What is accessory navicular syndrome?

Accessory Navicular Syndrome

Accessory navicular syndrome is a condition characterized by a symptomatic accessory ossicle at the medial aspect of the navicular bone, causing pain and dysfunction due to inflammation at the synchondrosis between the accessory bone and the main navicular, often associated with posterior tibial tendon pathology. 1

Anatomy and Classification

• Accessory navicular bone is a common anatomic variant occurring in approximately 19-23% of the population, with higher prevalence in females (67.5%) than males (32.5%) 2
• There are two main types of accessory navicular:
  • Type 1: A sesamoid bone within the posterior tibial tendon that is anatomically separate from the navicular 3
  • Type 2: An accessory ossification center medial to the navicular that is connected to the main navicular by a cartilaginous synchondrosis 3
• Type 1 is the most common variant, with a prevalence of approximately 42.1% 2
• The accessory navicular can be unilateral or bilateral, with bilateral presentation being more common (65.8% of cases) 2

Clinical Presentation

• Patients typically present with:
  • Medial foot pain and tenderness over the navicular tuberosity 3, 4
  • Pain that worsens with activity, particularly activities involving repetitive stress on the medial arch 4
  • A visible bony prominence on the medial aspect of the foot 4
  • Symptoms often beginning in adolescence, especially in athletic individuals 3
• The condition may be associated with:
  • Posterior tibial tendon dysfunction or insufficiency 2
  • Flat foot deformity (pes planus) 5
  • Wider native navicular bones that protrude more medially than feet without an accessory navicular 6

Diagnostic Approach

• Radiography of the foot is the appropriate initial imaging study for suspected accessory navicular syndrome 7
  • The 45-degree eversion oblique view is particularly important for identifying this condition 4
  • The accessory ossicle typically appears triangular or heart-shaped on radiographs 3
• MRI without IV contrast is the next appropriate imaging study if radiographs are negative or equivocal 7
  • MRI allows visualization of bone marrow edema within the ossicle, the synchondrosis, and associated tendon pathology 7, 1
  • MRI is superior to CT for characterization and differentiation of soft tissues 7
• CT may be useful to confirm the presence of an accessory ossicle and provide detailed characterization of the ossicle and synchondrosis 7
• Bone scintigraphy (99mTc MDP imaging) may be valuable when the clinical significance of the ossicle is uncertain, as increased radionuclide activity occurs only on the symptomatic side even when the radiographic variant is bilateral 3

Treatment Options

Conservative Management

• Initial treatment should be conservative for 6-8 weeks before considering surgical options 1
• Conservative measures include:
  • Rest, activity modification, ice application, elevation, and NSAIDs for pain relief 1
  • Mechanical support such as orthotic devices, arch supports, shoe modifications, and taping or bracing techniques to stabilize the foot and reduce strain on the posterior tibialis tendon 1
  • Cast immobilization may be used in some cases, though results are variable 3

Surgical Management

• Surgical intervention is indicated when conservative measures fail to relieve symptoms 5
• Surgical options include:
  • Simple excision of the accessory navicular with contouring of the medial surface of the main navicular bone to prevent residual prominence 5
  • Kidner procedure, which involves excision of the accessory navicular and re-routing of the main insertion of the tibialis posterior tendon 5
• Both simple excision and the Kidner procedure are effective in relieving symptoms in the majority of cases, with failures typically resulting from errors in patient selection or surgical technique 5
• Simple excision is as effective as the Kidner technique, provided that the medial surface of the main navicular bone is properly contoured 5

Prognosis and Complications

• Histologic examination of surgically excised specimens reveals inflammatory chondro-osseous changes in the navicular-accessory navicular synchondrosis compatible with chronic trauma and stress fracture 3
• If left untreated, the condition can lead to:
  • Chronic foot pain and disability 4
  • Progressive posterior tibial tendon dysfunction 2
  • Flat foot deformity 5
• Surgical treatment has a high success rate in relieving symptoms when conservative measures fail 5
• Correction of associated flat foot is generally secondary to growth and maturation of the foot rather than to the surgical procedure 5

Differential Diagnosis

• Accessory navicular syndrome should be differentiated from:
  • Navicular tuberosity avulsion fractures 2
  • Other midfoot and hindfoot fractures 2
  • Posterior tibial tendon dysfunction without accessory navicular 2
  • Charcot neuroarthropathy, which may present with similar inflammatory signs but typically shows bony destruction on X-ray 7