Avulsion fracture of the base of the fifth metatarsal is most commonly associated with injury to which tendon?

• A. Fibularis brevis
• B. Tibialis anterior
• C. Peroneus tertius
• D. Fibularis longus

Answer: (C)

The main idea is that this specific avulsion fracture occurs where a tendon attaches to a bone fragment; pulling on the tendon can tear off a piece of bone. The fibularis brevis inserts onto the tuberosity at the base of the fifth metatarsal. When this tendon pulls, especially during an inversion or sudden force, it can avulse that tuberosity, producing the fracture seen at the base of the fifth metatarsal. The other tendons listed don’t attach to that tuberosity in a way that would cause this particular fracture—their insertions are elsewhere, so they’re not the typical source of this injury. Therefore, the tendon most commonly involved is fibularis brevis.