High Yield Topics

Accessory Navicular

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Ovid: 5-Minute Orthopaedic Consult

Editors: Frassica, Frank J.; Sponseller, Paul D.; Wilckens, John H.
Title: 5-Minute Orthopaedic Consult, 2nd Edition
> 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.

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