The incidence of physiolysis of the hip: a population-based study of 175 patients.

We studied the epidemiology of physiolysis of the hip (or slipped capital femoral epiphysis) between 1946 and 1992 in 175 patients from a well-defined population. The incidence of physiolysis of the hip was calculated using the attack rate method, i.e., the sum of the annual incidences in each 1-year group. The risk of developing physiolysis was 1:998 for boys, 1:1756 for girls and 1:1267 for both sexes and did not change significantly during this period. The average age at diagnosis was 13.6 (7-17) years in boys and 12.1 (8-15) years in girls and did not change to a significant degree during this period. The difference in the boy:girl ratio (1.8:1) and in the preponderance of the left hip being affected first (64% for boys and 52% for girls) did not change significantly during this period. No significant monthly variation was found in the onset of symptoms of physiolysis of the hip.