Background: The age-weight test was described to aid the clinician
in defining demographic predictors of an atypical slipped capital femoral
epiphysis. We wished to retest the accuracy and applicability of the
age-weight test and height differences in children with atypical and typical
slipped capital femoral epiphyses.
Methods: A retrospective review of the records for all children with
slipped capital femoral epiphysis from 1998 through 2003 was performed.
Gender, race, chronological age, weight, height, the duration of symptoms, and
the laterality of the slip were recorded. The slip angle was classified as
mild (<30°), moderate (30 to 50°), or severe (>50°).
Statistical analyses were performed.
Results: The study included 105 children (thirty-eight girls and
sixty-seven boys) with 141 slipped capital femoral epiphyses; ten children had
fifteen atypical slipped capital femoral epiphyses, and ninety-five children
had 126 typical slipped capital femoral epiphyses. Sixty-nine children had
unilateral involvement, and thirty-six had bilateral involvement. The average
age at the time of presentation for the first slipped capital femoral
epiphysis was 12.1 ± 2.0 years. The average duration of symptoms was
3.7 ± 5.5 months. In the group of 128 slipped capital femoral epiphyses
for which the slip angle was known, there were ninety-three mild, twenty-seven
moderate, and eight severe slips. The average slip angle was 24° ±
18°. The age-weight test demonstrated a sensitivity of 50%, a specificity
of 89%, a positive predictive value of 33%, and a negative predictive value of
94%. The age-height test, involving the same definition as the age-weight test
except that the percentiles apply to height and not weight, demonstrated a
sensitivity of 88%, a specificity of 73%, a positive predictive value of 30%,
and a negative predictive value of 98%. The height test, which was defined as
positive if the child's height was at or below the tenth percentile for age
and as negative if it was above the tenth percentile, demonstrated a
sensitivity of 75%, a specificity of 97%, a positive predictive value of 75%,
and a negative predictive value of 97%.
Conclusions: The present study reaffirmed the accuracy and
applicability of the age-weight test for differentiating between typical and
atypical slipped capital femoral epiphyses, and it further defined the
age-height and height tests. If the height of a child can be obtained, the
height test is likely to be most useful for differentiating between typical
and atypical slipped capital femoral epiphysis. When height is not known, the
age-weight test will result in a similar negative predictive value but with a
lower sensitivity, specificity, and positive predictive value.
Level of Evidence: Diagnostic Level I. See Instructions
to Authors for a complete description of levels of evidence.