ASSESSING SESAMOID SUBLUXATION - HOW GOOD IS THE AP RADIOGRAPH

Subluxation of the metatarsosesamoid joints frequently occurs with the development of hallux valgus deformity, and the restoration of a norm al metatarsosesamoid articulation has been proposed as essential for a chieving 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 s ubjects with hallux valgus and 30 control subjects participated in thi s study by undergoing both AP and tangential weightbearing radiographs . The sesamoid station on the AP radiographs was compared with the pos ition of the sesamoids on tangential radiographs, using a new continuo us measure to estimate subluxation. In approximately half of the cases , we found a difference between the apparent sesamoid station on the A P radiograph and the true position on the tangential one. Increased me tatarsal rotation was associated with misclassification of the sesamoi d station on the AP radiograph. We conclude that the standard method f or measuring the sesamoid station on the AP radiograph is not valid. S urgeons wishing to evaluate the metatarsosesamoid joint should obtain weightbearing tangential radiographs.