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A large cohort study has confirmed several risk factors associated with hallux valgus: female sex, African-American race, older age, pes planus and knee/hip osteoarthritis (OA). The study, published online in found the highest prevalence of hallux valgus in African-American women: 70%.

"Early prevention and intervention approaches may be needed in high-risk groups," wrote researchers from the University of North Carolina in Chapel Hill and Harvard Medical School in the first study to report hallux valgus -- known colloquially as bunions -- by sex and race subgroups. They noted that hallux valgus is a major driver of foot and ankle surgery and is associated with functional disability, foot pain, poor balance, and a high risk of falling in older adults. "Identifying adults with hallux valgus earlier in the life course may aid in preventing later functional limitations, such as impaired balance, in older populations," they said.

Led by physical therapist , a research assistant professor of epidemiology at the University of North Carolina, investigators conducted a cross-sectional analysis of 1,695 participants in the prospective, population-based in rural North Carolina. Complete clinical and demographic data was available for 1,502 subjects. Mean age of subjects was 68.4 years (SD 8.9 years, range 50 to 95), 68% were women, and 30% were African Americans. Mean body mass index (BMI) value was 31.3 (SD 6.9).

The presence of hallux valgus was determined visually using a validated foot-examination diagram identifying angulation of the great toe greater than 15º. Foot pain was determined by asking subjects if they experienced pain or stiffness in either foot or both feet on most days. For pes planus, plantar pressure was evaluated by the , and foot structure was assessed by the Modified Arch Index.

To determine the presence of OA, a single musculoskeletal radiologist rated knee and hip radiographs, with a of 2-4 or a total joint replacement qualifying as OA.

Multivariate logistic regression models for the total sample and gender and race subgroups assessed the effects on hallux valgus of age, BMI, foot pain, pes planus, and knee/hip OA.

The prevalence of hallux valgus in the total sample was high at 64%. Prevalence in race-gender subgroups was as follows:

• African-American men, 69%
• African-American women, 70%
• Caucasian men, 54%
• Caucasian women, 65%.

Frequency of foot pain and pes planus was 39.6% and 27%, respectively. OA in at least one hip or knee was common at 66.4%. Mean BMI and the frequency of OA were higher in the female African-American subgroup. Pes planus was less common in Caucasians.

The link between hallux valgus and foot pain was elevated but not statistically significant, with adjusted odds ratios (aORs) of 1.17-1.48. Aching and stiffness in the feet were significantly associated with hallux valgus only among Caucasian men and African-American women.

An association between hallux valgus and older age was statistically significant for all subgroups except African-American men (aORs 1.17-1.49).

Counter to the researchers' hypothesis, subjects with a higher BMI had a lower odds of hallux valgus versus those with a normal BMI (aORs 0.54-0.72) -- an inverse association not reported in other large cohort studies and requiring further investigation. This finding prompted the investigators to say that "genetics and improper shoe wear should be explored as risk factors for hallux valgus among those with normal body weight."

The authors noted that the association between hallux valgus and knee-hip OA may signify lower-extremity OA, as reported in the Clearwater Osteoarthritis Study. "Hallux valgus may represent a tendency for bone formation in certain adults or may occur with or as a result of OA of the first metatarsophalangeal joint and would likely be associated with OA at other joint sites," they wrote.

Given the 50-plus age range of the sample, early factors contributing to later hallux valgus development were not easily identifiable, they said, and "future studies should include younger individuals and employ longitudinal analytic methods." Future investigations should also examine footwear, occupational factors, weight changes across adulthood, genetic variables, and first metatarsophalangeal OA to guide early intervention.

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