Developmental hip dislocation, also known as developmental dysplasia of the hip (DDH), is one of the most common extremity deformities and refers to a spectrum of hip conditions that occur before and after birth in which the femoral head and acetabulum are abnormal in their development and/or anatomical relationships. It can be a very mild form of acetabular dysplasia or a dislocated hip lesion that leads to severe loss of joint function in adulthood. In the past, this hip dysplasia was thought to be caused by primary acetabular dysplasia and laxity of the articular ligaments, so it was called congenital hip dislocation. In the 1980s and 1990s, as research progressed, more and more experts believed that in addition to congenital factors, acquired factors also play an important role, and that this hip dislocation can be prevented to a certain extent. Therefore, in the early 1990s, the North American Society for Pediatric Orthopaedic Surgery was the first to rename congenital dislocation of the hip (CDH) as developmental dysplasia of the hip. Subsequently, the name was changed in Europe, Japan and Hong Kong. At the end of the last century, pediatric orthopedic surgeons in China also generally accepted this concept.
The incidence of developmental hip dislocation accounts for about 0.1% of surviving newborns. However, extensive surveys conducted by many medical centers around the world have found that it varies greatly by race and by region. Worldwide, the incidence is highest in Caucasians, followed by Yellow and lowest in Blacks. In a survey of 85,000 newborn infants in six cities in China, including Beijing, Shanghai and Dalian, the incidence of developmental hip dislocation ranged from 0,91‰ to 8,2‰, with an average of 3,9‰, and showed a trend of gradually increasing incidence from south to north, which may be due to the cold in the north of China, where infants are often swaddled and bound with both lower limbs after birth, so that the hip joint is in a straight position. The incidence of developmental hip dislocation is higher in these regions and races. On the contrary, the incidence of developmental hip dislocation is significantly lower in some minority groups in the south of China, which are accustomed to carrying their babies on their backs with both hips abducted. Developmental hip dislocation is mostly seen in girls, and according to statistics, about 80% to 90% of developmental hip dislocation cases are girls.
Developmental hip dislocation is often divided into three types due to different degrees of pathology.
1, acetabular dysplasia: also known as unstable hip joint. Early asymptomatic, a high percentage of postnatal hip instability, often characterized by increased acetabular index on X-ray, and gradually stabilized with growth and development. If the appropriate hip joint external booth is used, the hip joint will heal spontaneously; a small number of persistent acetabular dysplasia changes, and symptoms appear after growing older, requiring surgical treatment.
2.Hip subluxation: the femoral head and acetabulum are poorly developed, and the femoral head is displaced outward and upward, but not completely out of the acetabulum; X-ray films show that the femoral head is displaced outward and the acetabular index increases to more than 35°, but the femoral head can still be felt in front of the groin. Hip subluxation is neither a result of acetabular dysplasia nor a transitional stage of hip dislocation, but an independent type that can exist for a long time.
3, hip dislocation: this type is the most common, the femoral head has obviously detached from the acetabulum, but outward and upward displacement, the glenoid lip is embedded in the joint in arthrography, so that the acetabulum is isolated from the femoral head, the femoral head cannot enter the acetabulum, with age, many secondary changes occur, making treatment more difficult. There are three degrees of dislocation of the femoral head according to the height of the dislocation. Although the femoral head is dislocated outwardly, it is located at the same level of the acetabulum as degree I; the femoral head is dislocated outwardly and upwardly, corresponding to the level of the outer upper edge of the acetabulum as degree II; the femoral head is completely dislocated posteriorly and upwardly, located on the iliac wing as degree III; some scholars propose that for high dislocation of the femoral head, reaching the level of the sacroiliac joint, it should be classified as degree IV.
Clinical examination: If every newborn can be routinely examined after birth and treated within 3-7 days with a clear diagnosis, the results are most satisfactory; a clear diagnosis and successful treatment within 1 year of age can lead to a completely normal X-ray examination later on, indicating the importance of early diagnosis and treatment.
Careful clinical examination during the neonatal period and in the young infant (from birth to 6 months) is particularly important. Routine clinical examinations include the Ortolani test and the Barlow test, which involves gentle abduction and adduction of the hip joint during hip flexion to check for incorporation and prolapse of the femoral head. In children with hip dislocation, when the hip joint is abducted or adducted to a certain degree and the femoral head is incorporated into or dislodged from the acetabulum, the hip joint appears to be bouncing, which is one of the most reliable signs for diagnosing developmental hip dislocation. Barlow’s test is positive. This test confirms hip dysplasia or hip instability with potential subluxation or posterior dislocation.
