Osteochondrosis of the femoral head epiphysis

　　The etiology of osteochondrosis of the femoral head epiphysis is various, but the true cause is still unclear. It may be related to the following factors:

　　1. Defect in blood supply to the femoral head:Trurta et al. found that only one blood vessel supplies the blood to the femoral head in children aged 4 to 8, namely the external epiphyseal artery, and the blood supply from the metaphyseal artery is often blocked by the growth plate. The external epiphyseal artery is also prone to be compressed by the external rotator muscle group, leading to interruption of blood supply. After the age of 8, the round ligament vessels also participate in the blood supply to the femoral head, thus reducing the incidence of the disease. Additionally, the variations in the vascular arches of the femoral head in children, especially male children, are very large, and even absent, which is also a cause of ischemia of the femoral head.

　　2. Intra-articular hypertension:Any factor that can cause an increase in intra-articular pressure, such as joint effusion after trauma, infection, and transient synovitis, can lead to the disease by compressing the blood vessels supplying the epiphysis of the femoral head. Ma Chengxuan et al. measured the intramedullary pressure at the upper end of the femur in 17 children with the disease and found that the pressure on the affected side was significantly higher than that on the healthy side. Venography also showed that the epiphysis veins on the affected side were not visible and the rate of visibility of the circumflex veins was significantly lower than that on the healthy side, thus suggesting that increased intra-articular pressure leads to venous reflux obstruction at the upper end of the femur, causing the disease.

　　Three, other factors

　　1. Trauma factors:Since the disease often occurs in boys, and the hip joint is an active weight-bearing joint, some scholars have proposed the trauma theory, considering the disease to be caused by multiple repeated minor injuries at the upper end of the femur.

　　2. Environmental factors:Including perinatal and postnatal living conditions. Some scholars reported that the incidence rate of breech presentation is 4 times higher than that of normal delivery, and children born to older parents, third-child and later children, and children from poor families are more prone to the disease.

　　3. Endocrine factors:TirozaTanara measured the serum growth factor A (SMA) content in 47 children with the disease and found it significantly lower than that in normal children. The main function of SMA is to stimulate cartilage growth, so it is considered that the decrease in SMA level is a triggering factor for the disease.

　　4. Genetic factors:Perthes disease has a certain family history, and the risk of onset in the brothers and first and second-degree relatives of patients is increased, but relevant studies have not yet found genetic evidence.

　　In recent years, abnormal coagulation function has been considered as a potential factor causing the disease. Gregosiewicz et al. found that the plasma α1-2 antitrypsin in children with Perthes disease was significantly higher than that in the control group, indicating a decrease in fibrinolysis and an increased risk of intravascular thrombosis, which may trigger the disease. Glueck discovered that there were abnormal activities of antithrombin III (AT2III), protein C (PC), protein S (PS), and anticoagulant protein C (APCR) positivity in children with Perthes disease, thus proposing the thrombophilia hypothesis for the etiology of Perthes disease, considering thrombophilia (defects in PC, PS, and positivity of APCR) and low fibrinolysis (tPA, PAI, and hyperlipoproteinemia) to be closely related to the onset of Perthes disease.

　　The study on the relationship between Perthes disease and endocrine disorders, especially thyroid hormone, shows that although the thyroid function of children with Perthes disease is normal, the levels of free thyroid hormone and free triiodothyronine are significantly increased, and the degree of involvement of the femoral head is proportional to the level of free thyroid hormone in plasma. However, it is still unclear whether these changes are the cause or the consequence of the disease. Some scholars have proposed the hypothesis of growth and development delay, and Kealey measured that the serum growth hormone A (SMA) content in children with Perthes disease is significantly lower than that in normal children, indirectly supporting the hypothesis of growth and development delay. Some other scholars suspect that Perthes disease is related to heredity. Wansbrough (1959) first reported that the disease has a genetic predisposition, Renwick (1972) pointed out that the parents of children with Perthes disease have a 0.3% risk, siblings have a 3.8% risk, and relatives have a 0.3% risk of the same disease. Catterall (1970) noted that Perthes disease is related to constitutional factors, but no obvious genetic evidence has been found.

　　The pathological process of avascular necrosis of the femoral head includes bone necrosis, followed by absorption of dead bone and formation of new bone, as well as the remodeling of the femoral head, a series of pathological changes that can generally be divided into four stages.

　　First, the initial stage, which is the synovitis stage:The joint capsule swells, the synovium becomes congested and edematous, and the joint fluid exudes more, but the synovial fluid does not contain inflammatory cells. This stage lasts for 1 to 3 weeks.

