What is the management for a moderate sized unfused accessory navicular?

Management of Moderate Sized Unfused Accessory Navicular

For symptomatic moderate sized unfused accessory navicular, surgical excision with anatomic repair of the posterior tibialis tendon is the recommended treatment when conservative measures fail.

What is an Accessory Navicular?

An accessory navicular is an extra ossicle (small bone) that occurs adjacent to the navicular bone in the foot. There are three types:

• Type I: Small ossicle within the posterior tibial tendon
• Type II: Larger ossicle connected to the navicular by a synchondrosis (cartilaginous connection)
• Type III: "Cornuate navicular" - possibly representing the end stage of Type II

A "moderate sized unfused accessory navicular" typically refers to a Type II accessory navicular that has not fused with the main navicular bone.

Diagnostic Approach

MRI is the preferred imaging modality after initial radiographs for evaluating symptomatic accessory navicular bones 1:

• MRI allows optimal visualization of:
  • Bone marrow edema within the ossicle
  • The synchondrosis (connection between accessory navicular and navicular)
  • Associated tendon pathology
  • Soft tissue abnormalities

Conservative Management (First-Line)

Initial management should be non-surgical:

1. Activity modification to reduce stress on the medial foot
2. Orthotic devices to support the arch and reduce tension on the posterior tibial tendon
3. Cast immobilization for more severe cases
4. Anti-inflammatory medications to reduce pain and inflammation

Surgical Management

When conservative measures fail to provide relief, surgical intervention is indicated 2, 3:

1. Simple excision with anatomic repair of the posterior tibialis tendon:

   • Excision of the accessory navicular and its synchondrosis
   • Anatomic repair of the posterior tibial tendon
   • This approach has shown excellent results with an average AOFAS Midfoot Scale score improvement from 48.2 to 94.5 2

2. Modified Kidner procedure:

   • Excision of the accessory navicular
   • Reattachment of the posterior tibial tendon to the inferior surface of the navicular
   • Success rates of 90% good to excellent results have been reported 4

Surgical Outcomes

Research demonstrates high success rates with surgical intervention:

• Simple excision with tendon repair yields 94.5% satisfaction rates 2
• Modified Kidner procedure shows 90% good to excellent results 4
• Most patients report significant pain relief and return to normal activities 2, 5

Key Considerations

1. Relationship to flat foot: Research indicates that accessory navicular does not play a significant role in the development of flat foot 6

2. Mechanism of pain: Pain is likely caused by:

   • Tension, shear, and compression forces on the synchondrosis
   • Microscopic changes similar to physeal fractures
   • These changes may not be visible on radiographs but can be detected on bone scans 3

3. Surgical technique: Simple excision without formal tendon relocation appears to be as effective as the traditional Kidner procedure 6

Follow-up Care

After surgery:

• Protected weight-bearing for 2-4 weeks
• Progressive return to activities
• Physical therapy to strengthen the posterior tibial tendon and intrinsic foot muscles
• Orthotic support may still be beneficial in some cases

The prognosis following surgical management is excellent, with most patients experiencing complete pain relief and return to full activities.