The index to ring finger length ratio (2D:4D) has been known to have sexual differences:
- Men typically have shorter second than fourth digits; in women, these fingers tend to be about equal in length.
- Smaller 2D:4D ratios have intriguing hormonal connections, including higher prenatal testosterone levels, lower estrogen concentrations, and higher sperm counts.
- Reduction in this ratio has also been linked to athletic and sexual prowess.
Now, according to researchers at the University of Nottingham in the United Kingdom, the index to ring finger length ratio (2D:4D) affects the risk of osteoarthritis (OA).
For the study, 2,049 case subjects were recruited from hospital orthopedic surgery lists and a rheumatology clinic in Nottingham. All had clinically significant symptomatic OA of the knees or hips, requiring consideration of joint replacement surgery.
Recruited from hospital lists of patients who had undergone intravenous urography (IVU) within the past five years, 1,123 individuals with no radiographic evidence of hip or knee OA, no present hip or knee symptoms, and no history of joint disease or joint surgery served as controls. The study population was comprised of both men and women, with an average age of roughly 67 years for cases and 63 years for controls.
Radiographs of both knees and the pelvis were obtained for all participants. Every participant also underwent separate radiographs of the right and left hands. Researchers then assessed the 2D:4D length ratio from radiographs using three methods: a direct visual comparison of the 2 finger ends, the measured ratio from the base to the tip of the upper finger joints, and the measured ratio of the metacarpal bone lengths.
Hands radiographs were classified visually as either type 1, index finger longer than the ring finger; type 2, index finger equal to the ring finger; or type 3, index finger shorter than the ring finger. Not surprisingly, men were 2.5 times more likely than women to have the type 3 pattern.
The findings – reported in the January 2008 issue of Arthritis & Rheumatism – suggest that having uncommonly long ring fingers raises the risk for developing OA of the knee, independent of other risk factors and particularly among women.
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