In hip dislocation, the thigh and calf are out of proportion, the hip is wide, the inguinal crease is asymmetrical, and the affected side is short or absent. The hip skin lines are also different, with one elevated or more on the affected side, and the entire lower extremity is shortened and in a mildly externally rotated position. This dermatoglyphic asymmetry is usually only a sign that requires further examination. Normal infants may have asymmetrical skin lines, and children with hip dislocation may also have symmetrical skin lines. As a result of hip dislocation, the femoral artery is deprived of the village support of the femoral head and the pulsation is significantly weakened.
When the child is between 6 and 18 months of age, there are some changes in the clinical presentation. For example, the femoral head has dislocated from the acetabulum and it is no longer possible to incorporate the femoral head into the acetabulum by simply abducting the hip joint. Several other clinical signs become more evident, the first and most reliable sign being limited abduction of the already dislocated hip due to contracture of the adductor muscle groups. When the infant is lying flat on the examination table with the knees and hips flexed at 90° each, the examiner faces the child’s hips and holds the child’s knees in both hands while abducting them, the lateral surface of the normal knee can touch the table, but in the case of dislocation the affected side can only reach 75-80°, which is called a positive hip abduction test. However, in cases of hip dislocation, there can be no abduction restriction, and in infants and children with normal hips, there can be hip abduction restriction. When the femoral head is dislocated not only laterally but also upward, causing relative shortening of the femur on the dislocated side, a positive Allis sign or Galeazzi sign is observed. As one side of the hip is dislocated, the child lies flat on his back, bends the knee 85-90°, and both feet are placed flat on the table, and the two ankles are seen close together with unequal height of the two knees.
In children entering walking age, lameness is often the only complaint of the child presenting to the clinic. When the hip is dislocated on one side, the child has a limp, and when the hip is dislocated bilaterally, the child has a “duck stance” with a pronounced posterior protrusion of the hip and a swaying gait. As the hip joint dislocated, the femoral head lost its fixed position in the acetabulum and rose to the side of the pelvis, involving the gluteus medius muscle and weakening the muscle strength, which showed a positive Trendelenburg test. The line from the anterior superior iliac spine to the sciatic tuberosity normally passes through the apex of the greater trochanter and is called the Nelaton line, and the greater trochanter is above this line during dislocation.
The diagnosis of developmental hip dislocation by ultrasound has been carried out in many countries and regions around the world, promoting early detection and early treatment of developmental hip dislocation and effectively reducing the late incidence of the disease and the incidence of complications. Ultrasound, with its ability to penetrate cartilage without radiographic damage, is particularly suitable for examination in newborns and infants whose femoral heads have not yet ossified, and has become the preferred alternative to radiography for the diagnosis and evaluation of developmental hip dysplasia in newborns and infants. As the ossification center of the femoral head forms and increases in size, the ability of ultrasound to penetrate the femoral head is obscured and its ability to visualize the acetabular floor decreases. In general, ultrasound examination of the hip joint is no longer appropriate for infants older than 6 months of age.
There are two types of ultrasound hip examinations: static and dynamic; Graf’s static examination and classification is the most widely used method and classification today. The Graf method requires that a straight iliac bone, a rounded bony acetabular roof and a cartilaginous acetabular roof must be seen on the standard image; the angle α of the iliac bone with the bony acetabular roof and the angle β of the cartilaginous acetabular roof are measured with the iliac bone as the baseline, and the examined hip is classified into four types according to the α and β angles types.
The dynamic examination was based on the static one, and the femoral head in the acetabulum was observed by compression and traction on the examined hip respectively.
Although ultrasound hip examination is a sensitive, accurate, non-invasive and easy to perform, many studies have concluded that it is highly subjective and may result in false positives, thus exposing the child to unnecessary treatment.
Although X-rays are not very reliable in diagnosing developmental hip dysplasia in newborns and small infants, they can show acetabular dysplasia and deformed hip dislocations. As the child ages and develops soft tissue contractures, X-rays become not only more reliable but also helpful in diagnosis and treatment.
