Mitsuru Nishino

Early magnetic resonance imaging and histologic findings in a model of femoral head necrosis

The authors examined early magnetic resonance images and histologic findings of avascular necrosis of the femoral head in a canine model. The avascular necrosis of the femoral head model was surgically induced. Animals were euthanized at 3 days, 1, 2, and 4 weeks, and the proximal femurs were retrieved. Magnetic resonance images and histologic sections were performed on each of the specimens obtained. Twenty-five mongrel dogs were studied, 4 dogs at 3 days and 7 dogs at each of the other intervals. Findings suggest that histologic changes may be seen as early as 3 days, with marrow edema and hemorrhage as early findings, and fibrous marrow transformation and appositional bone growth as later findings. Magnetic resonance imaging abnormalities did not occur until 1 week after injury and were seen in all animals by 4 weeks.

Histopathologic study of veins in steroid treated rabbits

Although arterial factors have been regarded as playing an important role in the pathogenesis of osteonecrosis, more attention has been given to venous factors because steroids cause an increase in the intraosseous pressure despite a decrease in blood flow in the femoral head. The authors examined changes in the veins of steroid treated rabbits. Forty rabbits were used: 30 rabbits (the steroid treated group) were injected with methylprednisolone acetate (4 mg/kg) weekly and 10 rabbits (the control group) were treated without steroids. The veins around the femoral head, ear veins, femoral veins, and inferior vena cava were obtained after 8 weeks of treatment, and the specimens were examined by immunohistochemical staining and electron microscopy. In the steroid treated group, proliferation of foam cells was observed in the intima of the vein in 7 of 30 rabbits. Immunohistochemical studies, using monoclonal antibodies for smooth muscle cells and macrophages, showed that the foam cells were derived from smooth muscle cells. Electron microscopy showed damage to the endothelial cells and smooth muscle cells. These results indicated that corticosteroids damaged the venous system. It is suggested that steroid induced disturbance of the draining veins causes stasis and that steroids are an important factor in osteonecrosis of the femoral head.

Pathological and hemodynamic study in a new model of femoral head necrosis following traumatic dislocation.

The blood of the femoral head is thought to be supplied by vessels originating from the medial and lateral circumflex femoral arteries and via the marrow cavity of the neck. Therefore, it is difficult to induce osteonecrosis of the femoral head when the marrow cavity of the neck is preserved. In the present study, we established a new model of femoral head necrosis by dislocating the hip joint and ligating the medial and lateral circumflex femoral arteries and veins. Measurement of femoral head blood flow revealed that a marked decrease to 14.7% of the control value was achieved by both hip dislocation and ligation of blood vessels. Pathologic examination showed no necrosis with either dislocation or ligation alone, whereas at 2 and 4 weeks 80% of the animals subjected to both procedures showed widespread necrosis. These pathologic findings considered in the light of results of the blood flow measurements suggest that a decrease in femoral head blood flow below 20% of the control value is needed to cause osteonecrosis. In addition, magnetic resonance images (MRI) of the model were evaluated in the combined dislocation and ligation group at 4 weeks (n = 5). Changes on MRI were seen in 3 of 5 dogs. The necrotic changes of the femoral head are thought to be detectable on MRI within 4 weeks after ischemia without enhancement.

ACETABULUM-IMPACTING TOTAL HIP ARTHROPLASTY FOR SEVERE ACETABULAR DYSPLASIA

We report our experience using the acetabulum-impacting total hip arthroplasty technique and describe the results of short-term follow up. This technique is new method of acetabular plasty for the patients with severe dysplastic hip.

A Study on Development of the Total Hip Prosthesis Design Fitted for Japanese Patients with Secondary Osteoarthrosis

The cementless prostheses used in the total hip replacement (THR) have been predominantly developed in Western countries. Although many cementless prostheses developed in Western have been applied to THR of Japanese osteoarthrosis (OA) patients, they have not been always fitted to shape of Japanese OA femurs. Because they have been designed for the primary OA which is general in Western but not the secondary OA. There are many cases of the secondary OA which has large deformation of femoral head caused of long-term subluxation in Japan. Unfitted prosthesis design gives a worse influence on its stability and stress distribution in proximal femur, and then it can cause serious stress-shielding. To develop the prosthesis suitable for Japanese OA, it is important to consider their characteristic shape of proximal femur. In this study, three-dimensional models of proximal femur with the secondary OA were constructed by using computer aided design (CAD) based on computed topographic (CT) images, and canal shapes of the femurs were geometrically classified by comparing these models each other. We found that the secondary OA femurs were divided into three groups. Three types of prosthetic stem were designed to fit the canal shape of the femur. Furthermore, finite-element analyses were carried out for the OA femurs with the fitted or unfitted stem. Stress distribution of each femur type with fitted stem was almost same in spite of shape differences, but particular stress concentration and reduction were found in the case of femur with unfitted stem. From the results, effectiveness of the prosthetic stem designs based on proposed classification is ensured.