Computer-assisted image analysis of the rat postosteonecrotic remodeled femoral head

Effect of arterial deprivation on growing femoral epiphysis: quantitative magnetic resonance imaging using a piglet model

Objective

To investigate the usefulness of dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) and diffusion MRI for the evaluation of femoral head ischemia.

Materials and Methods

Unilateral femoral head ischemia was induced by selective embolization of the medial circumflex femoral artery in 10 piglets. All MRIs were performed immediately (1 hour) and after embolization (1, 2, and 4 weeks). Apparent diffusion coefficients (ADCs) were calculated for the femoral head. The estimated pharmacokinetic parameters (Kep and Ve from two-compartment model) and semi-quantitative parameters including peak enhancement, time-to-peak (TTP), and contrast washout were evaluated.

Results

The epiphyseal ADC values of the ischemic hip decreased immediately (1 hour) after embolization. However, they increased rapidly at 1 week after embolization and remained elevated until 4 weeks after embolization. Perfusion MRI of ischemic hips showed decreased epiphyseal perfusion with decreased Kep immediately after embolization. Signal intensity-time curves showed delayed TTP with limited contrast washout immediately post-embolization. At 1-2 weeks after embolization, spontaneous reperfusion was observed in ischemic epiphyses. The change of ADC (p = 0.043) and Kep (p = 0.043) were significantly different between immediate (1 hour) after embolization and 1 week post-embolization.

Conclusion

Diffusion MRI and pharmacokinetic model obtained from the DCE-MRI are useful in depicting early changes of perfusion and tissue damage using the model of femoral head ischemia in skeletally immature piglets.

Core decompression and alendronate treatment of the osteonecrotic rat femoral head: computer-assisted analysis

Femoral head avascular necrosis is a process leading to femoral head deformity and osteoarthritic changes in the hip joint. Alendronate slows down bone resorption and remodelling in rats, while core decompression hastens the healing processes. We evaluated the influence of daily alendronate treatment on the rat femoral head shape after surgical osteonecrosis with core decompression, compared with controls. No differences were found in shape factor and femoral head height/length ratios. It was concluded that alendronate treatment slows down the process of replacing osteonecrotic bone by new bone and prevents early immature new bone collapse resulting from early revascularization because of core decompression.

Visualization and analysis of the deforming piglet femur and hip following experimentally induced avascular necrosis of the femoral head

Childhood avascular necrosis (AVN) of the femoral head leads to its progressive deformation and compensatory changes of the adjacent acetabulum. To simulate this disease for laboratory study, we used an AVN model of the hip in a skeletally immature piglet. The 3-D visualization and analysis of this piglet's deforming femur and hip form the basis for this paper. In particular, the data for this analysis were generated via serial CT images of bilateral femurs and acetabula of a piglet at regular time intervals following experimental unilateral induction of femoral head AVN. The contralateral femur and acetabulum served as the control. We applied a shape analysis technique that effectively captured not only the temporal shape changes of the femurs and acetabula, but also their codependencies. The resulting computational framework not only confirmed the widely accepted deformational changes of the femoral head following AVN; it also revealed the underappreciated compensatory changes of the surrounding acetabulum. The 3-D visualization of these dynamically changing structures provided a visual understanding of the shape changes associated with the AVN and control models. By quantitatively mapping the deformation trajectory of these shapes over time, we created an objective tool for clinical decision making.

Alendronate preserves femoral head shape and height/length ratios in an experimental rat model: A computer-assisted analysis

BACKGROUND

Surgical osteonecrosis of the rat femoral head was induced by detaching the ligamentum teres and stripping the femoral neck periosteum. Bone and marrow necrosis were found from the fifth postoperative day and replaced by creeping substitution. Osteonecrosis of the femoral head results in the flattening to various degrees of roundness and osteoarthritic changes of the hip joint. Alendronate, an osteoclast inhibitor, slows down bone resorption and remodeling. The purpose of this study was to evaluate objectively the influence of alendronate treatment on the rat femoral head shape after six weeks of daily treatment, when compared with controls.

MATERIALS AND METHODS

The blood circulation of right femoral head of 20 female Sprague-Dawley rats was interrupted. Twelve were treated by alendronate injections of 200 microg/kg/day and eight controls were treated with saline, both for a total of 42 days. Both femoral head specimens were obtained for computed-assisted morphometry. For each rat, the right operated head was compared with the left, and the alendronate treated group was compared with the control group.

