Why a Head Injury Shows Up in Your Ankle

The SparkNotes

• Athletes reporting a concussion history also reported more lateral ankle sprains, knee injuries and lower limb muscle strains.

• The odds ratios ran between roughly 1.6 and 2.9.

• The associations were strongest for the concussions that were never reported or never recognized.

• This is a survey. It shows an association, not a cause.

• Which does not make it useless — it makes it a reason to ask a question nobody asks.

The Whole Story

Two injuries that seem unrelated: a concussion in October, a rolled ankle the following spring.

There is a growing body of work suggesting those two things sit closer together than anyone assumed.

What the study did

Researchers surveyed 335 collegiate athletes across 13 sports at the end of their playing careers — after the last season, when there was nothing left to lose by being honest. Roughly 62% were women, which matters, because much of the earlier work on this was done in male professional football and soccer.

They were asked about concussions, including ones they had never reported, and about lower body injuries: ankle sprains, knee injuries, and muscle strains.

What it found

Athletes who had experienced any concussion reported significantly more lateral ankle sprains, more knee injuries, and more lower limb muscle strains. The odds ratios sat between about 1.6 and 2.9 — so somewhere between half again and nearly three times the reported rate.

Then it gets more interesting.

When the concussions were split by type, the pattern was not uniform. Reported concussions were associated with knee injuries. Concussions the athlete had knowingly hidden were also associated with knee injuries. But the associations with ANKLE SPRAINS and MUSCLE STRAINS came specifically from the concussions that had never been recognized as concussions at all — the ones where somebody saw stars and nobody, including them, called it anything.

The authors make the obvious point: if you only count the diagnosed ones, you miss a large part of the picture.

Why it might happen — and this is where honesty is required

The mechanism people propose is reasonable. A concussion can leave measurable deficits in balance, postural control and reaction time that outlast the symptoms. Studies using instrumented measures have found lingering changes months and even years after apparent clinical recovery. If your balance and reaction time are subtly off and you are cutting on grass at full speed, an ankle or a knee is a plausible place for that to show up.

Plausible is not proven, and this study cannot prove it.

What this study genuinely cannot tell you

It is a cross-sectional survey. Athletes were asked at the end of their careers to remember injuries across several years, which is exactly the kind of question memory handles badly. It is rated Level 3 evidence by its own authors.

So it establishes association, not causation, and it cannot reliably tell you which came first. Some evidence elsewhere runs the other way — one study found soccer players had an elevated injury rate in the year BEFORE their concussion, which raises the possibility that some athletes are simply more injury-prone, or take more risk, or play in a way that produces both.

Anyone selling you this finding as "concussions cause ankle sprains" is overstating it.

What it is still good for

A survey like this cannot tell you why. It is very good at telling you what to ask about.

And the question it raises is one almost nobody asks in a lower limb assessment: has this person had a concussion, including one nobody ever called a concussion?

If the answer is yes, and especially if the answer is "well, there was that one time," then balance, reaction time and dual tasking are worth measuring rather than assuming. Those are testable. They are also trainable.

That is a modest, defensible use of an imperfect study — not a claim about your ankle, but a reason to widen the history.

What I make of it

Honestly, nobody connected the two at the time. It is not a question that tends to get asked.

What I do find interesting is an athlete with a serious injury — an ACL, say — who also has a history of concussions. I think it is a stretch to call that cause and effect.

What it speaks to is the process. If it points at anything, it is that returning to sport after a concussion should include some vestibular and oculomotor work, not just cardiovascular conditioning, strength training and getting back into practice.

If you are the athlete in this

The practical version.

• If you have had a concussion — reported or not — mention it when you get a lower body injury looked at, even years later. Most people never think to.

• If your rehab from an ankle or knee injury has never included balance, reaction time or dual tasking, that is a gap regardless of your concussion history.

• And if you are still playing and you got your bell rung last month, the athletes in this study who did not report gave reasons you will recognize. Nearly two thirds said they did not want to miss future games.

Follow along as Resurgo comes together.

Read next: The Concussion Nobody Diagnosed · Cleared to Play Isn't the Same as Ready to Compete