Previously known as congenital hip dysplasia, developmental dysplasia of the hip (DDH) is a common disorder that affects infants and young children. This change of name reflects how DDH is a condition that develops over time. It may not necessarily be present at birth, developing either in the uterus or during the first year of life.

In DDH, there is a disruption in the normal relationship between the head of the femur and the acetabulum (hip socket). The severity of DDH can range from mild to severe, affecting either one or both of the hips. Mild cases are referred to as unstable hip dysplasia, where the hip is in the joint but is easily dislocated. More severe cases are partially or completely dislocated. A partial dislocation is known as a subluxation.

In this article, we will cover:

• area of the hip involved
• causes of DDH
• available treatment options

The hip joint is where the femur, also known as the thighbone, is connected to the pelvis. It is made up of two parts, the femoral head and the acetabulum. The femoral head is the ball-shaped upper end of the femur. The acetabulum is the socket in the pelvis that the femoral head fits into. Together, the ball and socket joint are what allows the leg to move in various directions in relation to the body.

The hip joint develops normally when there is a right amount of contact and pressure between the surfaces of the femoral head and acetabulum. At birth, most of the acetabulum is cartilage. The head of the femur inside the acetabulum helps to shape the joint as it forms. In DDH, there is a disruption in the contact between the femoral head and the acetabulum.

If the femoral head is in an abnormal position, it can lead to a dysplastic hip. Other times, the acetabulum is too shallow or sloping instead of a usual cup shape. As a result, it cannot hold the femoral head in place.

If this issue is not diagnosed and treated early, the soft tissues surrounding the hip may start to stretch out. As a result, there may be changes in the blood supply to the hip. At times, the hip joint may try to form another hip socket known as a false acetabulum. This false acetabulum can lead to even more problems as there are no proper ligaments, soft tissues and joint capsule to hold the femoral head in place.

Unfortunately, there is no single known cause of DDH. In certain cases, there is laxity or looseness of the ligaments surrounding the joint, which may be hereditary. In other cases, the infant’s position may affect how the hip joint forms, either in the womb or after birth. First-born babies may be more affected too, as their fit in the uterus is tighter than in later babies.

For example, a breech (buttocks first) position in the womb limits movement. It also puts the fetus in a position with hips bent, knees straight and legs together. This places an abnormal amount of stress on the joint, which does not foster normal development.

The position and free movement of the hip remain vital during the first few months after birth. At this stage, the hip continues developing and forms a deep socket and stable joint. If an infant is carried on the parent’s hip with the child’s hips bent and open wide, they will be less likely to develop DDH. In certain cultures such as Chinese, Korean and African American, infants are swaddled or wrapped with their legs extended out straight together. Spending a significant amount of time in such a position can put an infant at a greater risk of DDH. 

In addition, DDH is more common in girls than in boys. This may be due to hormonal differences. Estrogens and a hormone known as relaxin, which are present in the womb and at birth, may cause a general laxity or loosening of the ligaments. Usually, the left hip is more affected than the right hip. This is probably due to the fetus’ position before birth. This is because the most common position in the uterus is one where the fetus’ left hip is next to the mother’s spine. As a result, the hip motion is limited.

On top of that, children with developmental disabilities, who are unable to stand up and walk or move normally, are also at risk for DDH.

The newborn, infant or young child may not experience any symptoms such as pain to signal an issue. Although, there may be some differences in how the legs and buttocks look when compared side by side. For example, the leg on the side of the dislocated hip may appear shorter and turn outward. The folds in the skin of the thigh or buttocks may be uneven, and there may be a wider space between the legs. At times, the problem goes unnoticed until the child begins to walk. If only one hip is affected, the child may walk with a limp. However, if both hips are affected by DDH, the child may waddle or sway from side to side. When both hips are dislocated, it may be hard to spot an abnormality in the way the child walks.

The most essential diagnostic tool is the physical examination performed by the paediatrician. It is important to diagnose DDH early in newborns and young infants to avoid major problems later on. As such, all newborns and infants should be screened as early as possible. Out of all, babies born breech or with a family history of DDH are of more concern.

