Impact of coronal and sagittal hindfoot alignment on metatarsus primus elevatus in patients with rheumatoid foot deformities

Abstract Background Typical foot deformity patterns of patients with rheumatoid arthritis (RA) include hallux valgus, claw toes, splay foot, flat foot, and hindfoot valgus deformities. However, some patients present deformities that are different from a typical pattern, such as metatarsus primus elevatus, described as dorsal elevation of the first metatarsal in relation to the lesser metatarsals. We speculated that metatarsus primus elevatus might be associated with calcaneal inclination and hindfoot varus alignment; however, studies on the association of hindfoot alignment with metatarsus primus elevatus in patients with RA are limited. Objective To elucidate the impact of hindfoot coronal and sagittal alignment on metatarsus primus elevatus in patients with RA. Methods We performed a retrospective analysis of weight-bearing anteroposterior and lateral radiographs of 58 patients (112 feet) with rheumatoid foot deformities who underwent surgery. The degree of metatarsus primus elevatus (dMPE) was assessed based on the distance between the dorsal cortical bones of the first and second metatarsals, as measured on lateral radiographs. The intermetatarsal angle between the first and second metatarsals (M1M2), calcaneal pitch, and the naviculocuboid (N/C) overlap ratio were assessed. Patients were divided into four subgroups representing dMPE quartiles (Q1–Q4) as closely as possible. Analysis of covariance was used to calculate the adjusted means of the radiographic parameters. Logistic regression was used to assess the association between clinical and radiographic parameters and the risk of being in the highest dMPE quartile (i.e., Q4). Results The median dMPE in patients with RA was 2.0 mm (interquartile range, 0.2–5.4 mm). Analysis after adjusting for sex, age, body mass index, and disease duration revealed that the M1M2 angle and N/C overlap ratio in the Q4 subgroup were significantly smaller than those in the Q1 subgroup (p < 0.01 for both parameters). Only the N/C overlap ratio showed a significant inverse association with the risk of being in Q4 (adjusted odds ratio: 0.94, 95% confidence interval: 0.91–0.97). Conclusion A subset of patients with RA exhibits metatarsus primus elevatus, which is associated with hindfoot alignment. Recognizing this less common deformity pattern is important when planning treatment strategies for the rheumatoid foot.