Valgus slipped capital femoral epiphysis: subcapital growth plate orientation analysis.

The aim of the study was to determine the risk factors of unusual, lateral direction of epiphyseal displacement in primarily unilateral slipped capital femoral epiphysis (SCFE) patients with a special focus on radiological parameters of an unaffected hip. A total of 115 patients (75 boys, 40 girls), mean age 13.2 years (8.4-18.6), were analyzed. The mean follow-up time was 11 years (2-29). The proportion of valgus slip among SCFE patients was 11 of 115 cases (9.6%). The patients with valgus slip compared with the classic ones were predominantly females (55 vs. 33%), were younger (11.1 vs. 13.4 years), had a greater epiphyseal-shaft angle (67.4 vs. 59.1°), smaller displacement in the frontal plane (absolute value 6.7 vs. 15°), and a lower risk of contralateral slip (27 vs. 65%). There was no difference in the neck-shaft angle and epiphyseal-neck angle value. A more horizontal orientation of the subcapital growth plate, assessed by epiphyseal-shaft angle, can be considered a conducive factor in the valgus direction of epiphyseal slip in SCFE. In valgus SCFE cases, there is a smaller degree of epiphyseal displacement in both the sagittal and the coronal plane and a lower risk of consecutive contralateral slip.