**4. Discussion**

HAV is a forefoot pathology related to PPH in valgus and abduction deviations plus the IMTT bone in adduction deviation [1,2,51]. Previous studies [18,52–54] have shown the relationship between HAV development and the narrow toe tip footwear typical of the high heel shoes; other groups [1,27] speculated that high heels have an etiology factor in HAV development with only one prior review [12] considering the isolated high heels's effect on first MPJ deviation on its conclusions but without any further study. This research was the first study to use the Polhemus Fastrack® to assess the effects of high heels on static and dynamic conditions on PPH and IMTT. Thus, many statistically significant variables have been obtained, but of the 96 variables studied here across 80 subjects, only a few had statistically significant correlations. Due to the independent evaluation of the bones, we could not establish a direct discussion with the findings of other authors who interpreted HAV as a global forefoot disease [34]. In addition, this work has studied a healthy population without any limitation of mobility in their joints. Thus, a small difference in segment movements was expected.

Our results on the effect of high heels on PPH during dynamic testing showed that a high heel of 6 cm had a statistically significant increase in abduction in the transverse plane and valgus movement in the frontal plane through IMPJ. There was positive correlation of these values as well as a statistically significant reduction in the adduction; there was negative correlation to the barefoot condition. In addition, during static tests, there was a statistically significant abduction increase in PPH for high heels 6 cm or higher with a corresponding positive correlation; therefore, abduction is the only movement that appeared to have a positive correlation and statistical significance in both static and dynamic tests. Thus, we conclude that heels over 6 cm correlated with an abduction effect on PPH without the narrow shoe box interference. This agrees with arguments on the biomechanical development of HAV processes that claimed that the PPH was the first precursor bone segment to begin the HAV pathology [51,55–57] due to medial capsular tension ligaments that become hyper-elastic and let the PPH proceed to abduction deviation [7]. The PPH then has a strong push forward to the IMTT in the push off phase that can lead to adduction deviation.

More recently, Wang et al. [34] reported an increase in forefoot abduction while wearing 5 cm high-heeled shoes during walking vs. barefoot arguing that the squeezing effect of the high heels on the foot had a displacement toward the toe tip. This produced valgus and abduction of PPH. We agree with these conclusions, but we showed that the foot produces this "abductor effect" on PPH; it is not from the narrow box of the shoes. In addition, we obtained a large increase in the value of PPH abduction with a 3 cm heel. This result was not statistically significant.

The effects of high heels had contradictory effects on IMTT movements. There were no statistically significant results to justify its implication on HAV development in contrast with other groups that identified IMTT adduction and valgus [1,2] as well as inclination of the IMTT axis as risk factors of bunion [58] or IMCJ hypermobility [59]; both movements on transverse and frontal planes are under doubt because of a lack of objective data [60]. Surprisingly, it seemed that wearing any high heel might decrease valgus deviation of IMTT although this condition only had statistical significance with 6 cm heels; there was no positive correlation. The absence of concrete IMTT values related with typical HAV development suggests that PPH may be the principal bone to start the pathological process. This agrees with a study that identified the presence of HAV with greater reduction in size of the adductor hallucis muscle [61] as one of the most important muscles to balance the PPH.

In contrast to previous studies [62] that found no association between footwear characteristics (heel height and narrow box) and HAV development, our cohort had (18–38 years) had movement deviation of PPH in heels over 6 cm. This agrees with other studies where older women reported HAV. They wore shoes with heels over 5 cm [12]. This work showed data on IMTT and PPH from the two different static and dynamic conditions and 3 kinds of high heels. Thus, we selected and summarized heel heights and determined that high heels could develop HAV. 6 cm was the common height for both static and dynamic situations; these different variables converged to induce HAV development.

Most of the main limitations in other similar studies were equivocal results secondary to small sample size [19], differences in anthropometric characteristics of the subjects groups [63], or the inclusion of participants wearing their own high-heeled shoes [64]. This leads to a heterogeneous sample [19]. We studied a homogeneous sample that improved the measurement conditions of other groups that also failed to show ICC, CCC, SEM or MDC values [10,34]; our data had low to moderate correlation, and we considered these statistical parameters.

Coupling relationships between hindfoot inversion/eversion and forefoot abduction/adduction (*R*<sup>2</sup> = 0.5) and hallux dorsiflexion/plantarflexion (*R*<sup>2</sup> = 0.7) were the only prior references found on this topic [65]. It had similar Spearman values in that work but did show any contrast between data because the authors did not assess individual movements of any segment bone as PPH or I MTT, like in the present work. These are the only specific correlations done relative to PPH and IMTT in the literature and confirm the low Spearman correlations of our values.
