Page 49 - Slipped Capital Femoral Epiphysis Pathogenetic and Clinical aspects

defined from the year of entry until 2010. We estimated the number of boys and girls in each cohort as the average number of boys and girls in that cohort over its follow-up period. The total number of children at risk over the period 1998–2010 was estimated by summing each estimated cohort-size (Table 2).
Statistical analysis
Incidence was defined as the population-proportion of surgical procedures for
SCFE in children. The difference in the incidence rates between boys and girls was 3 assessed by relative risks, with corresponding 95% confidence intervals (95 % CIs).
The Cochran–Armitage test for trend was used to test for a linear trend of the
yearly incidence rates over time. A 95 % CI not containing the value 1 or a p value
of <0.05 was considered to be significant, while a p value of <0.1 was considered
to be a trend. All statistical analyses were performed using SPSS ver. 15.0 (SPSS,
Chicago, IL).
Results
Incidence
The total number of surgical procedures for SCFE was 609 in the period 1998– 2010 for children between 5 and 19 years in the Netherlands. This translated into an incidence of 11.6 surgical procedures per 100,000 children over that period in the combined NT and T SCFE group. When the T SCFE group was not included in the analysis, the incidence of surgical procedures for NT SCFE was 8.8 per 100,000 children. The total incidence over the combined group for children aged 10–19 years was 13.7 surgical procedures per 100,000 children.
Gender ratio
In the combined group of NT and T SCFE the relative risk of exposure of boys compared to girls aged 5–19 years was 1.11 (95 % CI 0.95–1.30) over the period 1998 to 2010. The 95 % CIs over all years imply that there was no significant difference in the risk of being exposed to SCFE between boys and girls (Table 3). The annual incidence of surgical procedures for SCFE (Fig. 1) increased significantly for girls aged between 5 and 19 years (p = 0.034). The incidence of the total group (boys and girls combined) did not increase significantly (p = 0.384) nor did the incidence for boys (p = 0.438).
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