Hallux valgus (HV) is a progressive foot deformity presenting with lateral deviation of the hallux and medial deviation of the first metatarsal head. Increasing HV severity is associated with subluxation of the first metatarsophalangeal joint (MTPJ) and presence of osteoarthritis (OA)[1]. HV is very common, affecting approximately 23% of adults[2], and surgical correction is frequently sought, making HV the most common indication for orthopaedic forefoot surgery[3].

While HV is basically regarded as a structural deformity, there is debate surrounding the association between abnormal foot structure and related pain and disability. Several studies in elderly populations have found no association between HV and self-reported foot pain and disability[4–9]; whereas, another study reported a significant association between HV and disabling foot pain in older adults[10]. Although fewer studies have investigated these associations in populations with a wide age range, recent studies have linked HV to greater self-reported foot pain and functional limitation in adults aged 40 to 69 years[11], and big toe pain in adults aged over 30 years[12]. Furthermore, there is evidence for impaired quality of life associated with HV and big toe pain in adults aged over 30 years[13], and poorer health-related quality of life and greater foot pain and disability with increasing HV severity in adults aged over 50 years[14].

In addition to self-reported pain and disability, the impact of HV on functional performance has been investigated with inconsistent findings. Impaired balance and gait patterns, toe muscle weakness, and an increased risk of falls in elderly individuals with moderate or severe HV have been reported by several studies[8, 15–21]; however, other studies have shown no association between HV and postural sway[22], walking performance[4, 6] or history of falls[5]. No previous studies have reported on physical measures of functional performance in adults of all ages with HV.

Two additional factors considered most important by patients and orthopaedic surgeons are concerns about cosmetic appearance and difficulty with footwear[23, 24]. While a few population studies have investigated footwear factors such as past usage of high-heeled shoes[9] and shoe fit[5, 25], no previous studies have investigated self-reported difficulty with footwear or concerns about foot appearance in individuals with HV not seeking surgical correction. Therefore, the primary aim of this cross-sectional study was to investigate differences in foot pain, functional limitation, concerns about appearance and difficulty with footwear in a group of adults with HV compared to matched controls. A secondary aim was to explore possible associations between these variables and severity of deformity in HV subjects.

This study investigated self-reported foot pain and disability, functional performance, concerns about appearance and difficulty with footwear experienced by healthy adults with HV. We secondarily explored possible associations between severity of HV angle and other variables in participants with HV.

Our results show that the presence of HV deformity is associated with self-reported foot pain and disability. Significant differences were found between HV and control groups for FHSQ and FPDI subscales, as well as worst and average pain VAS (Table2). With reference to the minimal important difference for the FHSQ and VAS previously reported by Landorf et al.[43], these differences between groups can be considered clinically meaningful. Our findings are similar to those reported by Cho et al.[11] who showed that HV was associated with more self-reported foot pain and poorer self-reported physical functioning in adults aged 40 years and older (n = 563). Abhishek et al.[13] further highlighted the importance of big toe pain accompanying HV, reporting that health-related quality of life was progressively impaired in adults aged 30 years and older (n = 3082) with HV alone, big toe pain alone, and HV with big toe pain. In our study there was also some evidence of mechanical hyperalgesia around the medial aspect of the first MTPJ, as indicated by a lower PPT in HV subjects (p < 0.05). However, this result should be interpreted with caution as the difference between groups (MD = −133.3, CI: -251.5 to −15.1) did not reach the calculated MDC₉₀ (255.2) (Additional file1: Table S1) and therefore may not represent a meaningful difference.

In addition to self-reported foot pain and functional limitation, participants with HV in our study presented with hallux plantarflexion and abduction weakness and increased mediolateral postural sway. Our finding of decreased hallux plantarflexion strength in people with HV is consistent with that of Mickle et al.[21]. However, our study also showed a significant inverse correlation between HV angle and an individual’s ability to abduct the hallux (rho = −0.41), a finding which has been suggested by electromyographic investigations[47, 48] but previously has not been investigated clinically. With regard to standing balance, results reported by Mickle et al.[22] are in contrast to our findings, as these authors reported no difference in postural sway between older adults with HV and controls. However, other studies in elderly populations have found poorer lateral stability, poorer coordinated stability, and increased postural sway to be associated with HV[17, 19]. Finally, no significant between-group differences were found in walking performance in our study, which is consistent with previous findings in elderly populations[4, 5, 8, 19].

Despite no differences between groups in relative heel height or relative ball width of footwear worn to the examination, participants with HV reported significantly more difficulty with footwear and concerns about foot appearance than controls. Concerns about appearance and general foot health appeared to increase with severity of deformity in the HV group (appearance VAS: rho = 0.43, FHSQ general foot health: rho = −0.41). To our knowledge, this is the first study to investigate self-reported difficulty with footwear and concerns about appearance in a HV population not seeking surgical correction compared to age and gender-matched controls. Our data suggest that clinicians managing HV should place particular priority on footwear concerns. This is supported by Saro et al.[24], who showed that free choice of footwear was significantly associated with health-related quality of life outcomes after HV surgery.

