The navicular bone is a unique, boat-shaped structure located in the midfoot, positioned on the arch’s inner side. This bone is one of seven tarsal bones, which create the complex framework of the ankle and foot. It acts as a central junction, linking the talus bone of the hindfoot to the three cuneiform bones that connect to the forefoot. This small, yet important, bone is important for transmitting body weight across the foot and maintaining the foot’s structural integrity.
Anatomical Role in the Foot
The navicular bone’s shape is technically described as scaphoid, meaning boat-like, and it is positioned on the medial, or inner, side of the foot. It forms a direct joint with the head of the talus posteriorly, while articulating with the three cuneiform bones anteriorly. This positioning places the navicular at the highest point of the foot’s medial longitudinal arch, making it a central pillar for the structure.
This physical placement allows the bone to function as the “keystone” of the arch, similar to the central stone in a masonry archway. Its location is fundamental to the foot’s mechanics, distributing forces and absorbing shock during activities like walking and running. The posterior tibial tendon attaches directly onto a prominence on the navicular bone. The stability and flexibility of the arch rely heavily on the navicular’s connections, including the strong spring ligament that runs beneath it.
Common Conditions Affecting the Bone
The navicular bone is susceptible to injuries and conditions because of its central load-bearing position and specific anatomical characteristics. Acute fractures are relatively uncommon, usually resulting from high-impact trauma that compresses the bone or low-energy twisting injuries causing small avulsion fractures. These traumatic injuries typically cause immediate pain, swelling, and difficulty bearing weight on the affected foot.
The bone’s central location and limited blood supply make it vulnerable to stress fractures, especially in high-impact athletes such as runners and jumpers. The repetitive strain causes tiny cracks that can lead to chronic midfoot pain that worsens with activity. Another condition is Köhler disease, a form of avascular necrosis that primarily affects children between the ages of three and seven. In this condition, the blood flow to the navicular is temporarily interrupted, causing the bone tissue to become damaged and collapse. Köhler disease is generally managed non-operatively with rest and immobilization, such as a cast, as the bone typically regains its normal structure over time.
Accessory Navicular Syndrome
A specific developmental variation is the presence of an accessory navicular, an extra piece of cartilage or bone located on the inner side of the foot. This piece is congenital, present from birth, and occurs in approximately 10 to 14 percent of the population, though it often remains asymptomatic. When this extra bone or cartilage becomes painful, the condition is referred to as Accessory Navicular Syndrome.
The pain often arises when the extra piece is irritated by friction from footwear or by the pulling action of the posterior tibial tendon, which attaches nearby. This condition is categorized into three types: Type I is a small, round bone piece embedded within the tendon; Type II is connected to the navicular by a fibrous or cartilaginous bridge; and Type III is a bony enlargement of the navicular itself. Initial management focuses on conservative treatments like rest, anti-inflammatory medication, and custom orthotics to support the arch and reduce pressure. If pain persists despite extended non-surgical care, the accessory bone may be surgically removed, a procedure that often includes reattaching the posterior tibial tendon to the main navicular bone.