　　Second, ischemic necrosis stage:The earliest involvement is in the anterior and lateral epiphysis of the femoral head, or the entire epiphysis may undergo necrosis due to ischemia. At this time, the bone structure remains normal, but the bone lacunae are often empty, the medullary cavity is filled with amorphous debris, the trabeculae fracture into sheets or compress into lumps. Due to the ischemic necrosis of the femoral head, the ossification center cartilage of the epiphysis is temporarily suppressed, while the superficial cartilage of the joint surface can continue to grow due to nutrition from synovial fluid. On X-ray films, the epiphysis of the femoral head appears smaller and the joint space wider. The necrotic trabeculae, due to fracturing, compression, and new bone deposition on the surface of the necrotic trabeculae, become denser. At the same time, the diaphyseal end becomes疏松 and decalcified due to local congestion, which is caused by the invasion of vascular soft tissue, absorbing the tissue reaction of the necrotic bone. During this period, there are no significant changes in the gross morphology and the contour of the femoral head, the necrotic period is relatively long, lasting from 6 to 12 months, and clinically, there are usually no symptoms. Salter refers to this stage as the clinical stationary phase, which is a potential osteonecrosis of the femoral head. If blood supply can be restored at this time, it is expected that severe deformities will not be left behind.

　　Third, the fragmentation or regeneration period:Due to the stimulation of dead bone, the connective tissue composed of capillaries and monocytes invades the necrotic area, absorbs the fragments of necrotic trabeculae, and forms fibrous tissue in the medullary cavity. Osteoclasts increase in number and are highly functional, participating in the resorption of necrotic trabeculae. At the same time, the activity of osteoblasts is enhanced, forming normal osteoid between and on the surface of the necrotic trabeculae. These vascular tissues come from the round ligament, periosteum, and diaphyseal epiphysis, which either enter the epiphyseal plate or connect with the tissue around the epiphyseal plate. Initially, the newly formed osteoid formed trabeculae are relatively thin, and later transform into lamellar bone. The cartilage around the necrotic area still shows no obvious changes, but the basal cartilage, being far from the joint surface and not receiving the nutrition of synovial fluid, may lose its activity. At this stage, the newly formed bone tissue has low strength and gradually shapes into normal bone or changes shape according to the stress it withstands. Salter calls this process 'biological shaping'. The above process takes about 2 to 3 years.

　　Fourth, the healing period:Because the newly formed trabeculae are immature lamellar bone, which is thin and fragile, and is prone to be compressed together with the unabsorbed necrotic trabeculae, the compression area is often limited to the anterior and lateral aspect of the femoral head. On the frog position X-ray film, it appears as a cup-shaped defect, while on the anteroposterior X-ray film, this cup-shaped defect overlaps with the intact bone, showing cystic changes. If the entire epiphysis is involved, various degrees of deformation may occur, resembling a mushroom-like appearance (mushroom shape), ultimately leading to the significant enlargement of the femoral head, changing from a circular femoral head located in the center of the acetabulum (coxamagna) to a flat femoral head (coxaplana).

　　Salter emphasizes that femoral neck deformation is due to subchondral fracture concurrent with the necrosis period, which triggers the resorption of necrotic bone and the precipitation of primary woven bone, and at the same time, it may cause synovial reaction and muscle spasm, followed by contraction of the adductor and iliopectineal muscles, causing the femoral head to subluxate forward and laterally, limiting hip joint movement. If the stress concentration area of the femoral head bears excessive stress, the femoral head may become flat or saddle-shaped畸形, further causing the femoral head to subluxate forward and laterally. The persistent ischemia of the femoral head not only leads to the ischemic necrosis of the epiphysis but also causes the premature closure of the epiphyseal plate, affecting the longitudinal growth of the lower limb, especially the growth of the femoral neck is suppressed. Meanwhile, the growth of the greater trochanter is not disturbed, resulting in the shortening of the femoral neck and the greater trochanter can exceed the level of the femoral head. Although this deformity is different from hip varus, in terms of functional impairment, it is similar to hip varus, which is not conducive to the activity of the abductor muscles, forming a flexed hip gait, known as functional hip varus. In summary, the pathogenesis of childhood ischemic necrosis of the femoral head.

　　As the lesion progresses, the pain of Perthes disease becomes persistent, the child's limping is obvious, the gluteal and thigh muscles atrophy due to disuse, the Thomas test is positive, the hip is屈曲内翻, causing the affected limb to become relatively shorter. With the formation of flat hips, the absolute length of the limb is also shorter than that of the healthy side, leading to early osteoarthritis in adulthood.