While participants with HV in our study reported significantly more foot-specific functional disability, participation in physical activities, general health and physical functioning were not adversely affected (Table1). To the contrary HV subjects reported higher levels of habitual physical activity at work and in sports, which may have led to improved performance on other physical parameters such as walking and balance tests. Furthermore, correlations between HV angle and SF-36v2® subscales suggest that in our sample HV participants with more severe deformity experienced less bodily pain and better social functioning. This finding is in contrast to results of a recent study by Menz et al.[14] who found a trend towards poorer scores on all SF-36v2® subscales with increasing HV severity in adults aged 50 years and older (n = 2681). It is possible that general health and functioning may be more impacted by increasing HV severity in populations of older adults; alternatively, it may be that our findings were a consequence of a volunteer sample of HV participants, who were active individuals with a high level of physical functioning. Furthermore, perhaps those with more severe HV in our sample had adapted their lifestyle or footwear choices to accommodate for a severe foot deformity.

Caution must be applied when comparing reports from different studies as varying case definitions (present/absent or mild/moderate/severe) and means of diagnosing HV (i.e. self-reported or diagnosed by an examiner) are used[2]. Studies have used a range of methods to evaluate the presence and severity of HV, including weight-bearing radiographs[11, 49], and the Manchester Scale[10, 17, 19, 22, 50], which includes a series of four standardised photographs used by an examiner to classify HV as “none,” “mild,” “moderate,” or “severe.” Other larger studies have used a validated self-report instrument based on five line drawings representing increasing HV severity[12–14, 51]. Our study used standardised weight-bearing radiographs and a widely accepted angular definition to classify HV as being present (HV angle > 15°)[52]. This definition meant that several mild and asymptomatic HV cases were included, which was considered appropriate to address the primary research question of whether the presence of HV was associated with foot pain and disability.

Our study findings should be interpreted with consideration of our recruitment methods and sample, which may affect the generalisability of results. First, volunteers with HV responding to advertisements were likely aware that they had a foot problem. This may have introduced an element of bias to their self-reported foot health measures compared to controls. Second, only ten males participated in this study, and the age range of study participants was relatively wide. Nevertheless, these sample characteristics were considered representative of a clinical population. Third, whilst our sample included participants with mild, moderate and severe HV, the sample size in the current study was not sufficient to examine subgroups according to HV severity. While there is some evidence that increasing HV severity has a greater impact on foot pain and disability[14], further research using large population-based samples is warranted to determine whether HV severity is associated with increased foot pain or poorer functional performance.

Reliability of measurement methods must be considered as a potential limitation in any clinical research. All measurements in our study were performed by the same examiner, and intra-rater reliability was very good for most physical measurements (Additional file1: Table S1). Inter-rater reliability was not addressed by this investigation. Reported intra-rater reliability for hallux plantarflexion and abduction strength was lower than desirable (ICC_3,1 = 0.73 to 0.75), and as a result the calculated values for MDC₉₀ (plantarflexion: 47.8 N; abduction: 14.5 N) were quite large for these measures. While the differences between HV and control groups were statistically significant (plantarflexion: MD = −37.1 N; abduction: -9.8 N), the clinical significance of these results should be interpreted with caution. Methods previously reported to measure hallux plantarflexion strength include the clinical paper grip test[53], strain gauge scales[54], force plate[55] or pressure platform systems[21]. We developed a novel method that would not only give a continuous-scaled quantitative measurement, but would also allow us to examine participants’ ability to abduct the hallux.

Finally, some discussion is warranted regarding self-report data obtained in our study. Both foot-specific questionnaires (FHSQ, FPDI) produced significantly skewed data, and consequently non-parametric statistical tests were used. In particular the summed FPDI scores cannot be interpreted as a true interval scale unless a Rasch analysis is performed[36], which was not undertaken for the current study. Potential for recall bias and variation between individuals’ interpretation of pain rating scales should also be considered when interpreting self-report data[56, 57]. It is interesting to note that self-report measures of foot-specific pain and disability showed large differences between groups, while self-reported general functioning and physical performance tests were less indicative of limitations in participants with HV. Study participants reported more pain and disability than was evident on physical performance tests, thus it may be that foot-specific questionnaires (FHSQ, FPDI) capture more than typical measures used for physical function. For example, while general physical functioning (SF-36v2®), activity participation and walking performance were not impaired in this sample, HV subjects reported significant functional disability on the FPDI, which considers the influence of foot pain and other aspects such as walking distance and rough or hard surfaces. Future studies could utilise more challenging physical performance tasks to explore functional difficulty experienced by healthy adults with HV.

HV deformity is accompanied by significant foot-specific pain and disability, muscle weakness around the first MTPJ and increased mediolateral postural sway. Concerns regarding appearance and footwear are also important factors to consider for clinicians managing this common deformity. Global physical functioning and participation in activities were not adversely affected in our sample, indicating that HV may not prevent participation in an active lifestyle in otherwise healthy adults.