A 50-year-old male coach presented with a twelve-month history of dorsal foot pain. He described a minor twisting injury to his foot around this time. This did not seem like a big problem initially. At the time of his clinic visit the pain had deteriorated to the point that he was unable to wear boots due to the pressure on his foot, had difficulty wearing any tight shoes and had dorsal foot pain while walking.
On examination the major findings were of localised tenderness over the dorsum of the navicular, a normal mid-foot range of motion and a normal gait.
The lateral x-ray image shows a well corticated ossicle related to the dorsal navicular consistent with an os supranaviculare. There is no other abnormality seen in the mid-foot. A subsequent CT scan shows that the os measures 7 x 7 x 12 mm. There is sclerosis and a small amount of subchondral lucency in the navicular adjacent to the ossicle. No fracture is identified within the navicular. The remainder of the mid-foot was unremarkable. An MRI was not conducted in this case but would be expected to show increased signal with in the os and related to the synchondrosis.
As this patient had experienced prolonged pain in his foot, he elected to have the ossicle excised. This was done without complication. He was able to return to all normal activities about three months following his surgery.
The os supranaviculare is an accessory ossicle located at the proximal and dorsal aspect of the navicular. It is also known as a Pirie’s bone, talonavicular dorsale or dorsal navicular ossicle. It is a normal variant that is present in approximately 1% of the population. The ossicle may be fused with the talus or with the navicular bone and is generally held in place by a synchondrosis. In the majority of cases the ossicle is an incidental finding on x-rays and other imaging studies. It can however become symptomatic when the synchondrosis is disrupted (as likely happened in this case). When present an os supranaviculare may also increase the risk of a player developing a navicular stress fracture. An avulsion fracture from the dorsal navicular can also occur after an acute traumatic incident. These fractures are generally more irregular and are not corticated.
In most cases an os supranaviculare does not require any specific treatment. If the synchondrosis becomes disrupted a player’s symptoms will often resolve with a short period of rest. Where the pain is more refractory, excising the os is generally an effective treatment.
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