[Correlation between fourth brachymetatarsia and hallux valgus]

To investigate the correlation between fourth brachymetatarsia and hallux valgus, and to provide evidence-based support for clinical decision-making.

A retrospective analysis was conducted on 68 patients (89 feet) with congenital fourth brachymetatarsia treated between August 2021 and November 2025. All patients were female, aged 18-44 years (mean, 28.1 years). The hallux valgus angle (HVA), intermetatarsal angle (IMA), and shortening length of the fourth metatarsal were measured on standardized weight-bearing anteroposterior foot X-ray films. Hallux valgus-related complications were recorded. The prevalence of hallux valgus was compared with the reference value reported for the general adult female population in China (14.74%). Spearman rank correlation analysis was used to evaluate the correlations of HVA and IMA with age and metatarsal shortening length.

In the entire cohort, HVA ranged from 5.65° to 44.95° (mean, 20.56°), IMA ranged from 6.46° to 20.45° (mean, 11.61°), and the shortening length of the fourth metatarsal ranged from 5.62 to 18.01 mm (mean, 12.05 mm). Hallux valgus was present in 55 feet, giving a prevalence of 61.80%, which was significantly higher than the reference value for the general adult female population in China ( Z=12.523, P<0.001). Associated symptoms in feet with hallux valgus included bunion (31 feet, 56.36%), transfer metatarsalgia of the second metatarsal head (16 feet, 29.10%), transfer metatarsalgia of the third metatarsal head (10 feet, 18.18%), plantar callosity (8 feet, 14.55%), and dorsal callosity (4 feet, 7.27%). In patients with hallux valgus, HVA ranged from 15.83° to 44.95° (mean, 26.16°) and IMA ranged from 9.01° to 20.45° (mean, 13.35°). Correlation analysis showed that both HVA and IMA were positively correlated with the shortening length of the fourth metatarsal ( r=0.290, P=0.016; r=0.420, P<0.001), whereas no correlation was found between HVA or IMA and age ( r=-0.061, P=0.751; r=0.132, P=0.525).

Patients with fourth brachymetatarsia have a significantly higher prevalence of hallux valgus, which is positively correlated with the degree of metatarsal shortening but not with age, suggesting an anatomical rather than age-related etiology. The study redefines the clinical nature of fourth brachymetatarsia, promoting a paradigm shift from "cosmetic correction" to "functional reconstruction". It is recommended that this deformity be included as a screening indicator for populations at high risk of hallux valgus.