Index to ring finger length ratio (2D:4D) is a trait known for its 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.
Researchers with the University of Nottingham in the United Kingdom conducted a case-control study to assess the relationship between the 2D: 4D ratio and the risk of knee and hip OA. For the study, 2,049 case subjects were recruited from hospital orthopedic surgery lists and a rheumatology clinic in Nottingham.
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.
Using blind comparisons of hand radiographs with both knee and hip radiographs from random case and control samples combined with statistical analysis and odds ratios, researchers assessed the relationship between 2D:4D length ratio and OA. Compared with the other finger types, the type 3 finger was associated with an increased risk of OA involving any part of the knee or the hip, and including the presence of arthritic finger nodes. Of particular note, the risk of knee OA in participants with the type 3 finger pattern was nearly double that of the risk for participants without this pattern.
Women with this finger pattern had a greater risk of knee OA than men. Among participants of both sexes, researchers also found an interesting trend: the smaller the 2D:4D upper finger joint ratio, the greater the risk of OA of the tibiofemoral knee joint. Finally, after adjusting for established OA risk factors — age, sex, body mass index, joint injury, and lack of physical activity — the strong association of smaller 2D:4D length ratio with the risk for knee OA was deemed independent.
MEDICA.de; Source: Wiley-Blackwell