• One snowboarding injury is often mistaken for a sprain. A break in a small knob of bone on the outer side of the ankle (the lateral process of the talus) — “snowboarder’s ankle” — makes up around 15% of snowboarding ankle injuries, and an ordinary X-ray can look normal in up to 40% of cases.
• Missing it matters. Up to two in three people with this break go on to have long-term pain. Left untreated, the bone may not heal and the joint just below the ankle can become badly arthritic, even in young, healthy people.
• A CT scan is the right test, not an X-ray. If the way you were injured and where it hurts both fit, a normal X-ray does not rule it out.
• It takes more than a simple roll of the ankle. In laboratory tests, ankles did not break when the foot was only bent upwards and rolled inwards — but six out of eight did once the foot was also twisted outwards.
• Most ski injuries do not happen to daredevils. Of 346 leg, ankle and foot fractures at one resort, about two in three were in beginners or intermediates, and about two in three happened on easy or intermediate runs.
• Skiers tend to break legs; snowboarders tend to break ankles. “Boot-top” fractures, where the shin snaps over the top of the ski boot, made up 57% of breaks through both shin bones in that study.

Before snowboarding became popular, a break of the lateral process of the talus was rare. The talus is the bone at the top of the foot that forms the lower half of the ankle joint; the lateral process is a small wedge of bone on its outer side. It is now common enough in this group to have earned a nickname. The largest early study put it at 2.3% of all snowboarding injuries and 15% of all snowboarding ankle injuries.

The problem is that it behaves, to the examining doctor, almost exactly like a sprained ankle. Same mechanism. Same location. Same swelling. And this bit of bone sits in an awkward spot, hidden behind other bones on a standard X-ray.

Ordinary X-rays look normal in up to 40% of cases.

• Tenderness and swelling just below and in front of the tip of the outer ankle bone — slightly lower and further forward than a typical sprain
• Pain when moving the ankle and when turning the heel in and out (which uses the subtalar joint, the joint just below the ankle)
• Difficulty putting weight on the foot, often lasting beyond the first two weeks
• An injury that involved a twist, not just a roll

Surgeons sort these breaks into types, because the type decides the treatment. You may hear your surgeon mention one of these systems.

There is good reason to treat these breaks properly, and early. In the largest early study of people treated in plaster alone, nearly half still had symptoms bad enough to need surgery six months later. In some reports, around 60% of breaks treated without surgery did not heal, compared with about 5% after early surgery. Breaks that are missed or left untreated for more than two weeks do noticeably worse: pain can continue even after later surgery, and up to 1 in 5 people eventually need an operation to fuse the joint below the ankle.

By contrast, results after prompt treatment are good. In one study from China of 21 patients, larger pieces, or pieces that had moved, were fixed with screws, and smaller ones were removed, pinned or treated in plaster. All of the breaks healed, on average in about ten weeks, and 20 of the 21 patients had an excellent or good result. Most of those injuries came from falls rather than snowboarding, but it is the same break and the same treatment.

Ligament damage matters too. Where the ligaments on the outside of the ankle were also torn, the surgeons repaired them during the same operation to stop the ankle becoming unstable — another reason to check the whole ankle, not just the broken bone.

The scan is the key point to take away. A CT scan is the best test. It shows how many pieces there are, where they sit, whether the joint below the ankle is involved and whether anything else is injured — none of which an ordinary X-ray reliably shows. In the Chinese CT study above, about 1 in 5 breaks (9 of 43) showed up on CT but not on X-ray. On an X-ray, the best hint is fluid at the back of the joint below the ankle, which strongly suggests a hidden break. Recent research also shows that other breaks in the same bone are often missed on X-ray — another reason for a scan when this injury is suspected.

I routinely use weight-bearing CT for this kind of problem. You stand in the scanner, so it shows the joints and how they line up under your body weight, rather than lying flat.

• Get fit before, not during. The injury data points to tiredness and inexperience more than to difficult slopes.
• Have bindings professionally set to your weight, height, ability and boot sole length, and have them checked rather than assumed.
• Lessons are injury prevention, not just technique — the majority of these fractures occurred in self-described beginners and intermediates.
• Boot fit matters. Boots that are too loose allow the ankle movement that causes snowboard ankle injuries; boots that are poorly fitted cause their own problems.
• Stop when you are tired. The last run of the day is a cliché for a reason.
• Snowboarders: consider stiffer boots or ankle support, particularly while learning, though it is worth saying that the evidence for this specific intervention is thin.

If you came back from the slopes with an ankle that has not settled — or you were told it was a sprain and it still is not right months later — that is worth imaging properly. Weight-bearing CT shows what X-rays in this region often cannot.

Book a consultation: matthewwelck.com/appointments

Evidence identified via PubMed and Consensus. For general information only; this does not replace individual medical advice. Mr Matthew Welck is a Consultant Orthopaedic Foot & Ankle Surgeon at the Royal National Orthopaedic Hospital, Stanmore.