A Jones fracture is a specific type of break that occurs near the base of the small toe bone, known as the fifth metatarsal. The injury is named after British orthopedic surgeon Sir Robert Jones, who first described the condition in 1902. This break is distinct from other foot fractures due to its precise location and the unique challenges it presents for healing.
Anatomy of the Fifth Metatarsal
The fifth metatarsal is the long bone located on the outer side of the foot, connecting the little toe to the midfoot. Its proximal end, the part closest to the ankle, is divided into three distinct zones for classification purposes.
The first zone is the tuberosity, where an avulsion fracture often occurs. Zone 3 is the proximal shaft, a common site for stress fractures. A Jones fracture is strictly defined as a break occurring in Zone 2, the narrow junction between the expanded base and the long shaft of the bone. This specific location dictates both the mechanism of injury and the prognosis for recovery.
Specific Biomechanics of the Injury
A Jones fracture typically results from an indirect, high-magnitude force rather than a direct impact. The physical motion involves a combination of two specific foot movements: plantar-flexion and adduction. Plantar-flexion means the foot is pointed downward, and adduction refers to the forefoot being forcefully turned inward.
This mechanism often occurs when an individual is bearing weight on the lateral, or outside, edge of the foot. The combination of the foot being pointed down and rolled inward causes concentrated stress where the fifth metatarsal meets the cuboid bone in the midfoot. This pressure creates a transverse or oblique fracture line directly across the Zone 2 junction.
The injury is frequently seen in sports requiring quick directional changes or pivoting, such as basketball, soccer, or football. Planting the foot awkwardly while changing direction subjects the metatarsal to the combined forces needed to cause the break. A Jones fracture can also develop over time as a chronic fatigue injury from cumulative, repetitive stress during activities like running.
Why This Fracture Requires Special Attention
The location of the Jones fracture in Zone 2 requires special attention because this area is a “vascular watershed area.” This means its blood supply is less robust than the surrounding bone tissue. The proximal end receives blood from metaphyseal arteries, while the main shaft is supplied by a nutrient artery.
The Zone 2 junction exists between these two primary blood sources, creating a region of poor blood flow. When a fracture occurs here, the limited vascularity compromises the delivery of cells and nutrients needed for healing. This anatomical disadvantage contributes to a higher rate of delayed union or non-union, where the bone fails to fuse back together.
Non-union rates can be as high as 15 to 30% when treated conservatively with casting and non-weight bearing. Because of this high risk, treatment often requires more aggressive measures, particularly for active individuals and athletes. Many patients are advised to undergo surgical intervention to stabilize the fracture with a screw, promoting faster and more reliable healing.