Triplanar Quantitative Radiographic Analysis of the First Metatarsal-Phalangeal Joint in the Hallux Abductovalgus Deformity.

Although hallux abductovalgus (HAV) is widely considered to be a triplanar deformity involving the transverse, sagittal, and frontal planes, most of the published literature has focused on evaluating the deformity in only the transverse plane, and we are unaware of any investigation objectively evaluating the relationship among the 3 planes in the setting of HAV deformity. The objective of this investigation was to quantitatively evaluate radiographic measurement of the relationship between the transverse, sagittal, and frontal planes in the HAV deformity. Anteroposterior, lateral, and sesamoid axial radiographs from 42 consecutive feet were evaluated with measurement of the first intermetatarsal angle, hallux abductus angle, metatarsal sesamoid position, first metatarsal inclination angle, sesamoid rotation angle, and tibial sesamoid grade. Variables were graphically depicted against each other on frequency scatter plots with calculation of a regression line and Pearson's correlation coefficient. As transverse plane deformity increased, the frontal plane deformity also tended to increase and the first metatarsal inclination angle tended to decrease. And as frontal plane deformity increased, the first metatarsal inclination angle tended to decrease. To our knowledge, these are the first quantitative and objective data in support of a triplanar component to the HAV deformity, and we believe this reinforces the evaluation of this deformity with emphasis on all 3 planes.