Localization of vascular endothelial growth factor during the early reparative phase of the rats' vessels deprivation-induced osteonecrosis of the femoral heads

Therapeutic Study of Thermosensitive Hydrogel Loaded with Super-Activated Platelet Lysate Combined with Core Decompression Technology for the Treatment of Femoral Head Necrosis

Super activated platelet lysate (sPL) is a derivative of platelet-rich plasma (PRP) that contains high levels of several growth factors. In this study, we synthesized a temperature-sensitive hydrogel that contained temperature-sensitive Poly(DL-lactide-glycolide-glycolide acid) (PLGA), SrCl2, and HA, and loaded it with different concentrations of sPL. The hydrogel showed satisfactory encapsulation efficiency and release of the growth factors in a sustained manner, indicating its suitability as a drug carrier. The sPL-loaded hydrogel was inserted into the necrotic femoral head of a rat model and core decompression was applied and resulted in significantly accelerated bone repair and regeneration. Therefore, encapsulation of sPL in a hydrogel scaffolding may be an effective strategy for treating femoral head necrosis.

Epidermal growth factor (EGF) promotes bone healing in surgically induced osteonecrosis of the femoral head (ONFH)

Angiogenic effects of epidermal growth factor (EGF), a potent mitogen, have been demonstrated previously. Moreover, different in vitro studies showed that EGF affects processes associated with bone healing, such as osteoblast differentiation and bone resorption. The aim of this study was to investigate the effect of combined core decompression (CD) and recombinant human EGF (rhEGF) treatment on early-stage osteonecrosis of the femoral head (ONFH) surgically induced in rats. ONFH was induced by dissecting the cervical periosteum and placing a ligature tightly around the femoral neck. Thirty rats were assigned to one of the following groups (n = 10 each group): sham-operated control, CD, and CD+rhEGF group. rhEGF was injected intraosseously into infarcted areas 2 weeks after the surgery. Preservation of femoral head architecture was assessed at 8 weeks post treatment by radiographic and histomorphological analyses. Osteopontin (OPN) and cluster of differentiation 31 (CD31) were detected by immunochemistry, as indicators of bone remodeling and vascular density, respectively. Inter- and intra-group (non-operated left and operated right femur) differences in radiographic and histomorphological results were analyzed. The femoral head area and sphericity were more preserved in CD+rhEGF compared to CD and sham-control group. CD31 levels were significantly different between the three groups, and were higher in CD+rhEGF compared to CD group. OPN levels were increased in CD and CD+rhEGF groups compared to sham control, but with no significant difference between CD and CD+rhEGF groups. Overall, our results indicate that EGF promotes bone formation and microvascularization in ONFH and thus positively affects the preservation of femoral head during healing.

3D-printed porous titanium changed femoral head repair growth patterns: osteogenesis and vascularisation in porous titanium

Osteonecrosis of the femoral head (ONFH) is a major cause of morbidity, and total hip arthroplasty is both traumatic and expensive. Here, we created a gelatine scaffold embedded in uniquely shaped, 3D-printed porous titanium parts, which could attract and promote the proliferation of osteoblasts as well as bone regeneration, as the extracellular matrix (ECM) does in vivo. Interestingly, after hybridisation with platelets, the scaffold exhibited a low yet considerable rate of stable, safe and long-term growth factor release. Additionally, a novel ONFH model was constructed and verified. Scaffolds implanted in this model were found to accelerate bone repair. In conclusion, our scaffold successfully simulates the ECM and considerably accelerates bone regeneration, in which platelets play an indispensable role. We believe that platelets should be emphasised as carriers that may be employed to transport drugs, cytokines and other small molecules to target locations in vivo. In addition, this novel scaffold is a useful material for treating ONFH. An overview of the novel scaffold mimicking the extracellular environment in bone repair. a and b: A gelatine scaffold was cross-linked and freeze-dried within 3D-printed porous titanium. c: Platelets were coated onto the gelatine microscaffold after freeze-drying platelet-rich plasma. d: The microscaffold supported the migration of cells into the titanium pores and their subsequent growth, while the platelets slowly released cell factors, exerting bioactivity.

