Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

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Accessory Navicular

Basics
Description

  • This anatomic variant consists of an accessory ossicle located at the medial edge of the navicular
  • Accessory ossicles are derived from unfused ossification centers.
  • Considered an incidental finding on radiographs, but may become symptomatic
  • Classification: 3 major types of accessory navicular adjacent to the posteromedial navicular tuberosity
    • Type I: Small, 3-mm sesamoid bone in the PTT; referred to AS tibiale externum
    • Type II:
      • Larger ossicle than type I
      • Secondary ossification center of the navicular bone
    • Type III: Enlarged navicular tuberosity, considered a fused variant of a type II, often with pointed shape
  • Synonyms: Os tibiale; Os tibiale externum; Naviculare secundum
Pediatric Considerations
Often presents in adolescent patients or young adults, with flatfoot deformity and arch pain.
 
Epidemiology
Incidence
  • 21% incidence; 89% of cases are bilateral .
  • One of the most common accessory ossicles in the foot
  • It is seen over the medial pole of the navicular bone, usually in adolescent patients.
  • It is most commonly symptomatic in the 2nd decade of life and causes medial foot pain .
  • <1% of patients become symptomatic.
  • Incidence by classification :
    • Type I: ~30% of all accessory navicular bones
    • Type II: ~50%
    • Type III: ~20%
Prevalence
  • Usually affects teens and young adults
  • More frequent in females
  • May be seen in older adults as incidental finding or, in rare cases, as symptomatic
Etiology
  • The accessory navicular is a variant of normal anatomy.
  • It may become symptomatic from the bony prominence impinging against shoe wear.
  • The patient may have diffuse medial and plantar arch pain.
  • It may cause problems by destabilizing the insertion and diminishing the pull of the PTT.
  • In patients with associated severe flatfoot deformity, lateral pain may occur secondary to impingement of the calcaneus against the fibula.
  • A traumatic event can cause injury to the fibrocartilaginous synchondrosis that attaches the ossicle to the main navicular.
Associated Conditions
  • Flatfoot deformity
  • Secondary Achilles tendon contracture
Diagnosis
Signs and Symptoms
  • Pain may begin after wearing ill-fitting shoes, with weightbearing activities or athletics, or after trauma to the foot.
  • Characteristics:
    • Pain and tenderness along the medial aspect of the foot in the region of the accessory navicular
    • Pain or weakness when the patient attempts to rise on toes, run, or jump
    • Often increased prominence over the medial end of the navicular
History
  • The pain is localized to the medial aspect of the navicular.
  • Symptomatic accessory tarsal navicular may develop in young athletes.
  • Exacerbated by weightbearing, walking, athletic activity, or the wearing of narrow shoes
  • Pain often is relieved by rest.
Physical Exam
  • Tenderness is localized to the medial pole of the navicular.
    • May be exacerbated by abducting and adducting the foot
  • Assess the insole of the shoe, which may exacerbate symptoms.
  • Assess the strength of the PTT by manual resistance testing against plantarflexion-inversion and by determining the ability to perform multiple single-limb heel rises.
  • Assess ankle and subtalar joint motion.
  • Identify contracture of the Achilles tendon.
Tests
Imaging
  • Obtain routine standing AP, external oblique, and lateral radiographs of the foot.
    • Type-II accessory ossicle has smooth borders, is triangular or heart-shaped, and measures 9 — 12 mm in size.
    • The base is situated 2 mm from the medial and posterior aspects of the navicular bone.
    • The accessory ossicle may be best visualized on the internal oblique view.
    • Smooth margins with well-formed cortex differentiate this condition from acute fracture.
  • Bone scan:
    • May show increased activity over an accessory navicular
    • May be needed if a navicular stress fracture is suspected in the differential diagnosis
  • MRI:
    • Useful when plain films are unremarkable
    • Often, a type-II accessory navicular is attached to the tuberosity by a fibrocartilage or hyaline cartilage layer, and MRI may show soft-tissue edema consistent with a synchondrosis sprain or tear.
    • Shows altered signal intensity and bone marrow edema, suggestive of chronic stress and/or osteonecrosis
    • Also helpful in showing PTT degeneration
Pathological Findings
  • This separate osteocartilaginous fragment is located in place of the normal medial pole of the navicular.
  • The PTT inserts on the accessory navicular, navicular body, and cuneiforms.
Differential Diagnosis
  • Navicular fracture may mimic an acute avulsion fracture of the tuberosity of the navicular.
  • Posterior tibial tendinitis
  • Stress fracture of navicular


Treatment
General Measures
  • The patient should rest and avoid athletics or aggravating activities.
  • Anti-inflammatory medication
  • Shoe-wear modification, including use of a softer, wider shoe
  • If flatfoot is present, a medial arch support may be useful, but often the patient may not tolerate it because of direct pressure on the ossicle.
  • Below-the-knee walking cast or removable fracture boot may be used for 6 weeks for persistent symptoms.
  • Physical therapy, including strengthening exercises and cryotherapy, may be helpful.
Medication (Drugs)
No evidence suggests that one NSAID is superior to another.
 
Surgery
  • If pain is progressive or does not remit with nonoperative treatment, surgical excision may be considered.
  • In the Kidner procedure, the accessory navicular is excised, and the PTT is rerouted into a more plantar position .
  • Contemporary surgical treatment:
    • Includes excision of the ossicle and reattachment of the PTT insertion to the navicular, with suture anchors or sutures passed through drill holes
    • Typically provides satisfactory outcome and good pain relief, particularly in adolescents
  • Severe flatfoot deformity with lateral impingement symptoms may require concomitant osteotomy of the calcaneus and/or medial column of the foot to improve alignment and decrease mechanical stress of the PTT insertion.
Patient Teaching
  • Instruct patients on the typically benign nature of the condition.
  • If the condition is secondary to medial pressure from the shoe, suggest a wider, softer shoe.
  • Recommend rest from sports with gradual return when symptoms subside.
FAQ
Q: What is the most common type of accessory navicular seen radiographically?
A: Type-II, with a large accessory ossicle, is the most common.
 
Q: What are the standard treatment methods for initial management of a symptomatic accessory navicular?
A: Rest, NSAIDs, restriction from sports, immobilization with a boot brace or walking cast, physical therapy, and orthotic arch supports.

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