New radiographic analysis of sesamoid rotation in hallux valgus: comparison with conventional evaluation methods.

The position of the hallucal sesamoids needs to be included in evaluation of hallux valgus. In order to quantify the rotational position of the hallucal sesamoids, a new weightbearing tangential radiograph was established by means of a specially designed tangential positioning device. This device has a depression, and a tangential radiograph is taken with the metatarsophalangeal joint at 45 degrees dorsiflexion. A lead marker plate is placed on the depression to show the horizontal plane, and the sesamoid rotation angle (SRA) is measured. The SRA is the angle between the tangential line of the most inferior aspect of the medial-lateral sesamoids and the lead marker line. The SRA was compared with values of the four-grade scale and seven-position scale which were measured from the antero-posterior view, with respect to the hallux valgus angle (HVA), by means of conventional methods. Measurements were made of 58 feet in 29 patients with hallux valgus and 64 feet in 32 normal subjects. The SRA showed the highest correlation among the three parameters (r=0.817). Some cases had a disparity regarding the position of the sesamoids between the tangential view and the AP view due to misclassification on the AP view. We conclude that the scale of position of the sesamoid on the AP view is not valid in some cases, whereas the SRA is useful for assessing quantitatively the rotational position of the hallucal sesamoids in cases of hallux valgus.