ACCESSORY NAVICULAR AND TREATMENT OPTIONS

An accessory navicular, usually seen hand in hand with flat foot deformity, is a condition where there is a secondary bone with the navicular that is not fused.   If a sesamoid is present in the posterior tibialis tendon, it is known as os tibiale externum, and other names for the condition include: navicular secundum, prehallux, bifurcate navicular, accessory tarsal scaphoid, extra scaphoid, and divided navicular.  In some cases, the posterior tibialis tendon attaches more to the accessory navicular than the true navicular, resulting in a dropped arch and reduced function of the muscle, as it is attached to a mobile segment.  The condition may be present in 10-13% of the population, and may be asymptomatic.  Rubbing due to the prominence, or injury due to an ankle sprain may result in detection of the condition via a radiograph.  Girls are afflicted more than boys, and in 50% of the cases, the bones may fuse later in childhood. 

Treament is usually conservative in the initial stages of pain, with anti-inflammatories, rest, ice, and padding for pressure relief.  A doughnut pad can be cut to reduce friction inside the shoe, and casting or a cam-walker boot can be used to decrease the excessive foot mechanics that will agitate the condition.  Surgery is a last option, andt he Kidner procedure is removal of the accessory, with transfer of the posterior tibialis tendon to the natural navicular. 

Physical therapy should consist of a program to reduce other factors that can cause delayed and excessive pronation, which will further stress the joint and cause increased pull by the posterior tibialis.  This would include stretching of the gastroc and soleus, making sure there are no hip problems causing substitution pronation (tight rotators, leg length discrepancy, or even anteversion or retroversion).  Anti-inflammatory PT treatments such as US, iontophoresis, and ice are options.  Mobilization of any abnormal joints in the rest of the foot may reduce compensatory movement at the talonavicular joint, and supportive taping gives relief.  Orthotic fabrication needs to be done very carefully, as direct overpressure to support the navicular is not easily tolerated.  A contact digitizer may be necessary to control pronation, support the navicular, and not overstrain the midfoot.

If the posterior tibialis tendon itself is tender, treat as with other PTT problems, including gentle introductory TFM and tendon support.  Strengthen any foot musculature, both intrinsic and extrinsic that needs addressed.  Remember, a manual muscle test that reveals “normal” strength may not be enough, and additional strengthening is necessary.  This is a mistake I often see PT’s make-assuming that general normal strength is enough to  perform a task for which it is not up to.  Extra strength may allow the foot or other body part to produce a task with less strain on the musculotendinous and musculoskeletal tissues than a weaker, but still normal region.

Kohler’s disease, which is a self-limiting AVN of the navicular, can mimic a painful accessory navicular, and usually affects boys more than girls (at ages 4 and 5 respectively).