1. X-ray manifestations in newborns and small infants
(1) Von-Rosen (abduction and internal rotation) radiography: The infant is placed in the supine position, with both lower limbs abducted at 45o and rotated internally as far as possible. When normal, the longitudinal extension line of the femoral stem intersects between the L-5 and S-1 planes via the outer edge of the acetabulum. However, in the case of dislocation, the line intersects above the L-5 plane via the anterior superior iliac spine.
(2) pelvic plain film measurement method: on the X-ray pelvic orthopantomograph, the Y-shaped cartilage line of both acetabulum becomes Hilgeneriner line (H line), the distance of the upper femur from H line is the upper gap, normal 9,5cm; the distance of the upper femur bird’s mouth from the outer edge of the sciatic branch is the medial gap normal 4,3cm; the upper gap <8,5cm and the medial gap >5,1cm should be suspected of developmental If the acetabular index is >30o, or the upper gap is <7,5cm and the medial gap is >6,1cm, developmental hip dysplasia can be diagnosed.
2.X-ray performance of infants and children
(1) Perkin quadrant: the center of the acetabulum on both sides connects a straight line called Hilgenereiner line, referred to as H line; then make a vertical line P from the outer edge of the acetabulum to the H line, dividing the hip joint into four quadrants, and the normal femoral head epiphysis is in the inner lower quadrant. The normal femoral head epiphysis is in the inner lower quadrant.
(2) Acetabular index (AI): the acute angle formed by the intersection of the line from the outer edge of the acetabulum to the center of the acetabulum and the H line is called the acetabular index, and its normal value is 20o to 25o, which gradually decreases after walking in children and basically remains constant at about 15o at the age of 12. The hip joint is significantly increased, even in more than 30o.
(3) Shenton’s line: the arc of the upper edge of the normal closed foramen is connected to the medial arc of the femoral neck in a parabola, and this line disappears when dislocation occurs.
(4) Center edge angle (CE angle): the angle formed by the vertical line between the center point of the femoral head and the H line, and the line between the outer edge of the acetabulum and the center point of the femoral head, which has diagnostic value for acetabular dysplasia or subluxation. Normal is above 20o; when the CE angle is 0o, the hip joint is semi-dislocated; when the hip joint is fully dislocated, this angle is turned over.
(5) Sharp angle: an indicator to judge the development of the acetabulum after the Y-shaped cartilage of the acetabulum is closed. It is not a diagnostic indicator, but mainly an indicator to determine the hip flexion of acetabular development in follow-up.
(6) acetabullar head index (AHI): an index to check the coverage of the acetabulum on the femoral head. That is, the distance from the inner edge of the femoral head to the outer edge of the acetabulum (A) than the maximum transverse diameter of the femoral head (B), AHI = A/B × 100, its normal range is 84 to 85.
(7) Measurement of the anterior femoral neck inclination angle: the residual angle α angle of the neck stem angle is measured on the orthopantomograph of the pelvis, and then on the lateral radiograph of the hip joint with the knee flexed and hip flexed at 90o, in the abducted and externally rotated position, with the lateral thigh in contact with the X-ray machine table, the above angle formed is the β angle. The angle of the femoral neck is measured by CT, which is easy and accurate, and the angle between the midpoint of the femoral condyles and the longitudinal axis of the femoral neck is the angle of the femoral neck. Normal newborns are between 20o and 30o. Due to the normal stress of the hip joint, the anterior femoral neck tilt angle gradually decreases with age to 10o to 15o in adults.
Other examination methods include CT examination and magnetic resonance imaging (MRI).
The principles of treatment for developmental hip dysplasia are: to obtain and maintain concentric repositioning of the femoral head in the acetabulum without affecting or minimizing the blood supply to the femoral epiphysis, to stimulate acetabular development and achieve satisfactory coverage of the femoral head by the acetabulum, and to allow the dislocated or dysplastic hip to grow and develop toward the most normal anatomical relationship possible.
Overall early diagnosis creates the conditions for early treatment, which in turn allows for rapid resolution of the pathological changes in the hip joint. The younger the age at which treatment begins, the better the outcome. In the majority of cases, early diagnosis within the first few months of life allows for complete success of conservative treatment.
The treatment of developmental hip dysplasia is divided into two main categories: conservative treatment and surgical treatment. The choice of treatment method is related to the age of the child, the severity of the lesion, whether or not to walk and bear weight, and other factors.
