Scholarly article on topic 'Factors Related to Prevalence of Hallux Valgus in Female University Students: A Cross-Sectional Study'

Factors Related to Prevalence of Hallux Valgus in Female University Students: A Cross-Sectional Study Academic research paper on "Health sciences"

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Academic research paper on topic "Factors Related to Prevalence of Hallux Valgus in Female University Students: A Cross-Sectional Study"

J Epidemiol 2014;24(3):200-208 doi:10.2188/jea.JE20130110

Original Article

Factors Related to Prevalence of Hallux Valgus in Female University Students: A Cross-Sectional Study

Hiroto Okuda1,2, Sachiko Juman1, Ai Ueda1, Tomohiro Miki1, and Masayuki Shima2

'School of Pharmaceutical Sciences, Mukogawa Women's University, Nishinomiya, Hyogo, Japan 2Department of Public Health, Hyogo College of Medicine, Nishinomiya, Hyogo, Japan

Received August 7, 2013; accepted December 4, 2013; released online April 5, 2014

Copyright © 2014 Hiroto Okuda et al. This is an open access article distributed under the terms of Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

ABSTRACT-

Background: We investigated the prevalence of hallux valgus (HV) and examined its association with various factors in a cross-sectional study of Japanese female university students.

Methods: A questionnaire survey of foot symptoms, lifestyle, and body mass index (BMI) was administered to 343 women who provided informed consent at a women's university. Footprints were obtained and bone density was measured. Associations of HV with various factors were analyzed by logistic regression analysis. Results: Big toe pain was reported in 26.5% of the women. HV (HV angle, >15°) was present in the left foot in 22.4%, the right foot in 20.7%, and unilaterally or bilaterally in 29.7% of women. Mild HV (HV angle, >15° to <20°) was noted in the left foot and right foot in 13.4% and 13.1% of women, respectively; no severe HV (HV angle, >40°) was observed. HV was associated with big toe pain (adjusted OR: 3.56, 95% CI: 2.01-6.32), history of HV in the mother or maternal grandmother (adjusted OR: 2.45, 95% CI: 1.19-5.02), and history of HV in other family members (adjusted OR: 3.09, 95% CI: 1.35-7.06). Moderate HV was associated with big toe pain (adjusted OR: 4.58, 95% CI: 2.17-9.66) and history of HV in the mother or maternal grandmother (adjusted OR: 3.36, 95% CI: 1.40-8.07). The proportion of women with big toe pain increased significantly with HV severity.

Conclusions: HV was present in about 30% of female university students. Young women with big toe pain or a family history of HV should be evaluated for HV.

Key words: hallux valgus; female university student; big toe pain; family history; cross-sectional survey

INTRODUCTION

Hallux valgus (HV) is a deformity characterized by lateral deviation of the big toe at the first metatarsophalangeal joint and is more frequent among women.1 It is the most common foot deformity in adults, and its prevalence increases with age.2-6,9,12 In HV the first metatarsophalangeal joint protrudes due to big toe deformity, and inflammation with reddening and swelling may be induced by external stimulation from shoes. Pain and numbness of the big toe may be caused by compression of adjacent nerves. In the advanced stage, the big toe may sink under the second toe, causing callus or dislocation of the second toe. Marked deformation impairs weight bearing and balance, increases the risk of falling,7 and worsens physical performance and quality of daily life.5,8,9

HV was reported to be associated with gender,2,4,5,9-11

age,2-6,9 big toe pain,3,5,9,12 family history,1,11,13,14

footwear,1,4,10,11,15-19 body mass index (BMI),9,11 first

metatarsal length,1,10,20,21 first metatarsal head shape,21 flatfoot,10,11,22 race,11,23 knee pain,3,5 osteoarthritis,3,24 and

ligamentous laxity.25 The recent increase in HV prevalence is thought to be largely due to the effect of footwear, including

high-heeled shoes, particularly in middle-aged and older

people.4,15-18

The presence and severity of HV are evaluated on the basis of HV angle, which is usually measured clinically using radiographs. A diagnosis of HV deformity usually requires an HV angle greater than 15°.1 However, for ethical reasons HV severity is often evaluated in epidemiologic studies by measuring the HV angle in a traced outline of the foot rather

than by using radiographs.4,6,19,26

Many studies have examined associations of HV with various factors in patients, general populations, and middle-

aged to older people1,3-11,13,18,20-22,24; however, relatively

Address for correspondence. Hiroto Okuda, MD, School of Pharmaceutical Sciences, Mukogawa Women's University, 11-68 Kyuban-cho, Koshien, Nishinomiya, Hyogo 663-8179, Japan (e-mail: hirokuda@mukogawa-u.ac.jp).

