Treating The Accessory Navicular In Young Athletes

An accessory navicular or os tibiale externum is a normal anatomic variant developing just medial and plantar to the navicular bone.¹ The navicular bone is the last of the tarsal bones to develop with ossification occurring between the ages of 1 to 3 in females and 3 to 5 in males. When an accessory navicular bone is present, ossification occurs even later.¹ When the navicular tuberosity develops from a secondary ossification center and fails to unite during childhood, an accessory navicular bone results.² An estimated 5 to 14 percent of all feet develop an accessory navicular bone.²

Three types of accessory navicular bones have been classified. A Type I accessory navicular is a small sesamoid bone, less than 2 to 3 mm in diameter, located within the posterior tibial tendon. These are rarely symptomatic as they do not have an osseous attachment to the navicular.² Type II accessory naviculars are larger in size than Type I and often present with a fibrocartilaginous synchondrosis to the navicular proper.^1,2 The Type II variant is more commonly symptomatic and painful than the other forms of accessory naviculars. The final variant is the Type III accessory navicular, an osseous fusion between the accessory bone and the navicular proper. Similar to Type I, these are rarely symptomatic.^1,2

Tension, shearing or compression forces created by the posterior tibial tendon (PTT) at the fibrocartilaginous interface in the Type II variant, coupled with internal shoe pressures and abnormal biomechanics, generate midfoot pain.³ In some instances, the accessory bone acts as an irritant with areas of microfracture and inflammation developing.¹       

The symptomatic accessory navicular is not uncommon in the young athlete.³ Pain, which increases with exercise, mild edema and erythema will present over the accessory navicular in the medial aspect of the midfoot.^1,4 Pain is easily reproducible with direct palpation over the os tibiale externum and posterior tibialis insertion.⁴ Some patients will report a history of trauma, such as a twisting injury or injury from direct impact to the foot.³ Athletes requiring tight fitting shoes relate pain in wearing these shoes. Resisted inversion of the foot is often difficult to perform and painful. In an acute exacerbation, patients will demonstrate difficulty performing a single limb toe rise with pain at the insertion of the tibialis posterior on the accessory navicular. Researchers have suggested that a correlation exists between the pes planus foot type and a symptomatic accessory navicular, although the link has yet to be proven.^4,5       

Conservative treatment aims at relieving symptoms and reducing inflammation. One can utilize an algorithmic approach beginning with shoe modifications and padding to alleviate pressure over the area of the painful os tibiale externum, combining these treatments with rest from sporting activities for two to four weeks. Patients with pes planus may benefit from an over-the-counter insole with soft padding along the instep to assist the posterior tibial tendon in controlling motion of the midfoot and offloading pressure.

Following a short period of rest combined with shoe gear modifications, patients may begin to return to their sport with the assistance of a lace-up Ankle Stabilizing Orthosis (ASO) ankle brace (Medical Specialties). The brace stabilizes the midfoot and removes excess force and tension on the posterior tibial tendon. If the lace-up ASO ankle brace is successful, patients can use it into adolescence and adulthood. Patients wishing to transition out of the lace-up ASO brace should have two to four weeks of navicular strapping prior to going brace-free. When shoe gear modifications, padding, OTC inserts and rest are inadequate, a period of complete immobilization in a controlled ankle motion boot or cast may be necessary.       

If conservative measures fail to relieve pain, surgical intervention may be warranted. The original procedure described by Kidner involved excision of the accessory navicular combined with rerouting of the posterior tibial tendon to the plantar aspect of the navicular.⁴ Surgeons performed this procedure by detaching a small wafer of bone along with the posterior tibial tendon and suturing the bone wafer to the plantar aspect of the navicular proper.

Modifications of this procedure are in common use today but surgeons no longer remove a wafer of bone for reattachment. Instead, surgeons reattach the posterior tibial tendon alone to the plantar navicular using a suture anchor. In some instances, one splits the posterior tibialis tendon and shells out the ossicle with simple repair of the tendon.^4,6 Both procedures have demonstrated satisfactory outcomes in pain improvement and arch restoration on the American Orthopaedic Foot and Ankle Society midfoot scale and visual analogue scale.⁷ Regardless of the procedure surgeons perform, resection of the accessory navicular must include resection of the fibrocartilaginous synchondrosis and any remaining navicular prominence.⁴

References

1. Lee LH, Adedapo A. Evidence-based treatment of accessory navicular bone. Paediatric Orthopaedics. 2016; epub Nov. 25.
2. Scott AT, Sabesan VJ, Saluta JR, et al. Fusion versus excision of the symptomatic type II accessory navicular: a prospective study. Foot Ankle Int. 2009; 30(1):10-15.
3. Jegal H, Park YU, Kim JS, et al. Accessory navicular syndrome in athlete vs general population. Foot Ankle Int. 2016; 37(8):862-867.
4. Ugolini PA, Raikin SM. The accessory navicular. Foot Ankle Clin. 2004; 9(1):165-180. 
5. Kanatli U, Yetkin H, Yalcin N. The relationship between accessory navicular and medial longitudinal arch: evaluation with a plantar pressure distribution measurement system. Foot Ankle Int. 2003; 24(6):486-489.
6. Kopp FJ, Marcus RE. Clinical outcome of surgical treatment  of the symptomatic accessory navicular. Foot Ankle Int. 2004; 25(1):27-30.
7. Cha SM, Shin HD, Kim KC, Lee JK. Simple excision vs the Kidner procedure for type 2 accessory navicular associated with flatfoot in pediatric population. Foot Ankle Int. 2013; 34(2):167-172.
8. Grogan DP, Gasser SI, Ogden JA. The painful accessory navicular: a clinical and histopathological study. Foot Ankle. 1989; 10(3):164-169.