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The etiology and pathogenesis of non-traumatic osteonecrosis of the femoral head is still unknown although many studied has been performed. Using Magnetic resonance imaging, decision of the extent and location of the necrotic lesion, exist of bone marrow oedema has been developed. The revised criteria for diagnosis, classification, and staging of the disease from specific disease investigation committee of Japanese ministry of health, labor and welfare was established. As joint preservation operation, transtrochanteric rotational osteotomy, curved varus osteotomy were proved to be effective. Hip arthroplasty for maintaining bone stock has been developed for the treatment of young patients.

Five criteria which showed high specificity were selected as follows. 1) collapse of the femoral head or crescent sign, 2) demarcating sclelosis in the femoral head, 3) cold in hot in bone scan, 4) band -like pattern on T1 weighted image of magnetic resonance imaging (MRI) , 5) trabecular and marrow necrosis on histology. Definite idiopathic osteonecrosis of the femoral head (ION) is diagnosed by fulfilling any two of the five criteria. Staging is judged on both AP and lateral X-ray. Stage 1 is defined as a period of no abnormality on X-ray. Stage 2is a period of demarcating sclelosis seen in X-ray. Stage 3 is a period of collapse of the head. Stage 3 is subclassified into Stage 3A when collapse is less than 3mm and 3B when collapse is 3mm or more. Stage 4 is a period of osteoarthritic changes. According to location of necrotic lesion on T1 weighted images or on x-ray, the lesions are classified into into four types. Type A lesion is defined to occupy medial one third or less of weight bearing portion. Type B lesion is defined to occupy medial two third or less of weight bearing surface. Type C1 lesion is defined to occupy more than medial two third, but not beyond acetabular edge while Type C2 lesion is defined to extend lateral to the acetabular edge.

Steroid-induced osteonecrosis of the femoral head (steroid-induced ONF) is an aseptic and ischemic disease developing after steroid therapy. Functions of hip joint are markedly disturbed when collapse is developed on the femoral head. Steroid-induced ONF accounted for the majority of the ONF. The occurrence mechanism is unknown, and prevention methods and fundamental remedies remain to be established. The timing of the occurrence of steroid-induced ONF is within several months after steroid administration. During the continuous steroid administration, no expansion of necrotic area was found. Recurrence was not also noticed. Patients have no symptoms when steroid-induced ONF occurs due to the establishment of ischemic conditions, and pain appears when the collapse of femoral head develops. There is an interval of several months or years between the occurrence of ONF and the onset of symptoms. Generally, conservative treatment is chosen during the asymptomatic period, and surgical treatment is considered after the symptoms appear. Appropriate screening and early detection are important to rational remedy for steroid-induced ONF.

Using spontaneously hypertensive rats (SHRs), attempts were made to decide whether or not mechanical stress on the femoral head plays a role in the occurrence of the femoral head lesions, namely, avascular necrosis and ossification disturbance. The following measures were taken to reduce mechanical stress: severing of the sciatic nerve, severing of both the sciatic and femoral nerves, and amputation of the hind limb on one side. The frequency of the femoral head lesions was highest in the control group (85%). It was lower in the sciatic nerve severance group, sciatic and femoral nerve severance group, and hind limb amputation group, in that order, showing a direct correlation with the level of mechanical stress. Moreover, histological abnormalities of the growth plate were observed frequently in the outer portion of the femoral head in SHRs with femoral head lesions. These findings indicate that mechanical stress causes an impairment of the femoral head cartilage, resulting in the obstruction of blood vessels leading to the epiphyseal nucleus of the femoral head.

By CT scan, the author analyzed morphologically the proximal medullary canal of the femur in 52 cases of osteoarthritis of the hip. The purpose is to determine the stem shape of an artificial hip joint suitable for Japanese patients. The results were as follows: 1) The femoral head diameter indicated positive correlation with the height, the femoral length, the femoral shaft transverse diameter, and the medullary canal diameter. The proportionality of the femur was found in Japanese patients with osteoarthritis. 2) The femoral head offset indicated no correlation with any results obtained by various measurement. 3) The medullary canal diameter of the diaphysial portion as well as the ratio of the medullary canal to the femur increased with age. 4) The taper angle*, 3.8 degree on the average was positively correlated only with the medullary canal diameter. *"Taper angle" indicates the degree of tapering of the medullary canal.