few studies have investigated HV in young women.12,26 Reports indicate that the frequency of HV is increasing among junior high school students27 and that big toe deformity began before age 20 years in 46% of adults who underwent surgical treatment for HV.13 Thus, attention to HV and measures to prevent it at a young age are important. Opportunities to wear high-heeled footwear markedly increase as women enter university. Since such footwear greatly stresses the big toe, it likely increases the incidence and severity of HV. Young women need to be more aware of the characteristics and severity of HV and its relationship to footwear.

To assess HV prevalence, we analyzed the footprints of first-year female university students. In addition, associations of HV with various factors were investigated to identify measures to prevent HV.

METHODS-

Participants

The participants were 634 students newly admitted in 2010-2012 to the Faculty of Pharmacy of a private women's university in Hyogo Prefecture. Most were younger than 20 years. The survey objectives and methods were explained orally and in writing, after which the questionnaire survey forms were distributed.

Among a total of 634 first-year students admitted during the 3-year period (197 in 2010, 239 in 2011, and 198 in 2012), written consent to participate in the study was obtained from 353 (55.7%) women, and 343 women aged 20 years or younger (54.1%) were enrolled. A total of 258 (75.2%) participants lived with their families and commuted to and from the university. The survey was carried out on December 7-10, 2010; November 30 to December 3, 2011; and December 11-15, 2012.

Questionnaire survey on foot symptoms and lifestyle

A self-administered questionnaire contained items on age, body weight, height, and hallux valgus. In particular, big toe pain was assessed according to frequency of pain (none, occasional, always), time of pain (during rest/night, during walking/exercising, others), and treatment status for pain. The participants were also asked whether they had experienced knee pain and foot fatigue. Family history of HV was defined as presence of a relative (within the second degree of consanguinity) believed to have HV, and participants were asked to identify the relationship of such relatives with the participant. Footwear was assessed according to whether the participant used high heels with a narrow tow box, heel height, frequency of high heel use (none, occasional, every day), and duration of high heel use. Finally, participants were asked, in an open question, about sports they had played and how long they had played them.

Footprint measurement

In footprints obtained from plantar images, the HV angle was measured, the presence and severity of HV were evaluated, and the lengths of first and second toes were compared. Plantar images were obtained using Foot Look (FOOTLOOK Inc., Fukuoka, Japan), a device for plantar balance measurement that has a scanner capable of high-speed scanning of the plantar surface of the foot. The participants stood on the instrument barefooted, and the plantar surfaces in a weight-bearing state were scanned 3 times. The scanned images were printed on A4 paper, and HV angle was measured using outlines of full-scale footprints printed on paper.

For ethical reasons, radiographs were not used to assess HV in this study. The presence and severity of HV were evaluated according to HV angles determined from foot outlines.4'6'19'26 As shown in Figure 1(A), HV angle was measured as the angle between the tangent of the big toe and the medial tangent of the heel at the varus protrusion of the first metatarsophalangeal joint in the contour of the footprint. HV angle measurements based on foot outlines and radiographs were found to be highly correlated (r = 0.955, P <0.0001).6 Thus, the present technique of footprint measurement has been validated.4^19

Regarding assessment of severity, HV angles of 15° to 19°, 20° to 39°, and 40° or greater were classified as mild, moderate, and severe, respectively, according to the criteria on angular measurements of the ad hoc committee of the American Orthopedic Foot and Ankle Society.28

Flatfoot was judged using the Staheli Arch Index (SAI), which is significantly correlated with 3-dimensional arch structure on radiographs. As shown in Figure 1(B), flatfoot was defined as a central-to-heel arch width ratio of the plantar surface in the footprint (SAI) of 1.0 or greater.29

The minimum values for HV angle and SAI in the 3 scans were used in the analysis. The lengths of the first and second toes were measured along the long axes of the toes, from the most recessed point between the 2 toes in the plantar image.

