Factors For Developing Osteonecrosis in Children with SCFE
Slipped capital femoral epiphysis (SCFE) is a condition that affects the hip in teenagers between the ages of 12 and 16 most often. Cases have been reported as early as age nine years old. In this condition, the growth center of the hip (the capital femoral epiphysis) actually slips backwards on the top of the femur (the thighbone).
If untreated this can lead to serious problems in the hip joint later in life. Fortunately, the condition can be treated and the complications avoided or reduced if recognized early. Surgery is usually necessary to stabilize the hip and prevent the situation from getting worse.
Even with treatment, there is a risk of developing a condition called osteonecrosis (death of bone). What causes osteonecrosis to occur? A little understanding of the anatomy of the child's hip will help explain this phenomenon.
In the growing child, there are special structures at the end of most bones called growth plates. The growth plate is sandwiched between two areas of the bone called the epiphysis and the metaphysis. The growth plate is made of a special type of cartilage that builds bone on top of the end of the metaphysis and lengthens the bone as we grow. In the hip joint, the femoral head is one of the epiphyses of the femur.
The capital femoral epiphysis is somewhat unique. It is one of the few epiphyses in the body that is inside the joint capsule. The joint capsule is the tissue that surrounds the joint. Here's the key to osteonecrosis developing: the blood vessels that go to the epiphysis run along the side of the femoral neck and are in danger of being torn or pinched off if something happens to the growth plate. This can result in a loss of the blood supply to the epiphysis and then death of the bone (osteonecrosis).
Why do some children develop osteonecrosis and others don't? And how often does this really happen? Reports in the medical literature range from 10 to 60 per cent. That's quite a broad range. To help answer some of these questions, pediatric orthopedic surgeons from The Children's Hospital of Philadelphia (CHOP) reviewed 70 of their cases to see what they could find out.
One unique characteristic that all 70 children had in common was an unstable slipped capital femoral epiphysis (SCFE). Unstable means they were unable to put any weight on the affected leg. The pain was so severe that even with crutches or other supportive aids, they were unable to walk.
By going back and reading the medical records and comparing children with unstable SCFE who developed osteonecrosis with those who didn't, they hoped to shed some light on this situation. They also compared the type of surgery performed and individual patient factors. Those factors included age, weight, how long symptoms were present before diagnosis, and length of time between diagnosis and treatment.
X-rays taken before surgery were used to measure two things: the slip angle and change in translation. These measurements helped give the surgeons an idea of how severe the slip was before surgery and how much reduction took place as a result of the surgery.
They quickly saw that the children fell into one of three groups based on the type of surgical treatment. Group one consisted of children who had the slipped epiphysis held in place with a screw. This procedure is called in situ screw fixation.
Group two had a closed reduction. Reduction means the slipped epiphysis went back into place. Closed tells us this happened without open surgery with an incision. Sometimes just positioning the hip in a certain way will reduce or realign the hip. This can happen while moving the child or placing him or her on the operating table.
And group three had open surgery to put the slipped epiphysis back in place and hold it there with a long pin (screw) placed through the bone. This procedure is called an open reduction and internal fixation (ORIF).
After looking over all the information collected and analyzing the data, they found three factors that might be significant. The first was age. Younger children with very little warning symptoms before the problem was diagnosed had a higher incidence of osteonecrosis after surgery. The second was severity of slippage at the time of diagnosis. It's likely that the more severe the problem and the greater the instability, the shorter the time before symptoms develop.
The third significant factor was the type of surgery that was done. Group two (closed reduction) had the largest number of cases of osteonecrosis (26 per cent). Group one (in-situ fixation) had the second highest incidence (19 per cent).
Group three (open reduction and fixation) had only one patient develop osteonecrosis. For all the children in the study, the more severe the slip was before surgery, the greater the risk of developing osteonecrosis after surgery. The overall incidence of osteonecrosis for the entire group (all 70 children) was around 20 per cent.
The authors agree with other experts that treatment for slipped capital femoral epiphysis should be done as quickly as possible. Parents (and patients who are old enough) should be advised about the risk of osteonecrosis after surgery.
The authors further note that more study is needed to evaluate the role of treatment type in the development of SCFE. Even with 70 patients enrolled in this study, it wasn't enough to generate statistically significant findings in some areas. They concluded that the true difference among their three groups with different treatment approaches wasn't as clear as if there had been more people in the study.
Reference: Wudbhav N. Sankar, MD, et al. The Unstable Slipped Capital Femoral Epiphysis. Risk Factors for Osteonecrosis. In The Journal of Pediatric Orthopaedics. September 2010. Vol. 30. No. 6. Pp. 544-548.