High dose corticosteroid therapy constitutes one of major causes of osteonecrosis of the femoral head. To examine the early changes of the femoral head induced by corticosteroid therapy, 20 femoral heads were obtained at autopsy and the other 19 femoral heads without having been on steroid were served as controls. Histological examination from steroid treated group revealed that in areas of subchondral bone there were observed necrotic changes of osteocytes. The nucleus was so pressed to one side of the cell as to assume crescent like aspect. When stained with Sudan IV, fat positive materials were found in the osteocyte lacunae. Electron micrographic examination revealed intracellular fat as low electron dense droplets in these degenerative osteocytes. Examination of bone marrow showed an increase of the number of fat cells in steroid treated group. These changes in man may represent some failure in lipid metabolism, although it is unknown whether these events may produce osteonecrosis of the femoral heads.

In the present study, which was undertaken to elucidate the process of repair of the ischemic femoral head, the blood supply to the femoral heads of mature rabbits was interrupted artificially, and the forming process of new vessels was examined morphologically by microangiography and the findings were compared with histopathological findings. The results indicated that vessels penetrated the ischemic head in early stages after interruption of the blood supply, forming irregular network, becoming gradually increased in caliber and finally extending to the whole femoral head. Histologically, these vessels were capillaries in the beginning and became normal arterioles, finally. The repairing process progressed gradually and the tissues were restored almost to normal in 1 year. From these observations it is concluded that simple ischemia may be repaired completely and clinical osteonecrosis of femoral heads is probably due to the occurrence of ischemia due to secondary factors such as mechanical stress.

Microangiography was performed on 65 femoral heads with advanced osteoarthritis to investigate the vascular changes on disintegration and repair of the femoral head. Affected femoral heads were removed during prosthetic replacement. A needle was inserted into the nutrient vessel of the extraosseous area and the contrast medium was injected by manual pressure through the needle. After slicing the femoral head, decalcification was performed and Spalteholz's preparations were prepared. Anastomosis between the superior and inferior retinacular arteries was found in all cases. Hypertrophy and hypervascularity of the retinacular arteries were observed on the weight bearing region. On the cystic lesion corresponding to the weight bearing region, numerous arteries were extended around the cyst. On the surface of the eburnated femoral head, the peripheral arteries coursing to the joint was not tapered and dilatation of these arteries was demonstrated. On some areas of the head, however, repairing arteries reaching to the joint surface lay horizontally. From this result, it was assumed that numerous arteries proliferated to the eburnated area and to around the cyst for repairing reaction, but that these were damaged by mechanical stress.

In order to study the disease process of the hip joint in rheumatoid arthritis, roentgenological analysis was carried out along with histological studies on the resected femoral heads. For the roentgenological study, hip roentgenograms of seven patients with known natural course and sixty preoperative patients were used. For the histological study, sixteen resected femoral heads affected by various disease types were used. The histological findings were compared with the roentgenological findings. As specific roentgenological findings, there were osteoporosis, burrowing and inward protrusion of the acetabulum, and collapse and flattening of the femoral head. A sequential process of the femoral head destruction was demonstrated, starting from collapse, through flattening, and finally ending in disappearance. The collapse was divided into sclerotic collapse and porotic collapse, and their roentgenological and histological differences were discussed. In addition to the common destruction process, the presence of the following three uncommon types was suggested for a better understanding of clinical manifestations: stiff type (4.5%), synovial proliferation type (6.0%) and aseptic necrosis type (3.0%).

This experimental study was performed to clarify how a surgical procedure to the hip joint causes hypertrophy of the femoral head. Young rabbits were used for this experiment. The following results were obtained. In the rabbits with sectioned ligamentum teres, some cases showed complete dislocation on X-ray. The incidence of the hypertrophy of the femoral head was very low in this group. Except in these rabbits with dislocation, the hypertrophy of the femoral head appeared in any group subjected to surgical procedure, and at especially high rates in those subjected to the section of ligamentum teres and/or edge resection of acetabular cartilage. In the cases in which the edge of the acetabular cartilage was resected, and in other cases of surgical procedure as well, acetabular dysplasia often resulted. In these cases the hypertrophy of the femoral head was observed more frequently than in others. In summary, surgical procedure to the hip joint and postoperative abnormal stress to the femoral head contribute to the development of the hypertrophy of the femoral head especially in the cases in which acetabular factors are not negligible.