All measurements in the present study were done by the same physician, who has been engaged in foot care and treatment for more than 15 years.

Measurement of bone density

The bone density of the right calcaneus was measured using an ultrasound bone densitometer (A0S-100, ALOKA, Ltd., Tokyo, Japan). The osteosono-assessment index (OSI), which reflects bone density and bone mass, was calculated from the speed of sound passing through the right calcaneus, and the transmission index indicates the degree of ultrasound transmission. Bone mass was defined as reduced when the OSI was less than 2.428 (YAM-0.9SD; YAM: young adult mean, SD: standard deviation).30

Statistical analysis

Various factors were examined, including those associated

Figure 1. Use of footprints to measure (A) HV angle and (B) flatfoot. (A) A straight line is drawn through the most medial points of the first metatarsophalangeal joint and the heel (inside edge). A second straight line is drawn through the first metatarsophalangeal joint and the great toe (proximal phalanx). The hallux valgus angle is defined as the angle between these 2 straight lines. (B) Measurement of arch width in the central region (a) and heel region (b) of the foot. The Staheli Arch Index is calculated as (a)/(b).

with HV in previous studies.1-6,8-25 The relationship between mean HV angle and HV frequency was evaluated in relation to big toe pain (always, occasional, none), knee pain (present, absent), year of university admission, foot fatigue (present, absent), family history of HV (present, other), high heels with a narrow toe box (>6 cm, <6 cm, do not wear), high heels 6 cm or higher (wear every day, wear occasionally, do not wear), big toe length (longer than the second toe, not longer than the second toe), flatfoot (present, absent), history of sports for 6 years or longer (ballet, sports other than ballet, none), BMI (<19.0kg/m2, 19.0-21.4kg/m2, >21.5kg/m2), and OSI (>2.428, <2.428). Differences in mean values were examined by the t test, differences in ratios by the %2 test, and multiple comparisons were done using the Tukey procedure. To examine the association between HV severity and big toe pain, BMI- and age-adjusted logistic regression analysis was used to estimate adjusted odds ratios (ORs) and 95% confidence intervals (CIs). Logistic regression analyses were used to compare factors (big toe pain, knee pain, year of university admission, family history of HV, use of high heels with a narrow toe box, big toe length, flatfoot, sports history, BMI, and OSI) between women with and without HV, and adjusted odds ratios and 95% CIs were estimated. The analyses were performed using SPSS 19.0J for Windows. Statistical significance was defined as a P value less than 0.05 in all tests.

Ethical considerations

The survey was conducted with the approval of the Research Review Board of Mukogawa Women's University. The participants were enrolled in the survey only after they had given their written consent after receiving an explanation of the study objectives and methods using explanation/ recruitment and consent forms.

Table 1. Demographic characteristic of participants (n = 343)

Age in years, mean (SD) 18.7 (0.6)

Weight in kg, mean (SD) 51.2 (7.6)

Height in cm, mean (SD) 157.8 (5.4)

BMI in kg/m2, mean (SD) 20.6 (2.7)

OSI, mean (SD) 2.704 (0.276)

Year of admission, fiscal year

2010, no. (%) 131 (38.2)

2011, no. (%) 105 (30.6)

2012, no. (%) 107 (31.2)

Knee pain, no. (%) 23 (6.7)

Foot fatigue, no. (%) 114 (33.2)

Big toe pain, no. (%) 91 (26.5)

Period with big toe pain

During walking/exercising, no. (%) 79 (23.0)

During rest/nighttime, no. (%) 8 (2.3)

Others, no. (%) 4(1.2)

Frequency of big toe pain

Occasional, no. (%) 84 (24.5)

Always, no. (%) 7 (2.0)

Family history, no. (%) 86 (25.4)

Mother, no. (%) 39 (11.4)

Father, no. (%) 8 (2.3)

Sibling, no. (%) 20 (5.8)

Maternal grandmother, no. (%) 17 (5.0)

Paternal grandmother, no. (%) 24 (4.1)

Grandfather, no. (%) 4(1.2)

BMI: body mass index; OSI: osteosono-assessment index.

