Factors influencing medial sesamoid arthritis in patients with hallux valgus deformity: Magnetic resonance imaging evaluation

•Medial sesamoid arthritis was associated with advanced age.•Medial sesamoid arthritis was associated with lateral deviation during ambulation.•Medial sesamoid arthritis was associated with the 1st metatarsophalangeal arthritis.•Medial sesamoid arthritis can be assessed using magnetic resonance imaging.•Medial sesamoid arthritis can be predicted by forefoot axial radiographs. The importance of preoperative evaluation of the position and degree of arthritic changes of the medial sesamoid bone before hallux valgus correction is emerging. This is an observational study to evaluate the magnetic resonance imaging (MRI) findings of hallux valgus deformity, and assess the severity of and identify the factors that influence the arthritic changes in medial sesamoid-metatarsal (mSM) joints. We reviewed weight-bearing anteroposterior radiographs, forefoot axial radiographs and MR images of 514 feet of 405 patients who underwent hallux valgus correction. On MRI, the degrees of the arthritic changes in the first metatarsophalangeal (MTP) and mSM joints were categorized into 5 classes. Binary logistic regression analysis was performed to identify the factors affecting the arthritic changes. The binary logistic regression analysis showed that advanced age, more lateralized position of medial sesamoid bone on forefoot axial radiograph, and higher MRI grade of arthritic change of the 1st MTP joint were significant factors contributing to medial sesamoid arthritis (P