Developmental Dysplasia of the hip (DDH)

What is Developmental hip dysplasia?

Developmental hip dysplasia or DDH is a term used to describe a spectrum of conditions where the hip joint fails to develop properly in childhood. In the past terms such as congenital hip dislocation or CDH were used, though the current preferred term is DDH. The term Hip dysplasia is also commonly used. All of the above terms refer to the same condition.

Before we can understand what DDH is, it is perhaps useful to know a little bit about the hip joint itself. The hip is the largest joint in the body and consists of a ball (femoral head) and a socket (acetabulum). The bones are held together by strong ligaments. Being a ball and socket joint, the hip is freely mobile in all directions. There are numerous muscle groups around the hip that provide stability and movement.

As mentioned above, DDH represents a spectrum. On the less severe end of the spectrum is a slightly shallow acetabulum (or socket) but with the femoral head (ball) still inside the socket. This is a dysplastic hip which typically goes unnoticed during childhood but sooner or later will cause arthritis in the hip because of the poor articulation between the ball and socket. Patients with mild dysplasia present for the first time as adults with end-stage hip arthritis and need a hip replacement. These cases are however rare (no more than 10% of cases).

The more common scenario is where the hip is shallow at birth and during the first few months to years of life the hip joint gradually dislocates out of place. In developed countries (UK, USA and Europe) where babies are screened by clinical examination or ultrasound scanning, DDH may be diagnosed at birth or in the first few weeks of life. Diagnosis at an early age makes treatment much easier and the use of strapping around the hip (called a Pavlik Harness) cures the problem in most babies.

In India, there is no uniform protocol amongst obstetricians or paediatricians to screen for hip dysplasia in the neonatal period (first 4 weeks of life). DDH therefore goes unnoticed and the child presents at a much older age when surgery is the only option to treat the problem.

On the most severe end of the spectrum are the so-called Teratologic hip dislocations. Such dislocations occur when the baby is still developing in the womb. They are usually associated with genetic conditions such as Arthrogryposis (multiple joint contractures). Teratologic hips are difficult to treat and typically need surgery even at an early age.

What causes DDH?

There is no specific cause for DDH that happens in every child with the condition. However, there are many known risk factors that increase the statistical probability of a baby having DDH. These include

• First born female child
• Twins
• Oligohydramnios (where the amount of fluid around the baby is less than normal)
• Family history of DDH in first degree relatives
• Breech presentation
• Postural foot deformities (such as metatarsus adductus and calcaneovalgus feet)
• “Moulded baby syndrome” refers to a combination of DDH, Torticollis (Wry neck), foot deformity and plagiocephaly (flattened appearance to the back of the head). This is thought to result from abnormal pressure on the baby (moulding) within the womb.

A child with DDH may not have any of the above risk factors and the first indication may be a limp that is noticed when the child starts to walk. In India, we routinely see children as old as 10 years with dislocated hips, largely due to a failure to diagnose the problem at an early stage.

A significant number of all babies have shallow hips at birth (probably the result of developing in a cramped space within the womb) but the hips spontaneously become normal within the first 6 weeks of life as the baby starts to move the legs freely. In a small proportion of children, this process fails to occur and these hips gradually dislocate over a period of time.

What are the symptoms of DDH?

There are a wide variety of symptoms that vary with age of the child at diagnosis.

0 – 1 year:

• No symptoms are apparent, though observant parents sometimes notice that the legs are different lengths.
• In severe dislocations, it may be difficult to open the legs (called hip abduction) to change nappies. At this age, DDH is diagnosed by doctors during examination or by ultrasound scanning.

Walking age (1 – 16 years):

• Limping is the commonest symptom. It is typically a painless limp and can be difficult to spot.
• Pain is a relatively late symptom and indicates the onset of damage to the hip (tear of a cartilage ring in the hip joint called the labrum) or early arthritis. The pain may be sharp and worse with certain hip movements or just a “dull ache” after activity. Clicking or “giving way” of the hip can also occur.

How is DDH diagnosed?

The investigation of choice depends on age of the child.

0 – 4 months of age: Ultrasound scanning of the hips using the Graf method. Alpha and Beta angles have to be calculated and these angles guide treatment. The Graf method is precise and has been standardised to a high degree. Specific training in ultrasound scanning for hip dysplasia is necessary in order to obtain good quality ultrasound scans.

Children older than 4 months: A good quality AP pelvis x-ray will clearly demonstrate the problem. Various lines are drawn on the x-ray by orthopaedic surgeons but these are probably of little interest to parents.

Arthrogram: This is a dye test which requires a general anaesthetic. In babies and young children up to the age of 18 months, a large part of the ball of the hip joint is made of cartilage not bone. The cartilage is not visible on x-rays and some contrast agent on the outside is required to outline the entire ball (cartilage + bone). An arthrogram also provides useful information to the surgeon about whether the hip can be put back in place without the need for open surgery.

CT Scans: are obtained post-operatively after a body cast (Hip spica) has been applied. X-rays performed through a spica are difficult to interpret. A CT scan clearly shows whether the operation to reduce the hip has been successful. Most good paediatric orthopaedic centres would insist on a CT scan prior to discharging the patient from hospital.

A CT scan is also sometimes obtained to visualise the hip in 3-D where the anatomy is abnormal or unusual. It is a good investigation in cases where previous surgery has been performed.

MR scans/ MR arthrograms: These tests are of use in teenagers or adults with symptoms suggestive of damage to acetabular labrum. Labral tears can be quite painful and restrict activities particularly sports.

In most cases, a simple x-ray of the hips is sufficient to confirm DDH.

What are the treatment options?

