Slipped Capital Femoral Epiphysis
What is Slipped Capital Femoral Epiphysis?
Slipped capital femoral epiphysis is a condition of the hip that usually affects adolescents, in which the head of the femur (the thighbone), which acts as the ball that normally sits in the socket of the hip joint, becomes displaced slightly from the rest of the bone. As a result, a child or adolescent may experience mild to moderate pain in the hip and thigh region, and can develop a limp. While the cause of the condition is unknown in most cases, it has a very strong association with obesity. Abbreviated as SCFE, slipped capital femoral epiphysis does not significantly debilitate patients, but does generally necessitate preventative treatment measures, due to the significant risk of hip arthritis in untreated cases. However, unlike previous decades, the various treatment modalities utilized today are quite effective at preventing worsening of the condition and allowing patients to avoid any functional limitations in the future.
Some basic facts about SCFE
- Slipped capital femoral epiphysis is fairly common, compared to most musculoskeletal conditions, and affects between 2 and 10 adolescents per every 100,000 in the U.S.
- The incidence of SCFE is higher than normal in children with the following characteristics, known as risk factors:
- Male sex (around 60% of cases occur in boys)
- Obesity (most children who develop SCFE are significantly overweight, or obese, and the more obese a child is, the more likely they are to develop the condition at a younger age)
- Pacific Islanders (have the greatest prevalence of SCFE of any ethnic group or geographical region)
- African-Americans (the condition is around twice as common in black children than white children)
- SCFE usually affects children between 9 and 16 years-old, with an average age at the time of diagnosis of 13-14 years-old in boys and around 12 years-old in girls.
- Between approximately 20% and 60% of SCFE patients will develop the condition bilaterally, meaning that both hips will be affected, either at the same time or, less commonly, at different times in adolescence. For unknown reasons, bilaterality is more common in blacks than whites, Hispanics, or Asians.
- A few rare factors have been identified as causes of a small portion of cases of SCFE, such as the kidney disease renal osteodystrophy, a history of radiation therapy (used as treatment for some pediatric cancers), and several endocrine (i.e. hormonal) disorders. However, the vast majority of cases are considered idiopathic, which means it is not understood what initially causes the condition. Idiopathic SCFE will be the focus of this summary.
The Normal Hip
The hip joint, like all joints, is the connection point between 2 bones – in this case, the femur and the pelvis. The femur is the longest bone in the body, with a shaft that begins at the knee and runs into the very upper part of the thigh. The femoral neck is essentially a thick branch that extends, at an angle of about 125 degrees, off of the end of the shaft in an area called the trochanteric region. The neck also connects the shaft to the femoral head, which is the femoral portion of the hip joint.
The hip’s unique combination of structural features permit the transmission of tremendous forces (including the weight of the body) between the pelvis and the lower extremity, while still allowing for an extensive range of motion. The largely spherical head of the femur sits in an area of the pelvis bone, called the acetabulum, which acts as a smooth, cup-shaped socket. There is a joint capsule that sits around the joint and is made up of a series of ligaments, thick fibrous structures found throughout the musculoskeletal system that attach bones to other bones. This capsule surrounding the joint insures that the ball remains snugly in the socket, throughout the movements of the upper legs. Smooth, slippery cartilage at the center of the socket and at the tip of the ball, as well as a thin layer of the body’s natural lubricating material, called synovial fluid, allow the two bones to slide past each other, much like a well-greased ball bearing.
Like all long bones in the human body, the femur does most of its growing not in the middle but towards the ends of the bone during childhood, in a region of the bone known as the growth plate, or physis. The physis separates the region at the end of the bone, called the epiphysis, from the region where the bone begins to splay outwards from the thin shaft into the larger end, called the metaphysic. The upper metaphysis of the femur is located in the femoral neck. The epiphyseal-metaphyseal region is the site of the problem in SCFE.
What Causes Slipped Capital Femoral Epiphysis?
