The Spine–Foot Connection: Investigating Compensatory Mechanisms in Degenerative Spine Disease Through Foot Deformity Patterns

Background and Objectives: In degenerative spine disease, compensatory mechanisms are activated to maintain upright posture, extending beyond the spine to involve the pelvis, lower limbs, and feet. These adaptations may be accompanied by differences in foot alignment, which could be associated with sagittal balance. The aim of this study is to investigate the relationship between foot alignment and spinal posture in patients with degenerative spine disease and evaluate whether foot deformities are associated with sagittal imbalance in degenerative spine disease. Materials and Methods: We retrospectively reviewed 98 patients with degenerative spine disease who underwent preoperative standing EOS imaging between 2017 and 2025 at a single academic spine centre. Meary’s angle, talocalcaneal angle, and calcaneal pitch were measured on lateral EOS images to classify feet as flat, normal, or cavus. Spinopelvic parameters were extracted from EOS and conventional radiographs. Differences in spinal parameters across foot groups were compared using ANOVA, and linear regression evaluated associations between sagittal vertical axis (SVA) and foot angles. Results: Among spinopelvic parameters, only SVA significantly differed between foot groups, with flatfoot patients showing greater forward imbalance (p = 0.035). Regression analysis demonstrated an inverse relationship between SVA and both talocalcaneal angle (p = 0.003) and calcaneal pitch (p = 0.034), suggesting that greater forward trunk inclination was associated with flatter feet. Degenerative scoliosis patients demonstrated a bimodal pattern with more flat and cavus feet (p = 0.006), while herniated disc patients more often exhibited flatfoot (p = 0.031). Conclusions: Foot posture abnormalities, particularly flatfoot, are associated with sagittal spinal imbalance, suggesting foot posture may be associated with global alignment and could reflect distal postural adaptations.