Characteristics of Intermetatarsal Angle Between the Second and Fifth Metatarsals (M2-M5A) in the Rheumatoid Foot

Background: Increasing of intermetatarsal angle between the first and second metatarsals (M1-M2A) has been reported as a risk factor for recurrence of hallux valgus (HV) deformity, on the other hand, increasing of intermetatarsal angle between the second and fifth metatarsals (M2-M5A) has been reported as a risk factor for resubluxation of the metatarsophalangeal (MTP) joint of the lesser toe after rheumatoid forefoot surgery. In this study, parameters related to increasing M2-M5A were investigated, as compared with M1-M2A and M1-M5A. Methods: Radiographic parameters including M1-M2A, M1-M5A, and M2-M5A were retrospectively evaluated for 119 lower limbs from 68 patients with rheumatoid arthritis (RA). To clarify the clinical importance of these intermetatarsal angles, relationships with results from the timed up-and-go (TUG) test were also investigated. Results: M1-M5A showed no correlation with mid-hind foot parameters, whereas M1-M2A and M2-M5A correlated with valgus/varus parameters. An increased M1-M2A was associated with lateral shift of the loading axis in the tibial plafond, whereas an increased M2-M5A was associated with medial shift, but M1-M5A showed no associations. M2-M5A/M1-M2A was significantly lower (1.7) in the normal TUG group than in the delayed TUG group (2.8) (p=0.045). Conclusions: Different patterns of spread are seen for the forefoot. One has a predominantly increased M1-M2A with lateral shift of the loading point in the tibial plafond, whereas the other has a predominantly increased M2-M5A with medial shift of the loading point in the tibial plafond. M2-M5A also should be calculated, and M2-M5A/M1-M2A might be meaningful in understanding physical mobility in RA patients.