A slipped capital femoral epiphysis is a condition in which the epiphysis over the head of the femur slips outward and backwards, putting the hip joint in outward rotation and altering the relation of the femoral neck and head.

The slip may be acute or chronic, and occurs through the growth plate. It usually takes place during the growing years, from 12-16 years in boys and 10-14 years in girls. The overall incidence of SCFE in the US is 10.8 out of 100,000 children. Boys are more frequently affected, with 13.3 out of every 100,000 boys developing the condition compared to approximately 8 out of 100,000 girls.

Risk factors

The etiology of SCFE is not yet known, but the following factors are thought to increase the risk. It is noteworthy that all of them lead to reduced shear resistance or higher stress across the proximal growth plate of the femur, so that any force acting in the right direction results in pushing the femur head and neck apart across the cartilaginous plate.

1. Obesity: Children, especially boys, whose body mass index is above the 95th percentile for their age and sex, account for 80% of the cases. This may be due to both increased loading on the femoral head and the associated metabolic conditions. In addition, femoral anteversion is also reduced and the growth plate is more vertical in these children. All these reasons underlie the link between the rising prevalence of obesity worldwide and the increasing incidence of SCFE.
2. Rapid growth: This contributes to the risk of SCFE in obese children because of the rapid increase in body weight over a short period that is typical of pre-puberty, and which may overwhelm the load-bearing capacity of the physis.
3. Femoral retroversion: A femur which is retroverted, or twisted more laterally than normal, is more likely to undergo SCFE than a normal femur.
4. Ethnic factors: SCFE is almost 4 times more common in African-Americans, and more than 2.5 times more common in Hispanics, than in Caucasian children.
5. Medication: Certain drugs including steroids may adversely affect bone health and may lead to slippage of the epiphysis.
6. Radiation: Radiotherapy can increase the risk of SCFE.
7. Metabolic conditions: Children with hypothyroidism or with diabetes mellitus are at greater risk for SCFE. Renal failure with osteodystrophy can also predispose to this condition. A metabolic cause may be sought if the child with SCFE is less than 10 years old, or has a body weight which is below the 50th percentile.
8. Trauma: The unstable form of SCFE , when the individual is unable to put any weight on the affected hip, is often preceded by a fall or minor injury which may not seem to be very severe.
9. Family history: Having other family members who had SCFE may increase a person’s risk of developing the condition.
10. Climatic and seasonal factors: One study has also suggested that there is seasonal variation in the incidence, with a rise in cases north of 40 degrees latitude during the summer and south of this line during the winter. Geographically, the northeastern and western parts of the USA have a higher incidence than the midwestern and southern states.

Mechanism

SCFE arises because of the forces that act on the growth plate. It occurs as a result of weakness in the hypertrophic zone of the growth plate cartilage which allows the neck of the femur to move forward and rotate externally, while the epiphysis remains in the acetabular cavity.

References

1. Medline Plus, Slipped capital femoral epiphysis, https://medlineplus.gov/ency/article/000972.htm
2. Slipped Capital Femoral Epiphysis: Prevalence, Pathogenesis, and Natural History, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3492592/
3. SCFE: clinical aspects, diagnosis, and classification, http://online.boneandjoint.org.uk/doi/pdf/10.1302/1863-2548-11-170025
4. Cleveland Clinic, Slipped Capital Femoral Epiphysis, https://my.clevelandclinic.org/health/articles/slipped-capital-femoral-epiphysis
5. University of Rochester Medical Center, Slipped Capital Femoral Epiphysis in Children, https://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=90&ContentID=P02782
6. Slipped capital femoral epiphysis, https://www.schn.health.nsw.gov.au/files/factsheets/slipped_capital_femoral_epiphysis_scfe-en.pdf
7. OrthoInfo, Slipped Capital Femoral Epiphysis, http://orthoinfo.aaos.org/topic.cfm?topic=a00052
8. The Epidemiology of Slipped Capital Femoral Epiphysis: An Update, http://journals.lww.com/pedorthopaedics/Abstract/2006/05000/The_Epidemiology_of_Slipped_Capital_Femoral.2.aspx