　　A considerable number of patients with Perthes disease will have sequelae, mainly including:

　　1. Abduction of the greater trochanter.

　　2. Shortening of the affected limb.

　　3. Bilateral deformity.

　　4. Osteoarthritis, which is a long-term sequelae of the disease. The first three deformities will promote the early occurrence of osteoarthritis to varying degrees.

　　5. Hip subluxation.

　　Perthes disease is insidious in onset and has a long course, with pain and limping of the affected hip as the main symptoms.

　　1. Early stage:There may be no obvious symptoms, or only weakness of the affected limb, painless limping appears after long-distance walking. The site of pain may be the inguinal region, anterior and medial thigh, and knee.

　　2. Osteonecrosis stage:Obvious hip pain, accompanied by muscle spasm and shortening of the affected limb. Muscle spasm is mainly seen in adductor muscles and iliacopsoas muscles, while gluteal and thigh muscles atrophy. The range of hip joint motion is limited to varying degrees, especially abduction and internal rotation.

　　3. Late stage:Pain and other symptoms are relieved or disappear, the range of joint motion returns to normal, or there is limited abduction and rotation of the joint.

　　There are many classifications of osteonecrosis of the femoral head introduced in literature, such as Catterall, Lloyd-Roberts, Salamon, Salter-Thompson, and Herring, etc. The purpose of classification is to select treatment methods based on the degree of lesion. Regardless of which classification method is used, it is based on the findings on X-ray films to judge the range and degree of involvement of the femoral head. In order to facilitate understanding and mastery of these many classification criteria, the common points of these classifications are summarized before introducing specific classification methods: If the range of involvement of the femoral epiphysis is less than half or only a small part, it is classified as Type I. If it involves more than half, it is classified as Type II or III. If it involves the entire epiphysis, it is classified as Type IV. The Salter-Thompson classification is different from the others. They classify based on the range of subchondral fracture during the overt phase (active phase) of femoral head epiphysis necrosis. If the range of subchondral fracture line does not exceed half of the arc of the femoral head hemispheric, it is classified as Type A. If it exceeds half, it is classified as Type B. The prognosis of the former is good, while the latter is poor. The commonly used classification in clinical practice is as follows:

　　1. Catterall Classification:Catterall classified osteonecrosis of the femoral head into 4 types based on pathological changes and the range of involvement of the femoral head on X-ray films. This classification is of guiding significance for clinical treatment selection and prognosis judgment, and has been widely accepted and applied by clinical doctors.

　　Type I: The anterior part of the femoral head is involved, but no collapse occurs. The epiphyseal plate and metaphysis do not show any lesions, and no obvious deformity is left after healing.

　　Type II: Partial necrosis of the femoral head, on the anteroposterior X-ray film, the necrotic part shows increased density. At the same time, there is normal bone tissue in a columnar appearance on the lateral and inner sides of the necrotic bone, which can prevent the collapse of the necrotic bone. Especially on the lateral X-ray film, the complete bone tissue column of the femoral head on the lateral side is of great significance for the estimation of prognosis. In this type, the metaphysis has lesions, but the epiphyseal plate is protected from damage by the normal bone tissue of the lingual metaphysis extending to the front, and the formation of new bone is active. The height of the femoral head is not significantly reduced because the epiphyseal plate maintains its integrity, and its shaping potential is not affected. After the lesion stops, if there is still several years of growth period, the prognosis is very good.

　　Type III: About 3/4 of the femoral head has necrosis, the normal bone tissue column on the lateral side of the femoral head disappears, the metaphysis is involved and shows cystic changes, the epiphyseal plate loses the protective effect of the metaphysis and also undergoes necrotic changes. X-ray films show severe collapse, and the collapsed necrotic bone pieces are large. The longer this process, the poorer the prognosis.

　　Type IV: The entire femoral head has necrosis, the femoral head collapses, and it often cannot completely recover its normal contour. During this period, the epiphyseal plate is directly damaged. If the epiphyseal plate is severely damaged, normal growth ability is lost, which will seriously inhibit the shaping potential of the femoral head. Therefore, regardless of the treatment method used, the final outcome is usually poor, although appropriate treatment can alleviate the degree of deformity of the femoral head.