Three-year outcomes of intracapsular femoral neck fractures fixed with sliding hip screws in adults aged under sixty-five years

INTRODUCTION

Intracapsular femoral neck fractures remain associated with high rates of post-traumatic femoral head necrosis, non-union, and revision surgery.

AIM

Our aim was to identify factors associated with revision surgery in intracapsular femoral neck fractures treated with sliding hip screws (SHS) in adults aged <65 years.

PATIENTS AND METHODS

Consecutive admissions were identified retrospectively from the Royal Victoria Hospital, Belfast, which was the largest volume hospital on the National Hip Fracture Database. Of 2201 hip fractures between 1st August 2008 and 31st December 2010, 97 (4%) intracapsular fractures treated with SHS in adults <65 years were followed for a mean of 2.9 years (range 0-6.6).

RESULTS

Twenty-one (22%) hips were revised to arthroplasty. Avascular necrosis developed in 28 (29%) femoral heads. Eight (8%) fractures proceeded to non-union. Displaced fractures (p<0.001, Fisher's exact [FE]), posterior comminution (p=0.049, FE), chronic respiratory disease (p=0.006, FE) and residual distraction (p=0.011, χ²) were associated with revision to arthroplasty. Multiple regression found displaced fractures (p=0.006) and chronic respiratory disease (p=0.017) significant; in the latter 4 of 6 were revised (67%), including all four patients with chronic obstructive pulmonary disease (COPD). Eleven (11%) individuals required walking aids before injury, which rose to 34 (35%) at one year (p<0.0001, χ²). Eighty-nine (92%) individuals could walk alone outdoors before injury, but only 76 (78%) at one year (p=0.009, χ²).

CONCLUSIONS

Displaced fractures in individuals with chronic respiratory disease should be considered high risk for revision to arthroplasty. Posterior cortex deficiency should be evaluated prior to choice of operation. Fracture biology and revascularisation play a greater role than operation timing. A significant proportion of individuals do not recovery pre-morbid mobility by one year.

Blockage of Src by Specific siRNA as a Novel Therapeutic Strategy to Prevent Destructive Repair in Steroid-Associated Osteonecrosis in Rabbits

Vascular hyperpermeability and highly upregulated bone resorption in the destructive repair progress of steroid-associated osteonecrosis (SAON) are associated with a high expression of VEGF and high Src activity (Src is encoded by the cellular sarcoma [c-src] gene). This study was designed to prove our hypothesis that blocking the VEGF-Src signaling pathway by specific Src siRNA is able to prevent destructive repair in a SAON rabbit model. Destructive repair in SAON was induced in rabbits. At 2, 4, and 6 weeks after SAON induction, VEGF, anti-VEGF, Src siRNA, Src siRNA+VEGF, control siRNA, and saline were introduced via intramedullary injection into proximal femora for each group, respectively. Vascularization and permeability were quantified by dynamic contrast-enhanced (DCE) MRI. At week 6 after SAON induction, proximal femurs were dissected for micro-computed tomography (μCT)-based trabecular architecture with finite element analysis (FEA), μCT-based angiography, and histological analysis. Histological evaluation revealed that VEGF enhanced destructive repair, whereas anti-VEGF prevented destructive repair and Src siRNA and Src siRNA+VEGF prevented destructive repair and enhanced reparative osteogenesis. Findings of angiography and histomorphometry were consistent with those determined by DCE MRI. Src siRNA inhibited VEGF-mediated vascular hyperpermeability but preserved VEGF-induced neovascularization. Bone resorption was enhanced in the VEGF group and inhibited in the anti-VEGF, Src siRNA, Src siRNA+VEGF groups as determined by both 3D μCT and 2D histomorphometry. FEA showed higher estimated failure load in the Src siRNA and Src siRNA+VEGF groups when compared to the vehicle control group. Blockage of VEGF-Src signaling pathway by specific Src siRNA was able to prevent steroid-associated destructive repair while improving reconstructive repair in SAON, which might become a novel therapeutic strategy.

