Some anatomy around the hip

The hip joint is a ball and socket joint. The 'ball' is the upper end of the femur (the thigh bone) and this sits in the 'socket' which is called the acetabulum. The acetabulum is part of the pelvic bone. Surrounding ligaments and muscles help to stabilise the hip joint.

The femur is the longest bone in the body. The area at each end of the femur (or any other long bone in the body) is called the epiphysis. Growth of the long bones of the limbs is a slow process and is usually not fully completed until about age 18 or 20 years. Whilst long bones are growing, the epiphysis is separated from the main part of the bone (called the shaft, or the diaphysis) by some cartilage known as the growth plate (epiphyseal plate).

Eventually, the epiphysis at each end fuses with the diaphysis to form a complete bone. In the femur, the epiphysis that is nearest to the hip is called the upper or capital femoral epiphysis.

What is a slipped capital femoral epiphysis and what causes it?

A slipped capital femoral epiphysis is exactly as you would expect. It is when the upper, or capital, epiphysis of the femur slips in relation to the rest of the femur. It tends to affect children in their adolescent period when they are rapidly growing. During this time, there is a considerable increase in the forces and stresses placed on the upper part of femur which can pull or twist it. If these forces are great enough, they can actually cause movement of the epiphysis, and the epiphysis slips. In children who are overweight or obese, an extra strain is put on the upper femur by their body weight and so slipped capital femoral epiphysis most commonly affects such children.

The slip can occur acutely (suddenly) or chronically (over a longer period of time). A chronic slip is much more common. Your child may complain of symptoms for weeks or months which can get worse as the slip progresses. An acute slip can happen after a fall or other injury and your child's symptoms will come on suddenly. They can be severe, and can mean that they are unable to put any weight on the affected leg. An acute on chronic slip can also occur if a chronic slip has already started and then a minor injury such as a fall causes the degree of slip suddenly to get worse.

In about 1 in 5 children with slipped capital femoral epiphysis the condition affects both femurs at the same time. Slipped capital femoral epiphysis is sometimes called slipped upper femoral epiphysis.

Note: some would say that the term slipped capital femoral epiphysis is actually a misnomer because the epiphysis does not actually move out of the acetabulum of the hip joint. It is held in there by a ligament. It is actually the rest of the femur that moves in the condition.

How common is it and who gets it?

A slipped capital femoral epiphysis is one of the most common reasons for a painful hip in an adolescent. Between 1 and 7 per 100,000 children will get a slipped capital femoral epiphysis.

As mentioned above, a slipped capital femoral epiphysis is more common in overweight or obese children. In fact, rates may be increasing due to rising levels of childhood obesity. However, it can also affect very tall and thin children.

It is three times more likely to affect boys than girls. It usually affects boys between the ages of 13 to 15 years and girls between the ages of 11 to 13 years.

Rarely, a slipped capital femoral epiphysis can occur in children with known hormone disorders (such as underactive thyroid gland, sex hormone problems, growth hormone problems), kidney failure, or in children who have had previous radiotherapy for cancer.

What are the symptoms of a slipped capital femoral epiphysis?

The symptoms can vary depending on whether the slip is acute or chronic. However, hip pain is usually the main symptom.

In an acute slip, pain in the hip is so severe that your child is unable to walk or stand. You may notice that one leg seems shorter than the other. Movement of their hip will be difficult and painful. You may notice that their leg is turned outwards.

In a chronic slip, symptoms tend to be more mild and come on gradually. Pain, which your child may describe as groin pain, is usually felt in the affected hip. But sometimes in a chronic slip, pain can be felt in the knee or lower thigh rather than the hip. That is, the pain is 'referred' along nerves from the hip to the knee or the lower thigh. This can sometimes be misleading and, in some cases, the diagnosis of slipped capital femoral epiphysis can be missed and the symptoms put down to a knee problem. Your child will still be able to walk but you may notice a limp and walking may be painful. Pain can be made worse by running, jumping or other activities. Your child may complain of stiffness in their hip joint. Again, the leg on the affected side may appear shorter. You may also notice that the muscles in your child's thigh start to waste (become less strong and look less bulky) if they have a chronic slip.

In an acute-on-chronic slip, your child will usually have complained of pain and may have been limping for several months. Then a minor injury such as a fall suddenly makes the hip become very painful as the degree of slip is made worse.

As mentioned above, in most children, only one hip is affected. But, some children have symptoms due to a slipped capital femoral epiphysis affecting both hips.

How is slipped capital femoral epiphysis diagnosed?

Your doctor may suspect that your child has a slipped capital femoral epiphysis because of their typical symptoms and their age or other risk factors. Your doctor will then usually examine your child's leg, including their hip and their knee. They will notice reduced and painful movement of the hip if your child has a slipped capital femoral epiphysis.

X-ray is the main investigation that is used for diagnosis. Both hips should be X-rayed and the slipped capital femoral epiphysis can be seen. CT scanning may sometimes be used.

If complications such as avascular necrosis are suspected (see below), an MRI scan or a special bone scan may be suggested.

What is the treatment for slipped capital femoral epiphysis?

A child who is found to have a chronic slipped capital femoral epiphysis is usually admitted to hospital so that they can have complete bed rest. This helps to avoid any acute-on-chronic slip. Also, an operation is usually advised to stabilise the slipped epiphysis and to prevent it from moving any more. Usually, a pin or a screw is used to hold the epiphysis in place. Sometimes, a doctor may suggest that the unaffected hip be stabilised with a pin or a screw at the same time. If there has been a more serious slip, more major surgery may be needed.

Acute slips need to be treated urgently. Again, a pin or a screw can help to stabilise the slipped epiphysis but sometimes more complex surgery is required.

Are there any complications?

If a chronic slipped capital femoral epiphysis is diagnosed and treated promptly, complications are less likely to occur. However, sometimes complications are possible after a slipped capital femoral epiphysis.

One complication is avascular necrosis. This is where the blood supply to the head (the ball) of the femur is damaged due to the slipped epiphysis. This most commonly happens after an acute slip. It can also sometimes be a complication of surgery. Your child will usually complain of pain in their groin or knee and they will have a reduced degree of movement of their hip. Crutches are usually suggested so that the weight is taken off your child's affected leg. Physiotherapy and painkillers may also help. In severe cases of avascular necrosis, either fusion of the bones around the hip joint or a hip replacement may be needed.

Chondrolysis is another potential complication of slipped capital femoral epiphysis. This is where there is necrosis (death) of articular cartilage of the affected hip joint. Again, this can be a complication of surgery. Treatment is similar to that for avascular necrosis.

What is the prognosis (outlook)?

The key to the best outlook for slipped capital femoral epiphysis is to detect a chronic slip before an acute-on-chronic slip occurs and to treat it. This is because an acute slip has a worse outcome. There is an increased risk of the complication of avascular necrosis.

If a chronic slip is treated early and the epiphysis is stabilised, the outcome is generally very good and there are unlikely to be long-term effects. However, if a slipped capital femoral epiphysis is not diagnosed and treated, it can lead to persistent pain, deformity and also early osteoarthritis around the hip.

Once you have had a slipped capital femoral epiphysis on one side, it is possible to have one on the other side in the future. This is why some orthopaedic surgeons advise pinning or screwing of the epiphysis on the other, unaffected, side at the same time as treatment for a slipped capital femoral epiphysis.

Can a slipped capital femoral epiphysis be prevented?

Weight control in children may help to prevent a slipped capital femoral epiphysis to some extent.