Clinical History
A 15 years old male left ankle eversion injury while playing soccer 2 months ago – stepped in a hole. Tender on palpation on the medial arch and navicular. Poor response to physiotherapy. Query posterior tibialis or plantar ligament injury.
Ultrasound Findings:
The posterior tibial tendon navicular insertion contains a focal calcification (5 mm long) with a cartilaginous connection to the navicular. The navicular has bone irregularity with increased echogenic maternal filling the gap between the focal area of the bone. There is increased vascularity within the tendon insertional part with the patient reporting this is the region of pain. Comparison with the right side shows a 10 mm long irregular shaped bony area within the tibialis posterior tendon insertional part at the navicular. There is also mild vascularity with mild tenderness present.
Figure 1. Posterior tibial tendon insertion calcification less than 3 mm from navicular
Figure 2. Power Doppler shows vascularity in the posterior tibial tendon
Opinion
Bilateral posterior tibial tendon insertions accessory navicular Type II, with increased vascularity and focal tenderness on the left indicating injury to the synchondrosis.
Left foot X-ray (following the ultrasound)
Figure 3a. Left foot showing accessory navicular Type II
Figure 3b. Bilateral accessory navicular Type II
On the left side there looks to be partial avulsion of an accessory ossicle or sesamoid bone at the tubercle of the navicular perhaps suggesting some injury at the tibialis posterior insertion. A small ossicle is seen in the right foot but this lies much closer to the bone. An ultrasound might give some more information about the state of these tendon insertions.
Figure 4. Diagram of posterior tibial tendon accessory navicular
Follow up
Rest and ice on the foot without any intensive treatment “feels almost normal now”.
Discussion
Accessory navicular aka os navicularum or os tibiale externum
Figure 5.
Type I ossicle/sesamoid within tendon > 3mm from navicular
Type II ossicle cartilage connection (synchondrosis)
Type III enlarged medial horn of the navicular