Src inhibitor reduces permeability without disturbing vascularization and prevents bone destruction in steroid-associated osteonecrotic lesions in rabbits

To examine the therapeutic effect of Src inhibitor on the VEGF mediating vascular hyperpermeability and bone destruction within steroid-associated osteonecrotic lesions in rabbits. Rabbits with high risk for progress to destructive repair in steroid-associated osteonecrosis were selected according to our published protocol. The selected rabbits were systemically administrated with either Anti-VEGF antibody (Anti-VEGF Group) or Src inhibitor (Src-Inhibition Group) or VEGF (VEGF-Supplement Group) or a combination of VEGF and Src inhibitor (Supplement &Inhibition Group) or control vehicle (Control Group) for 4 weeks. At 0, 2 and 4 weeks after administration, in vivo dynamic MRI, micro-CT based-angiography, histomorphometry and immunoblotting were employed to evaluate the vascular and skeletal events in different groups. The incidence of the destructive repair in the Anti-VEGF Group, Src-Inhibition Group and Supplement &Inhibition Group was all significantly lower than that in the Control Group. The angiogenesis was promoted in VEGF-Supplement Group, Src-Inhibition Group and Supplement &Inhibition Group, while the hyperpermeability was inhibited in Anti-VEGF Group, Src-Inhibition Group and Supplement &Inhibition Group. The trabecular structure was improved in Src-Inhibition Group and Supplement &Inhibition Group. Src inhibitor could reduce permeability without disturbing vascularization and prevent destructive repair in steroid-associated osteonecrosis.

Prednisolone-induced predisposition to femoral head separation and the accompanying plasma protein changes in chickens

Femoral head separation (FHS) is an idiopathic bone problem that causes lameness and production losses in commercial poultry. In a model of prednisolone-induced susceptibility to FHS, the changes in plasma proteins and peptides were analyzed to find possible biomarkers. Plasma samples from control and FHS-susceptible birds were depleted of their high abundance proteins by acetonitrile precipitation and were then subjected to cation exchange and reverse-phase (RP) fractionations. Analysis with matrix assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF-MS) showed several differentially expressed peptides, two of which were isolated by RP-HPLC and identified as the fragments of apolipoprotein A-I. The acetonitrile fractionated plasma proteins were subjected to reduction/alkylation and trypsin digestion followed by liquid chromatography and tandem mass spectrometry, which showed the absence of protocadherin 15, vascular endothelial growth factor-C, and certain transcription and ubiquitin-mediated proteolytic factors in FHS-prone birds. It appears that prednisolone-induced dyslipidemia, vascular, and tissue adhesion problems may be consequential to FHS. Validity of these biomarkers in our model and the natural disease must be verified in future using traditional approaches.

BIOMARKER INSIGHTS

Lameness because of femoral head separation (FHS) is a production and welfare problem in the poultry industry. Selection against FHS requires identification of the birds with subclinical disease with biomarkers from a source such as blood. Prednisolone can induce femoral head problems and predisposition to FHS. Using this experimental model, we analyzed the plasma peptides and proteins from normal and FHS-prone chickens by mass spectrometry to identify differentially expressed peptides and proteins. We found two peptides, both derived from apolipoprotein A-I, quantitatively elevated and two proteins, protocadherin 15 and VEGF-C, that were conspicuously absent in FHS-susceptible birds.