While the infant is still in the nursery, the doctor carries out special tests. The aim of these tests is to look for signs of an unstable hip. The two most accurate physical examinations are the Ortolani maneuver and Barlow’s test. They are meant to detect if the hip is sliding in and out of the acetabulum. In these tests, the doctor first places the infant on a table in a supine position, where they are placed on their back. Next, the doctor abducts the hips by moving the bent hips and knees apart. If the hip feels like it can be pushed out the back of the socket, it is considered abnormal. This is known as a positive Barlow’s test and is a sign of instability in the hip. As the hip is abducted further, the doctor might feel the femoral head slide forward as it slips back into the socket. This is known as a positive Ortolani maneuver and is another sign of hip instability. If any of these tests turn out positive, the child will be watched closely or be given immediate treatment with a brace.

Alternatively, for infants who are three months and older, Allis’ or Galeazzi’s test can be performed. In this examination, the child is placed in the supine position with the hips and knees bent and feet flat. Any unevenness between the knees is observed. If one knee is lower than the other, it may be an indication of a dislocated hip on the lower side.

As DDH can develop over time, infants are advised to go for repeated hip examinations. This should be included in well-baby check-ups, until the child begins to walk normally with no sign of limping or an altered gait pattern. In these examinations, the doctor also observes for uneven skin folds around the thigh and buttocks, changes in the hip’s range of motion and a difference in the two legs’ lengths.

Although X-rays are not reliable in infants, they may be able to help in diagnosing older children. Ultrasound, on the other hand, is more accurate for infants six months and below.

For DDH, the aim of the treatment is to keep the femoral head in good contact with the acetabulum. As mentioned, a stable hip encourages the development of a normally-shaped socket and rounded head of the femur. In order to stabilize the joint, the hip must be maintained in a proper position for enough time. The proper positioning of the hip should be one where it is flexed to 95 degrees and abducted at least 90 degrees. This position keeps the femoral head in the best place and allows the ligaments to and joint capsule to tighten up.

Nonsurgical treatment

Depending on the child’s age and severity of the condition, there are several different ways to treat DDH. In the first six weeks, double and triple diapering may be all that is needed. However, if the problem persists, a Pavlik harness can be worn for three to nine months. This special harness keeps the hip in flexion and abduction. It may be worn until the hip can no longer be moved in and out of the socket. Additionally, X-rays may be used to confirm that the hip is stable in older children.

As for children with developmental disabilities, a standing program may be required. Special standing boxes or equipment are used to hold them upright and give the hip the mechanical force needed to develop normally.

Surgical treatment

In cases where the infant is older than 6 months, the Pavlik harness may not work. This is because the child may be too large to wear the harness or too active to keep the harness on all day. Therefore, for children of this age group, a closed reduction under general anaesthesia may be the best option. If the hip is not able to be easily reduced, the child may be put in traction to loosen the soft tissues surrounding the hip. When the surgeon determines it is time for the hip to be reduced, the child is taken to the operating room and placed under general anaesthesia. During the procedure, the surgeon gently moves the hip to feel if it can be placed in the socket. Fluoroscopy is used to view the bones of the pelvis and hip as they align. Fluoroscopy is a kind of X-ray in which the surgeon watches the X-ray image on a TV screen.

Once the hip is able to be put back into the socket with ease, the child is placed in a hip spica cast from waist to toe. This cast holds both legs so that the hip joint is fixed in the socket, while the soft tissues surrounding the hip tighten to hold the hip reduced. The cast may be needed for several months to hold the hip in place. During this period, it is typically replaced once every two weeks to a month. Every time the cast needs to be changed, the child is taken the operating room and placed under general anaesthesia. This form of treatment is referred to as a closed reduction.

If the hip is unable to be stabilised and kept in the socket, surgery may be required. This is more likely to be the case for children 18 months old and above. Before the procedure, the child may be placed in traction to loosen the soft tissues surrounding the hip. Next, they will be put in a full hip spica cast from waist to toe. This cast may be required for several months while it holds the hip in position. In cases where the hip dysplasia has not been corrected and the child is two years old and above, an open reduction may be conducted. During this procedure, the surgeon removes any abnormal tissues preventing the femoral head from fitting inside the acetabulum and cuts any tight ligaments in the joint capsule around the hip joint. A tenotomy may be performed during the surgery to cut the tightly contracted tendons or muscles in the hip area. This is done to relax the tight structures surrounding the hip joint, As a result, the hip can be placed in the socket. These tissues will then grow back with scar tissue as the child heals. After the surgery, the child is typically placed in a spica cast for several months.

