Non-Invasive Clinical Assessment of Medial Longitudinal Arch Morphology and Its Interrelationships in Foot and Ankle Musculoskeletal Pain: a Cross-Sectional Analytical Study.

Objectives: Accurate non-radiological assessment of the medial longitudinal arch (MLA) is essential for diagnosing foot deformities and guiding musculoskeletal pain management, yet no consensus exists on which method most reliably reflects MLA morphology in populations with ankle-foot pain, and comparative data across methods within the same clinical sample remain limited. This study evaluated and compared four non-radiological MLA measures and examined their interrelationships with ankle-foot musculoskeletal pain, physical activity and ankle-foot range of motion. Materials and methods: A cross-sectional analytical study was conducted in 158 participants (66 males, 92 females; mean age 46.7±12.4 years) attending the Orthopaedic Outpatient Department of AIIMS Rajkot, India. Four measures were assessed bilaterally: medial longitudinal arch height (MLAH), arch height index (AHI), longitudinal arch angle (LAA) and Feiss line deviation; physical activity was classified with the IPAQ-SF (High PA ≥600 MET-min/week; Low PA <600 MET-min/week). Analyses included Shapiro-Wilk testing, Mann-Whitney U and t-tests, Kruskal-Wallis H with Dunn's post-hoc, Spearman correlations and hierarchical regression. Results: Pes cavus was the predominant arch type (71.5%), followed by normal arch (22.8%) and pes planus (5.7%). All four measures showed good-to-excellent intra-rater reliability (ICC 0.931-1.000) and MLAH and AHI correlated very strongly (ρ = 0.846, p<0.001); Feiss-line agreement with the final foot type reference was definitional, since that reference incorporates Feiss-line data. Plantarflexion, subtalar inversion and eversion differed significantly across arch types (all p<0.001). MLAH, AHI and Feiss line correlated significantly with both the numeric rating scale (NRS) and American Orthopaedic Foot and Ankle Society (AOFAS) scores (all p<0.05). Pes cavus was associated with higher pain (NRS 7.0 vs 6.0, p_adj = 0.006) and lower function (AOFAS 70.0 vs 74.0, p_adj = 0.005) than normal arch. In regression, sex (OR = 2.869, p = 0.012) and body mass index (BMI) (OR = 1.129, p = 0.002) were the strongest independent predictors of high pain. Conclusions: Non-radiological MLA assessment is reliable and clinically feasible. Pes cavus predominated in this ankle-foot pain population and was associated with restricted plantarflexion and increased subtalar inversion. Physical activity level was independently associated with pain intensity beyond arch morphology, but with higher, not lower, pain among more active participants; this cross-sectional association does not show that activity affects pain in either direction. A multimethod classification approach is recommended when arch type directly informs treatment.