What's Actually Going On
The fibula is the thin outer bone of the lower leg, and it ends at the outer ankle bump. The Weber system labels the break by how high it is: at the level of the ankle's ligament junction (type B, the most common) or above it (type C). But height isn't stability. Stability is set on the inner side, by a strong ligament called the deltoid, and by whether the main foot bone stays centered under the shin. Intact inner side, centered joint: stable. Torn inner side, shifting joint: unstable.
These breaks rarely travel alone. Up to 40% also injure the ligament junction above the ankle, and cartilage damage inside the joint rides along in roughly half of cases, which is part of why some ankles ache long after the bone has healed.
How to Identify It
Bony tenderness over the outer ankle after a twist points to a fracture rather than a simple sprain. The decisive check, though, is the inner side. An ultrasound of the inner ligament catches a tear almost every time catches ~100%, and a "gravity stress" X-ray, taken with the ankle tipped so gravity loads it, reveals a joint that shifts under load even when a normal standing film looks fine catches 71–100%.
This is the whole game: a plain, still X-ray can look normal on an ankle that is actually unstable. Confirming the inner side is intact is what makes "just a boot" safe.
The Debate
Old guidance vs recent trials
Then: six weeks in a cast, and surgery for unstable breaks.
Now: for stable breaks, three weeks is enough, a removable boot beats a cast on complications, and early weight helps. For the borderline-unstable break, a five-year randomized trial found surgery was not clearly better than a boot, and routinely fixing the ligament junction with a screw did not improve outcomes.
This is a field where the trials have moved ahead of the official guidelines. That's not a reason to ignore either, but it explains why treatment can feel inconsistent from clinic to clinic.
Honest Limitations
The trials mostly studied stable breaks
"A boot is fine" is well proven for stable and barely-shifted breaks. It is not proven for a badly displaced ankle, which was largely left out of the trials and still usually needs surgery.
The safety check depends on skill
The inner-side check that makes conservative care safe relies on good ultrasound or stress imaging. Where that isn't available, the safe move is to treat a doubtful ankle as unstable and refer.
The Nuance
Two truths sit side by side. Most broken ankles, when stable, do beautifully without surgery, and the modern trend is toward less. At the same time, grossly unstable breaks and the higher type C pattern still usually need surgery, a normal static X-ray does not rule out an unstable joint, and putting a screw across a ligament junction that still works adds hardware without a clear benefit. The skill isn't picking a side. It's correctly reading the inner side of the ankle.
