Radiographic Morphologic Characteristics of Bunionette Deformity.

Abstract

Background: Bunionette deformity is characterized as head hypertrophy, lateral bowing, or splaying of the fifth metatarsal, or a combination of these deformities. Most previous studies have focused on the fourth and fifth metatarsals; few have analyzed the radiographic morphologic characteristics of the entire foot. The morphologic characteristics of the entire foot in cases of symptomatic bunionette deformity were analyzed with a radiographic image-mapping system. Methods: The system was used for the morphologic analysis of 112 feet with symptomatic deformity and 123 asymptomatic control feet. The mapping system includes 2-dimensional coordinates. We compared morphologies of both groups on the basis of simple models prepared from x and y coordinates of each reference point, calculated by using the mapping system and various angle measurements. We set cutoff values and categorized cases according to Fallat’s system. We evaluated the characteristics of each type and a new deformity type (type V) wherein no measurement exceeded the cutoff values. Results: The heads of the third, fourth, and fifth metatarsals were more laterally displaced, and the angles between the metatarsal axes were larger in the deformity group. Comparison of deformity types showed that the morphology of the fifth metatarsal might be only one cause of deformity. The intermetatarsal angles between the second and third metatarsals and between the third and fourth metatarsals were larger in deformity type II and type V feet than in control feet. Additionally, the intermetatarsal angles between the third and fourth metatarsals and between the fourth and fifth metatarsals were larger in deformity type III and type IV feet than in control feet. Conclusion: We believe it is necessary to not only focus on the fourth and fifth metatarsals, but also assess the morphologic characteristics of the entire foot in patients with a bunionette, including splaying of all the metatarsals and the forefoot width, when planning surgery. Level of Evidence: Level III, retrospective comparative study.