Hip dysplasia explained

Paediatrician Anne Tait explains what creases, clicks and clunks mean to the health of your baby’s hips.

From the moment your baby is born, it can seem like there is a fascination amongst your medical care team with the creases and clicks around your baby’s hips. All newborns should have their hip rotation checked and then your Plunket nurse will continue to screen and monitor creases around your baby’s hip and buttock area. Hip creases (specifically mismatched creases) can cause a great deal of worry, but it's often not made entirely clear why they are important to a baby’s health. 

The hip joint is made up of a ball and socket; the femoral head of the thigh bone (femur) is the ball and the acetabulum of the pelvis is the socket. Loose ligaments around the joint can allow for misalignment to occur. The hip joint is referred to as ‘displaced’ when the ball and socket do not fit together in their ‘normal’ position.

What’s in a name?
Developmental dysplasia of the hips (DDH) is also often referred to as clicky hips. It used to be called congenital dislocation of the hip (CDH), which was a term parents found easier to understand. However, it is technically inaccurate and was previously a good source of revenue for lawyers suing doctors in America. The more accurate term is DDH, which indicates that this is a developmental condition and there is abnormal development (dysplasia) of the hip or hips that develops over time and might not be apparent at birth.

Why does it happen?
DDH is due to abnormal growth of the hip, but what actually causes that is uncertain. What is known is that there are various risk factors:

● Breech position (there are higher rates of DDH for vaginal birth compared with Caesarean birth)
● Family history of DDH
● Gender (girls are about four times more likely to have DDH)
● Large birth size (bigger than 5kg)
● Other risk factors include oligohydramnios (deficiency of amniotic fluid during pregnancy), torticollis (a condition causing a tilted head or twisted neck), and other developmental conditions (such as cerebral palsy and spina bifida).

The occurrence of DDH is approximately one in 1000 but can vary between 1% and 3% of the population depending on definitions used. For children with a risk factor, the approximate rate of DDH is one in 75. So the key to early diagnosis is knowing a full medical history and also careful examination with imaging done at the right time, and by the right practitioners.

Let’s examine
While assessment of hip creases is routinely done by Plunket, crease checks alone aren't conclusively accurate with approximately 25% of children having asymmetric creases.

There are specific hip examinations that should be done at birth and then at regular Well Child checks. The Ortalani and Barlow tests are best in children younger than three months. The tests try to dislocate an unstable hip and then relocate it back in. There are particular sounds and feelings that are characteristic of DDH and can be picked up in these tests. While DDH is referred to as ‘clicky hips’, the sound that indicates a problem is more like a clunk.

After three months of age, the tests of Galeazzi and hip abduction in flexion (bending and flexing) are more reliable. These are testing for leg length discrepancy (Galeazzi) and limited movement. All of these tests need to be done by experienced practitioners who know what they are testing for and how to do the tests correctly.

Either ultrasound or hip x-rays can be used for diagnostic testing of children with one or more risk factors and/or an abnormal hip examination. The hip ultrasound prior to six weeks of age is prone to false positive results, so should be done after this age. It is also operator-dependent, so should be done by ultrasonographers practised in scanning hips of young children. Hip x-rays are done after four months of age. The reason for this delay is that a specific part of the hip anatomy (the femoral heads) do not appear until three months of age.

Screening for DDH at birth has been the subject of controversy, as is the case with screening for various other conditions. The main issue is the rate of over-diagnosis (false positives) and the lack of prevention of late complications by screening. The reason for over-diagnosis is that newborns' hips can be unstable because of soft tissue laxity, but there is a high rate of spontaneous resolution as the soft tissues tighten. Therefore screening at birth would pick up babies whose ‘unstable’ hips would have spontaneously improved within a few weeks and would not require treatment.

However, in those babies whose hips are unstable or dislocated, soft tissue contractures can occur, with associated anatomy changes, if their hip issues aren't corrected. Experts now agree that a combination of both identification of risk factors and examination should be used to identify imaging required (ultrasound or x-ray) for those babies with suspected hip instability after six weeks of age.

Treatment options
DDH is managed by paediatric orthopaedic specialists. The aim of treatment is to prevent premature degeneration of the hip, and avascular necrosis (AVN), which is death of the hip tissue. Early detection is important, as the risk of AVN is 2% for children referred when younger than six months of age, but 10% if referred when older than six months of age.

There are various options but the main aim of treatment is to relocate the femoral head (ball of the hip) into the hip socket. This can be done through various means including:

● Pavlik harness – a device which holds the hip(s) in place as the child’s hips mature and grow. Most babies wear the harness for only three months.

● Closed or open reduction (in other words, a surgical repair).

In summary, DDH is an important preventable cause of premature degeneration of the hip as a result of unstable or dislocated hips. Effective screening can be done through imaging (ultrasound or x-ray) of those with a positive history and/or abnormal examination. This goes a long way to pick up babies with dislocated hips in a timely fashion and enable early successful treatment.

Dr Anne Tait is a general paediatrician employed at Starship Children’s Hospital who also works in private practice at Auckland Medical Specialists. She has an interest in all areas of children’s health and wellbeing.

Disclaimer: Dr Tait has no financial or any other relationships with any manufacturers of medical products or pharmaceutical companies either currently or in the past. Dr Tait only receives remuneration from her public and private practice.

References
●  Hip problems from infancy to adolescence, David L Skaggs,  Clinical Pearls conference, July 2016
●  Developmental dysplasia of the hip, http://emedicine.medscape.com/article/1248135
●  BMJ 2009; 339:b4454. Clinical Review - Developmental dysplasia of the hip.