I can't remember why, but I was reading an article on WebMD when I saw a sidebar linking to a sports injury quiz. Since a large part of what I do every day is working to get to the bottom of running injuries, I decided to check it out. Though most of the questions were about traumatic injuries to the upper body, which are much more common in contact sports, there were a few on running injuries. I'm pretty used to seeing misconceptions all over the place when it comes to the causes and optimal treatments for running injuries, but one slide bothered me because a) it was so aggressively incorrect and b) WebMD content is supposed to be vetted and approved by a medical doctor, which lends it an air of authority.
I've reproduced the offending slide below:
The available answers, by the way, were "torn ligaments," "inflammation," "tiny fractures," and "all of the above," none of which are wholly satisfactory.
As readers who have perused my Injury Series articles will know, "shin splints" is a vague term that usually refers to medial tibial stress syndrome, which is a well-defined problem that occurs on the medial edge of the tibia (your shinbone). Unfortunately, the term "shin splints" has morphed into a catch-all term for any exercise-related pain in the shin. WebMD's picture of an athlete icing the lateral side of the upper shin certainly doesn't help. The equation of "shin splints" to "shin pain of any sort" causes mundane things like shin muscle fatigue and more serious things like anterior compartment syndrome to be conflated with medial tibial stress syndrome under the improperly-used umbrella term of "shin splints."
Worse, the answer—"inflammation of muscles, tendons, bone, and other tissue surrounding the shin bone"—is demonstrably incorrect. Though the main purpose of this post is to address the larger issue of outdated or simply incorrect information about running injuries that's all over the place on the internet, I should be thorough and formulate a more proper answer to the question of what "shin splints"—understood to be medial tibial stress syndrome—are caused by.
Swiftly stated, shin splints (understood to be medial tibial stress syndrome) are the result of localized areas of low bone density in the tibia itself. There is no significant involvement of the muscles or tendons surrounding the shin, and only partial involvement of the periosteum, the "skin" that surrounds the tibia bone.1 Exposure to high-impact exercise like running strengthens your bones over time, but in order for this to happen, your bone tissue needs to be remodeled first. This creates small, localized pockets of low bone density. It's just like remodeling your kitchen: before you get to work, you need to tear out a few walls. This is a normal phenomenon that's observed in healthy runners in training.
But when this occurs too fast (as is often the case in novice runners or people with very ambitious training plans), this localized loss of bone density is amplified and causes pain. A masterful review study by Moen et al. outlines four reasons why overloading of bone tissue in the tibia is the best explanation for shin splints:1
1) Bone scans of runners with shin splints show abnormalities in the bone and periosteum
2) CT scans of runner with shin splints show areas of low bone density, which also occur to a lesser extent in healthy athletes in training
3) MRI scans of runners with shin splints display abnormalities in the bone and periosteum
4) Bone mineral density is lower in athletes with shin splints, and returns to normal after they are healthy again.
There is also convincing evidence that directly refutes the "soft tissue inflammation" theory: anatomic studies of the lower leg show that the insertion points of the muscles most often blamed for "pulling" on the tibia don't actually occur at the most common site of shin pain, one third of the way up from the ankle on the medial edge.2 Further, computational modeling of the areas of greatest mechanical stresses on the bone during the "active" phase of gait do correspond to where shin splint pain is most common.3
Now, it's unfair to criticize WebMD too heavily. You'll find the same type of misinformation about running injuries all over the internet and in books and other medical literature as well. But the question I'm grappling with is this: why are so many websites and resources for runners so inadequately informed on even the most common running injuries? In many ways, it's easier to forgive doctors and PTs who still believe that shin splints are caused by muscle or tendon inflammation—they learned about injuries a long time ago, perhaps back when that was the best available theory. And medical professionals don't always have the time to peruse through the latest scientific research. But someone should be doing this. If a DIII runner with a bachelor's in chemistry figure all this out, you'd think that a place like WebMD or About.com or the Mayo Clinic would be at least be somewhat keyed-in on what the current scientific opinion is.
Unfortunately, you'd be wrong. What appears to happen instead is every website saying more or less the same (incorrect) thing. Let's have a look:
Shin splints generally occur after cumulative stress causes microtrauma to the soleus muscle at the point of attachment to the shinbone. Repetitive stress can also cause irritation of the posterior tibialis muscle and inflammation of the periosteum, the connective tissue that covers the tibia.
Medically known as medial tibial stress syndrome, shin splints often occur in athletes who have recently intensified or changed their training routines. The muscles, tendons and bone tissue become overworked by the increased activity.
Shin splints are injuries to the front of the outer leg. While the exact injury is not known, shin splints seem to result from inflammation due to injury of the tendon (posterior peroneal tendon) and adjacent tissues in the front of the outer leg.
|[Shin splints] can be caused by:
*Irritated and swollen muscles, often from overuse
*Stress fractures, which are tiny breaks in the lower leg bones
*Overpronation or ''flat feet" -- when the impact of a step makes your foot's arch collapse
I want to emphasize that all four of these sources claim their articles are reviewed by doctors or other medical experts! And unfortunately, I'm not just cherry-picking from specific websites or specific running injuries. The internet (and books for public consumption, for that matter) are woefully inadequate when it comes to the causes, risk factors, and optimal treatments for pretty much every running injury that I have researched.
It is certainly true that two major motivations for health information websites are to 1) make ad revenue and/or 2) get you to go see a doctor, which is indirectly a revenue stream as well. For fun, try searching Google for "heel pain [name of your state or city]" for a taste of the kind of aggressive "information marketing" that the medical community is prone to. But I think the problem runs deeper than this. There appears to be a disconnect between the scientists doing the research and the people (runners, doctors, and so on) the research can benefit the most.
I don't have any answers on how to bridge that gap just yet. Expecting new biomechanical or medical discoveries to trickle down on their own to broader audiences doesn't seem to be working. Until there are some solutions to this, I'd be irresponsible not to caution runners against trusting what they read on general medical websites like the ones in the table above. I don't think there's any malicious intent, but there isn't an incentive for academic rigor in citing the information on these web pages and keeping it up to date, and too much of their information is just plain wrong—often in a harmful way.
Worse, this sort of thing makes me question if these kinds of websites are up to date on the kinds of really important medical questions that people go searching the internet about. I certainly hope not. But then again, how do I know?
1. Moen, M. H.; Tol, J. L.; Weir, A.; Steunebrick, M.; De Winter, T. C., Medial tibial stress syndrome: a critical review. Sports Medicine 2009, 39 (7), 523-546.
2. Beck, B. R.; Osternig, L. R., Medial tibial stress syndrome. The location of muscles in the leg in relation to symptoms. Journal of Bone and Joint Surgery 1994, 76 (1057-1061).
3. Franklyn, M.; Oakes, B., Tibial stress injuries: aetiology, classification, biomechanics and the failure of bone. In An international perspective on topics in sports medicine and sports injury, Zaslav, K. R., Ed. Intech: 2012; pp 509-534.