Radiographic classification for fractures of the fifth metatarsal base.

Abstract

Avulsion fractures of the fifth metatarsal base (MTB5) are common fore foot injuries. Based on a radiomorphometric analysis reflecting the risk for a secondary displacement, a new classification was developed. A cohort of 95 healthy, sportive, and young patients (age ≤ 50 years) with avulsion fractures of the MTB5 was included in the study and divided into groups with non-displaced, primary-displaced, and secondary-displaced fractures. Radiomorphometric data obtained using standard oblique and dorso-plantar views were analyzed in association with secondary displacement. Based on this, a classification was developed and checked for reproducibility. Fractures with a longer distance between the lateral edge of the styloid process and the lateral fracture step-off and fractures with a more medial joint entry of the fracture line at the MTB5 are at higher risk to displace secondarily. Based on these findings, all fractures were divided into three types: type I with a fracture entry in the lateral third; type II in the middle third; and type III in the medial third of the MTB5. Additionally, the three types were subdivided into an A-type with a fracture displacement <2 mm and a B-type with a fracture displacement ≥ 2 mm. A substantial level of interobserver agreement was found in the assignment of all 95 fractures to the six fracture types (κ = 0.72). The secondary displacement of fractures was confirmed by all examiners in 100%. Radiomorphometric data may identify fractures at risk for secondary displacement of the MTB5. Based on this, a reliable classification was developed.