillary density quantified. Bone blood flow and capillary density were significantly greater in transiently immunosuppressed recipients with a patent AV pedicle. We conclude that neoangiogenesis from implanted host-derived AV-bundles, combined with short-term immunosuppression maintains blood flow in vascularized bone allografts, and offers potential for clinical application.

The Physiology of Bone Blood Flow: A Review

Bone circulation plays an important role in bone physiology, but has been relatively poorly studied, because most techniques of circulatory research are difficult to apply to bone. This article summarizes briefly some of the important aspects of the physiology of bone blood flow most relevant to orthopaedics. The gold standard for experimental measurement of bone blood flow is the radioactive microsphere technique, though advances are being made in other techniques, such as positron emission tomography, laser and ultra-sound Doppler velocimetry, and near infrared spectroscopy, that may provide useful clinical measurement in the future. Multiple vascular pathways contribute to an adaptive response to traumatic disruption of bone circulation. The microcirculation is not merely a passive conduit for blood flow, but plays an active role in controlling bone processes such as osteochondral ossification. The pathophysiology of bone circulation has been associated with osteonecrosis, but more and more evidence is pointing to the importance of bone circulation in fracture repair and osteoporosis, both of which are potentially very exciting areas for future studies.

Non-invasive continuous estimation of blood flow changes in human patellar bone

A photoplethysmographic (PPG) technique to assess blood flow in bone tissue has been developed and tested. The signal detected by the PPG consists of a constant-level (DC) component-which is related to the relative vascularization of the tissue-and a pulsatile (AC) component-which is synchronous with the pumping action of the heart. The PPG probe was applied on the skin over the patella. The probe uses near-infrared (804 nm) and green (560 nm) light sources and the AC component of the PPG signals of the two wavelengths was used to monitor pulsatile blood flow in the patellar bone and the overlying skin, respectively. Twenty healthy subjects were studied and arterial occlusion resulted in elimination of PPG signals at both wavelengths, whereas occlusion of skin blood flow by local surface pressure eliminated only the PPG signal at 560 nm. In a parallel study on a physical model with a rigid tube we showed that the AC component of the PPG signal originates from pulsations of blood flow in a rigid structure and not necessarily from volume pulsations. We conclude that pulsatile blood flow in the patellar bone can be assessed with the present PPG technique.

Vasoconstriction via voltage‐gated Ca 2+ Channels is impaired in the Femoral Principal Nutrient Artery of Aged Rats

Age-related declines in skeletal blood flow may contribute to reduced bone mass and increased fracture risk. Previous reports linked impaired endothelium-dependent vasodilation of the femoral principal nutrient artery (PNA) with declines in femoral bone blood flow. However, enhanced vasoconstriction of the PNA with advancing age may also contribute to reduced skeletal perfusion. PURPOSE: We evaluated the vasoconstrictor properties of the PNA via voltage-gated Ca2+ channels and α-adrenergic stimulation. METHODS: PNAs from Fischer-344 young (4–6 mo) and aged (24–26 mo) rats were isolated and cannulated. Vasoconstriction to potassium chloride (KCl; 10–100 mM) and norepinephrine (NE: 10−9 – 10−4 M) was assessed. RESULTS: KCl-induced vasoconstriction was attenuated ~31% in aged vs. young rats. No differences in vasoconstriction occurred in the presence of NE, an α1- and α2-adrenoceptor agonist. DISCUSSION: Age-related declines in femoral bone blood flow may result from altered vasomotor properties of the femoral PNA (e.g., reduced vasodilator capacity, enhanced vasoconstrictor capacity, or both). Results from the present investigation indicate that vasoconstriction is not enhanced in the femoral PNA of aged rats. In fact, vasoconstriction via voltage-gated Ca2+ channels is impaired and no differences in α-adrenergic vasoconstriction occurred between young and aged rats. Therefore, age-related declines in femoral bone perfusion appear to result from attenuated endothelium-dependent vasodilation as opposed to enhanced vasoconstriction of bone resistance arteries. Supported by NASA grant NCC2-1166.