Introduction
The accessory navicular (AN) is one of the most common accessory ossicles of the foot, present in approximately 4-21% of the population. It represents a developmental variation of the tarsal navicular bone and is often asymptomatic. However, when symptomatic, it can cause medial foot pain, particularly in adolescents and young adults. This condition is frequently associated with posterior tibial tendon dysfunction (PTTD) and flatfoot deformity.
Anatomy and Embryology
Normal Navicular Bone
- Located on the medial midfoot, articulating with the talus, cuneiforms, and cuboid.
- Serves as an attachment site for the posterior tibial tendon (PTT), which supports the medial longitudinal arch.
Accessory Navicular
- An extra bone or cartilaginous remnant adjacent to the navicular.
- Classically found posteromedial to the navicular tuberosity.
- May be bilateral in up to 50% of cases.
Embryological Basis
- Develops from a secondary ossification center that fails to fuse with the primary navicular.
- Genetic predisposition may play a role.
Classification (Geist System)
| Type | Description | Clinical Significance |
|---|---|---|
| Type I | Small sesamoid bone within the PTT (~5-10%) | Usually asymptomatic |
| Type II | Oval-shaped ossicle connected via fibrocartilage (~50-60%) | Most commonly symptomatic (due to stress at synchondrosis) |
| Type III | Fused ossicle (cornuate navicular) (~30%) | May cause bony prominence and irritation |
Clinical Presentation
Symptoms
- Medial midfoot pain (worsens with activity, improves with rest)
- Tenderness over the navicular prominence
- Swelling and redness (if inflamed)
- Flatfoot deformity (if PTT dysfunction develops)
Risk Factors
- Adolescents and young athletes (especially runners, dancers)
- Foot overpronation
- Trauma or repetitive stress
Diagnosis
Physical Examination
- Palpable bony prominence medial to the navicular.
- Pain on resisted foot inversion (due to PTT irritation).
- Single-leg heel raise test (assesses PTT integrity).
Imaging
- X-rays (Weight-bearing AP, Lateral, Oblique)
- Confirms presence and type of AN.
- Assesses foot alignment (e.g., pes planus).
- MRI
- Evaluates synchondrosis stress reaction, PTT pathology, or bone edema.
- Ultrasound
- Dynamic assessment of PTT function.
Differential Diagnosis
- Posterior tibial tendonitis
- Medial plantar nerve entrapment
- Tarsal coalition
- Stress fracture of the navicular
Management
A. Conservative Treatment (First-Line for Most Cases)
- Activity Modification
- Avoid high-impact activities.
- Footwear Modifications
- Arch-supportive shoes (e.g., motion control shoes).
- Orthotics (UCBL orthosis, medial heel wedge).
- Physical Therapy
- PTT strengthening (e.g., resisted inversion exercises).
- Calf stretching (gastrocnemius-soleus complex).
- Medications
- NSAIDs (e.g., ibuprofen) for pain and inflammation.
- Immobilization
- Walking boot or cast (for acute exacerbations).
B. Surgical Treatment (If Conservative Measures Fail After 6 Months)
1. Kidner Procedure (Excision + PTT Reattachment)
- Indications: Type II AN with PTT dysfunction.
- Technique:
- Remove accessory bone.
- Reattach PTT to the navicular.
- Success Rate: ~80-90%.
2. Simple Excision (For Type II Without PTT Dysfunction)
- Indications: Painful prominence without instability.
3. Arthrodesis (For Severe Flatfoot with Arthritis)
- Rarely needed.
Postoperative Care
- Non-weight-bearing for 2-4 weeks.
- Gradual return to activity (8-12 weeks).
Prognosis and Complications
Prognosis
- Most improve with conservative care.
- Surgery has good outcomes in refractory cases.
Complications
- Persistent pain (if PTT remains dysfunctional).
- Wound healing issues (due to thin medial skin).
- Recurrence of symptoms (rare).
Conclusion
The accessory navicular is a common anatomical variant that may become symptomatic due to mechanical stress or PTT dysfunction. Type II is most frequently associated with pain.
Key Takeaways
- Conservative management (orthotics, PT, NSAIDs) is first-line.
- Surgery (Kidner procedure) is effective for refractory cases.
- Early diagnosis prevents long-term PTT dysfunction and flatfoot deformity.
Future research for an accessory navicular may explore minimally invasive techniques and biologic augmentation for PTT repair.