📌 Metaphyseal Tibiofibular Synostosis

Added: 2026-05-11

[00:00:00]This patient was referred from an outside clinic with a concern for a bone tumor on plain radioraphs.

[00:00:07]Let's start there. On the X-ray, there is an abnormal bony bridge between the tibia and fibula located just below the proximal tibiular joint. There is minimal boeing of the fibula that this is a chronic adaptive process, not an aggressive lesion. The key question is what exactly is being connected and where? Is this arising from the joint?

[00:00:34]Is this an exostosis? Or is this a true fusion between two bones? CT makes the diagnosis obvious. There is a bony bridge between the tibia and fibula located at the metaphysial level just distal to the proximal tibiular joint.

[00:00:53]This is true senostosis.

[00:00:56]You can see cortical and medularary continuity across the bridge. That single finding matters. This is not hetererotopic oification, not post-traumatic callus, not an osteocondroma fragment. The proximal tibopiibular joint itself is relatively preserved but functionally bypassed.

[00:01:20]This is metaphysial tibofibular senostosis.

[00:01:24]rare, often incidental, but biomechanically important and easy to miss if you stop thinking once you reach the joint.

[00:01:34]On MRI, the synostosis itself is not aggressive. There is a bony bridge at the metaphysial level between the tibia and fibula corresponding exactly to what we saw on CT. There is no destructive marrow replacement, no mass-like soft tissue component. Now look at the vessels above the senostosis. The poplial artery branches normally. The anterior tibial artery passes anterior to the senostosis. The posterior tibial artery courses posteriorly.

[00:02:10]Here the posterior tibial artery is mildly compressed between the sinostosis and the tibialis posterior muscle. The poplil artery measures 9.3 mm just distal to the branching point. That's dilated but it does not meet aneurysm criteria. This is secondary remodeling not primary vascular pathology.

[00:02:36]Finally, the nerves. The tibial nerve and paronial nerve are intact with no signal abnormality and no compression.

[00:02:45]Here's the take-home message. Don't call it a bone tumor. Don't stop at the joint. Scroll inferiorly. If the tibia and fibula share cortex and marrow, CT will show it. Once they fuse, the problem is no longer local. It's mechanical. Thanks for watching. Slow down, look carefully, and I'll see you in the next case.