RESEARCH - Osteoarthritis risk linked to finger length ratio

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Osteoarthritis Risk Linked To Finger Length Ratio

ScienceDaily (Jan. 7, 2008) — People whose index finger is shorter

than their ring finger are at higher risk of osteoarthritis, a new

University of Nottingham study has found.

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A study of more than 2,000 people suggests that people whose index

finger is shorter than their ring finger are up to twice as likely to

suffer from the condition, which is the most common form of arthritis.

Index to ring finger length ratio (referred to as 2D:4D) is a trait

known for its differences between the sexes. 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

oestrogen concentrations, and higher sperm counts. Reduction in this

ratio has also been linked to athletic and sexual prowess.

Whether this trait affects the risk of osteoarthritis (OA), the most

common form of arthritis that may associate with both physical

activity and oestrogen deficiency, has not been examined — until now.

Researchers at The University of Nottingham conducted a case-control

study to assess the relationship between the 2D: 4D ratio and the risk

of knee and hip OA. Their findings suggest that having a relatively

long ring finger to index finger ratio raises the risk for developing

OA of the knee, independent of other risk factors and particularly

among women.

For the study, 2,049 case subjects were recruited from hospital

orthopaedic 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 a

control group.

The study population was comprised of both men and women, with an

average age of approximately 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 two 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.

Professor Doherty, lead researcher, said: " The 2D:4D length

ratio appears to be a new risk factor for the development of OA.

Specifically, women with the 'male' pattern of 2D:4D length ratio —

that is, ring finger relatively longer than the index finger — are

more likely to develop knee OA. "

As the first study to examine the relationship between 2D:4D length

ratio and OA, it also raises questions.

" The underlying mechanism of the risk is unclear, " Professor Doherty

stressed, " and merits further exploration. "

Journal article: " Index to Ring Finger Length Ratio and the Risk of

Osteoarthritis, " W. Zhang, J. on, S. Doherty, J.J. Liu, R.A.

Maciewicz, K.R. Muir, and M. Doherty, Arthritis & Rheumatism, January

2008; 58:1.

http://www.sciencedaily.com/releases/2008/01/080102155442.htm

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Not an MD