Treatment of DDH is entirely dependent on the age of the child. The younger the child at diagnosis, the less the intervention required. It is therefore important that the diagnosis is made soon after birth.

A proportion of babies have dislocated or dislocatable hips at birth. In most modern hospitals, paediatricians or obstetricians will examine babies for DDH. In certain developed countries, all babies have a hip ultrasound scan a few weeks after birth to rule out DDH. This system is obviously ideal in picking up all cases of DDH but it is expensive, difficult to implement and “over-treats” the problem. Remember that a proportion of babies with shallow hips get better by themselves. If the hip remains abnormally shallow at 3 months of age or if the hip is frankly dislocates, treatment is mandatory.

If your child has any of the risk factors mentioned previously, the safest course of action is to obtain an ultrasound scan of the both hips performed in accordance with the Graf method.

Pavlik Harness:

This is the least invasive method and therefore the most preferred by parents (and surgeons!). The harness can be used from birth to the age of approximately 4 months, though it can be difficult in children older than 3 months. It is a system of straps that is applied to both legs and keeps the legs opened (called hip abduction). The baby can kick both legs freely within the harness and it does not interfere with normal growth of the baby.

Once the baby has been placed in a harness, ultrasound scans must be repeated every week until the hip is anatomically located back in the hip joint. This may take 2 – 4 weeks. A further 6 weeks in the harness is necessary. If the baby grows out of the initial harness, it can be changed easily for a larger size. Average time in the harness is likely to be between 10 and 12 weeks.

In the vast majority of babies under 3 months (90% or more), treatment with the Pavlik harness is the only treatment that is necessary. There is good evidence to suggest that the hips become entirely normal when assessed at 5 years of age.

In summary, early diagnosis (soon after birth) and Pavlik harness treatment should be considered as the gold standard in managing hip dysplasia. Complications are minimal and it is effective.

Please click here for instructions on how to look after your baby in a Pavlik harness.

Closed Reduction and hip spica application:

If the child is older than 3 months at diagnosis, Pavlik harness is not appropriate. In this group (3 months to 12 months), an arthrogram will be necessary.  A short general anaesthetic is given. The hip is examined when the child is fully relaxed. A radio-opaque dye is also instilled into the hip joint to provide contrast. If the hip can be put back in place without undue force, a hip spica is applied. The term closed reduction refers to reducing a dislocated joint without the need for an incision. This is in contrast to an open reduction where an incision is necessary.

A post-operative CT scan is necessary to confirm that the hip is concentrically reduced, meaning that the ball is sitting in the centre of the socket. Sometimes the ball can appear on x-rays to be sitting well but the CT scan shows otherwise. Some centres use an ultrasound scan rather than a CT.

The hip spica is changed at 3 months under general anaesthesia. The total period in the spica is 6 months. This may seem a long time to some parents but children have not started walking at this age and there are no long-term adverse effects that result from hip spica treatment.

When the ball of the hip joint is dislocated, the socket also becomes quite shallow. Keeping the hip joint well reduced in a spica promotes development of the socket (remodelling) and improves stability of the hip. Children less than 1 year of age possess considerable remodelling capacity and it is important to harness this potential.

Medial open reduction:

This is a minimally invasive procedure undertaken in children under 18 months of age. There are numerous advantages with this procedure compared to a traditional “anterior open reduction”. The operation is performed through a small incision in the groin and therefore not visible to the outside. There is minimal blood loss and less postop pain.

The medial open reduction is also referred to as “assisted closed reduction” or “relaxed closed reduction”. This term is used because a forcible closed reduction causes damage to the blood supply of the femoral head and poor long-term results.

Medial open reduction is followed by immobilisation in a hip spica cast for 4 – 6 months. This will depend on a number of factors including ease of reduction, age of the child and progress of hip development within the spica.

Long-term results of medial open reduction have proven that this is a minimally invasive procedure that is safe and effective.

Anterior Open Reduction with femoral and pelvic osteotomy:

This procedure is typically used in children older than 18 months who have been walking for a period of time on the dislocated hip. A thick membrane called the capsule surrounds all joints of the body. When a child walks on a dislocated hip, the capsule enlarges and becomes quite lax. This enlarged capsule needs to be tightened up in order to prevent the hip from re-dislocating after surgery. The anterior open reduction procedure is designed to address this particular problem of a capacious and redundant capsule.

The anterior open reduction is performed through a “Bikini” incision. There are several tight structures (muscles, tendons and ligaments) that are divided or lengthened. The hip joint is relocated and the capsule repaired to keep the joint in place. Typically, the shallow socket (acetabulum) is also corrected by means of a pelvic osteotomy wherein the socket is divided and reset in the correct alignment. In addition to the pelvic osteotomy, the thigh bone may also need to be divided and reset, called a femoral osteotomy. Pelvic osteotomies sometimes need to be stabilised with a pin. Femoral osteotomies require plate and screws to maintain the bone in place during the healing process.

The child is placed in a hip spica for a period of 10 weeks after surgery. During this time, the hip joint stabilises and the osteotomies heal. On removal of the spica in the out-patients, the child is referred for a course of physiotherapy to improve hip movements and to encourage progressive weight-bearing. It may be up to 3 months from surgery before the child is able to walk normally.

If pins or metal plates have been used to secure an osteotomy, these require removal approximately 6 – 12 months later.

Who is at risk of DDH? How can DDH be prevented?

There is no way to prevent DDH from occurring but if your child has any of the risk factors mentioned above, obtaining an ultrasound scan of the hips by a trained sonologist and consulting a paediatric orthopaedic surgeon as soon as possible after birth will facilitate early treatment of the condition, typically without the need for any surgery.