RESULTS -

Characteristics of participants

Table 1 shows the number of women by year, enrollment rate, mean age, height, body weight, BMI, OSI, and percentages with big toe pain, knee pain, and foot fatigue. About 26.5% of participants complained of big toe pain, but only 4.3% had a

MEAN (SD) MAX 29.5°

10.0 (5.6)° MIN 0°

MEAN (SD) MAX 29.0°

11.0 (5.3)° MIN 0°

Figure 2. Frequency distribution of HV angle. Correlation of the HV angles of the left and right feet (Pearson correlation coefficient: 0.711, P <0.001).

Table 2. Proportions of participants with HV in the left and right feet, by severity

HV angle of right foot

Normal (<15°) Mild (15-19°) Moderate (>20°)

Normal (<15°) 241 (70.3%) 19 (5.5%) 6 (1.7%)

HV angle of left foot Mild (15-19°) 21 (6.1%) 18 (5.2%) 7 (2.0%)

Moderate (>20°) 10 (2.9%) 8 (2.3%) 13 (3.8%)

No. (%)

history of treatment for big toe pain. A family history of HV was noted in 25.4%. The Japanese translation of the term "hallux valgus" was known to 92.6% of participants.

HV angle and severity

Figure 2 shows the frequency distribution of HV angles in both feet. The mean angle was 10.0° for the right foot and 11.0° for the left foot, and the 2 sides were strongly correlated (Pearson correlation coefficient: 0.711, P <0.001). Table 2 shows the frequencies of HV by severity. No severe HV was observed. About 29.7% of women had HV in at least 1 foot.

Associations of mean HV angle and HV frequency with the investigated factors

Table 3 shows the mean HV angles of the right foot and left foot in relation to the examined factors. The mean HV angles of both feet were significantly larger among women with a higher prevalence of big toe pain and a family history of HV in the mother or maternal grandmother. In the right foot, the

mean HV angle was significantly larger among women with a big toe longer than the second toe than among those with a big toe not longer than the second toe.

Table 4 and eTable 1 show the frequencies of HV in relation to the investigated factors. HV frequency was significantly higher among women with a higher frequency of big toe pain and among those with a family history of HV.

Results of logistic regression analyses

Table 5 shows data on the association between HV and big toe pain. The frequency of big toe pain increased significantly in relation to HV severity, after adjustment for BMI and age.

Table 6 and eTable 2 show the results of logistic regression analyses of the investigated factors. In our participants, the presence of HV (HV angle, >15°) in at least 1 foot was related to presence of big toe pain, family history of HV in the mother or maternal grandmother, and family history in other relatives. In addition, the presence of moderate HV in at least 1 foot was related to presence of big toe pain and family history of HV in the mother or maternal grandmother.

Table 3.

Factors Related to Hallux Valgus in Young Women Mean HV angles of the left and right feet in relation to investigated factors

Right foot Left foot

Factor No. Mean degrees (SD) P value No. Mean degrees (SD) P value

Big toe pain Absent 252 9.1 (5.0) <0.001 252 10.1 (4.6) <0.001

Occasional 84 12.1 (6.1) 84 13.2 (5.9)

Always 7 18.0 (8.3) 7 19.1 (6.8)

Knee pain Absent 320 10.1 (5.8) 0.729 320 11.1 (5.3) 0.531

Present 23 9.7 (5.9) 23 10.3 (5.5)

Foot fatigue Absent 229 10.0 (5.4) 0.811 229 11.0 (5.3) 0.945

Present 114 10.1 (6.0) 114 11.0 (5.4)

Family history Absent 257 9.3 (5.3) <0.001 257 10.4 (5.0) 0.001

Mother/maternal grandmother 51 12.3 (6.2)a 51 13.2 (6.0)a

Other than mother/maternal grandmother 35 12.3 (5.5) 35 12.2 (5.1)

High heels with a narrow Absent 124 9.9 (5.8) 0.977 124 10.9 (5.4) 0.775

toe box <6 cm 151 9.9 (5.4) 151 10.8 (5.1)

>6 cm 51 10.1 (5.4) 51 11.4 (5.7)

