Navicular Bone: Stress Fractures, Accessory Navicular Syndrome, Causes, and Treatment

What causes navicular?

Problems with the navicular bone, such as stress fractures or accessory navicular syndrome, are typically caused by repetitive stress, biomechanical imbalances, or the presence of an extra bone, leading to pain and dysfunction in the midfoot.

Understanding the Navicular Bone

The navicular bone is one of the seven tarsal bones located in the foot, positioned on the medial (inner) side, just in front of the ankle joint. Its name, derived from the Latin word "navicularis" meaning "little ship," aptly describes its boat-like shape.

Functionally, the navicular bone plays a critical role in the biomechanics of the foot:

• Keystone of the Arch: It is a crucial component of the medial longitudinal arch, acting as a keystone that helps maintain the arch's integrity and distribute forces during weight-bearing activities.
• Muscle Attachment: The tibialis posterior tendon, a primary stabilizer of the arch, inserts onto the navicular bone, influencing its position and the overall foot structure.
• Articulation: It articulates with the talus (ankle bone) posteriorly, the cuneiform bones anteriorly, and sometimes the cuboid laterally, forming complex joints essential for foot flexibility and rigidity.

Due to its central and load-bearing position, the navicular bone is susceptible to specific conditions, especially in individuals engaged in high-impact or repetitive activities.

Common Conditions Affecting the Navicular Bone

When people ask "what causes navicular?", they are almost always referring to the etiology of painful conditions involving this bone. The two most common conditions are navicular stress fractures and accessory navicular syndrome.

Navicular Stress Fracture

A navicular stress fracture is a hairline crack in the bone, most commonly seen in athletes, particularly runners, dancers, and those involved in jumping sports. Unlike acute fractures caused by a single traumatic event, stress fractures develop gradually due to repetitive microtrauma.

Causes and Contributing Factors:

• Repetitive Overload: The primary cause is the repeated application of submaximal forces that exceed the bone's ability to remodel and repair itself. The navicular's unique anatomy—its central position, often poor blood supply (especially the central third), and the compressive forces it experiences—makes it vulnerable.
• Training Errors:
  • Sudden Increase in Volume or Intensity: Rapidly increasing mileage, speed, or duration of exercise without adequate progression.
  • Insufficient Rest: Lack of recovery time between training sessions, preventing bone repair.
  • Change in Training Surface: Transitioning from soft to hard surfaces (e.g., track to concrete) can increase impact forces.
• Biomechanical Imbalances:
  • Foot Structure: Both excessive pronation (flat feet) and supination (high arches) can alter load distribution across the navicular. Overpronation, in particular, can place increased stress on the medial aspect of the bone.
  • Muscle Weakness/Imbalance: Weak intrinsic foot muscles, gluteal muscles, or calf tightness can compromise shock absorption and alter gait mechanics, leading to increased stress on the foot.
  • Leg Length Discrepancy: Can cause asymmetrical loading.
• Inappropriate Footwear:
  • Worn-out Shoes: Lack of adequate cushioning and support.
  • Improper Fit: Shoes that don't accommodate the foot's natural mechanics.
• Nutritional Deficiencies:
  • Low Bone Mineral Density: Inadequate calcium and Vitamin D intake, or conditions like osteoporosis, reduce bone strength and make it more susceptible to stress fractures.
  • Energy Deficit: Insufficient caloric intake, common in athletes, can impair bone health and recovery.
• Female Athlete Triad/Relative Energy Deficiency in Sport (RED-S): Low energy availability, menstrual dysfunction, and low bone mineral density significantly increase fracture risk in athletes.

Accessory Navicular Syndrome

Accessory navicular syndrome occurs when an extra piece of bone or cartilage (an accessory navicular) is present adjacent to the main navicular bone. This is a congenital condition, meaning individuals are born with it. While many people with an accessory navicular never experience symptoms, it can become painful under certain circumstances.