　　2. Classification of the lateral pillar of the femoral head:A new classification method proposed by Hering in 1992 divides the femoral head epiphysis into three cylindrical regions: inner, middle, and outer on the standard anteroposterior pelvic X-ray. The outer region accounts for 15% to 30% of the width of the femoral head, the central region about 50%, and the inner region 20% to 35%. The author also refers to these areas as the lateral pillar (lateral pillar), central pillar (central pillar), and medial pillar (medial pillar). Then, based on the extent of involvement of the lateral pillar, the disease is divided into three types: Type A: The lateral pillar is not involved, the prognosis is good, and the femoral head is not flattened; Type B: The lateral pillar is involved, and its degree of compression and collapse is less than 50% of the normal lateral pillar, the prognosis is still good, and the femoral head is not flattened; Type C: The lateral pillar is involved, and its height is greater than 50%, the prognosis is poor, and the femoral head is flattened. In summary, the more severe the involvement of the lateral pillar, the poorer the prognosis.

　　Early diagnosis of this disease is very important, and timely diagnosis and treatment are closely related to the prognosis of the child.

　　When children aged 5 to 10 years present with unexplained hip pain, limping, and symptoms that persist for several weeks without improvement, the possibility of suffering from this disease should be considered. The earliest X-ray signs are joint capsule swelling and slight lateral displacement of the femoral head. It is necessary to take bilateral X-ray films for careful comparison and to follow up regularly. Once there is a change in the density of the epiphysis, the diagnosis can be confirmed. Radioisotope scanning can also be performed on suspicious cases, with gamma scintigraphy after intravenous injection of 99Tc, which can show early signs of radioactivity sparsity in the bone necrosis area or radioactivity accumulation in the bone regeneration area. Bone pressure measurement also helps in early diagnosis, but is less commonly used in clinical practice.

　　The etiology of osteochondrosis of the femoral head epiphysis is not very clear, and there are no effective preventive measures. It is worth mentioning that since the disease often has sequelae, if early subtle signs of various sequelae can be found in the early stage of Perthes disease, timely treatment may prevent the occurrence of sequelae. Scientific exercise, do well before exercise preparation, do not run, jump, squat excessively, progress gradually, avoid injury.

　　Clinical examination items for osteochondrosis of the femoral head epiphysis:

　　1. X-ray examination:It is the main means and basis for clinical diagnosis of femoral head ischemic necrosis. Regularly taking anteroposterior and frog position X-ray films of both hip joints can dynamically observe the morphological changes of the femoral head throughout the process of the lesion, and each stage of the X-ray film can reflect the pathological changes.

　　1. Synovitis stage:The main manifestation on the X-ray film is swelling of the soft tissues around the joint, with the femoral head slightly shifted laterally, but generally not more than 2 to 3mm. These non-specific changes can last for several weeks, during which X-ray films should be followed up.

　　2. Early involvement of the femoral head epiphysis:This is the radiographic feature of the pre-necrotic stage, mainly that the epiphysis is smaller than normal, and there is no growth after continuous observation for 6 months, indicating that intracartilaginous ossification temporarily stops. The joint space widens, and the superior margin of the femoral neck presents a circular prominence (Gage sign). The anteroposterior X-ray film shows that the femoral head shifts laterally by 2 to 5mm, followed by increased density of part or all of the epiphysis. The cause is:

　　(1) Disuse osteoporosis and decalcification of the proximal femur adjacent to the epiphysis, leading to increased density of the femoral head epiphysis.

　　(2) Compression of necrotic cancellous bone.

　　(3) Revascularization of early necrotic epiphysis, new bone formation is present on the surface of necrotic cancellous bone, resulting in true density increase. Some authors point out that the 'crescent sign' may be the first X-ray sign of bone necrosis. On frog position films, a clear linear area of decreased density is seen under the cartilage of the anterior and lateral aspect of the femoral head. Salter believes that the 'crescent sign' is a subchondral fracture of the joint, which has important clinical significance. It is not only the main basis for diagnosis but also helps to predict the extent of femoral head necrosis, judge the severity of the lesion, and estimate the prognosis.

　　3. Necrosis stage:The X-ray features are the necrosis of the anterior and lateral aspect of the femoral head, which shows unevenly increased density on the anteroposterior X-ray film. If a frog position X-ray film is taken, it can be seen that the dense area is located on the anterior and lateral aspect of the femoral head. In this case, it is often necessary to observe for 1 year to determine whether it is partial necrosis or complete necrosis. If it is complete necrosis, the epiphysis often presents with a flat畸形. However, arthrography can show that the femoral head epiphysis still retains its circular contour.

　　4, fragmentation period:The X-ray film shows alternating distribution of hardening and rarefaction areas, the hardening area is the result of compression of necrotic trabeculae and the formation of new bone, while the rarefaction area is the image of vascularized osteogenic tissue that has not yet ossified, the neck of the femur becomes shorter and wider, the corresponding metaphysis of the necrotic femoral head appears lesions, mild cases show osteoporosis, and severe cases show cystic changes, which may be due to the invasion of regenerating epiphyseal plate cartilage cells and vascular tissue.

