Background: The outcome of stable slipped capital femoral epiphysis
is directly related to the severity of the slip. If it is assumed that the
slip will be less severe if it is diagnosed early, then early diagnosis should
improve the prognosis. It was our purpose to determine demographic predictors
of the severity of a slipped capital femoral epiphysis.
Methods: A retrospective study of 243 children with a total of 328
stable slipped capital femoral epiphyses was performed. Gender, race, age, and
symptom duration were noted. Slip severity was classified as mild
(<30°), moderate (30° to 50°), or severe (>50°).
Statistical analyses included bivariate, multivariate, linear correlation, and
logistic regression techniques.
Results: There were 159 boys and eighty-four girls; 149 children had
unilateral and ninety-four had bilateral slipped capital femoral epiphysis. Of
the bilateral slips, forty-two were simultaneous and fifty-two were
sequential. The mean age (and standard deviation) was 12.6 ± 1.8 years,
the mean duration of the symptoms was 5.2 ± 7.4 months, and the mean
slip angle was 29° ± 20°. There were 199 mild, sixty-eight
moderate, and forty-five severe slips. The mean duration of symptoms was 3.5
± 5.0 months for the mild slips, 7.7 ± 9.0 months for the
moderate slips, and 8.8 ± 10.6 months for the severe slips (p <
0.0001). Older children had more severe slips: the average age was 12.3
± 1.8 years for the children with a mild slip, 13.0 ± 1.6 years
for those with a moderate slip, and 13.8 ± 1.8 years for those with a
severe slip (p < 0.0001). Multivariate analyses demonstrated that, among
the factors studied, only the age of the patient and the duration of the
symptoms were associated with the slip severity. Symptom duration and patient
age were used as predictors of slip severity in a logistic regression
analysis, with =30° and <30° used as the categories for slip
severity, older than 12.5 years old compared with 12.5 years old or younger
used as the categories for age, and more than 2.0 months compared with 2.0
months or less used as the categories for symptom duration. This model
predicted the probability of a slip with confidence (p < 0.0001). The odds
ratios (with 95% confidence intervals) for age and symptom duration were 2.0
(1.15 to 3.53) and 4.1 (2.34 to 7.12), respectively. Thus, a child with a
stable slipped capital femoral epiphysis is 2.0 times more likely to have a
moderate or severe slip if he or she is older than 12.5 years of age at the
time of the diagnosis and 4.1 times more likely to have a moderate or severe
slip if the duration of symptoms was longer than two months.
Conclusions: The only two known significant predictors of the
severity of a slipped capital femoral epiphysis are age at diagnosis and
symptom duration. For any individual child, slip severity and symptom duration
are unique; in a large population, there is a general correlation between slip
severity and increases in patient age and increases in the duration of
symptoms.
Level of Evidence: Prognostic Level II. See Instructions
to Authors for a complete description of levels of evidence.