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Paper text:
a healthy 45-year - old man was referred to our clinic with an atraumatic 3-year history of pain on the dorsomedial surface of the right foot , which worsened with activity .
the pain began as a diffuse dull pain during running , and progressed to an exquisite pain during standing or after a 10-minute walk since 6 months before our clinic visit .
his laboratory data , including his uric acid level , were also within the normal range .
radiographs of the right foot revealed a 10  15 mm sized accessory bone between the navicular and the medial cuneiform ( fig .
1 ) , but no equivalent in the left foot . computed tomography ( ct ) demonstrated that the accessory bone contacted the intermediate cuneiform and the navicular and medial cuneiform ; sclerotic change and a bony spur were observed between the accessory bone and the navicular ( fig .
his symptom had not improved despite the 6 months of conservative treatment for pain control , and finally , the accessory bone was excised .
intraoperatively , the tibialis anterior was not attached to the accessory bone , which articulated with the medial cuneiform and the intermediate cuneiform .
the patient reported pain relief during walking , but slight tenderness persisted on the surgical scar .
when a patient without a recent trauma history complains of medial side midfoot pain , several types of disease , such as , accessory bones around the navicular , osteonecrosis , and stress fracture of the navicular , and gout may be considered.1,3 - 6 ) the most common accessory bone around the navicular is located on the medial side of the navicular .
an accessory bone between the navicular , medial cuneiform , and intermediate cuneiform is extremely rare .
the condition was initially reported by dwight based on two macerated specimens in 1902 , and was named os intercuneiforme.7 ) the accessory bones were described as rounded , without an articulated connection with surrounding structures , and as being embedded in connective tissue .
the incidence rate of os intercuneiforme was reported to be one per 3,754 feet ( 0.026% ) in one series,7 ) and as one per 3,460 feet ( 0.029% ) in another.3 ) in the present case , although the accessory bone was located between the navicular , medial cuneiform , and intermediate cuneiform , it differed from os intercuneiforme , because it articulated with the medial cuneiform and the intermediate cuneiform .
the navicular was the only surrounding bone without articulation contacted by connective tissue , which means that the accessory bone was a secondary ossification center of the navicular , and thus , we name it os infranaviculare . accessory bones usually remain asymptomatic , but can become painful due to fracture , degenerative change , and avascular necrosis and due to irritation or impingement of adjacent soft tissues.8 ) in the described case , advanced degenerative change between the navicular and accessory bone was considered to be the main cause of foot pain .
symptoms caused by accessory bones are initially treated nonoperatively , and thus , we adopted conservative treatment ( rest , anti - inflammatory agents , and a shoe insert ) for 6 months , but those efforts were futile . finally , because the patient wanted to participate in sports activities , we decided on surgical treatment .
simple excision is recommended for an accessory bone of the foot and ankle , as long as excision does not create a large defect at the tendon insertion.8 ) in this case , we were able to simply excise the accessory bone without additional procedures , because the tibialis anterior tendon was not involved .
the author observed a new accessory bone of the foot in the distal portion of navicular , which articulated with the medial cuneiform and the intermediate cuneiform , and named it os infranaviculare . 
 a degenerative change was observed between the accessory bone and the navicular ; this caused midfoot pain to the patient during weight - bearing . 
 thus , the patient was treated by excision of the accessory bone . 
 the symptom was relieved at one - year postoperative .