Developmental Dysplasia of the Hip
What is Developmental Hip Dysplasia?
Developmental hip dysplasia or DDH is actually a spectrum of disorders that can affect the growth and maturation of a baby’s hip joints. The hip is a ball and socket joint, with the ball at the top of the thigh bone and the socket at the side of the pelvis. When the socket is shaped like a cup, the ball is held firmly and the hip joint is stable. However in some children the cup is shaped more like a saucer, and because the socket is not as deep the thigh bone is not held as securely. This leads to a risk that the hip might dislocate (slip out of the socket) and grow in an abnormal position.
The reason DDH is described as a spectrum is because the risk of dislocation can vary greatly between babies. For some the joint may just be a little bit more lax, or the hip may partially dislocate; but in more severe cases the hip may come out of its socket taking with it some of the joint tissue, which then blocks its return. Although hip dislocation is extremely painful for an adult, DDH dislocation is not painful for a baby; but it is important to treat the condition in order to avoid problems later in life such as osteoarthritis.
When joints are developing, it is important that the bones are in the right place not only for movements and activities; but also for the development of the bones themselves. The hip socket is moulded by its contact with the top of the thigh bone and the weight that goes through this area when a child learns to walk. As the socket shape is different in DDH, without treatment the weight-bearing surfaces are not in their normal location and therefore bones may grow abnormally. Treatment therefore aims to reunite the bones in their correct position and hold them there long enough for normal growth to stabilise the joint.
During a newborn baby check, the doctors do some tests to ensure that the hips are stable. These are repeated at the GP surgery when the baby is 8 weeks old. Between 5 and 20 of every 1000 newborn babies will be found to have some instability. Most of this instability will resolve within a few weeks and the baby’s hips will develop normally. If resolution has not occurred however, the baby will require some treatment.
Signs of DDH in newborns can vary, but the most common is limited abduction (the movement of the baby’s legs out to the side) which might be noticed during nappy changes, and can sometimes be accompanied by a clunk sound. It may also be noticed that one buttock crease is noticeably higher than the other side.
In rare cases, hip instability develops later and so may not be picked up at the newborn check. Some of the signs in toddlers and children are similar to those in newborns i.e. limited abduction with clunking sounds and buttock crease asymmetry. In addition one leg may be slightly shorter than the other causing a limp, and the walking pattern may look like a waddle with an exaggerated curve in the lower spine (swayback). It is important to note that DDH at this age is still extremely unlikely to be causing pain, it is also unlikely to delay the baby’s first steps.
What is the likelihood of Developmental Hip Dysplasia?
Around 8 in every 10 patients with DDH are female. There is increased likelihood if someone in the family has had a childhood hip disorder, or if the baby was in a breech position during the last month of pregnancy/born breech. For the majority of cases however, the reason for DDH is unknown.
The likelihood of DDH can also be affected by the position baby is in after they are born. Swaddling a baby keeps their legs straight and together, and may increase the risk of DDH. Once they’re old enough to be in a sling, using one that keeps their legs apart facilitates hip development in the correct position.
What are the Risks of Untreated Developmental Hip Dysplasia?
In untreated DDH, the initial symptoms i.e. limited movement, leg length differences and limp will persist. In addition although for young children DDH is extremely unlikely to cause pain, if untreated it can cause hip pain later in adolescence and adulthood. The pain may be located around the hip, lower back or knees due to the adapted walking style.
There is also a risk of early onset Osteoarthritis in the affected hip because the irregular joint surfaces are predisposed to accelerated wear and tear.
Managing DDH at this stage is much more complex, often requiring surgery, and in some cases joint replacement.
If a baby is found to have hip instability during their newborn or 8 week GP check, they will be referred for an ultrasound scan of the hips and the opinion of a specialist paediatric orthopaedic surgeon. The ultrasound scan allows the surgeon to see the position of the hip joint, and whether the bones are developing correctly. If the ultrasound scan is reassuring and the hip joint looks normal no treatment is needed but the baby may have a later follow up appointment. If the hip is not in the correct position and/or the bones are not developing as expected then treatment is required.
If DDH is not diagnosed until a baby is 6 months or older, Xrays are used to assess the hips.
For babies 6 months or younger:
The aim of treatment is to make sure the hip is in the correct position and to keep it there whilst baby grows enough for the joint to stabilise. To achieve this, a device called a Pavlik harness is most commonly used. This is a harness made from soft fabric straps that go around the baby’s shoulder’s, chest and legs. The soft nature means the infant can still move around, and because the device is made of straps it is still possible to change nappies as this area is left free.
Pavlik harnesses hold the baby’s legs so the hips are flexed and abducted (held out to the side) as this is the best position to stabilise the hips and allow them to develop normally. The device will be fitted either by the paediatric orthopaedic surgeon or a specialist physiotherapist, and may be adjusted at subsequent appointments depending on how much the baby has grown. At some of these appointments, additional ultrasound scans are carried out to check that the treatment is working.
The harness is usually required for 3 months, but this can vary depending on scan results. It is taken off for short trial periods once the hip/hips are more stable and treatment is nearly finished, but this must only be done under the guidance of the surgeon. It can be a difficult time, as wearing the harness may affect some day to day activities for example bathing. However, the benefit of treatment considerably outweighs the risk of complications as almost all babies who wear a Pavlik harness for the recommended time recover completely and have no issues later in life.
For babies over 6 months:
After 6 months of age Pavlik harnesses can no longer be used, and as the condition has likely been present for longer the treatment is more complex, often requiring surgery.
For children under the age of 4, the hip may be manipulated back into place under a general anaesthetic, this does not require any invasive surgery and is therefore referred to as a closed reduction. Following the procedure a hip spica cast is applied. This cast holds the hips in a similar position to a Pavlik splint, however it fully covers the child’s lower abdomen and both legs and does not permit any movement. Toileting is not affected however, as this area is left free. The cast is usually worn for a total of 3 months.