RESULTS

No differences were found in shape factor and femoral head height/length ratios in the alendronate treated femoral heads. Among the nontreated control group, shape-factor differences were found between the operated and the nonoperated femoral heads.

CONCLUSION

Alendronate treatment prevented the distortion and destruction of the femoral head. Osteoclast inhibition might prolong the bone creeping substitution process and could enable secondary bone maturity and mineralization that increases bone strength. Alendronate preserved the femoral head architecture, which might reduce morbidity and disability due to femoral head collapse.

Therapeutic ultrasound facilitates antiangiogenic gene delivery and inhibits prostate tumor growth

Gene therapy clinical trials are limited due to several hurdles concerning the type of vector used, particularly, the viral vectors, and transfection efficacy when non-viral vectors are used. Therapeutic ultrasound is a promising non-viral technology that can be used in the clinical setting. Here, for the first time, we show the efficacy of therapeutic ultrasound to deliver genes encoding for hemopexin-like domain fragment (PEX), an inhibitor of angiogenesis, to prostate tumors in vivo. Moreover, the addition of an ultrasound contrast agent (Optison) to the transfection process was evaluated. Prostate cancer cells and endothelial cells (EC) were transfected in vitro with cDNA-PEX using therapeutic ultrasound alone (TUS + pPEX) or with Optison (TUS + pPEX + Optison). The biological activity of the expressed PEX was assessed using proliferation, migration, and apoptosis assays done on EC and prostate cancer cells. TUS + pPEX + Optison led to the inhibition of EC and prostate cancer cell proliferation (<65%), migration (<50%), and an increase in apoptosis. In vivo, C57/black mice were inoculated s.c. with prostate cancer cells. The tumors were treated with TUS + pPEX and TUS + pPEX + Optison either once or repeatedly. Tumor growth was evaluated, after which histology and immunohistochemistry analyses were done. A single treatment of TUS + pPEX led to a 35% inhibition in tumor growth. Using TUS + PEX + Optison led to an inhibition of 50%. Repeated treatments of TUS + pPEX + Optison were found to significantly (P < 0.001) inhibit prostate tumor growth by 80%, along with the angiogenic indices, with no toxicity to the surrounding tissues. These results depict the efficacy of therapeutic ultrasound as a non-viral technology to efficiently deliver genes to tumors in general, and to deliver angiogenic inhibitors to prostate cancer in particular.

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

An impeded blood flow through the femoral head is incriminated in the etiopathogenesis of osteonecrosis of the femoral head. The disorder is either primary (idiopathic avascular osteonecrosis) or secondary to one condition or another, such as corticosteroid medication, fracture of the neck, coagulation defects, physical or thermal damage, storage disorders, alcoholism, and infectious, autoimmune as also marrow infiltrating diseases. In the wake of the necrosis, several mediators are released in increased amounts, prime among which is the vascular endothelial growth factor. The intermediates recruit endothelial progenitor cells, macrophages, osteoclasts, fibroblasts, and osteoblasts, which, pervading throughout the necrotic areas, initiate the reparative processes. The dead, soft, and hard tissular debris is substituted by fibrous - later on by hematopoietic-fatty tissue - and bone. The newly formed, appositional and intramembranous bone is deficient in its mechanical properties. The ordinary load-carrying functions suffice to deform these weakened femoral heads so that osteoarthritic changes develop. Considering contemporary assumptions of the causes of osteonecrosis, oxygenation, revascularization, and core decompression are the realistic therapeutic interventions. Necrosis of rats' femoral heads is studied as a model of osteonecrosis in both adults and children. In view of rodents' lifelong persisting physeal cartilage, vascular deprivation-induced osteonecrosis in rats mimics children's Perthes disease. The experimental model, which is well suited to test treatment modalities, has been used to investigate the effects of exposure to hyperbaric oxygen with and without non-weight bearing, medication of enoxaparin, and creation of an intraosseous conduit on the remodeling of the avascular necrotic femoral head. Intriguingly, the shape of treated rats' femoral heads is disfigured to a greater degree than that of untreated animals. This is most likely due to the reduced yield strength and elastic modulus as well as the raised strain-to-failure of the recently formed bone making up the post-necrotic femoral heads. It follows that expedited osteogenesis is, counter intuition, detrimental to maintaining the hemispherical shape of the femoral head, and thus to an articulation with congruent load-bearing surfaces. If this is indeed the case, the remodeling of the necrotic femoral head should be delayed, rather than sped up, as the present day paradigm would have it. Bearing in mind that the dead osseous structures keep their mechanical attributes for quite a while, a slowed down new bone formation would favor the gradual replacement of the necrotic by living bone. Therefore, management of the adult patients with osteonecrosis and children with Perthes disease should focus on a slowly progressive substitution so that the decline of the bone's mechanical properties is kept to a minimum. One viable therapeutic mode is a medication of inhibitors of the vascular endothelial growth factor.