While the mechanism behind the development of SCFE is fairly well understood, the factors initially triggering this mechanism remain idiopathic, or largely unknown. Most likely, a variety of different factors may be involved in the weakening of the region of bone at the top of the femur, which eventually becomes displaced. Interestingly, slipped capital femoral epiphysis is somewhat of a misnomer, because the physis is the primary site of weakening, which causes the metaphysis and the neck of the femur to slip upward and outward, while the femoral head (epiphyseal region) remains snugly in the socket (see Figure1). A number of hypotheses have been proposed to explain this phenomenon, and they range from biomechanical to biochemical. Because obesity is the strongest risk factor for SCFE, it is believed that the child’s increased weight creates excessive mechanical stress on the growing femur over time, and the metaphysis becomes the center point of this stress and the weak point in the upper thigh. Studies have also shown that obese children have a slightly different angle of rotation in their femurs, which predisposes them to SCFE as well. Other research has demonstrated that the acetabulum of the hip joint, described above, is a deeper socket, so to speak, in children with SCFE, which would cause the femoral head to become more tightly fixed in the socket and transmit more force to the metaphysic. The weakening of this region also likely stems from changes in the makeup of the bone due to hormones. The fact that the condition tends to occur around the time of puberty, and is more common in males than females, supports the idea that natural gonadotropin hormones like testosterone contribute to the weakening of the metaphysic. Despite the growing amount of scientific evidence for these and other hypotheses, the precise factor or combination of factors responsible for SCFE have yet to be firmly established. Research at various academic medical centers throughout the country continues to investigate SCFE in an effort to improve treatment and prevention of this prevalent condition.
How is it diagnosed?
Diagnosis of slipped capital femoral epiphysis involves taking a close history from the patient about the onset of symptoms, performing a comprehensive physical exam, and getting x-rays of the hip. In most cases of SCFE, symptoms become apparent gradually during adolescence, and may consist of pain in the upper thigh, knee or groin area, a limp, or leg weakness. These symptoms may arise or worsen as a result of exercise, or even standing or walking for a length of time. Onset of SCFE may alternatively be acute, in which the symptoms arise more suddenly, in less than 3 weeks. Physical examination often reveals that the leg cannot be rotated outward easily, or may be slightly shorter than the other leg. Definitive diagnosis of SCFE involves x-rays of the hip, and several cardinal radiographic signs of the condition will be recognized by an orthopaedic surgeon. In rare instances, x-rays do not allow for precise enough imaging, and other techniques, such as MRI, bone scan, and even CT scan, can aid in the diagnosis of SCFE and help prevent complications.
How is it treated?
If SCFE has been diagnosed, the primary goal of treatment is to prevent any further slipping or displacement in the head of the femur. While bilateral hip spica casts have been used in the past to immobilize the affected hip and to prevent SCFE in the (contralateral) hip on the other side, recent studies have shown that the results of this conservative form of treatment are inferior to surgical treatments and are associated with greater complication rates. Therefore, operative measures are generally pursued following the diagnosis of SCFE, rather than the use of an immobilizing cast. In most cases, a procedure called in-situ pinning is pursued, in which a single screw is inserted into the hip without making a major incision or opening. This screw is placed so as to extend up the length of the femoral neck and into the femoral head, thereby stabilizing the previously displaceable epiphysis. In rare, more severe cases, a more significant surgery may be warranted to attempt to correct a deformity that results from SCFE. These may include an osteotomy, in which a small wedge of bone in the femoral neck is removed, so as to re-align the hip joint properly, or an epiphysiodesis, in which is bone graft is attached to the femoral neck to secure and maintain its position. In general, in-situ pinning has excellent results with low complication rates.
Coping with SCFE
Slipped capital femoral epiphysis may arise suddenly, in an acute event, in some children, or symptoms may take their effects gradually in others. In either case, SCFE can represent a difficult challenge for adolescents and their parents, and surgery at such an age can naturally be unsettling for some people. However, the treatment for SCFE is very successful at returning adolescents to the high-functioning, active state they were in prior to the onset of the condition. Additionally, for children whose obesity may have contributed to the development of SCFE, the condition can serve as a positive signal for them to try to better maintain their weight and to lead a healthier lifestyle, both in terms of diet and activity, a step that will benefit them through adolescence and into adulthood.