A radiographic analysis of the contribution of hallux valgus interphalangeus to the total valgus deformity of the hallux.

BACKGROUND The hallux valgus interphalangeus (HVI) deformity is described as rare, but improved outcomes in hallux valgus (HV) surgery is associated with its surgical correction via an Akin osteotomy. The hypothesis of this study is that HVI is common and makes a significant contribution to the total valgus deformity of the hallux (TVDH). METHODS 285 pre-operative foot radiographs (193 with HV, 92 non-HV), utilising standardised radiographic and measurement techniques, were analysed retrospectively. The hallux valgus angle (HVA), intermetatarsal angle (IMA), interphalangeal angle (IPA) and distal metatarsal articular angle (DMAA) were measured. The TVDH was calculated as the sum of the HVA and IPA. RESULTS 163 (57.2%) of the study population were Caucasian, 119 (41.8%) African and 3 Indian (1.0%). 236 (82.8%) of the population was female. There was a statistically significant difference in the proportion of abnormal IPA in the Caucasian population 112 (68.7%) compared to the proportion of abnormal IPA in the African population 64 (53.8%), p=0.01. The average contribution of the IPA to the TVDH across the whole study population was a mean (SD) of 37.9% (21.2). The average contribution of IPA to TVDH was greater in feet without HV (58.0%) when compared to feet with HV (28.3%). HVI is common, particularly in Caucasians (p=0.01) and makes a significant contribution to the TVDH (p<0.01). The contribution to the TVDH is more significant in mild HV. There is an inverse relationship between the IPA and other angular measurements in the foot. CONCLUSION HVI is a common entity. The significant contribution of the IPA to the TVDH dictates that HVI must be incorporated in management algorithms. The TVDH should replace the isolated concepts of HV and HVI. LEVEL OF EVIDENCE Level III, retrospective cohort.