The navicular bone is a small, uniquely shaped structure within the human foot that plays a large role in our ability to stand and walk. Its name originates from the Latin word navis, meaning “ship,” a reference to its boat-like or kidney-shaped form. This foundational bone connects the ankle to the midfoot, helping to transfer forces and maintain the foot’s complex architecture.
Location and Structure of the Tarsal Navicular
The navicular is one of the seven tarsal bones, the collection of bones that form the ankle and upper part of the foot. It is situated on the inner side of the foot, placing it firmly in the midfoot region. This single bone is positioned like a central link in a chain, articulating with five neighboring bones.
The bone’s proximal, or rear, surface is concave and articulates with the rounded head of the talus, which is the ankle bone. Its distal, or front, surface is convex and connects with the three cuneiform bones. Laterally, the navicular also makes contact with the cuboid bone, making it a hub for movement and force transmission.
Essential Role in Foot Function
The navicular is often referred to as the keystone of the medial longitudinal arch, which is the highest arch along the inner side of the foot. This arch provides the necessary spring and flexibility for walking and running, and the navicular acts as its central support point. The bone’s role in force transmission is significant, particularly during the push-off phase of walking, as it transmits weight from the talus to the smaller cuneiform bones.
It serves as the attachment site for the posterior tibial tendon, which connects to a prominence on the inner side of the bone called the navicular tuberosity. This tendon is a primary dynamic stabilizer, wrapping around the ankle to help support the arch and invert the foot. The navicular acts like a pulley for the tendon, enabling it to pull upward and inward to counteract forces that would otherwise cause the arch to collapse.
Common Injuries and Developmental Variations
The navicular bone is particularly susceptible to certain issues, including stress fractures and a congenital variation known as Accessory Navicular Syndrome. Navicular stress fractures are overuse injuries common in athletes involved in repetitive, high-impact activities like running or basketball. The bone is prone to these fractures because its central third has a limited blood supply, making it less equipped to heal micro-damage caused by repeated mechanical loading.
This type of fracture typically presents as a vague, deep ache on the inner side or top of the midfoot that worsens with activity and may lead to a limp. The pain often begins gradually and can progress to constant discomfort. In contrast, Accessory Navicular Syndrome (ANS) is a condition where an extra piece of bone or cartilage exists next to the main navicular bone.
This accessory bone is an anatomical variation present in an estimated 4% to 14% of the population and is not needed for normal function. The condition becomes a syndrome when the accessory bone or its connection to the main navicular becomes irritated, often during adolescence or following trauma. This irritation typically stems from friction against footwear or strain on the posterior tibial tendon. Symptoms of ANS include a visible bony prominence on the inner arch, accompanied by pain, swelling, and tenderness in the area.
Identifying and Treating Navicular Issues
Diagnosing navicular issues begins with a physical examination, where a doctor assesses for localized tenderness and swelling in the midfoot. Standard X-rays are typically the first imaging step, which can reveal the presence of an accessory navicular or sometimes show signs of a stress fracture. Because of the bone’s limited blood flow and the subtle nature of the injury, advanced imaging like a Magnetic Resonance Imaging (MRI) or Computed Tomography (CT) scan is often necessary to confirm a stress fracture.
Treatment for navicular issues is often initiated with non-surgical, conservative methods. For stress fractures, this involves a period of non-weight-bearing rest, typically achieved through immobilization in a cast or boot for six to eight weeks to allow the bone to heal. Accessory Navicular Syndrome is often managed with rest, anti-inflammatory medication, and custom orthotics to relieve pressure on the irritated bone and support the arch. If conservative treatments fail to alleviate persistent pain, surgical intervention may be considered. Surgery for a stress fracture may involve internal fixation with screws to stabilize the bone, while the procedure for ANS usually involves excising the accessory bone and reattaching the posterior tibial tendon to the main navicular bone.