1. Conservative treatment
Conservative treatment is suitable for children under 18 months of age. The theoretical basis of conservative treatment is Harris’ law, that is, concentric head and socket is the basic condition for hip development. The younger the child, the faster the development, and within a certain period of time the hip joint can be restored to its normal state. This indicates that after the hip joint is repositioned, the acetabulum and femoral head stimulate each other to grow and develop according to the physiological and biomechanical laws, especially the joint movement can promote the development of the hip joint, in which the femoral head develops more rapidly than the acetabulum. Based on this principle, in order to obtain the ideal reset, it is important to maintain the stability of the hip joint after the reset. The following principles should be followed: (1) choose a posture to maintain the stability of the hip joint; (2) choose different fixation methods according to the age; (3) maintain a certain period of time after the reset to promote the development of the acetabulum and femoral head.
(1) Pavlik brace: Pavlik brace treatment is the most widely used method in conservative treatment, which is called “soft treatment”, and its treatment principle is to use the limb’s own weight to achieve and maintain the femoral head reset. The Pavlik brace should be worn around the clock until the hip is stable, i.e., Balow and Ortolani tests are negative, which usually takes 3 to 4 months. Thereafter, it can be removed for 2 hours per day, and the removal time can be extended by a factor of 1 every 2 to 4 weeks until it is worn only at night and continues until radiographs show a normal hip joint. The success rate of neonatal resurfacing has been reported in the literature to be over 90% and over 85% in small infants less than 6 months of age. Children older than 6 months, with negative Ortolani’s sign, IIIo dislocation and severe soft tissue contracture around the hip joint are not suitable for Pavlik retractor treatment.
(2) Traction repositioning: It is suitable for children under 6 months of age, with IIIo dislocation and severe contracture of the adductor muscles. The principle is to gradually abduct the hip joint through continuous traction, and then the femoral head is naturally repositioned. The biggest advantage of traction repositioning is that the head of the femur is gradually repositioned and ischemic necrosis is avoided. The disadvantage is that the hospitalization period is long, and the traction process is difficult to care for the skin damage caused by traction may hinder the treatment.
(3) Manipulative resetting: suitable for the treatment of infants and children aged 6 months to 18 months. A standard treatment plan includes adequate preoperative traction, adductor excision and closed repositioning. It is debated whether traction can reduce the incidence of ischemic necrosis of the femoral head. The medial adductor muscle is cut before resetting to relieve the compression of the medial vessels of the rotating femur between the iliopsoas muscle and the medial adductor muscle after hip flexion and abduction. Mild contractures can be cut percutaneously, while longer contractures require a small incision to cut the adductor muscle. Gentle manual repositioning under general anesthesia, if the repositioning fails, surgical treatment should be used instead, avoid repeated repositioning to prevent damage to the femoral head. After manual repositioning, human position plaster is used to fix the femoral head in a safe angle. The safety angle is the angle at which the head of the femur is re-dislocated after extreme abduction of the hip joint in the flexed position during manual repositioning. The safety angle helps to prevent ischemic necrosis of the femoral head. Plaster fixation generally needs to be maintained for at least 3 months to obtain stability of the hip joint, after which treatment can be maintained with an abductor brace or cast for 6 months or longer. During this period, the mutual stimulation between the femoral head and the acetabulum promotes the development of the hip joint and increases the coverage of the acetabulum on the femoral head.
2.Surgical treatment
The surgical treatment of developmental hip dysplasia usually consists of two aspects: first, incision and repositioning to remove the soft tissue structures that prevent repositioning and achieve central repositioning of the femoral head; second, correction of the deformity of the acetabulum and proximal femur by means of pelvic and femoral osteotomy. Orthopedic surgery for acetabular deformity is divided into two categories, one is reconstructive orthopedic surgery (reconstruction procedures), including iliac osteotomy (Salter osteotomy), acetabular osteoplasty (Pemberton osteotomy, Dega osteotomy), free acetabular osteotomy (Steel triple osteotomy, Ganz osteotomy), etc., of which Salter iliac osteotomy and Pemberton acetabular osteotomy are the most commonly performed reconstructive pelvic osteotomies; the other category is palliative surgery (salvage procedures), commonly used are Chiari internal pelvic osteotomy, Staheli acetabular extension, etc. The proximal femoral deformity is mainly corrected by femoral osteotomy.