The human foot is a complex structure made up of 26 bones, and five of the most important are the metatarsals, which form the bridge between the ankle and the toes. These long bones are responsible for distributing body weight and facilitating movement during walking and running. The fifth metatarsal, located on the outer border of the foot, is frequently the subject of discussion in sports medicine and orthopedics. Its unique anatomical position and biomechanical function make it distinctly susceptible to certain types of painful injuries.
Locating the Bone and Its Structure
The fifth metatarsal is situated along the lateral, or outside, edge of the foot, connecting the midfoot bones to the little toe. Like the other four metatarsals, this bone is divided into three distinct anatomical regions: the head, the shaft, and the base. The head forms the joint with the pinky toe, while the shaft is the long, slender body of the bone.
The proximal end, called the base, is the section closest to the ankle and articulates with the cuboid bone of the midfoot. A prominent, easily felt bony bump, known as the tuberosity or styloid process, juts out from the lateral side of the base. This tuberosity is a frequent site of injury and provides a strong anchor point for various tendons and ligaments.
The 5th Metatarsal’s Function in Movement
The fifth metatarsal plays a unique and supportive role, largely governing the stability of the foot’s outer edge, known as the lateral column. It helps maintain the foot’s lateral longitudinal arch, which is crucial for absorbing impact during initial ground contact. This bone endures significant forces, particularly during the propulsion or push-off phase of walking and running.
Its structural integrity is maintained by strong tendinous attachments, notably the peroneus brevis tendon, which inserts directly into the prominent tuberosity at the base. The tension exerted by this tendon helps control the foot’s position and supports the ankle during weight-bearing activities. The bone’s function is dynamic, acting as a pulley system to facilitate stable movement.
Anatomical Vulnerability to Stress
The structural design and positioning of the fifth metatarsal contribute directly to its high rate of fracture. Because it is located on the outermost edge, it acts as a primary fulcrum during an ankle sprain, a common mechanism for injury. When the foot rolls inward, a motion called inversion, the entire body weight can be leveraged against this single bone.
Another significant vulnerability lies in its vascular supply, especially in the area known as the metaphyseal-diaphyseal junction. This region, just beyond the base, is a “vascular watershed area” where the blood flow from two different arterial sources meets but does not fully overlap. This limited blood supply means that fractures occurring here are significantly slower to heal than breaks in other parts of the bone. Furthermore, the fifth metatarsal is only supported by an adjacent metatarsal on one side, unlike the middle three, making it less structurally reinforced against lateral stresses.
Recognising Common Injury Types
Injuries to the fifth metatarsal are generally categorized into three types based on their specific location and mechanism of trauma.
Avulsion Fracture (Zone 1)
The first and most common type is the avulsion fracture, often called a Pseudo-Jones or Dancer’s fracture, which occurs at the very base. This break is caused by an acute, forceful pull from the attached peroneus brevis tendon or the lateral band of the plantar fascia during a sudden inversion of the ankle.
Jones Fracture (Zone 2)
A Jones fracture is a more serious break that occurs at the proximal metaphyseal-diaphyseal junction, the area with the poor blood supply. This fracture typically results from a combination of repetitive microtrauma or a sudden indirect adduction force on the forefoot.
Stress Fractures
The third category includes stress fractures, which are hairline breaks resulting from cumulative, low-grade force over time, often seen in athletes due to increased training regimens.
Regardless of the specific type, symptoms often include immediate pain, tenderness, swelling, and bruising along the outer side of the foot. A person experiencing these signs, especially an inability to bear weight on the foot, should immediately cease activity and apply the RICE protocol—Rest, Ice, Compression, and Elevation. Timely medical evaluation is necessary, as the location of the fracture determines the appropriate treatment, which can range from non-weight-bearing immobilization to surgical intervention.