Background Several midfoot deformities are described to progress hallux valgus (HV) deformity . Involvement of hindfoot deformity in the 1st ray deformity is also suggested . In rheumatoid foot, complicated deformity in foot are often seen. Especially, dorsal dislocation of lesser toe MTP joint combined with HV is frequently observed in rheumatoid arthritis (RA) cases. Currently, clarified and comprehensive evaluations in RA foot deformity has not been done.
Objectives In this study, relationship between radiographic findings through hind to forefoot and HV angle was evaluated in RA cases, while grouping by existence of 2nd MTP joint dorsal dislocation.
Methods X-ray pictures at standing position in 160 RA feet and ankles were evaluated. 1st MTP Larsen grade, existence of 2nd MTP dorsal dislocation, HV· M1M2· M1M5 angle, shape of 1st mtetatarsal head  and position of sesamoid  which are index for pronation of 1st metatarsal, metatarsus primus varus (MPV) angle, M1M2 diastasis , angle between talus and navicular  (index for pronated foot), internal arch (IA) angle, Tibio-Calcaneal (TC) angle, distance between the axis of tibia and calcaneus (calcaneal lateral offset) were measured, and evaluated.
Results M1M2 angle and HV angle correlated (R2=0.7) in the group without 2nd MTP joint dislocation (D0), while dislocation group (D2) showed relatively weak correlation (R2=0.3). The mean HV angle in D0 was 21±14.1°, while 45±16.8° in D2, that was significantly greater (P<0.001). Larsen grade and HV angle did not correlate in D0 cases, whereas correlated in D2 cases (R2=0.3). MPV angle correlated with M1M2 and HV angle (R2=0.5) in D0 group, but not in D2 group. M1M2 diastasis related to MPV angle in both group (R2=0.3). Pronated foot index correlated with IA angle (R2=0.3) in both group, furthermore enlargement of IA angle worsened the M1M2 angle expansion (R2=0.3) in D0 group. Calcaneal lateral offset had no direct relationship to HV, but correlated with M1M2 angle (R2=0.3), and pronated foot index (R2=0.5) in both group.
Conclusions In RA cases, lateral offset hindfoot deformity is always involved in M1M2 angle expansion, followed by progression of HV. Correlation between M1M2 and HV angle was stronger in D0 cases than that of D2 cases. Especially, valgus hindfoot with flat foot deformity caused pronation of 1st metatarsal, leading to HV progression in D0 group, while 1st MTP destruction and 2nd MTP dislocation worsened HV in D2 group. The influence of hindfoot change also must be considered to evaluate the outcome after surgeries for HV. Furthermore, when 1st MTP joint preserved surgeries are selected for HV deformity in RA cases, adequate correction of 2nd MTP joint and making stable lateral support for hallux are strongly recommended to avoid the recurrence of HV.
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Disclosure of Interest None Declared
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