The term 'Developmental Dysplasia of the Hip (DDH)' is generally used to refer to a range of hip deformities and dislocations found in small children¹, the implication being that the ball of the hip is not stable in its socket and liable to dislocation. The term includes both congenital and acquired abnormalities of the hip² and is thus thought to be more suitable than the term 'Congenital Hip Dislocation'. While DDH does not perturb newborns, it requires early treatment to avoid damage to the hip joint later on. In the UK, all babies are examined for DDH, both after birth and at their six-eight week GP checks.

Risk Factors

DDH can develop before, during or after birth. The exact mechanism of DDH is not clear, but there are a number of known risk factors:

• Breech presentation, where a baby is sat upright in the womb with the legs or bottom being passed first during birth.

• Oligohydramnios, a severe reduction in volume of the fluid surrounding the foetus in the womb. This is often due to a defect in the production or passing of urine, such that the foetus is able to drink the amniotic fluid but does not pass it again. The compression caused by oligohydramnios can damage the hips before birth.

• Large birth weight³ will also lead to compression of the foetus and may cause DDH.

• A family history of childhood hip problems, which would suggest a genetic predisposition to DDH.

• Disorders such as Larsen syndrome (a connective tissue disorder), torticollis (muscle spasm in the neck pulling the head to one side) and clubfoot (congenital in-turning of the feet) are all associated with an increased risk of DDH.

• Excessive swaddling of infants after birth can put pressure on the hip joint by forcibly extending the legs. It is advisable to avoid holding an infant's legs out straight for extended periods of time. However, this risk factor is thought to be less important than those listed above.

Implications

Instability of the hip leads to early development of osteoarthritis, a condition due to wearing of the joint cartilage that leads to stiffness, pain and loss of mobility. Although the degree to which DDH causes dislocations varies between children, it is difficult to determine which children are at risk of developing osteoarthritis. So, children with only mild instability may still be treated. While DDH detected early on can be treated simply by keeping the legs in a certain position (see below), untreated dysplasia can lead to gross damage of the hip and pelvis, and requires surgical correction.

Diagnosis

Screening at birth consists of inspection of the skin folds around the hips for asymmetry, comparison of the leg length, and manoeuvres to establish if the hips can be dislocated. A discrepancy in leg length or skin folds would suggest one hip joint is out of place. The manoeuvres used are Ortolani's⁴, which attempts to re-locate a dislocated hip, and Barlow's⁵, which attempts to dislocate a dysplastic hip⁶. Limited abduction (outward movement) of the hip is another sign of DDH, and may be noticed while performing the manoeuvres. Around six per 1,000 live newborns will have an abnormality detected during newborn screening, though some are missed and only a quarter of those with positive screens will actually have DDH.

Newborns suspected of having DDH are sent for an ultrasound scan of the hips. Some centres perform a scan on all newborns to discover abnormalities that are too subtle to be picked up by examination. However, universal scanning has a high rate of false positives and is expensive. Meanwhile, children with undetected abnormalities or acquired dysplasia may not present until later on when they start trying to walk. In these cases, an abnormal gait (manner of walking) or limp may be present. An ultrasound scan will then reveal the extent of the dysplasia. X-rays may also be used to demonstrate the presence of DDH.

Treatment

As there is no test to determine which infants will develop hip problems as a result of DDH, all babies with DDH are followed up with X-rays, and treatment provided if necessary. In infants, treatment consists of holding the hip in the abducted (flexed outward) position for six to 12 weeks. This places the ball in the socket and encourages proper development of the joint. In infants under six months, this can be done with a Pavlik harness, which is essentially a series of straps that run from the ankles up to the torso and hold the legs in the correct position. The Pavlik harness needs to be adjusted regularly as the child grows, and requires regular follow-up appointments, but may be sufficient treatment in some cases.

In those for whom splinting does not work, it may be necessary to hold the joint in place with a 'spica cast'. Traction or surgery may be required to put the joint in place before this is done. The spica cast runs from the chest down to the thighs or knees and is usually worn for three to six months, with the cast replaced when the child outgrows it. Physiotherapy may be required to strengthen the thigh muscles once the cast is removed.

In children who remain undiagnosed beyond two years of age, surgery is usually required. Osteoarthritis may develop later in life, eventually leading to the need for a hip replacement.

Prognosis

Prognosis depends on the severity of the hip deformity and the timeliness with which it is treated. The vast majority of cases detected within a few months of birth can be treated successfully using a harness to brace the legs, with surgery being necessary in only a few cases. In cases where DDH is not detected within the first year or two, surgery is more common and the risk of osteoarthritis and permanent damage to the joint is higher. However, most children have good outcomes and are able to lead normal lives.