　　5, healing period or sequelae period:At this stage, the lesions have stabilized, and the osteoporotic area is filled with normal trabecular bone, so the density of ossification tends to be uniform and consistent, but the epiphysis of the femoral head is obviously enlarged and deformed, the X-ray film shows that the femoral head is oval, flat or mushroom-shaped, and is displaced or subluxated laterally, the acetabulum also appears compensatory expansion, and the medial joint space is widened.

　　Two, radioisotope examination:It can not only determine the blood supply of bone tissue, but also reflect the metabolic state of bone cells, which is of great significance for early diagnosis, early determination of the range of femoral head necrosis, and differential diagnosis. Clinically, intravenous injection of 99TC is often used, followed by gamma scintigraphy, which shows radioactive sparsity or defects in the necrotic area in the early stage, and local radioactive aggregation can be seen in the regeneration period. Crenshaw et al. believe that the radioisotope sparsity of the necrotic area of the affected side compared to the healthy side is less than 50% for early lesions, which is equivalent to Catterall's type I or II, or Salter's type A, otherwise it is late-stage, equivalent to Catterall's type III or IV, or Salter's type B. Compared with X-ray examination, radioisotope examination can determine the range of necrosis 6 to 9 months earlier, and show the regeneration of blood vessels in the necrotic area 3 to 6 months earlier.

　　Three, joint arthrography:It is generally not considered a routine examination, but some authors believe that joint arthrography can detect the enlargement of the femoral head early, which is helpful to observe the gross morphological changes of the joint cartilage, and can clearly identify the causes of early femoral head coverage, joint arthrography during the healing stage can more truly show the degree of joint deformation, which is of reference significance for selecting treatment methods, but this is an invasive examination, and some children who cannot cooperate with the examination may need to be anesthetized, therefore, joint arthrography should not be listed as an essential examination item.

　　In recent years, with the application of magnetic resonance imaging technology, some hospitals have also performed this examination for Perthes disease. Practice has proven that this examination is of great value in diagnosing bone ischemic changes, can make an early diagnosis, the ischemic area is manifested as a low signal area, and can clearly show the cartilage area and thickness of the femoral head acetabular margin, the hip joint in magnetic resonance imaging is like joint arthrography, which can clearly show whether the shape of the femoral head is normal, magnetic resonance imaging is superior to X-ray examination in determining ischemic lesions, and has no radioactive injury, but it cannot be widely applied at present.

　　Food suitable for patients with osteochondrosis of the femoral head epiphysis:Food rich in vitamin D, such as seafood, animal liver, egg yolks, and lean meat, etc. In addition, patients should also pay attention to avoiding spicy, greasy, and cold foods.

　　At the onset of osteochondrosis of the femoral head epiphysis, because the hip joint of the child is very sensitive, skin traction can be used first for 1-2 weeks, and further treatment can be considered after the acute symptoms subside.

　　I. Non-surgical Treatment: In the past, long-term hip orthopedic plaster casting was used, but due to its great impact on children's development and joint function, it is now rarely used or not used. Various types of abduction braces are currently commonly used treatment methods, and their purpose is to: 1. Place the femoral head deeply in the acetabulum; 2. Avoid the pressure of the acetabular labrum on the femoral head; 3. Make the pressure on the femoral head equal; 4. Maintain good mobility of the hip joint.

　　II. Surgical Treatment: It is envisioned that the blood supply between the ossification center of the femoral head and the femoral neck can be improved by surgical methods, but the effects of puncture, bone slice insertion, or communication between them have not been achieved. Some people advocate the use of hip joint synovectomy to treat the disease, which has certain effects, but the mechanism of the surgical action is not yet clear. Some people also use pedicle (muscle flap or blood vessel) bone grafting, vascularized bone grafting, and other methods. In recent years, it is relatively recognized abroad to perform subtrochanteric or intertrochanteric osteotomy. The advantages of this operation are: 1. Treatment can be completed within 6-8 weeks after surgery; 2. No further application of supports or other measures to restrict activity and weight is required after surgery; 3. Osteotomy can cause congestion in the upper segment of the femur; 4. The efficacy is not worse than that of long-term external fixation. The complications of osteotomy include limb shortening deformity, residual hip varus, nonunion of osteotomy site, and limited joint mobility. It is generally believed that the efficacy is good for those under 7 years old, and the effect will not continue to improve in the years after surgery. The healing process of femoral head epiphysis necrosis can be shortened. On average, the lower limb is shortened by 1.4 cm after surgery.