Combination of poly L-lactic acid nanofiber scaffold with omentum graft for bone healing in experimental defect in tibia of rabbits

PURPOSE: To investigate the osteoconductive properties and biological performance of Poly L-lactic acid (PLLA) with omentum in bone defects. METHODS: PLLA nanofiber scaffolds were prepared via electrospinning technique. Forty four New Zealand white female rabbits randomly divided into three groups of 18 rabbits each. Created defects in right tibias were filled in group I with omentum, in group II with PLLA nanofiber scaffold and in group III with combination of the omentum and PLLA. The same defects were created in left tibia of all groups but did not receive any treatment (control group). Histological and histomorphometric evaluations were performed at two, four and six weeks after the implantation. RESULTS: Histological changes on all groups along with the time course were scored and statistical analysis showed that the average scores in group III were significantly higher than the other groups. CONCLUSION: Histomorphometric analysis of bone healing was shown to be significantly improved by the combined PLLA with omentum compared with the other groups, suggesting this biomaterial promote the healing of cortical bone, presumably by acting as an osteoconductive scaffold.

Osteonecrosis of the femoral head: An update in year 2012

Osteonecrosis is a phenomenon involving disruption to the vascular supply to the femoral head, resulting in articular surface collapse and eventual osteoarthritis. Although alcoholism, steroid use, and hip trauma remain the most common causes, several other etiologies for osteonecrosis have been identified. Basic science research utilizing animal models and stem cell applications continue to further elucidate the pathophysiology of osteonecrosis and promise novel treatment options in the future. Clinical studies evaluating modern joint-sparing procedures have demonstrated significant improvements in outcomes, but hip arthroplasty is still the most common procedure performed in these affected younger adults. Further advances in joint-preserving procedures are required and will be widely studied in the coming decade.

An animal model of femoral head osteonecrosis induced by a single injection of absolute alcohol: an experimental study

Background

The lack of an experimental animal model that can reliably mimic all stages of osteonecrosis of the femoral head has hindered progress toward the successful prevention and treatment of the disease.

Material/Methods

A goat model of osteonecrosis of the femoral head (ONFH) was established and observed from the early to the intermediate-to-late stage of mechanical failure. Absolute alcohol was injected slowly into the center of bilateral femoral heads in 12 adult Small Tail Han goats. Postoperatively, the femoral heads were harvested and examined using macrostructural and histological analyses and radiographic and MRI examinations at weeks 4, 8, 12, and 25.

Results

Macrostructural and radiographic examinations revealed that the contour of both femoral heads was deformed slightly at 12 weeks, but a contour deformation with joint space narrowing was observed at 25 weeks. Histologically, a strong concordance with the natural history of ONFH in humans was found. The present model demonstrated bone trabeculae, marrow necrosis, a reconstruction deficiency and destruction of the microcirculation.

Conclusions

Among quadrupedal models, the goat model of ONFH, which is induced by a single injection of absolute alcohol, may be suitable and valuable for the evaluation of various therapeutics and side effects in the treatment of ONFH.

Prevention of osteonecrosis by intravenous administration of human peripheral blood-derived CD34-positive cells in a rat osteonecrosis model

Aseptic idiopathic osteonecrosis of the femoral head is a painful disorder of the hip that can lead to collapse of the femoral head and the need for total hip replacement following joint destruction. Treatment of this disease still remains a clinical challenge. Adult human circulating CD34(+) cells have been demonstrated to contribute to vasculogenesis and osteogenesis in immunodeficient rat non-union models in vivo. We hypothesized and proved that the transplantation of CD34(+) cells could have a role for improvement of osteonecrosis by promoting vasculogenesis and osteogenesis. Vascular deprivation-induced femoral head necrosis was developed in immunodeficient rats and we then administered human G-CSF mobilized CD34(+) cells intravenously. At 4 weeks after administration, the structure of the femoral head and neck were evaluated histologically and morphometrically with haematoxylin and eosin (H&E) staining and micro-CT imaging. Microangiography was carried out for macroscopic evaluation of neovascularization, and the contribution of human cells to vasculogenesis and osteogenesis was evaluated by immunofluorescent staining with human-specific antibodies. Our treatment resulted in an obvious improvement of osteonecrosis after CD34(+) cell administration and demonstrated the differentiation potential of CD34(+) cells into endothelial cells and osteoblasts. In conclusion, this new therapeutic approach using circulating cell fraction could be a promising cell-based therapy for early-stage osteonecrosis of the hip.