Frequency of the use of Absent 276 9.9 (5.7) 0.990 276 10.9 (5.4) 0.824

high heels with a narrow Occasional 25 10.1 (4.6) 25 11.5 (6.1)

toe box (>6 cm) Every day 26 10.1 (6.1) 26 11.3 (5.3)

Big toe length <second toe length 66 8.6 (5.0) 0.022 57 10.4 (5.5) 0.374

>second toe length 277 10.4 (5.7) 286 11.1 (5.2)

Flatfoot Absent 332 10.0 (5.5) 0.100 333 11.0 (5.3) 0.454

Present 11 12.8 (8.3) 10 12.3 (6.0)

Athletic history Absent 200 9.9 (5.5) 0.360 200 11.0 (5.3) 0.987

(>6 years) Ballet 12 8.5 (4.5) 12 10.9 (3.8)

Other than ballet 124 10.5 (5.0) 124 11.0 (5.3)

BMI <19.0 kg/m2 80 10.3 (5.8) 0.846 80 11.4 (5.3) 0.711

19.0-21.4 kg/m2 175 9.9 (5.5) 175 10.9 (5.2)

>21.5 kg/m2 86 10.1 (5.7) 86 10.8 (5.5)

OSI >2.428 295 9.8 (5.5) 0.059 295 10.9 (5.1) 0.591

<2.428 45 11.4 (5.9) 45 11.4 (6.1)

aMean HV angle was significantly larger than in the group with no family history (P = 0.001). BMI: body mass index; OSI: osteosono-assessment index.

DISCUSSION-

HV prevalence

In this study, HV, as determined using the HV angle measured in footprints, was observed in at least 1 foot of 29.7% of female first-year university students aged 20 years or younger. Moderate HV was noted in 12.8%. In a meta-analysis of 78 reports of HV primarily in the United States and United Kingdom the prevalence of HV was 15.0% (95% CI: 7.7%-22.3%) among people younger than 18 years and 26.3% (95% CI: 16.5-36.2) among those aged 18 to 65 years.2 In a 2004 study by Shibata et al, which used the trace method to study Japanese women, the mean HV angle was 10.0° among those aged 10 to 19 years and 13.0° among those aged 20 to 29 years; the prevalence of moderate HV (HV angle, >20°) was 12.5% among those aged 20 to 29 years.6 Mean HV angle and HV prevalence in the present study were very similar to values from previous reports.

HV angle and severity

HV is diagnosed according to HV angle, which is usually measured clinically using radiographs.1 In epidemiologic studies of healthy people, HV severity is often evaluated by

applying criteria such as the Manchester scale to photographs or diagrams of the foot3'5'10'12'31'32 or by measuring the HV angle in the outlines of foot traces.4'6'19'26 In this study' HV angle was measured using the outlines of plantar images obtained with a scanner' because this technique is known to yield values similar to those obtained using radiographs.4'6'19'33 This method is advantageous because it does not require X-ray exposure' is noninvasive' allows for more-objective evaluation of the plantar surface' easier data management' and superior device portability' and is considered appropriate for surveying a large number of participants.

HV and related factors

HV is usually a bilateral phenomenon—there is typically little difference between the right and left foot.3'12 However since there were differences between the left and right feet in the length of the big toe and prevalence of flatfoot' the relationships between HV and various factors were examined for each and both feet. The results showed similar associations between HV and the investigated factors. Relationship with big toe pain

Big toe pain was reported by 26.5% of the participants during walking or exercising' if not regularly. A number of studies

