Patients with developmental dysplasia of the hip shows higher digit ratio (2D:4D).

BACKGROUND: Developmental dysplasia of the hip (DDH) encompasses a range of hip disorders, from dysplasia to dislocation. One key factor is sex, with women being four to eight times more susceptible to DDH than men. However, there have been no studies investigating the second-to-fourth digit ratio (2D:4D), a biomarker of prenatal sex steroid exposure, in DDH patients. This study aimed to explore whether there is an association between the 2D:4D ratio and DDH. METHODS: Digital calipers were used to measure the second and fourth finger lengths of 250 patients treated for DDH and 200 patients in the healthy control group between January 2020 and January 2023. The Mann-Whitney U test was used for non-normally distributed variables and two-way analysis of variance to assess differences in measurements between DDH patients based on sex, side, and the interaction of sex and side. The intraclass correlation coefficient (ICC) was used to assess measurement repeatability. RESULTS: The median (min-max) age was 10.00 (6-16) years in the DDH group, 12.00 (6-16) years in the control group, and 10 (6-16) years for the whole cohort. There was no significant difference in terms of age between the patient and control groups (p = 0.083). When comparing the DDH group with controls the former showed higher right 2D:4D and Δ2D:4D and these differences were significant in both males and females. Among the patients, controlling for side of dysplasia did not affect right 2D:4D, left 2D:4D or Δ2D:4D. CONCLUSION: There was a significant association between higher 2D:4D ratios (both right and left hands) and DDH in both men and women. This indicates that the 2D:4D ratio, a marker of intrauterine estrogen/testosterone balance, is associated with DDH.