Coronal slab sections of 78 femoral heads removed from patients with fractures of the proximal end of the femur were examined by radiographical and histological methods and a classification of fracture types based on the epiphysial scar holding an anatomical landmark was presented. The transepiphysial type (type I) showed total necrosis, and in the subepiphysial type (type II) some new bone formation was found at the "subepiphysial" zone, though no such reactive changes were seen in most parts of the specimens. Although necrosis was observed in different degrees and extent in the subcapital type (type III), some reactive new bone formation was always observed in the vicinity of the fracture surface. In the type III which was most frequent, viabilities of the trabeculae were examined in cases of fresh and old fractures (over one month after fractures), with or without internal fixation in old cases. It was then found that bone viabilities were remarkable in the fresh head than the old, and the head excised for failed internal fixation proved to be more viable than the head for primary insertion of a prosthesis. In about a half to one third of the type III the inferior metaphysial vessels were spared. Considering the types of fractures with post-fracture course, the initial type III may be changed into types I, II or III and the initial type II can remain as it is or be transformed into type I.

The distribution of the trabecular microfractures in normal human proximal femora was investigated to see whether they were related to the femoral neck fracture of the elderly. In this study the epiphyseal scar was employed as an anatomical landmark in the proximal femur, since the authors' observation suggested that it remained throughout life and was located in constant connection with the margin of the articular cartilage. The medial aspect of the proximal femur was divided into three anatomical zones, which were called epiphyseal, subepiphyseal and subcapital ones, respectively. There were two areas in which trabecular microfractures concentrated; one was about the lateral end of the epiphyseal scar and another the subepiphyseal zone. Few microfractures were noted on the principal compressive trabeculae. A femoral neck fracture of the elderly usually provides a fracture line running from the lateral end of the epiphyseal scar down to the subcapital zone. Thus the fracture takes place just within the area of concentration of trabecular microfractures laterally, whereas it passes caudad to the medial group of microfractures. The authors hypothesize that the trabecular microfractures arising about the lateral end of the epiphyseal scar may have an etiological significance for the femoral neck fracture, in contrast that those in the subepiphyseal zone may not.

In order to obtain further information of the pathological changes and bone structure of aseptic necrosis (AN), the present author carried out histological investigation on 20 femoral heads removed by prosthesis or total hip replacement from 18 patients. Both decalcified and undecalcified sections were investigated by microscopy, contact microradiography (CMR) and fluorescent microscopy. Schemata of individual cases were drawn to know the relationship between femoral head deformity and bone reactivity. Moreover, 19 femoral heads with secondary osteoarthritis (OA) removed from 18 patients and 7 with rapidly destructive coxarthrosis (RDC) from 6 patients were similarly investigated to compare with AN. The following results were obtained; Histologically, there are four different areas in AN. From the top of the femoral head, the lesion consisted of (1) subchondral necrosis, (2) granulation tissue, (3) an area of variable bone formation, and (4) normal bone tissue. As the advancement of the head deformity, fibrous component in the granulation increases and seems to divide the femoral head into necrotic and living areas, which by fibrous as well as enchondral ossifications become more prominent in the edge of the demarcation. As for the bone formation, four different types of bone tissues are discernible by CMR; (1) low calcified appositional bone and its absorption, (2) low calcified, appositional bone on wide trabeculae, (3) low calcified appositional bone on narrow trabeculae, and (4) irregularly calcified woven bone. Although during the comparatively early stage, the bone formation is seen in almost all of the living area, as the advancement of the head deformity, its activity decreases and results in overt head deformity to resemble that of OA which would be caused by mechanical factor. Increase of fibrous component in the granulation along with decrease of the bone formation would reduce the repairing activity of the femoral head. In the femoral heads with OA, a wedge-shaped area of bone formation is formed of which peak is located on the medial thickened cortex. In the femoral heads with RDC, a large amount of woven bone with irregular calcification is found in the bone formation area, in the upper part of a femoral head.