Table 4. Prevalence of HV (HV angle >15°) in relation to investigated factors

Right foot Left foot At least 1 foot

Factor P P P

No. % No. % No. %

value value value

Big toe pain frequency Absent 252 14.3 <0.001 252 16.7 <0.001 252 22.2 <0.001

Occasional 84 35.7 84 35.7 84 48.8

Always 7 71.4 7 71.4 7 71.4

Knee pain Absent 320 20.3 0.593 320 22.2 0.613 320 29.1 0.346

Present 23 26.1 23 26.1 23 39.1

Year of admission 2010 131 25.2 0.262 131 25.2 0.585 131 32.8 0.535

2011 105 17.1 105 21.9 105 29.5

2012 107 18.7 107 19.6 107 26.2

Foot fatigue Absent 229 19.2 0.396 229 23.1 0.683 229 29.3 0.803

Present 114 23.7 114 21.1 114 30.7

Family history Absent 257 17.1 0.016 257 17.1 <0.001 257 23.7 <0.001

Mother/ 51 33.3 51 49.0 51 49.0

maternal grandmother

Other than the mother/ 35 28.6 35 45.7 35 45.7

maternal grandmother

High heels with a Absent 124 20.1 0.430 124 21.8 0.759 124 27.4 0.358

narrow toe box <6 cm 151 17.2 151 20.5 151 27.2

>6 cm 51 25.5 51 25.5 51 37.3

Frequency of the use Absent 276 18.8 0.532 276 21.4 0.739 276 27.5 0.341

of high heels with Occasional 25 20.0 25 28.0 25 40.0

a narrow toe box Every day 26 26.9 26 23.1 26 34.6

Big toe length <second toe length 66 13.6 0.130 57 21.1 0.863 — — —

>second toe length 277 22.4 286 22.7 — — —

Flatfoot Absent 332 20.2 0.248 333 22.2 0.699 328 29.3 0.393

Present 11 36.4 10 30.0 15 40.0

Athletic history Absent 200 22.0 0.513 200 24.0 0.644 200 30.5 0.899

>6 years Ballet 12 8.3 12 16.7 12 25.0

Other than ballet 124 20.2 124 20.2 124 29.0

BMI <19.0 kg/m2 80 21.3 0.962 80 21.3 0.812 80 31.3 0.941

19.0-21.4kg/m2 175 21.1 175 24.0 175 29.1

>21.5 kg/m2 86 19.8 86 20.9 86 30.2

OSI >2.428 295 20.2 0.695 295 21.4 0.442 295 28.5 0.487

<2.428 45 22.2 45 26.7 45 33.3

BMI: body mass index; OSI: osteosono-assessment index.

Table 5. Frequency of big toe pain according to severity

No. % Odds ratioa (95% CI) P value

HV angle of right foot

Normal 272 20.6 1.00

Mild 45 42.2 2.86 (1.47-5.57) 0.002

Moderate 26 65.4 7.25 (3.03-17.34) <0.001

HV angle of left foot

Normal 266 21.1 1.00

Mild 46 37.0 2.21 (1.13-4.34) 0.021

Moderate 31 63.2 5.93 (2.69-13.07) <0.001

aAdjusted for age and body mass index by logistic regression.

examined the relationship between the presence of HVand big toe pain3,5,8,9,12; some found no association,11 but the question remains open. The severity of big toe pain is believed to depend on the method used to assess pain, the characteristics and ethnicity of the study population, shoes currently worn, and history of treatment for HV.3,9,11 The present results showed a significant association between HV and big toe pain, presumably because the participants were young women and

big toe pain was partly caused by intense exercise and walking, which imposed much strain on their feet. Young women tend to be more active than middle-aged and elderly women and often wear fashion-oriented footwear, including high-heeled shoes, which puts direct pressure on the first metatarsophalangeal joint. Furthermore, they have few opportunities to receive treatment for HV and advice on appropriate footwear, even if they have HV.

In this study, HV prevalence was significantly higher in women with big toe pain as compared with those without such pain. In addition, the percentage of participants with big toe pain increased significantly with HV severity. However, because most participants had HV without big toe pain, attention to asymptomatic HV is necessary. Associations with causative factors

Internal factors such as anatomic characteristics associated with genetic predispositions and external factors such as footwear may be involved in the development of HV.1 In this study, HV prevalence was significantly higher in women with a family history of HV than in those without such a history.

