Joint capsule pathology as a contributor to pain in hallux valgus: a histological study

Pain in hallux valgus (HV) often arises from the medial aspect of the first metatarsophalangeal (MTP) joint, but its mechanisms remain unclear. This study investigated the histological and molecular features of the medial capsule (MC) and their association with pain. Fifty feet from 49 HV patients undergoing corrective surgery were analyzed histologically and immunohistochemically for calcitonin gene-related peptide (CGRP), matrix metalloproteinase-3 (MMP3), and collagen type I/III. The severity of capsular degeneration was scored, and pain was evaluated using the Self-Administered Foot Evaluation Questionnaire (SAFE-Q). MC degeneration correlated with deformity severity (rs = 0.63, P < 0.0001). CGRP was strongly expressed around vessels and chondrocyte-like cells, with sparse expression in fibroblasts, irrespective of deformity degree. CGRP levels correlated positively with MMP3 (rs = 0.35, P < 0.05) and inversely with pain-related SAFE-Q scores (rs = − 0.52, P < 0.0001). Feet with bunion tenderness showed higher CGRP expression and worse pain scores. These findings suggest that bunion pain in HV is more closely associated with CGRP expression than with deformity severity, highlighting CGRP as a potential therapeutic target.