The Mysterious “Shin Splint”

When I first started running about 7 years ago, I experienced pain in my right shin, which got worse with use and exercise. Specifically, this is pain in the medial tibia, exacerbated by stress and use (running). I asked around about it, and it was explained to me like this: these are “shin splints,” which are tears in the tendon which connects the muscle to the bone, specifically the calf muscle to the bone around that area. I was told that it was caused because the tendons are not strong enough to support the stress put on by the new exercise of the muscle pushing and pulling on it. The only thing to do is to rest and let it heal. So that’s what I was told. I let it heal by doing alternative cardio exercises like elliptical machine (which uses way fewer calories than running and doesn’t strengthen many muscles, but if you employ techniques to make it more difficult, you can strengthen the gluts & thighs) and rowing machine. After the pain went  away, I incorporated calf muscle-building exercise into my routine and never had a problem since. So that’s my anecdote.

What does the research say?

First of all the etiology (root biological cause) behind “medial tibial stress syndrome” is not known. So the story I was told, believed, and repeated, might not necessarily be true, but it is plausible. I found a pretty good review of risk factors (here).

What’s going on?

Hypothesized Causes in the Review Article

  1. Myofascial strainMyo– means it refers to skeletal muscle, –fascial means it refers to a bundle/layer of fibrous tissue (fasciae). So it literally means a strain of a bundle of muscle tissue. So a muscle strain (which muscle, and what does strain mean here?)
  2. EnthesopathyPathology (disease or disorder) of the entheses (attachment to the bone); sort of what I was told. Doesn’t say how or what … bone-tendon tearing; muscle-tendon connection tearing? (enthesitis would be inflammation here).
  3. Periosteal inflammationPeri-, around; –osteal, bone. A membrane that covers the outer surface of bones. When you cook a turkey, you might notice a thin crispy layer pealing away from the drum stick bone; we have this layer around bones, they harbor nutrients, blood, and progenitor cells which help bones heal and strengthen (osteoblasts & osteoclasts). Inflammation would be inflammation. In my opinion, this is the least likely etiology. Inflammation is usually accompanied by swelling and redness, which shin splints do not have (that I have seen).
  4. Bone stress reaction – A local lowering in bone density. Caused (potentially) by remodeling of the bone at the site of stress. Bone responds to load and stress (pushing and pulling from a muscle is like a “load” — it’s force applied) by removing tissue by osteoclasts and forming new tissue by osteoblasts; to change the shape in response to the new needs. Sort of like adding a lane to a bridge that suddenly gets new traffic in one direction at the expensive of removing a lane from the other direction. The review suggested that this is the most likely hypothesis.

Treatments

So what are some of the potential treatments? Well — on this point, what I was told seems to be correct. From a systematic review and meta-analysis of therapies to treat shin splints (here)…. “None of the studies are sufficiently free from methodological bias to recommend any of the treatments investigated.” Oy. All randomized controlled trials had high risk of bias. Non-randomized clinical trials were of poor quality.

Randomized trials showed no significant effect of: lower leg braces, iontophoresis.

Phonophoresis, ice massage, ultrasound therapy, periosteal pecking, or shockwave therapy could be effective vs. control. These were at the “Level 3 or 4” of evidence. Level 3 is a case-control study (therapeutic & prognostic); both the scientist and the patient are unblinded to what group they are in; no “gold standard.” Level 4 is a case-control study (diagnostic study); poor reference standard; lacking a Power analysis.  In comparison a “Level 1” of evidence is: prospective randomized trial, testing previously validated diagnostic criteria on consecutive patients; comparing sensible alternatives; values obtained in blinded/unbiased manner (e.g., objective laboratory measurements like “viral load” or “weight”).

Laser treatment, stretching & strengthening exercises, compression stockings, leg braces, and pulsed electromagnetic fields were not effective.

Risk Factors

What’s more interesting to me are the risk factors that were found to be associated with developing medial tibial stress syndrome.

These are: 1) Being female, 2) Fewer years of running experience, 3) Prior use of orthotics, 4) Previous medial tibial stress syndrome (probably people not completely healing), and 5) In males – increased external rotation range of motion of the hip.  I find this interesting because there are sex differences in the risk factors, and probably treatment studies to should take sex into consideration. Risk factor (2) supports the bone reaction theory, too. I find the result that compression stockings are useless to be interesting because recently someone told me that they “worked,” and the “pain went away.” Likely the pain went away because activating the baroreceptors (mechanoreceptor sensory neurons excited by stretch of a blood vessel — so the pressure sock squeezes the muscles and blood vessels, increasing the pressure inside the vessel, and activating the “stretch” sensation) …..   inhibits nociceptors — the pain receptors. here and if you wanna go old-school, here. So it’s essentially masking pain of damage that is there.  It also supports the simple (but WAY too often ignored) treatment recommendation: REST.

The studies linked to here are the following:

  1. Newman P, Witchalls J, Waddington G, Adams R. “Risk factors associated with medial tibial stress syndrome in runners: a systematic review and meta-analysis” Open Access J Sports Med. 2013 Nov 13; 4:229-241. PMCID: PMC3873798.
  2. Winters M, Eskes M, Weird A, Moen MH, Backx FJ, Bakker EW. “Treatment of medial tibial stress syndrome: a systematic review.” Sports Med. 2013 Dec; 43(12):1315-33. PubMed PMID: 23979968.
  3. Dworkin BR, Elbert T, Rau H, Birbaumer N, Pauli P, Droste C, Brunia CH. “Central effects of baroreceptor activation in humans: attenuation of skeletal reflexes and pain perception.” Proc Natl Acad Sci USA. 1994 Jul 5; 91(14):6329-33. Pubmed Central PMCID: PMC44195.
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