Experimental animal models of osteonecrosis

Osteonecrosis (ON) or avascular necrosis (AVN) is a common bone metabolic disorder, mostly affecting femoral head. Although many biological, biophysical, and surgical methods have been tested to preserve the femoral head with ON, none has been proven fully satisfactory. It lacks consensus on an optimal approach for treatment. This is due, at least in part, to the lack of ability to systematically compare treatment efficacy using an ideal animal model that mimics full-range osteonecrosis of femoral head (ONFH) in humans with high incidence of joint collapse accompanied by reparative reaction adjacent to the necrotic bone in a reproducible and accessible way. A number of preclinical animal ON models have been established for testing potential efficacy of various modalities developed for prevention and treatment of ON before introduction into clinics for potential applications. This paper describes a number of different methods for creating animal experimental ON models. Advantages and disadvantages of such models are also discussed as reference for future research in battle against this important medical condition.

COMP-Angiopoietin-1 ameliorates surgery-induced ischemic necrosis of the femoral head in rats

INTRODUCTION

Ischemic necrosis of the femoral head (INFH) can lead to loss of femoral head architecture and deformity. Moreover, the process of bone healing is intimately associated with angiogenesis. We considered that COMP-Ang1 (an angiogenic factor) might preserve femoral head structure and facilitate bone repair.

METHODS

INFH was induced in the femoral head of rats by dissecting the cervical periosteum and placing a ligature tightly around the femoral neck. Two weeks later, COMP-Ang1 was injected directly into infarcted areas. Rats were divided into the following groups; 1) the sham-operated group (the sham group), 2) the bovine serum albumin-injected group (the BSA group), and 3) the COMP-Ang1-injected group (the COMP-Ang1 group) (n=20/group). At 8 weeks post-surgery animals were sacrificed and radiologic and histomorphometric assessments were performed.

RESULTS

Radiographs obtained at 8 weeks post-surgery showed better preservation of femoral head architecture in the COMP-Ang1 group than in the BSA group. Histological findings and immunostainings of endothelial cells for factor VIII revealed that COMP-Ang1 group animals showed higher levels of vascularity in the secondary ossification center of infarcted femoral heads.

CONCLUSIONS

When INFH was surgically induced in rats, an intraosseous injection of COMP-Ang1 preserved the trabecular framework of the osseous epiphysis and prevented femoral head deformities by promoting angiogenesis and bone remodeling.

Glucocorticoids in osteonecrosis of the femoral head: a new understanding of the mechanisms of action