Another procedure known as derotational osteotomy may be required. In this procedure, the femur is cut and rotated to make it easier to keep the femoral head inside the acetabulum. After this is done, the soft tissues will loosen up and the forces of the muscle tend to keep the femoral head reduced. Similar to the other procedures, the child is put in a spica cast for several months while the bone heals. To confirm successful reduction before removing the cast, a CT scan may be conducted. A CT scan is a special kind of X-ray that takes slices of the body. This produces a much better image of the hip and acetabulum as compared to plain X-rays.

In children above 18 months old, additional surgery may be required to change the acetabulum and femur. This is because the condition has been present longer and the anatomy has become more distorted over a longer period of time. In such situations, surgery may be recommended to alter the way that the acetabulum is aligned. There are several different kinds of pelvic osteotomies designed and still used today.

Different kinds of osteotomies, such as the Steele, the Salter and the Pemberton osteotomies, are used to tilt the acetabulum in a more horizontal angle to the floor. As a result, the femoral head will be less likely to slide up and out of the socket with weight-bearing.

In Chiari osteotomy, the bone of the pelvis just above the acetabulum is cut. This allows the bone to slide out and form a new roof over the hip joint. As a result, the femoral head is prevented from sliding up and out of the socket. As time passes, this shelf of bone above the acetabulum remodels and creates a deeper acetabulum.

Another type of osteotomy used is Staheli osteotomy. In this procedure, a bone graft is inserted right above the hip joint to create a wider, new roof or shelf over the acetabulum. As a result, the femoral head is kept from sliding up and out of the socket. Additionally, as it heals, a larger weight-bearing surface is formed to spread out the weight that needs to be transferred from the femoral head to the acetabulum and pelvis.

Lastly, there is the Dial osteotomy, which is not as common. In this procedure, the whole acetabulum is cut free of the pelvis and moved or dialled at the best angle, leaving it to heal in that position.

Thankfully, the healing process in young children is usually very fast. Because the skeleton is still developing, surgery is able to effectively remodel and create a hip socket that will serve well into adulthood with minimal issues. However, children who have undergone surgery to address a dysplastic hip are at a greater risk of developing wear and tear arthritis of the hip as they age into adulthood. Many age well into their 40s and 50s before running into any significant issues with their hip. On the other hand, some never experience any additional issues.

Nonsurgical rehabilitation

Children in a Pavlik harness benefit from as much motion in the hip as possible. Motion allows for the nutrition of the developing bone and cartilage inside the hip joint. However, it is important to still keep the hip reduced. A therapist will review positions to avoid such as side-lying with the top leg down toward the other leg past the midline. The child must keep using the harness until the hip is stable. When it is nearing the time to stop usage, the child may only need to wear it at night.

As for infants in the harness, extra attention should be taken not to set the harness in too much abduction. Abduction is the motion when the thighs are pulled apart from each other. Pavlik harnesses are designed to hold the legs bent at 95 degrees at the hip and abducted about 45 degrees each. One should be careful not to tighten the harness too much. This can pull the legs apart too much, putting too much force into an abduction. As a result, the blood supply to the femoral head may be blocked, causing a condition called avascular necrosis. This is a serious complication that can prolong the treatment of the hip and cause other issues. One’s surgeon or physical therapist should provide instructions on the right way to adjust the Pavlik harness. It is important for the child’s caretaker to understand how to do this properly and to ask questions if any.

Post-surgery

The child will not be able to walk after the surgery due to the spica cast. A special hole is cut open to allow older children to use the bathroom, while younger children remain in diapers. The physical therapist will assist the family with any special equipment required for transportation and everyday tasks. Additionally, special advice for handling and positioning will be reviewed as well.

Extra attention should be taken not to get the cast wet with water or urine. The cast may only be removed and replaced if the child grows or if there is evidence of skin breakdown. The child should be examined several times a day for changes in skin colour or sensation. If there are any signs of cool or numb toes, leg or foot pain or loss of motion in the feet, the physician must be informed immediately.

Lastly, physical and occupational therapy is a crucial part of the postoperative period in the cast. Opportunities to move and develop gross motor skills are limited during this time. The therapist will closely monitor the child’s overall gross and fine motor skills over this period.