Causes and Contributing Factors for Symptom Onset:

• Direct Trauma: A specific injury, such as a sprain or direct blow to the midfoot, can irritate the accessory bone or the fibrous/cartilaginous connection to the main navicular.
• Repetitive Friction or Pressure:
  • Footwear: Tight or ill-fitting shoes can rub against the prominent accessory bone, causing irritation.
  • Activity: Repetitive motions or activities that place stress on the medial midfoot can inflame the area.
• Activity Overload: Increased physical activity, especially those involving the tibialis posterior tendon (which attaches to the navicular and often the accessory navicular), can lead to inflammation and pain.
• Biomechanical Stress:
  • Pes Planus (Flat Feet): Individuals with flat feet often have increased tension on the tibialis posterior tendon. This tendon attaches to the accessory navicular, and increased pulling can irritate the accessory bone or its synchondrosis (fibrous/cartilaginous joint) with the main navicular, leading to inflammation and pain.
  • Overpronation: Similar to flat feet, excessive inward rolling of the foot during gait can exacerbate stress on the medial midfoot structures.

Recognizing Symptoms

Symptoms of navicular-related issues often include:

• Pain in the midfoot: Typically on the inner side, which worsens with activity and improves with rest.
• Tenderness to touch: Directly over the navicular bone.
• Swelling: Localized swelling around the affected area.
• Pain with weight-bearing: Especially during running, jumping, or prolonged standing.
• Limping: To offload the painful foot.
• Bony prominence: In the case of accessory navicular syndrome, a noticeable bump on the inner side of the foot.

Diagnosis and Treatment Principles

Diagnosis typically involves a thorough clinical examination, including palpation and assessment of foot biomechanics. Imaging studies are crucial:

• X-rays: Can identify accessory navicular bones and sometimes stress fractures (though early stress fractures may not be visible).
• MRI: Considered the gold standard for diagnosing stress fractures, as it can detect bone edema (swelling) before a visible fracture line appears. It also helps assess soft tissue involvement.
• CT Scans: Can provide detailed bone imaging, useful for surgical planning in complex cases.

Treatment for navicular conditions generally follows a conservative approach initially:

• Rest and Immobilization: Reducing weight-bearing activity, often with a walking boot or cast, is critical for healing stress fractures.
• Pain and Inflammation Management: NSAIDs and ice can help alleviate symptoms.
• Physical Therapy: Once pain subsides, rehabilitation focuses on restoring range of motion, strengthening intrinsic foot and lower limb muscles, and correcting biomechanical imbalances.
• Orthotics: Custom or off-the-shelf orthotics can help support the arch, improve foot mechanics, and redistribute pressure.
• Footwear Modification: Ensuring proper, supportive footwear.
• Surgery: Reserved for cases that fail conservative management, such as non-union of stress fractures or persistent pain from accessory navicular syndrome (excision of the accessory bone).

Prevention Strategies

Preventing navicular problems involves addressing the underlying causes and risk factors:

• Gradual Training Progression: Adhere to the "10% rule" (do not increase weekly mileage or intensity by more than 10%) to allow bones and tissues to adapt.
• Proper Footwear: Wear supportive shoes appropriate for your activity, replace them regularly, and consider professional gait analysis.
• Biomechanical Assessment and Correction: Work with a physical therapist or kinesiologist to identify and address muscle imbalances, gait abnormalities, and foot mechanics.
• Strength and Flexibility Training: Strengthen core muscles, glutes, and intrinsic foot muscles. Maintain flexibility in calves and hamstrings.
• Adequate Nutrition: Ensure sufficient intake of calcium, Vitamin D, and overall calories to support bone health.
• Cross-Training: Incorporate low-impact activities (swimming, cycling) to maintain fitness while reducing repetitive stress on the feet.
• Listen to Your Body: Do not ignore persistent foot pain. Early intervention can prevent minor issues from becoming severe.

When to Seek Professional Help

If you experience persistent midfoot pain, especially if it worsens with activity, does not improve with rest, or is accompanied by swelling or tenderness, it is crucial to seek evaluation from a healthcare professional. This could be a sports medicine physician, orthopedist, or physical therapist. Early and accurate diagnosis is key to effective management and preventing long-term complications.