Glucocorticoid (GC) usage is the most common non-traumatic cause of osteonecrosis of the femoral head (ON). Despite the strong association of GC with ON, the underlying mechanisms have been unclear. Investigators have proposed both direct and indirect effects of GC on cells. Indirect and direct mechanisms remain intimately related and often result in positive feedback loops to potentiate the disease processes. However, the direct effects, in particular apoptosis, have recently been shown to be increasingly important. Suppression of osteoblast and osteoclast precursor production, increased apoptosis of osteoblasts and osteocytes, prolongation of the lifespan of osteoclasts and apoptosis of endothelial cells (EC) are all direct effects of GC usage. Elevated blood pressure through several pathways may raise the risk of clot formation. High-dose GC also decreases tissue plasminogen activator activity (t-PA) and increases plasma plasminogen activator inhibitor-1 (PAI-1) antigen levels increasing the procoagulant potential of GC. Inhibited angiogenesis, altered bone repair and nitric oxide metabolism can also result. Also, GC treatment modulates other vasoactive mediators such as endothelin-1, noradrenalin and bradykinin. Thus, GCs act as a regulator of local blood flow by modulating vascular responsiveness to vasoactive substances. Vasoconstriction induced in intraosseous femoral head arteries causes femoral head ischemia. GCs also cause ischemia through increased intraosseous pressure, which subsequently decreases the blood flow to the femoral head by apoptosis of ECs as well as elevating the level of adipogenesis and fat hypertrophy in the bone marrow. It is difficult to predict which patients receiving a specific dose of GC will develop ON, indicating individual differences in steroid sensitivity and the potential of additional mechanisms. The textbook model of ON is a multiple hit theory in which, with a greater number of risk factors, the risk of ON increases. While more effort is needed to better comprehend the role of GC in ON, newer data on GC action upon the endothelial cell and the regional endothelial bed dysfunction theory sheds new light on particular GC mechanisms. Better understanding of GC pathomechanisms can lead to better treatment options.

Chemotherapy-associated osteonecrosis in cancer patients with solid tumours: a systematic review

Non-traumatic osteonecrosis of bone is recognized as a potential complication in solid-tumour cancer patients receiving treatment with cytotoxic chemotherapy. This review summarizes recent reports of osteonecrosis associated with chemotherapy in cancer patients, and describes the possible underlying pathophysiology and options available for its diagnosis, prevention and treatment. Fifty-four reported cases of non-traumatic osteonecrosis in adult patients with solid tumours receiving chemotherapy were identified by searching for reports in the medical literature. Osteonecrosis was observed most commonly in men receiving chemotherapy for testicular cancer. Osteonecrosis was also seen in patients receiving chemotherapy for breast, ovarian, small-cell lung cancer and osteosarcoma. Most patients had received corticosteroids, had femoral head involvement and had delayed onset of osteonecrosis. It appears that patients at higher risk for osteonecrosis with chemotherapy are identifiable. As the long-term survival of patients with solid tumours receiving chemotherapy increases, the prevalence of treatment-related osteonecrosis may also increase. Patients should be informed that osteonecrosis is a potential complication of cancer treatment. Measures to reduce risk should be taken, and patients should be monitored for early symptoms. Routine screening for chemotherapy-associated osteonecrosis is not recommended; however, a high index of clinical suspicion in patients at risk may allow for early intervention and preservation of the joints.

Vasculature deprivation-induced osteonecrosis of rats' femoral heads associated with the formation of deep surface depressions

BACKGROUND

Shallow or deep bowl-shaped depressions often develop after drilling an intraosseous conduit in the necrotic, avascular femoral head of rats. The etiopathogenesis of tissue loss at the articulation surface after a drilling procedure was elaborated in the authors' previous reports.

GOALS

To scrutinize a large collection of femoral heads of rats in order to search for similar changes in cases in which no drilling procedure was carried out.

STUDY

This retrospective study comprised the specimens of 386 rats with vessels-deprived osteonecrosis of the femoral heads, none of the animals having undergone a drilling procedure.

RESULTS

Shallow or deep bowl-shaped depressions were encountered at an incidence as low as 2.8% of the femoral heads of the above mentioned 386 rats. It is not feasible to distinguish histologically the "spontaneously" arising from and drilling-related depressions.

CONCLUSIONS

No assured explanation can be offered for the evolving depressions of the surface of femoral heads of rats, which have not undergone a drilling procedure. It is hypothesized that the synovial fluid forces its way via slits in the articulation surface and bores cavities in the substance of femoral heads, which display a postosteonecrotic osteoarthritis-like disorder. The rising pressure in the arthritic joints results, firstly, in an enlargement of these cavities and, secondly, loss of fibro-cartilaginous tissue such that the cavities come to communicate with the articular space.