It is important to know the possibilities of allogenic transplantation of the joint in the present modes of the artificial joint replacement. In order to clarify the fate of osteochondral allograft, an experimental study of fresh "shell" transplantation was made on the femoral head of the dogs. Fifteen adult mongrels, around 15 kg in weight, were used as a recipient, and the same number as a donor. Special instruments of the same sized male and female reamer were made to cut an osteochondral shell with 2 to 4 mm thickness. Transplanted animals were killed at the interval from 2 weeks to 3 years. Femoral heads from the transplanted side and the opposite side for control were observed by histo-morphometric techniques. Usual decalcified sections were stained with H-E and safranin-O to observe the articular cartilage, and undecalcified ground specimens were made to understand the remodeling of the subchondral bone. The underlying subchondral bone was completely remodeled by 1 year, the grafted shells were well adapted and fixed to the host bone. Although a number of cartilage cells on the superficial layer were decreased from an early stage, the whole articular cartilage could possess its original thickness and well functioned for three years. However, in some animals, the pannus formation and chondrolytic reaction which is thought to be an immunological rejection were observed at the margin of the grafted articular cartilage. This experiment has demonstrated that allogenic osteochondral graft with 2 to 4 mm thickness was very successful even on the femoral head, and clinical trials might be expected if the histocompatibility of the tissue is settled.

To correlate the magnetic resonance (MR) images with the histopathological findings in the femoral head, the histopathology of 24 femoral heads, 15 with osteonecrosis, five with osteoarthritis and four with other hip disorders were subjected to preoperative MR imaging which demonstrated low intensity areas due to long T1 relaxation time in the femoral head. The MR signal was low where fibrovascular tissue, disintegrated fibrovascular tissue, amorphous necrotic material, bone, or cartilagenous tissue occupied the medullary space. From this study, it seems possible to predict the histopathologic changes in the femoral head using MR images.

In order to investigate the influences of artificial socket made of stainless-steel, pure titanium, high-density polyethylene (HDP), and polycrystal ceramics upon the articular cartilage of the femoral head, experimental artificial sockets were developed. This artificial socket was inserted into the hip joint in a dog, and the changes in the articular cartilage of the femoral head were studied at varying intervals after insertion of the socket. The results revealed that both the stainless-steel and the ceramic sockets caused slight atrophy and degeneration in the articular cartilage of the femoral head since one month after the operation, and these changes were increasingly more appreciable as time advanced. Any changes were hardly noted in the articular cartilage of the femoral head by titanium socket at the end of one month after the operation, whereas the HDP socket caused substantial changes. At the end of one year after the operation, marked degeneration was noted in the articular cartilage of the femoral head by socket made of stainless-steel, titanium, and HDP, and also the femoral head developed deformity. On the basis of the scanning electron microscopic findings on the surface of the articular cartilage of the femoral head affected by each of these artificial socket, and of the metal microscopic examinations of the surface of the artificial sockets, and furthermore on the basis of the findings of gradual deformation of femoral heads due to the artificial sockets, it was shown that articular cartilage of the femoral head was mainly influenced in the case of metallic socket and that both sides of the artificial socket and the articular cartilage of the femoral head were worn out in the case of HDP socket. The ceramic socket was found cracked, developing a loosening in some cases. In summary, it was concluded that the articular cartilage of the femoral head is affected by the artificial socket at a relatively early stage after its application despite materials of the sockets.

This paper describes an experimental study on vascular bundle transplantation into the femoral head of puppies before epiphyseal arrest. Sixty-seven young mongrel dogs, about 3 months of age, were used in this study. Necrotized femoral heads were made by interruption of blood supply to the femoral head, extramedullary and intermedullary. The transplantation of a vascular bundle was performed on intact and necrotized femoral heads. One month after the interruption of blood supply, deformity, atrophy and cystic formation of the head, and wide radiolucent shadow in the metaphysis were noted. Observation over nine months revealed flattening of the femoral head, shortening of the femoral neck and disappearance of the femoral head in severe cases. In the transplantation to intact femoral heads, transplanted vascular bundles maintained patency and anastomosed with preexisting vessels. Neither hypertrophy of the head nor distinctive pathological change was seen in the transplanted head or in the control side. In the transplantation to necrotized femoral heads, proliferation of new blood vessels was seen in the whole head. One month after the transplantation, new bone formation was active with proliferation of capillaries. Two months after the transplantation, dense cancellous bone or lamellar bone was made within the head, which showed atrophy in four months after the surgery and bone marrow was restored. In the case of severe changes in the epiphyseal cartilage, deformity of the femoral head and shortening of the neck were noted although better restoration was obtained than in the control.