Accessory Navicular

Editors: Frassica, Frank J.; Sponseller, Paul D.; Wilckens, John H.

Title: 5-Minute Orthopaedic Consult, 2nd Edition

Copyright ©2007 Lippincott Williams & Wilkins

> Table of Contents > Accessory Navicular

Accessory Navicular

Kris J. Alden MD, PhD

Basics

Description

• This anatomic variant consists of an accessory ossicle located at the medial edge of the navicular (Fig. 1).
• 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 (1)
  • Type I: Small, 2–3-mm sesamoid bone in the PTT; referred to AS “os 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

• 4–21% incidence; 89% of cases are bilateral (2).
• 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 (3).
• It is most commonly symptomatic in the 2nd decade of life and causes medial foot pain (4).
• <1% of patients become symptomatic.
  
  
  

  Fig. 1. AP radiograph showing an accessory navicular.

• Incidence by classification (1):
  • 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 (5,6,7).
• 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 1–2 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 (8)
  • 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

P.3

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 3–6 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 (9).
• 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.

Follow-up

Complications

Weakness, incomplete pain relief, continued deformity

References

1. Sella EJ, Lawson JP, Ogden JA. The accessory navicular synchondrosis. Clin Orthop Relat Res 1986;209:280–285.

2. Miller TT. Painful accessory bones of the foot. Semin Musculoskelet Radiol 2002;6:153–161.

3. Lawson JP, Ogden JA, Sella E, et al. The painful accessory navicular. Skeletal Radiol 1984;12:250–262.

4. Romanowski CAJ, Barrington NA. The accessory navicular—an important cause of medial foot pain. Clin Radiol 1992;46:261–264.

5. Mygind HB. The accessory tarsal seaphoid [sic]. Clinical features and treatment. Acta Orthop Scand 1953;23:142–151.

6. Ray S, Goldberg VM. Surgical treatment of the accessory navicular. Clin Orthop Relat Res 1983;177:61–66.

7. Veitch JM. Evaluation of the Kidner procedure in treatment of symptomatic accessory tarsal scaphoid. Clin Orthop Relat Res 1978;131:210–213.

8. Demeyere N, De Maeseneer M, Osteaux M. Quiz case. Symptomatic type II accessory navicular. Eur J Radiol 2001;37:60–63.

9. Kidner FC. The prehallux (accessory scaphoid) in its relation to flat-foot. J Bone Joint Surg 1929;11:831–837.

Additional Reading

Coughlin MJ. Sesamoids and accessory bones of the foot. In: Coughlin MJ, Mann RA, eds. Surgery of the Foot and Ankle, 7th ed. St. Louis: Mosby, 1999:437–499.

Kidner FC. The prehallux in relation to flatfoot. JAMA 1933;101:1539–1542.

Kopp FJ, Marcus RE. Clinical outcome of surgical treatment of the symptomatic accessory navicular. Foot Ankle Int 2004;25:27–30.

Miscellaneous

Codes

ICD9-CM

• 754.61 Pes planus, congenital
• 755.56 Accessory navicular

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.