Avascular necrosis of the femoral head: vascular hypotheses

Vascular hypotheses provide compelling pathogenic mechanisms for the etiology of avascular necrosis of the femoral head (ANFH). A decrease in local blood flow of the femoral head has been postulated to be the cause of the disease. Several studies in human and animal models of ANFH have shown microvascular thrombosis. Endothelial cell damage could be followed by abnormal blood coagulation and thrombus formation with any resulting degeneration distal to the site of vascular occlusion. Other studies suggest that thrombophilia, particularly impaired fibrinolysis, plays a potential role in thrombus formation in ANFH. Reduction in shear stress due to decreased blood flow could lead to apoptosis of endothelial cells, which can ultimately contribute to plaque erosion and thrombus formation. Dysregulation of endothelial cell activating factors and stimulators of angiogenesis or repair processes could also affect the progression and outcome of ANFH. Likewise, regional endothelium dysfunction (RED), referred to as a potential defect in endothelial cells located in the feeding vessels of the femoral head itself, may also have a crucial role in the pathogenesis of ANFH. Molecular gene analysis of regional endothelial cells could also help to determine potential pathways important in the pathogenesis of ANFH.

Vasculature deprivation--induced osteonecrosis of the rat femoral head as a model for therapeutic trials

Experimental Osteonecrosis

The authors' experience with experimentally produced femoral capital osteonecrosis in rats is reviewed: incising the periosteum at the base of the neck of the femur and cutting the ligamentum teres leads to coagulation necrosis of the epiphysis. The necrotic debris is substituted by fibrous tissue concomitantly with resorption of the dead soft and hard tissues by macrophages and osteoclasts, respectively. Progressively, the formerly necrotic epiphysis is repopulated by hematopoietic-fatty tissue, and replaced by architecturally abnormal and biomechanically weak bone. The femoral heads lose their smooth-surfaced hemispherical shape in the wake of the load transfer through the hip joint such that, together with regressive changes of the joint cartilage and inflammatory-hyperplastic changes of the articular membrane, an osteoarthritis-like disorder ensues.

Therapeutic Choices

Diverse therapeutic options are studied to satisfy the different opinions concerning the significance of diverse etiological and pathogenic mechanisms: 1. Exposure to hyperbaric oxygen. 2. Exposure to hyperbaric oxygen and non-weight bearing on the operated hip. 3. Medication with enoxaparin. 4. Reduction of intraosseous hypertension, putting to use a procedure aimed at core decompression, namely drilling a channel through the femoral head. 5. Medication with vascular endothelial growth factor with a view to accelerating revascularization. 6. Medication with zoledronic acid to decrease osteoclastic productivity such that the remodeling of the femoral head is slowed.

Glucocorticoid-related osteonecrosis appears to be apoptosis-related, thus differing from the vessel-deprivation-induced tissue coagulation found in idiopathic osteonecrosis. The quantities of TNF-α, RANK-ligand and osteoprotegerin are raised in glucocorticoid-treated osteoblasts so that the differentiation of osteoclasts is blocked. Moreover, the osteoblasts and osteocytes of the femoral cortex mostly undergo apoptosis after a lengthy period of glucocorticoid medication.

Pyogenic granuloma-like reaction in the necrotic, vessels-deprived femoral head of the rat

Osteonecrosis of the femoral head was produced in rats by cutting the ligamentum teres and incising the cervical periosteum. As of the second postoperative week, fibrous tissue pervaded the necrotic epiphyses, macrophages and osteoclasts removed the debris, osteoblasts deposited lamellar-fibred and woven-fibred intramembranous bone, and remodeling began. In 16% of the rats killed during the 2nd postoperative week, the epiphyses contained big fragments of necrotic bone enclosed by densely packed, capillary-sized vessels. Ingrowth of this hypervascularized, pyogenic granuloma-like tissue is presumably due to the presence of excessive growth factors, reflecting an exaggerated pathophysiological reaction within the framework of organization of the necrotic epiphyses.