Table 6. Odds ratio (ORs) and 95% CIs for an HV angle >15° in relation to investigated factors

Right foot Left foot At least 1 foot

Factor Odds ratioa P Odds ratioa P Odds ratioa P

(95% CI) value (95% CI) value (95% CI) value

Big toe pain Absent 1.00 1.00 1.00

frequency Occasional 3.01 (1.56-5.81) 0.001 2.29 (1.21-4.31) 0.011 3.56 (2.01-6.32) <0.001

Always 21.52 (2.15-215.30) 0.009 23.48 (2.38-231.67) 0.007

Knee pain Absent 1.00 1.00 1.00

Present 1.32 (0.40-4.34) 0.650 0.90 (0.26-3.16) 0.874 1.46 (0.50-4.29) 0.489

Year of 2010 1.00 1.00 1.00

admission 2011 0.66 (0.31-1.43) 0.290 0.80 (0.39-1.61) 0.528 0.82 (0.42-1.59) 0.554

2012 0.79 (0.38-1.64) 0.526 0.79 (0.38-1.61) 0.510 0.91 (0.48-1.72) 0.761

Family history Absent 1.00 1.00 1.00

Mother/ 1.94 (0.86-4.37) 0.110 2.78 (1.31-5.91) 0.008 2.45 (1.19-5.02) 0.007

maternal grandmother

Other than the mother/ 1.85 (0.72-4.74) 0.199 3.63 (1.56-8.49) 0.003 3.09 (1.35-7.06) 0.007

maternal grandmother

High heels Absent 1.00 1.00 1.00

with a narrow <6 cm 0.75 (0.39-1.47) 0.403 0.85 (0.44-1.61) 0.610 0.89 (0.49-1.61) 0.705

toe box >6 cm 1.46 (0.63-3.40) 0.380 1.27 (0.55-2.95) 0.573 1.68 (0.78-3.62) 0.187

Big toe length <second toe length 1.00 1.00 — —

>second toe length 1.61 (0.68-3.81) 0.278 0.80 (0.37-1.73) 0.566 — —

Flatfoot Absent 1.00 1.00 1.00

Present 1.57 (0.37-6.79) 0.543 1.56 (0.33-7.29) 0.575 1.65 (0.50-5.46) 0.410

Athletic history <6 years 1.00 1.00 1.00

>6 years 0.89 (0.65-1.22) 0.462 0.93 (0.69-1.26) 0.630 0.92 (0.70-1.21) 0.535

BMI <21.5 kg/m2 1.00 1.00 1.00

>21.5 kg/m2 1.05 (0.51-2.16) 0.906 1.14 (0.58-2.25) 0.718 1.24 (0.66-2.31) 0.508

OSI >2.428 1.00 1.00 1.00

<2.428 1.43 (0.62-3.29) 0.398 1.60 (0.72-3.52) 0.246 1.48 (0.70-3.11) 0.307

aAdjusted for all variables in table by logistic regression.

Previous studies reported that 63% to 84% of patients scheduled to undergo surgical correction of HV had a family history of HV and that maternal inheritance was present in 68% to 94% of those with such a history.1,10,13 Moreover, in a study of French patients with painful HV, more than 90% had a history extending over 3 generations, which suggests the presence of incomplete autosomal dominant inheritance.14 The high frequency of family occurrence suggests the involvement of inheritance of anatomic and morphologic characteristics that increase vulnerability to HV, such as foot morphology, joint shape, and ligament flexibility.

In this study, the prevalence of moderate HV was significantly higher in participants with a mother or maternal grandmother with HV than in those without such a family history, even after adjustment for other factors, which suggests maternal inheritance. Among all participants with HV, 47.7% had a family history of HV, and maternal inheritance was suspected in 60.4% of those with a family history. These proportions are lower than those reported previously, probably because the populations differed in age and HV severity.

Regarding foot morphology, the mean HV angle of the right foot was significantly larger in women with a big toe longer than the second toe, but no significant difference was noted in HV prevalence. Also, the presence of flatfoot was not related to mean HV angle or HV prevalence. Generally, feet with a big toe longer than the second toe (Egyptian type) are more

susceptible to the effects of footwear and weight-bearing and are more likely to develop HV than feet with a big toe shorter than or equal in length to the second toe (Greek type; square type).21 However, the effects of big toe length are considered to be limited in young people.