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.

Experimentally gained insight - based proposal apropos the treatment of osteonecrosis of the femoral head

An impeded blood flow through the femoral head is incriminated in the etiopathogenesis of osteonecrosis of the femoral head. The disorder is either primary (idiopathic avascular osteonecrosis) or secondary to one condition or another, say, corticosteroid medication, fracture of the neck, coagulation defects, physical or thermal damage, storage disorders, alcoholism, and infectious, autoimmune as also marrow infiltrating diseases. In the wake of the necrosis, several mediators are released in increased amounts, prime among which is the vascular endothelial growth factor. The intermediates recruit endothelial progenitor cells, macrophages, osteoclasts, fibroblasts, and osteoblasts, which, pervading throughout the necrotic areas, initiate the reparative processes. The dead, soft and hard tissular debris is substituted by fibrous - later on by hematopoietic-fatty tissue - and bone. The newly formed, appositional and intramembranous bone is deficient in its mechanical properties. The ordinary load-carrying functions suffice to deform these weakened femoral heads so that osteoarthritic changes develop. Considering contemporary assumptions of the causes of osteonecrosis, oxygenation, revascularization, and core decompression are the realistic therapeutic interventions. Necrosis of rats' femoral heads is studied as a model of osteonecrosis in both adults and children. In view of rodents' lifelong persisting physeal cartilage, vascular deprivation-induced osteonecrosis in rats mimics children's Perthes disease. The experimental model, which is well suited to test treatment modalities, has been used to investigate the effects of exposure to hyperbaric oxygen with and without non-weight bearing, medication of enoxaparin, and creation of an intraosseous conduit on the remodeling of the avascular necrotic femoral head. Intriguingly, the shape of treated rats' femoral heads is disfigured to a greater degree than that of untreated animals. This is most likely due to the reduced yield strength and elastic modulus as well as the raised strain-to-failure of the recently formed bone making up the post-necrotic femoral heads. It follows that expedited osteogenesis is, counter intuition, detrimental to maintaining the hemispherical shape of the femoral head, and thus to an articulation with congruent load-bearing surfaces. If this is indeed the case, the remodeling of the necrotic femoral head should be delayed, rather than sped up, as the present day paradigm would have it. Bearing in mind that the dead osseous structures keep their mechanical attributes for quite a while, a slowed down new bone formation would favor the gradual replacement of the necrotic by living bone. Therefore, management of the adult patients with osteonecrosis and children with Perthes disease should focus on a slowly progressive substitution so that the decline of the bone's mechanical properties is kept to a minimum. One viable therapeutic mode is a medication of inhibitors of the vascular endothelial growth factor.

Osteonecrosis of the femoral head of laboratory animals: the lessons learned from a comparative study of osteonecrosis in man and experimental animals

Animal models of osteonecrosis of the femoral head are indispensable to the understanding of successful treatment modalities for avascular necrosis of the femoral head in adults and in children with Legg-Calvé-Perthes disease. Many of these models adequately reflect the current "vascular deprivation" theory regarding the etiology of the disease. In addition to spontaneous occurrence, surgical- and corticosteroid-induced models are suitable, common experimental ones. Osteonecrosis of spontaneously hypertensive rats appears to be due to defective bone formation and compression of the arteries entering the femoral head at its lateral facets by daily weight-bearing loads. Successful modeling of surgical-induced femoral capital necrosis can be a challenge in animals with a dual epiphyseal blood supply. High doses of corticosteroids are a pivotal risk factor in the development of osteonecrosis. The pathogenesis of corticosteroid-induced osteonecrosis likely resides in reduced blood flow. Steroids may reduce blood flow by numerous mechanisms, including marrow adipocytic hypertrophy leading to sinusoidal compression, venous stasis and, eventually, obstruction of the arteries, and arterial occlusion by fat emboli and lipid-loaded fibrin-platelet thrombi. Other, less common varieties of osteonecrosis include those secondary to endotoxin-induced disseminated intravascular coagulation, immune reactions, immoderately low or high temperatures, and high-impact-related injuries. Common to these diverse forms of osteonecrosis are fibrin thrombi clogging arterioles and small arteries.