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.
The blood supply of rats' femoral heads was severed by cutting the ligamentum teres and stripping the periostium. Histologically, necrosis of the marrow was apparent on the 2nd postoperative day, necrosis of the bone on the 5th postoperative day and fibrous ingrowth on the 7th postoperative day. During the following 5 weeks, progressive resorption of the intertrabecular necrotic debris and necrotic bony trabeculae and subchondral bone plate and, concurrently, appositional and intramembranous new bone formation resulted in remodeling of the femoral heads. In 2 of 7 femoral heads, replacement of the necrotic bone by viable bone was complete at the 42-day postoperative interval. Also, the articular cartilage of the deformed and flattened femoral heads was undergoing degenerative changes. Reduplicating the pathogenically inferred clinical settings of blood supply deprivation, it is proposed that this model, in a small laboratory animal, satisfies the requirements sought for preclinical studies of treatment modalities of avascular osteonecrosis in man.
The authors propose to encompass under the designation of "fasciitis-panniculitis syndromes" (FPS) a group of disorders characterized by induration of the skin due to chronic inflammation and fibrosis of the subcutaneous septa and muscular fascia. The prototype of the FPS is eosinophilic fasciitis. Thirty-two consecutive patients with FPS were cared for at the author's hospital during a 10-year period. The association of the FPS with other diseases, clinical presentations, histologic features, and response to treatment were analyzed. Idiopathic FPS, that is, eosinophilic fasciitis, was diagnosed in 14 patients. In the remaining 18 cases, the FPS were ascribed to vascular disorders (n = 6), infections (n = 6), and neoplastic disorders (n = 3), while trauma, insect bites, and Sweet syndrome antedated the FPS in 1 patient each. The lesions had a sleeve-like distribution in 20 patients, plaque-like distribution in 7, and a combined pattern in 5. Skin biopsies revealed lesions in the deep subcutaneous layers with the pathologic triad of septal and fascial fibrosis, chronic inflammatory infiltration, and small-vessel vasculopathy. Spontaneous improvement occurred in 4 cases. Following cimetidine monotherapy, complete remission was achieved in an additional 3 of 5 patients. The concept of the FPS serves to advance our understanding on several fronts: emphasizing the clinical and etiologic diversity; recognizing a stereotypic tissue reaction pattern; highlighting the panniculitis in addition to the fasciitic component; and describing a similar response to drug therapy in different clinical settings. Based on the results of the present series, cimetidine may be recommended as first-line treatment.
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