The fracture is the result from an inversion force. The peroneus brevis contracts while the fifth metatarsal is fully loaded. As the peroneus brevis contracts forcefully it avulses the base of the fifth metatarsal.
AP, lateral and oblique x-rays confirm the diagnosis.
The Jones fracture is an extraarticular fracture.
It occurs in the relatively poorly vascularized metaphyseal bone between the insertions of the peroneus tertius and the peroneus brevis tendons which combine to produce a deforming force, as illustrated. The poor blood supply and loading of the fracture by continuing muscle force even without weight bearing increase the risk of delayed healing or non-union.
The Torg classification has three parts:
Torg I: The fracture is an avulsion fracture of the base of the fifth metatarsal.
Torg II: The fracture is intraarticular into the cuboid metatarsal joint.
Torg III: The fracture is through the metaphyseal diaphyseal junction.