Use of finger length ratio as a marker for knee osteoarthritis: A case-control study of 2,456 patients

Background: In the human hand, the index and ring finger present a considerable variation in their relative lengths and the ratio of their lengths (2D:4D ratio). This ratio is associated with a variety of behavioral and physiological traits possibly linked to variation in sex hormones levels. Previous studies have revealed inconsistent results while assessing the association of 2D:4D ratio as a risk factor for occurrence of knee osteoarthritis (KOA). This study was designed as a prospective observational study to analyze this association using a better methodology. Methods: Patients were enrolled into KOA group (1396 patients) and non-KOA group (1060 patients) based on ACR criteria for OA knee. Knee and hand radiographs of all patients enrolled were assessed. The 2D:4D length ratio was calculated for phalanges, metacarpal bones and for the combined (metacarpal & phalanx) finger lengths on radiographs and visual finger lengths. The finger patterns were classified and assessment was done between these ratios and finger pattern types for occurrence and severity of KOA. Results: A lower 2D:4D ratio in an individual was associated with an increased chance of KOA and a dose response relationship was found between radiographic grading of KOA and 2D:4D ratio. Conclusion: Based on the findings of this study one can predict the risk of developing KOA using this simple technique which can be used as a screening tool whereby preventive intervention can be started if someone presents early with a low 2D:4D finger length ratio. Keywords: Fingers; Geriatrics; Odds ratio; Osteoarthritis, Knee; Risk assessment; Risk

Finger Length Ratio (2D:4D) and Aging

This study aimed to evaluate the association between the index to ring (2D:4D) finger length ratio and aging-related traits (hand osteoarthritis (OA), the osseographic score (OSS), and reproductive period), as well as to assess the heritability of finger length. A Chuvashian population-based sample included 802 males (mean age 46.98±17.10 years) and 738 females (mean age 48.65±16.62 years). Age, sex, basic demographics, anthropometric data, reproductive indices (age at menarche, menopausal age, and length of the reproductive period), and x-rays of both hands were collected. Finger length ratio was measured on x-ray and each hand was visually classified as either type 1 – 2D>4D; type 2 ― 2D=4D; or type 3 ― 2D<4D. Hand OA was defined by the number of affected joints (Kellgren-Lawrence score ≥2) and the total of Kellgren-Lawrence scores (total OA score). OSS is a skeletal biomarker that comprises osteoporotic and OA changes observable on a hands x-ray. We calculated the familial correlations and performed a heritability analysis of 2D:4D ratio traits in a studied sample. After comparing the OA variables of individuals with different finger length ratio types (after adjustment for age and BMI) significant differences were found only in females between finger ratio types of the right hand in a number of affected joints (F=3.153, p=0. 043) and finger ratio types of the left (F=3.330, p=0. 036) and right (F=2.397, p=0. 047) hands of the total OA score. Females with type 3 ratio had the highest adjusted values of hand OA parameters. Results of one-way ANCOVA for finger length ratio types of the right hand showed a significant difference in OSS (df =2, F=7.569, P=0.001), after adjustment for age, sex, and BMI. The posthoc comparison showed that individuals with type 3 (2D<4D) ratio showed significantly higher OSS scores than ones with type 1 (p=0.012) and type 2 (p=0.003). In an analysis of finger length ratio types of left hand also a significant difference in OSS was found (df=2, F=3.290, P=0.038). The posthoc comparison showed that individuals with type 3 ratio showed significantly higher OSS scores than ones with type 2 (p=0.33) ratio. We found that a low finger length ratio, a masculine visually evaluated finger length ratio type, was associated with later menarche and a shorter reproductive period. No association was found with menopausal age. Familial correlations of finger length ratio traits showed no significant correlation for spouses, however, parent-offspring (0.15―0.28, p<0.001) and sibling correlations (0.13―0.38, p<0.009) were found significant. Heritability (H2) of visual classification of finger length ratio was 0.36 for the left and 0.28 for the right hand; finger ratio was 0.55 and 0.66, respectively; the ray ratio was 0.49 and 0.59, respectively, thus indicating the existence of a clear familial aggregation of finger length ratio variation in the Chuvashian pedigrees, which cannot be explained by pure common environmental effects.

Sex differences in relationship between body composition and digit length ratio (2D:4D) in students of military courses

It is believed that the second to fourth finger length ratio is an indirect indicator of fetal testosterone levels. It is pointed out that there is a relationship between the 2nd to 4th finger length ratio and the body structure in women and men. Studies on the relationship between body composition and 2D:4D finger length among military students have not been carried out so far. The work aims to determine the dependence of body composition and the quotient of the 2nd and 4th fingers length of military students. The research material has been gathered as a result of examinations of women and men studying military subjects. The study involved 55 women and 65 men. The tests included anthropometric measurements (body height, body weight, length of the second and the fourth fingers) and body composition measurements. As a result of the tests, no dimorphic differentiations in the digit length ratio (2D:4D) was indicated. The BMI, muscle mass, lean body mass and water in the body demonstrated higher values in men than in women. However, the fat content in men was low. It was found that the relationship exists between muscle mass, lean mass and total water content in the body and the 2D:4D finger length ratio in the left hand in women. A higher level of fetal testosterone, characterized by lower values of the 2nd to 4th finger length ratio, may be associated with a higher content of muscle mass, lean body mass and water in the body of adult women leading a similar lifestyle.