External factors related to HV include footwear1,4,10,11,15-19 and overweight.9,34 The human foot has 3 arches, which support body weight, efficiently transmit power to the ground during locomotion, and absorb impact during walking. Loss of these arch functions due to external factors leads to HV. When shoes with a narrow toe box are worn, the big toe, which is normally introverted by contraction of the abductor muscle during weight bearing, is compressed in the valgus position. Moreover, as shoes with higher heels are worn, the foot is fixed in a more dorsiflexed position, and a stronger force is applied to the anterior foot. This flattens the transverse arch and makes the foot more vulnerable to HV. Shine et al studied HV prevalence among residents of the island of Saint Helena and reported that HV was present in 2% or fewer of those who did not wear shoes in daily life, as compared with 16% of men and 48% of women who had worn shoes in daily life for 60 years or longer.4 HV was also reported to be prevalent in ballet dancers, who wear narrow toe shoes and dance by tiptoeing.35 However, among the present participants, no significant association was noted between HV and external factors such as fashionable footwear, ballet experience, and

high BMI. This absence of a relationship may be explained by limited use of high heels, the low percentage of participants practicing ballet, and the short time spent practicing ballet as compared with professional ballet dancers. In addition, the self-reported BMI (20.6 ± 2.7 kg/m2) of participants was similar to the mean BMI of all newly admitted students over the past 3 years (20.9 ± 3.1 kg/m2), which was calculated based on data obtained at check-ups. Most participants had a lower BMI than that of middle-aged and elderly people, as reported in a previous study,9 few participants were obese, and the effects of BMI on the feet were likely minor. Thus, genetic factors are considered to have an important role in HV in young women, and the effects of external factors such as footwear appear to be limited. However, in children younger than school age, HV angle was reported to increase when shoe length was short for the foot,19 so the effects of the duration of use and size of footwear other than high heels need to be evaluated further.

Study limitations

First, consent for participation in the study was obtained from only 55.7% of all students. Reasons for refusal to consent are believed to include aversion to having others observe their plantar images and unwillingness to participate; however, to avoid bias it is important to improve the consent rate in future studies. Second, this study was cross-sectional, and longitudinal follow-up of changes in HV angle is necessary in order to evaluate associations of onset and exacerbation with external factors. Moreover, evaluation of the effects of footwear other than toe shoes and high heels is necessary. Third, footprints were used to evaluate HV. The use of radiographs as a reference would have allowed more-accurate measurement of HV angle, ascertainment of flatfoot, comparison of big toe and second toe lengths, and evaluation of the relationship of HV with the metatarsal head, osteoarthritis, etc. Fourth, since HV can be induced by diseases that cause ligamentous laxity such as Ehlers-Danlos syndrome, examination for underlying diseases is also necessary. Fifth, because family history of HV, weight, and height were evaluated using a self-administered questionnaire, the present results may be inaccurate. To perform a more accurate evaluation, it is important to assess family members in an objective manner, using their footprints, and to measure their height and body weight during footprint measurements; however, self-reported BMI (20.6 ± 2.7 kg/m2) was similar to the BMI (20.7 ± 2.6 kg/m2) of women of the same age, as indicated by data collected in the Japan National Health and Nutrition Survey in 2011.36

Study significance and future research

Although HV is a common foot deformity among adult women, there have been few studies of HV in young women. In this study, we evaluated HV in a general population of young women and its associations with various factors

and confirmed the association of HV with big toe pain and family history of HV in this population. Therefore, young women with big toe pain or a family history of HV should be evaluated for HV, to identify the condition at an early stage.

Young women often value style over function in footwear. Prolonged use of shoes with a narrow toe box or high heels may lead to development or exacerbation of HV. HV can be exacerbated by internal and external factors, particularly among those with a family history of HV (especially in the mother or maternal grandmother). Future longitudinal studies should attempt to clarify the effects of external factors on the development and exacerbation of HV in young women. The results of this study provide basic data that will assist in obtaining accurate assessments.

Conclusion

HV in young women was significantly positively associated with big toe pain and family history of HV but not with external factors such as heel height or morphologic characteristics such as big toe length and flatfoot. The percentage of participants who reported big toe pain increased with HV severity. HV should be considered among young women with big toe pain or family history of HV.

ONLINE ONLY MATERIALS-

eTable 1. Incidence of HV (HV angle >20%) in relation to investigated factors.

eTable 2. Odds ratios (ORs) and 95% CIs for an HV angle >20° in relation to investigated factors. Abstract in Japanese.

ACKNOWLEDGMENTS-

The authors are grateful to the students who understood the intention of this study and participated in the measurements and questionnaire survey.

Conflicts of interest: None declared.

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