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Thursday, December 6, 2012

Images for Os Navicularis: Accessory Navicular

These are a series of images from a patient having surgery on the right os tibial externum AKA os navicularis AKA accessory navicular AKA second ankle bone. Surgery was done to explore the area and fix any problems seen. The patient was 16 at the time of the surgery and started having significant symptoms when she was 13. At the time of the surgery, the physician did not think the accessory navicular needed to be removed, so left it in. The patient is now 18 years old and has not had pain relief. This series of images at least shows what is going on inside the foot. 

Above the marker on the right is the accessory navicular. If you look at the exact same area on the left side, no such extra bone exists. The statistics I learned was only 30% of the time is this problem bilateral (involving both sides). The posterior tibial tendon, the main support of the arch, attaches into the large navicular bone, and then spreads out throughout the arch. If part of the tendon instead attaches into the accessory navicular, this gives less tendon to support the arch, and the arch can collapse more. This collapse can cause major problems at any age. Current wisdom is to remove that extra bone when the patient is symptomatic, if the symptoms can not be alleviated by a period of constructive conservative treatments including: stabilizing foot orthotics, tape, some periods of immobilization, strengthening, and anti-inflammatory. 

Here is the same image just alittle higher on the foot. Again, I placed the marker just behind the extra bones which look even less attached and more unstable next to the parent navicular bone. 

What strikes me in this image is the whiteness of the accessory navicular compared to the other bones. What does this mean? The whiter bone is the more stress it has been taking. If you stress bone, you stimulate the bone forming cells, causing more bone growth. The stronger the bone becomes, the whiter it looks. So why would this accessory navicular be so stressed? The arrow is in the normal arch of the foot. If the arch is collapsing, the posterior tibial tendon attaching into the accessory bone is working overtime to stabilize the arch. If the strain is too great, symptoms will occur as there will be some breakdown of the normal tissue.

This is the exact same part of the accessory navicular as the image above. Again see how white the bone is. Here you can also is the shadow of the large posterior tibial tendon coming from the ankle above, and attaching directly into the os navicularis.

Here is one image deeper into the foot with the accessory navicular more irregular and tendon next to it is the tendon to the same toes (flexor digitorum longus).

Another image exactly shows that there is a small os navicularis on the left side also.

Large accessory navicular seen with separation from the parent bone (navicular). When the tendon pulls on the navicular in a young child, if they have a situation like this, the weakest link in the chain is the junction of the accessory navicular and the navicular itself. It is normally this tissue that gets irritated as the tendon pulls to stabilize the arch only to find an unstable attachment, a weak spot, that will strain very easily.

The Arrow points to the accessory navicular and you can see the darker posterior tibial tendon attaching into it.

This image shows the arrow pointing to the posterior tibial tendon. You can see it attaching into the os navicularis.

The tendon again is being pointed to. The tendon is attaching into the side of the accessory navicular , not where it should. Surgery is designed to remove the extra bone, and using an anchoring system, attach the posterior tibial tendon solidly where it should be attaching (the normal navicular).

This arrow also points to the accessory navicular. The chronic pain is causing inflammation into the tendons going up into the ankle. Tendinitis of multiple tendons is predictable due to this chronic situation.

Here obvious attachment of the posterior tibial tendon (arrow) shows not only inflammation but attachment into the accessory navicular.

Here the arrow points to the posterior tibial tendon attaching and surrounding the accessory navicular. 

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Thank you very much for leaving a comment. Due to my time restraints, some comments may not be answered.I will answer questions that I feel will help the community as a whole.. I can only answer medical questions in a general form. No specific answers can be given. Please consult a podiatrist, therapist, orthopedist, or sports medicine physician in your area for specific questions.