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Subluxation of the metatarsosesamoid joints frequently occurs with the development of hallux valgus deformity, and the restoration of a normal metatarsosesamoid articulation has been proposed as essential for achieving a biomechanically sound operative result. The position of the sesamoid bones on the AP radiograph is used often to assess the pre- and postoperative relationship between the hallucal sesamoids and the metatarsal sulci. We evaluated the validity of this approach. Thirty subjects with hallux valgus and 30 control subjects participated in this study by undergoing both AP and tangential weightbearing radiographs. The sesamoid station on the AP radiographs was compared with the position of the sesamoids on tangential radiographs, using a new continuous measure to estimate subluxation. In approximately half of the cases, we found a difference between the apparent sesamoid station on the AP radiograph and the true position on the tangential one. Increased metatarsal rotation was associated with misclassification of the sesamoid station on the AP radiograph. We conclude that the standard method for measuring the sesamoid station on the AP radiograph is not valid. Surgeons wishing to evaluate the metatarsosesamoid joint should obtain weightbearing tangential radiographs.

A method for measuring hallucal rotation or weightbearing tangential radiographs is described. Under controlled conditions using cadaver specimens, 10 degree changes in hallucal rotation were associated with a mean change in radiographically measured rotation of 10.6 degrees (S.D. = 2.3 degrees). A clinical study of 30 control patients and 39 patients presenting with a chief complaint of a bunion deformity was undertaken to assess the reliability of the measurement method. The overall reliability was high for both groups (r = 0.98). A significant difference was found between mean values for hallucal rotation in the two groups (P < 0.005). There is a modest association between increasing valgus deviation and increasing rotation of the hallux (r = 0.43, P < 0.01). This study suggests that bunion deformities involve variable degrees of axial and coronal plane rotations of the first metatarsophalangeal joint and that the concept of a planar "hallux valgus" deformity may insufficiently describe this three-dimensional clinical condition.

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