Hip dysplasia is not just one entity. It is a wide spectrum of disease, ranging from mild hip instability to long standing hip dislocation. Hip Dysplasia means malformation of the hip joint. Hip Instability, which is also discuses here refers to abnormal motion of the hip within its socket. The treatment of hip dysplasia and instability is varied and depends on the severity of the problem and the age of the child.
The hip is a ball and socket joint. The ball is the femoral head and the socket is the acetabulum. Both the ball and the socket must be in the proper orientation to each other for the hip joint to form correctly.
The outer edge of the acetabulum is very soft growing bone. If the femoral head is unstable, (can move within the socket) it will push on the outer edge of the socket and bend it up, causing the socket to become more shallow. A shallow socket allows more instability creating a shallower socket and so on until the ball can dislocate from the socket all together. In this way, hip instability will lead to hip dysplasia if left untreated over time.
On the left is an x-ray showing this childs right hip is dislocated. The 3-D reconstruction CT scan on the right allows you to better appreciate how far the femoral head is from the hip socket.
The cause of hip dysplasia is often multifactoral. Hip dysplasia is more commonly diagnosed in girls than boys, in left hips then right, in first born, and in families where previous children were born with hip dysplasia.
The incidence of hip instability is higher immediately after birth then in infants four weeks old. Newborns have some level of maternal hormones circulating in their bloodstream for a few weeks after birth. Some of these hormones, especially estrogen and relaxin, help loosen the ligaments around Moms pelvis allowing for babys delivery. These hormones also loosen the infants ligaments which can lead to hip instability. After a few weeks, maternal hormones are no longer found in the infants bloodstream and any hip instability caused by them should resolve without treatment. The hip instability in these infants does not go on to create hip dysplasia.
Hip instability or dislocation is primarily diagnosed by physical examination and the hip exam is part of all well baby examinations done by pediatricians. The his are stressed to see if there is any instability or if the hip is dislocatable.
This is an x-ray of a child with left hip dysplasia. This x-ray points out some of the things we look for when evaluating an x-ray for hip dysplasia. Shentons line is pictured on both sides. Notice how Shentons line seems to be almost a continuous curve on the left side of the image but does not line up on the right side of the image. A broken line is a sign of hip dysplasia. The acetabular index is a measure of the slope of the hip socket. Lower numbers mean a deeper and more developed socket. The socket on the right side of the image is dysplastic
Recent advances in the use of ultrasound has greatly improved our ability to diagnose and document improvement of hip instability. Using ultrasound, the hip can be imaged while being put thru a range of motion and stressed, so we can see the instability as it is happening.
These ultrasound images demonstrate a hip that is stable and one which is unstable. The femoral head is represented by the circle and the pelvis is represented by the straight line. The straight line should be at the middle of the circle. Notice on the right image that the circle is higher so the straight line would pass thru the bottom of the circle. This femoral head is able to slide partially out of its socket and is unstable.
This ultrasound image shows the femoral head (circle) to be completely dislocated from its socket.
The treatment of hip instability depends on the age of the patient. There are two goals we want to achieve. The first goal is to make the hip stable and the second goal is allow the hip to remodel (regain a normal shape). The younger the child the more remodeling potential the hip has. Older children (>18 months) may require surgery to normalize the shape of the socket.
The goal for treating hip instability and dysplasia is to ensure the hip develops normally. Even mild hip dysplasia has been shown to be a major predisposing factor to the development of degenerative arthritis in adults.
Treatment for children less than six months old usually involves using a Pavlik Harness which is a strap and buckle device which holds the ball of the hip joint deep in the socket by flexing the hip up and allowing the leg to abduct (open to the outside).
The harness, as pictured above, is usually worn for a period of eight to twelve weeks. After the harness is placed, we obtain an ultrasound of the infants hips in the harness to check their stability. If the hips are stable, we continue having the infant wear the harness full time for at least another six weeks to allow remodeling. If the instability persists, we continue the harness and repeat the ultrasound in two to three weeks to check stability. We should be able see some improvement of the hip with harness treatment in three to four weeks.
The harness is well tolerated by the infants, but requires a little getting used to by the parents. It is worn full time, so the parents have to sponge bath the children while they are in the harness. The harness is very safe to use if it is applied properly and fits correctly. If the harness is too tight, it can potentially damage the femoral head or the femoral nerve. We see the infants that are in a harness every two to three weeks to check the fit of the harness and adjust it as needed.
If the child is older then six months old when diagnosed, the harness is not well tolerated. These children are treated with a closed reduction of the effected hip or hips. This means that under anesthesia the ball is placed in the socket and is held there using a spica cast. For information about spica cast care, click here. Often lengthening of some muscles around the hip are lengthened in order to allow the ball to sit in the socket with no stress upon it. The cast may be needed for three months or longer. Often, an abduction brace is needed after the cast until the hip is fully remodeled.
Children older then one year at the time of diagnosis or children, in whom, the closed reduction is not satisfactory, require an open reduction of the effected hip or hips. This means that the the hip joint is surgically opened and all impediments to hip reduction are removed so the ball can rest in the socket without any stress on it. The child is placed in a spica cast for at least six weeks and then wears the hip abduction brace until the hips are fully remodeled.
Children older then eighteen months do not have a lot of remodeling potential left. Their hip sockets will often remain shallow, even if the ball is properly positioned by using the treatments outlined above. There are a wide variety of osteotomies, which involve cutting the pelvic or femur bones, that can be performed to help the hip socket normalize its shape.