The accessory navicular is an anatomical variant found in the foot, characterized by the presence of an extra bone or piece of cartilage located on the medial side of the foot, adjacent to the navicular bone. While it is a relatively common anomaly, present in up to 12% of the population, it is often asymptomatic and discovered incidentally on radiographs. However, in some individuals, it can become symptomatic, leading to pain, dysfunction, and the need for medical intervention. This essay provides a comprehensive overview of the accessory navicular, including its anatomy, classification, clinical presentation, diagnostic approach, and management strategies.
Anatomy and Classification
The navicular bone is a key structure in the medial longitudinal arch of the foot, articulating with the talus proximally and the cuneiforms distally. The accessory navicular is an ossicle that develops from a secondary ossification center, which fails to fuse with the main navicular bone during growth. There are three primary types of accessory navicular, classified based on their morphology and relationship to the navicular bone:
- Type I: A small sesamoid bone embedded within the posterior tibial tendon, proximal to the navicular tuberosity. It is usually round or oval and measures 2-3 mm in diameter.
- Type II: The most clinically significant type, this is a triangular or heart-shaped ossicle that is up to 12 mm in size. It is connected to the navicular bone by a synchondrosis (fibrocartilaginous joint), and the posterior tibial tendon often inserts partially onto this accessory bone. This type is more likely to become symptomatic due to its size and the mechanical forces exerted by the tendon.
- Type III: Represents a fused accessory navicular, where the ossicle has fused with the navicular bone, resulting in an enlarged navicular tuberosity. This type is sometimes referred to as a cornuate navicular.
Clinical Presentation
Most cases of accessory navicular are asymptomatic. However, when symptoms do occur, they are typically associated with the Type II variant. Common clinical features include:
- Medial foot pain, especially over the navicular tuberosity
- Swelling and tenderness over the medial aspect of the foot
- Redness or local irritation, often aggravated by footwear
- Flatfoot deformity or pronation, as the posterior tibial tendon’s function is compromised
- Difficulty with physical activities such as running or jumping
Symptoms may be triggered or worsened by trauma, overuse, ill-fitting shoes, or increased physical activity. Adolescents, especially females, are more commonly affected, likely due to increased activity levels and skeletal maturation during this period.
Diagnosis
The diagnosis of an accessory navicular is primarily clinical, supported by imaging studies. Key steps in the diagnostic process include:
- History and Physical Examination: The clinician should elicit a history of medial foot pain, swelling, and any aggravating factors. Palpation over the navicular tuberosity often reproduces symptoms.
- Radiography: Standard foot X-rays (anteroposterior, lateral, and oblique views) can readily identify the accessory navicular and help differentiate between the types. Type II is the most easily visualized due to its size and position.
- MRI/Ultrasound: These modalities may be used to assess the integrity of the posterior tibial tendon, the presence of inflammation, or to rule out other causes of medial foot pain.
Differential Diagnosis
The differential diagnosis for medial foot pain includes:
- Tibialis posterior tendon dysfunction
- Navicular stress fracture
- Medial plantar neuritis
- Bursitis
- Other accessory ossicles (e.g., os tibiale externum)
It is essential to distinguish between these conditions to ensure appropriate management.
Management
The management of symptomatic accessory navicular is initially conservative. The main goals are to reduce pain, inflammation, and mechanical irritation. Conservative treatment options include:
- Rest and Activity Modification: Reducing activities that exacerbate symptoms, such as running or jumping.
- Ice and Anti-inflammatory Medications: Application of ice packs and use of NSAIDs to control pain and swelling.
- Footwear Modification: Shoes with a wide toe box and good medial support can minimize pressure on the navicular area.
- Orthotic Devices: Custom foot orthoses or arch supports to correct pronation and offload the medial foot.
- Physical Therapy: Strengthening and stretching exercises for the posterior tibial tendon and intrinsic foot muscles.
If conservative measures fail after several months, or if symptoms are severe and disabling, surgical intervention may be considered. Surgical options include:
- Excision of the Accessory Navicular: Removal of the ossicle with repair or advancement of the posterior tibial tendon (Kidner procedure).
- Osteotomy: In rare cases, realignment procedures may be necessary to correct significant deformity.
Postoperative rehabilitation is crucial for restoring function and preventing recurrence. Most patients achieve good outcomes with appropriate management.
Prognosis and Prevention
The prognosis for individuals with accessory navicular is generally excellent, especially with early diagnosis and appropriate management. Most patients respond well to conservative treatment, and surgical outcomes are favorable when indicated. Preventive strategies include proper footwear, early intervention for foot pain, and attention to biomechanical abnormalities in at-risk individuals.
The accessory navicular is a common anatomical variant that can cause significant discomfort and functional impairment when symptomatic. Accurate diagnosis, patient education, and a structured approach to management are essential for optimal outcomes. With appropriate care, most individuals can return to their usual activities without long-term sequelae.
