Progressive distance mapping of the plantar fat pad in hallux valgus reveals subgroup-specific morphologic subtypes

Hallux valgus (HV) is a prevalent three-dimensional foot deformity, yet it is primarily assessed in the anteroposterior plane radiographs. The role of the sagittal plane and specifically the plantar fat pad remains poorly understood. This study aimed to quantitatively explore the relationship between plantar fat-pad geometry and HV progression.

In this retrospective study, we analysed 274 feet from 144 patients who underwent HV corrective surgery at Hasharon Hospital, Israel (2014-2024). Using custom Python-based software, we annotated 22 anatomical landmarks on preoperative, weight-bearing lateral radiographs (3 plantar fat pads and 19 plantar bony points). For each fat pad, 19 Distance features were generated (total 57), comprising 19 pairwise standardised distances. Associations between these distances and standard HV angles (HVA, IMA, DMAA, HIA) were assessed using Pearson and Spearman correlations, A subgroup analysis was carried out to compare patients aged below and above 40 years, as well as between male and female patients.

In the full cohort, no distance feature correlated with standard HV angles at the prespecified threshold ([Formula: see text] or [Formula: see text], two-sided [Formula: see text]). Stratified analyses revealed subgroup-specific patterns: females showed three significant relationships (mainly involving the calcaneal fat pad), whereas males showed 29 predominantly negative forefoot-hindfoot correlations (e.g., base of 5th metatarsal fat pad [Formula: see text] calcaneal fat pad vs. HIA: [Formula: see text], [Formula: see text], both [Formula: see text]). The [Formula: see text] y group exhibited six significant features (including sesamoid-based positives), while the [Formula: see text] y group showed two first-ray-focused associations. Several effects were stronger on Spearman than Pearson, consistent with nonlinearity, and many between-group differences were significant by Fisher's [Formula: see text]-to-[Formula: see text] ([Formula: see text]). Progressive Distance Mapping (PDM) summarized these effects into composite, radiograph-overlaid maps.

Progressive Distance Mapping (PDM) may suggest subgroup-dependent, progressive associations between plantar fat-pad-anchored distance geometry and hallux valgus (HV) severity. Despite no universal cohort-level correlations, PDM identifies four distinct morphologic subtypes within each subgroup (stratified by age and sex), this may suggest differing pathogenesis and patterns of plantar fat-pad involvement. These subtype-specific signatures are often nonlinear.